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Background/aim In chronic liver disease, various immune cell subsets exert pro or anti-tumour effects by releasing reactive oxygen and nitrogen species (ROS, RNS). Here, we evaluated the oxidative and nitrosative pattern in peripheral blood leukocyte subpopulations of early hepatocellular carcinoma (HCC) patients compared with HCC-free cirrhotic patients. Materials and methods Venous blood samples from 18 HCC-free cirrhotic patients and 17 early stage HCC patients were collected to determine ROS, RNS and reduced glutathione levels in isolated leukocytes analyzed by flow cytometry. Results Intracellular levels of ROS and glutathione were higher in lymphocytes, monocytes, and neutrophils from HCC patients as well as mitochondrial superoxide in neutrophils and monocytes whereas intracellular levels of nitric oxide were lower in lymphocytes, monocytes, and neutrophils. Conclusion Early HCC alters intracellular levels of ROS and RNS of some circulating leukocytes subsets. This finding may represent a potential area of interest concerning the development of new treatments and prognostic markers.

We propose an empirical framework to scale the effects of bioturbation on sediment resuspension to population bioturbation activity, approximated as population metabolic rate. Individual metabolic rates have been estimated as functions of body size and extrapolated to population level. We used experimental flumes to test this approach across different types of marine, soft-sediment bioturbators. We observed that a large part of the variance in biota-mediated sediment resuspension can be explained by a positive relationship with population metabolic rate. Other mechanisms can strongly influence the outcome, such as bioturbation of deep sediment strata, biotic interactions with hydrodynamic stress and overlapping areas of influence must be further investigated. By relating the biota-mediated changes in resuspended sediment to metabolism, we can place our observations within the broader context of the metabolic theory of ecology and to formulate general expectations about changes in biota-mediated sediment resuspension in response to changes in population structure and climate change.

Background and Aim Increased basal release of nitric oxide (NO) in the splanchnic circulation contributes to elevated plasma levels of NO observed in decompensated cirrhosis. We evaluated in rat mesenteric arteries whether the differences in basal release of NO, revealed by asymmetric dimethylarginine (ADMA)- and NG-nitro-L-arginine methyl ester (L-NAME)-induced contractions, were associated with changes in messenger RNA (mRNA) expression of endothelial NO synthase (eNOS) and dimethylarginine dimethylaminohydrolases (DDAHs). Methods Rat small mesenteric arteries from 14 Sham-control, from 14 with partial portal vein ligation (PPVL), and from 14 with bile duct excision (BDE)-induced cirrhosis were precontracted under isometric conditions with norepinephrine, and additional contractions were induced with ADMA and L-NAME. mRNA expression of eNOS, DDAH-1, and DDAH-2 in mesenteric arteries were evaluated by real-time polymerase chain reaction. Results ADMA and L-NAME caused concentration- and endothelium-dependent contractions. pD2 values to L-NAME were similar in all groups. In contrast, pD2 values to ADMA were similar in PPVL and BDE but were significantly lower than those of the L-NAME and the Sham groups. Relaxation to acetylcholine was not modified by ADMA or L-NAME but was abolished by charybdotoxin plus apamin. There was an increased mRNA expression of eNOS, DDAH-1, and DDAH-2 in mesenteric arteries from PPVL and BDE compared with the Sham group. Conclusion Basal release of NO is increased in mesenteric arteries of PPVL and BDE rats. The rise in expression of DDAHs indicates a higher degradation of ADMA. This would result in an increased generation of endothelial NO and mesenteric vasodilation.

We studied the role of K(+) channels and Na(+),K(+)-ATPase in the presynaptic inhibitory effects of prostaglandin E(1) (PGE(1)) and PGE(2) on the adrenergic responses of human vas deferens. Furthermore, we determined the effects of increasing extracellular K(+) concentrations ([K(+)](o)) and inhibition of Na(+),K(+)-ATPase on neurogenic and norepinephrine-induced contractile responses. Ring segments of the epididymal part of the vas deferens were taken from 45 elective vasectomies and mounted in organ baths for isometric recording of tension. The neuromodulatory effects of PGEs were tested in the presence of K(+) channel blockers. PGE(1) and PGE(2) (10(-8) to 10(-6)M) induced inhibition of adrenergic contractions. The presence of tetraethylammonium (10(-3)M), charybdotoxin (10(-7)M), or iberiotoxin (10(-7)M), prevented the inhibitory effects of PGE(1) and PGE(2) on the adrenergic contraction. Both glibenclamide (10(-5)M) and apamin (10(-6)M) failed to antagonize PGE(1) and PGE(2) effects. Raising the [K(+)](o) from 15.8mM to 25.8mM caused inhibition of the neurogenic contractions. Ouabain at a concentration insufficient to alter the resting tension (10(-6)M) increased contractions induced by electrical stimulation but did not alter the contractions to norepinephrine. The inhibition of neurogenic responses induced PGE(1), PGE(2) and increased extracellular concentration of K(+) was almost completely prevented by ouabain (10(-6)M). The results demonstrate that PGE(1) and PGE(2) inhibit adrenergic responses by a prejunctional mechanism that involves the activation of large-conductance Ca(2+)-activated K(+) channels and Na(+),K(+)-ATPase.

The functional properties of the endothelium of human thyroid arteries remain unexplored. We investigated the intervention of nitric oxide (NO), prostacyclin (PGI(2)) and endothelium-derived hyperpolarizing factor (EDHF) in the responses to acetylcholine and noradrenaline in isolated thyroid arteries obtained from multi-organ donors. Artery rings were suspended in organ baths for isometric recording of tension. The contribution of NO, PGI(2) and EDHF to endothelium-dependent relaxation was determined by the inhibitory effects of N(G)-monomethyl-L-arginine (L-NMMA), indomethacin, and K(+) channel inhibitors respectively. Acetylcholine induced concentration-dependent relaxation; this effect was not modified by indomethacin and was only partly reduced by L-NMMA, but was abolished in endothelium-denuded rings. The relaxation resistant to indomethacin and L-NMMA was abolished by using either apamin combined with charybdotoxin, ouabain plus barium, or a high-K(+) solution. Noradrenaline induced concentration-dependent contractions which were of greater magnitude in arteries denuded of endothelium or in the presence of L-NMMA.In conclusion, the results indicate that in human thyroid arteries the endothelium significantly modulates responses to acetylcholine and noradrenaline through the release of NO and EDHF. EDHF plays a dominant role in acetylcholine-induced relaxation through activation of Ca(2+)-activated K(+) channels, inwardly rectifying K(+) channels and Na(+)-K(+)-ATPase.

In arteries, agonists such as acetylcholine release an endothelium-derived hyperpolarizing factor (EDHF) that is neither nitric oxide nor prostacyclin.To examine the responses to acetylcholine in segments of forearm veins from patients with chronic renal failure who either had never received dialysis or had undergone long-term dialysis, and to determine the contribution of nitric oxide and EDHF to endothelium-dependent relaxation in veins from patients with chronic renal failure.Isometric tension was recorded in rings of forearm vein from 34 non-dialysed patients, 27 dialysed patients and 14 multiorgan donors (controls).Relaxation in response to acetylcholine was reduced in veins of non-dialysed and dialysed patients. The inhibitors of nitric oxide synthase NG-monomethyl-l-arginine (l-NMMA) and NG,NG-dimethyl-l-arginine (ADMA) reduced by 50% the maximum relaxation in response to acetylcholine in veins from controls and non-dialysed patients; the remaining relaxation was inhibited by 20 mmol/l KCl or by the K+ channel blockers tetraethylammonium chloride, iberiotoxin, charybdotoxin and the combination of barium plus ouabain, but not by apamin or glibenclamide. Relaxation in veins from dialysed patients was inhibited by K+ channel blockade but not by l-NMMA or ADMA.The results demonstrate that the endothelium-dependent relaxation in forearm veins from controls and non-dialysed patients is mediated by release of nitric oxide and EDHF. In contrast, the relaxation in veins from dialysed patients is mediated mainly by EDHF. EDHF-induced relaxation involves activation of large-conductance Ca2+-activated K+ channels.

Arginine vasopressin (AVP) not only acts directly on blood vessels through vasopressin V1 receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments. The aim of the present study was to assess whether subpressor concentrations of AVP could contribute to an abnormal adrenergic contractile response of human renal arteries.Renal artery rings were obtained from 27 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension.AVP (10(-10) mol/l) and the vasopressin V1 receptor agonist [Phe2, Orn8]-vasotocin (10(-10) mol/l) produced a leftward shift of the concentration-response curve to noradrenaline (half-maximal effective concentration decreased from 1.1 x 10(-6) mol/l to 3.1 x 10(-7) mol/l). The enhancement of noradrenaline-induced contractions was inhibited by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)AVP (10-8 mol/l) and unaffected by endothelium removal or pretreatment with the inhibitor of nitric oxide (NO) synthase NG-monomethyl-l-arginine (l-NMMA). The vasopressin V2 receptor agonist 1-desamino-8-D-arginine vasopressin (dDAVP) (10(-10)-10(-8) mol/l) did not modify contractile responses to noradrenaline. In the presence of the dihydropyridine calcium antagonist nifedipine (10(-6) mol/l), vasopressin failed to enhance the contractile response to noradrenaline.The results demonstrate that subpressor concentrations of vasopressin potentiate the contractile effects of noradrenaline without intervention of the NO system. The effects appear to be mediated by vasopressin V1 receptor stimulation, which brings about an increase in calcium entry through dihydropyridine-sensitive calcium channels.

We studied the relaxant effects of milrinone, an inhibitor of phosphodiesterase 3, and rolipram, an inhibitor of phosphodiesterase 4, on contracted human penile dorsal artery and deep dorsal vein. Vascular rings from 12 multi-organ donors were suspended in organ baths for isometric recording of tension. Both milrinone and rolipram inhibited (100%) the contraction induced by noradrenaline and shifted the relaxation–response curves to the cAMP forming agents prostaglandin E1 and forskolin to the left. The findings indicate that the cAMP pathway appears to be a main determinant of relaxation in human penile vessels.

Background: Plasma levels of endogenous guanidine compounds are increased in various pathologic conditions, including chronic renal failure. In the present study we tested the effects of some of these compounds on basal and stimulated nitric oxide activity in human renal arteries. Methods: Rings from human renal arteries were obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ baths for isometric recording of tension. We then studied the effects of N G -monomethyl- l -arginine (L-NMMA), N G , N G -dimethyl- l -arginine (asymmetrical dimethylarginine [ADMA]), aminoguanidine (AG), and methylguanidine (MG) on artery rings under basal and stimulated conditions. Results: In precontracted arteries, L-NMMA (1 μmol/L to 1 mmol/L) and ADMA (1 μmol/L to 3 mmol/L) caused concentration- and endothelium-dependent contractions (median effective concentrations [EC 50 ] = 13.3 μmol/L and 17.5 μmol/L, respectively; Emax = 15 ± 4% and 17 ± 4% of the response to 100 mmol/L KCl, respectively). Aminoguanidine (0.01 to 3 mmol/L) and MG (0.01 to 3 mmol/L) produced endothelium-independent contractions (Emax = 9 ± 3% and 16 ± 2% of the response to 100 mmol/L KCl, respectively). l -arginine (1 mmol/L) but not d -arginine (1 mmol/L) prevented the contractions by L-NMMA and ADMA, but did not change contractions induced by AG and MG. In precontracted arteries, the relaxation to acetylcholine was decreased but not abolished by L-NMMA and ADMA. The remaining relaxation was reduced by charybdotoxin (0.1 μmol/L) and tetraethylammonium (1 mmol/L). Conclusions: The results demonstrate that L-NMMA and ADMA reduce basal and stimulated nitric oxide activity in human renal arteries. An increase in the plasma concentrations of methylarginines associated with renal disease should be considered as a risk factor for endothelial dysfunction and abnormal vasomotor tone in human renal arteries.

Sildenafil (0.1 - 30 microM), a cyclic GMP phosphodiesterase 5 (PDE 5) inhibitor, induced inhibition of electrically evoked contractions of ring segments of human vas deferens from 34 vasectomies. Zaprinast (0.1 - 100 microM), another PDE 5 inhibitor, and the nitric oxide (NO) donor sodium nitroprusside (SNP) (0.1 - 100 microM) had no effect on neurogenic contractions. The inhibition induced by sildenafil was not modified by the inhibitor of guanylate cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) (1 - 30 microM) but it was abolished by the K(+) channel blockers tetraethylammonium (TEA, 1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM). Sildenafil, zaprinast and SNP did not affect the contractions induced by noradrenaline. SNP (10 microM) caused elevation of cyclic GMP levels that was potentiated by sildenafil (10 microM) and zaprinast (100 microM). ODQ (10 microM) inhibited the increase in cyclic GMP. Sildenafil inhibits adrenergic neurotransmission in human vas deferens. The inhibition is not related to accumulation of cyclic GMP but is probably due to activation of prejunctional large-conductance Ca(2+)-activated K(+) channels.

Background . Sildenafil is currently used in the treatment of erectile dysfunction. However, assessment of direct effects of sildenafil on coronary arteries and on arteries used as coronary grafts is unknown. This study was designed to investigate the effects of sildenafil on contracted human coronary, internal mammary, and radial arteries obtained from multiorgan donors. The observations were extended to forearm veins. Zaprinast was included in this study for comparison. Methods . Segments of left coronary, internal mammary, and radial arteries, and forearm veins were obtained from 16 multiorgan donors. Vascular rings were suspended in organ bath chambers and isometric tension was recorded. Then the effects of sildenafil, zaprinast, and sodium nitroprusside on precontracted vessels were studied. Results . Sildenafil (10 −8 − 3 × 10 −5 mol/L) caused concentration-dependent relaxation in the internal mammary arteries, radial arteries, and forearm veins. In the coronary arteries, sildenafil had a modest relaxant effect. In addition, sildenafil amplified the relaxation induced by sodium nitroprusside in all four vessels. Relaxation was unaffected by the inhibitor of nitric oxide synthase N G -monomethyl-L-arginine (10 −4 mol/L). Compared with zaprinast, sildenafil was eight to ten times more potent in terms of EC 50 values. Conclusions . The direct relaxant effects of sildenafil together with its synergistic interaction with nitric oxide donors should be considered in patients undergoing coronary bypass surgery, patients with low blood pressure, and patients receiving antihypertensive regimes.

Objectives: Plasma levels of endogenous guanidino-substituted analogues of L -arginine are increased in various pathologic conditions. In the present study we determined the effects of some of these compounds on basal and stimulated release of nitric oxide in human internal thoracic and radial arteries. Methods: Rings of human internal thoracic and radial arteries were obtained from 16 multiorgan donors. The rings were suspended in organ baths for isometric recording of tension. Results: N G -monomethyl L -arginine (10 –6 to 10 –3 mol/L) and N G ,N G -dimethyl L -arginine (10 –6 to 10 –3 mol/L) caused concentration- and endothelium-dependent contractions. Maximal force of contractions for N G -monomethyl L -arginine and N G ,N G -dimethyl L -arginine in the internal thoracic artery were 18.0% ± 4.3% and 17.8% ± 3.8%, respectively, of the contraction to 100 mmol/L KCl, and those found in the radial artery were 9.6% ± 2.5% and 9.1% ± 2.4%, respectively. Aminoguanidine (10 –5 to 3 × 10 –3 mol/L) and methylguanidine (10 –5 to 3 × 10 –3 mol/L) produced endothelium-independent contractions. L -Arginine (10 –3 mol/L) prevented the contractions by N G -monomethyl L -arginine and N G ,N G -dimethyl L -arginine but did not change contractions induced by aminoguanidine and methylguanidine. N G -monomethyl L -arginine and N G ,N G -dimethyl L -arginine inhibited, in a concentration-dependent manner, the endothelium-dependent relaxation to acetylcholine in the internal thoracic artery and had little attenuating effect in the radial artery; aminoguanidine and methylguanidine were without effect. Conclusions: The results suggest that the contractions induced by N G -monomethyl L -arginine and N G ,N G -dimethyl L -arginine are due to inhibition of both basal and stimulated nitric oxide production, whereas aminoguanidine and methylguanidine do not affect the synthesis of nitric oxide. An increase in the plasma concentration of N G -monomethyl L -arginine and N G ,N G -dimethyl L -arginine is likely to represent a risk factor for abnormal vasomotor tone in conduit arteries used as coronary grafts. (J Thorac Cardiovasc Surg 2000;120:729-36)

Objectives. To evaluate the effects of sertraline, fluoxetine, and amitriptyline on the contractile responses of the human vas deferens muscle elicited by norepinephrine, electrical field stimulation, and KCl, because the therapeutic action of antidepressants may be accompanied by sexual dysfunction related to the contractility of the vas deferens smooth muscle. Methods. Ring segments of the epididymal part of the vas deferens were taken from 32 elective vasectomies and mounted in organ baths for isometric recording of tension. We then studied the effects of sertraline, fluoxetine, and amitriptyline on the neurogenic and agonist-induced contractile responses. Results. Amitriptyline caused concentration-dependent inhibition of neurogenic and norepinephrine-induced contractions. In contrast, only the highest concentration (10−5 M) of sertraline and fluoxetine reduced the adrenergic contractions. The dihydropyridine calcium antagonist nifedipine (10−6 M) completely prevented the inhibitory effect of sertraline and fluoxetine on neurogenic and norepinephrine-induced contractions but did not change the inhibition caused by amitriptyline. Sertraline, fluoxetine, and amitriptyline (all at 10−5 M) attenuated contractions elicited by KCl and reduced contractions induced by CaCl2 in KCl-depolarized preparations. Conclusions. The results indicate that sertraline and fluoxetine inhibit vas deferens motility through inhibition of Ca2+ entry, with no effect on the adrenergic receptors, and amitriptyline acts as an adrenoceptor antagonist and inhibitor of the entry of calcium.

Aims The therapeutic action of tricyclic agents may be accompanied by unwanted effects on the cardiovascular system. The evidence for the effects on vascular and nonvascular smooth muscle comes from animal studies. Whether these studies can be extrapolated to human vessels remains to be determined. Therefore, the present study was designed to investigate the influence of amitriptyline, nortriptyline and sertraline on the contractile responses of human isolated mesenteric arteries to electrical field stimulation, noradrenaline and potassium chloride. Methods Arterial segments (lumen diameter 0.8–1.2 mm) were obtained from portions of the human omentum during the course of 41 abdominal operations (22 men and 19 women), and rings 3 mm long were mounted in organ baths for isometric recording of tension. In some artery rings the endothelium was removed mechanically. Results In precontracted artery rings amitriptyline, nortriptyline and sertraline (3×10−7–10−4 m ) produced concentration-dependent relaxation that was independent of the presence or absence of vascular endothelium. Incubation with indomethacin (3×10−6 m ) reduced the pD2 values thus indicating the participation of dilating prostanoid substances in this response. Amitriptyline and nortriptyline inhibited both the neurogenic-and noradrenaline-induced contractions. In contrast, only the highest concentration of sertraline reduced the adrenergic responses. Amitriptyline, nortriptyline and sertraline inhibited contractions elicited by KCl and produced rightward shifts of the concentration-response curve to CaCl2 following incubation in calcium-free solution. Conclusions These results indicate that amitriptyline and nortriptyline could act as adrenoceptor antagonists and direct inhibitors of smooth muscle contraction of human mesenteric arteries, whereas sertraline might principally exert its action only as direct inhibitor of smooth muscle contraction. This relaxant mechanism involves an interference with the entry of calcium.

The effects of deamino-8-D-arginine vasopressin (desmopressin), a V2 receptor antidiuretic agonist, were studied in isolated rings from branches of renal arteries obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension. In precontracted rings with norepinephrine (10(-6) to 3 x 10(-6) mol/L), desmopressin (10(-11) to 3 x 10(-7) mol/L) caused endothelium-dependent relaxation (81%+/-4% reversal of the initial contraction in arteries with endothelium; 20%+/-4% in arteries without endothelium; P < .05). The relaxation to desmopressin in rings with endothelium was reduced significantly by indomethacin (10(-6) mol/L) and unaffected by the inhibitor of nitric oxide synthase NG-nitro-L-arginine methyl ester (10(-4) mol/L). Two V1 receptor antagonists (a peptidic and a nonpeptidic) had no effect on desmopressin-induced relaxation. However, V2 receptor antagonists (three peptidic and a nonpeptidic) reduced significantly (P < .05) the maximal response to desmopressin. The results of this study show that desmopressin exerts powerful endothelium-dependent relaxation of human renal arteries, probably through stimulation of V2-like receptors that may bring about the release of dilating prostaglandins.

The present study was designed to characterize the response of human penile dorsal artery and deep dorsal vein to dilator drugs used in the diagnosis and treatment of erectile dysfunction with special emphasis on the effects on sympathetic neurotransmission. Ring segments of penile dorsal artery and deep dorsal vein were obtained from 20 multi-organ donors during procurement of organs for transplantation. The rings (3 ;mm long) were suspended in organ bath chambers for isometric recording of tension. We then studied the relaxant responses to prostaglandin E1 (PGE1), vasoactive intestinal peptide (VIP), papaverine (PV), sodium nitroprusside (SNP) and linsidomine chlorhydrate (SIN-1), and analysed the effects of these drugs on contractions induced by stimulation of perivascular sympathetic nerves. In artery and vein rings contracted by noradrenaline, all the drugs tested caused concentration-dependent relaxation. The order of potencies in terms of IC50 values (concentration of agonist causing 50% of the maximal relaxation) was PGE1 = VIP > SNP > SIN-1 = PV. Both arteries and veins contracted to electrical field stimulation (15 ;V, 0.5–2 ;Hz, 0.2 ;ms duration for 15 ;s) in a frequency-dependent manner. All relaxant drugs caused concentration-dependent inhibition of neurogenic contractions; the relative order of potencies was PGE1 > VIP > SNP > SIN-1 = PV. It is concluded that inhibition of sympathetic activity constitutes an effective relaxing mechanism in penile dorsal artery and vein. Modulation of sympathetic activity together with the direct effects on smooth muscle should be considered to evaluate adequately the efficacy of relaxant drugs to increase human penile blood supply.

We studied the effects of vasopressin on the adrenergic responses of in vitro preparations of circular muscle from the vas deferens obtained from 28 men undergoing elective vasectomy. Vasopressin (3 x 10(-9)-3 x 10(-8) M) enhanced the phasic contractions elicited by electrical field stimulation and noradrenaline. This potentiation was blocked by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)vasopressin (10(-6) M) but not by the vasopressin V2 receptor antagonist [d(CH2)5, D-Ile2,Ile4,Arg8]vasopressin (10(-6) M). The Ca2+ antagonist nifedipine (10(-6) M) did not affect the potentiation of electrical field stimulation induced by vasopressin and noradrenaline but reduced KCl-induced contractions and abolished the induction of phasic activity by vasopressin in the presence of KCl. The results demonstrate that vasopressin, in addition to its direct contractile effects, strongly potentiates contractions of human vas deferens elicited by adrenergic stimulation. Both the direct and indirect effects of vasopressin appear to be mediated by vasopressin V1 receptor stimulation and are independent of Ca2+ entry through dihydropyridine Ca2+ channels.

The aim of the present study was to characterize neurogenic and pharmacological responses of human penile deep dorsal vein and to determine whether the responses are mediated by nitric oxide from neural or endothelial origin. Ring segments of human penile deep dorsal vein were obtained from 22 multiorgan donors during procurement of organs for transplantation. The rings were suspended in organ bath chambers for isometric recording of tension. We then studied the contractile and relaxant responses to electrical field stimulation and to vasoactive agents. Electrical field stimulation (0.5–2 Hz) and noradrenaline (3×10−10–3×10−5M) caused frequency- and concentration-dependent contractions that were of greater magnitude in veins denuded of endothelium. The inhibitor of nitric oxide synthesis NG-nitro-L-arginine methyl ester hydrochloride (L-NAME, 10−4M) increased the adrenergic responses only in rings with endothelium. In preparations contracted with noradrenaline in the presence of guanethidine (10−6M) and atropine (10−6M), electrical stimulation induced frequency-dependent relaxations. This neurogenic relaxation was prevented by L-NAME, methylene blue (3×10−5M) and tetrodotoxin (10−6M), but was unaffected by removal of endothelium. Acetylcholine (10−8–3×10−5M) and substance P (3×10−11–3×10−7M) induced endothelium-dependent relaxations. In contrast, sodium nitroprusside (10−9–3×10−5M) and papaverine (10−8–3×10−5M) caused endothelium-independent relaxations. The results provide functional evidence that the human penile deep dorsal vein is an active component of the penile vascular resistance through the release of nitric oxide from both neural and endothelial origin. Dysfunction in any of these sources of nitric oxide should be considered in some forms of impotence.

Background —Arginine vasopressin (AVP) not only acts directly on blood vessels through V 1 receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments in vivo and in vitro. The aim of the present study was to investigate whether AVP can contribute to an abnormal adrenergic constrictor response of human saphenous veins. Methods and Results —Saphenous vein rings were obtained from 32 patients undergoing coronary artery bypass surgery. The vein rings were suspended in organ bath chambers for isometric recording of tension. AVP (3×10 −9 mol/L) enhanced the contractions elicited by electrical field stimulation at 1, 2, and 4 Hz (by 80%, 70%, and 60%, respectively) and produced a leftward shift of the concentration-response curve to norepinephrine (half-maximal effective concentration decreased from 6.87×10 −7 to 1.04×10 −7 mol/L; P 1 vasopressin receptor antagonist d(CH 2 ) 5 Tyr(Me)AVP (10 −6 mol/L) prevented the potentiation evoked by AVP. The selective V 1 receptor agonist [Phe, 2 Orn 8 ]-vasotocin (3×10 −9 mol/L) induced potentiation of electrical stimulation–evoked responses, which was also inhibited in the presence of the V 1 receptor antagonist (10 −6 mol/L). In contrast, the V 2 receptor agonist desmopressin (10 −9 to 10 −7 mol/L) did not modify neurogenic responses, and the V 2 receptor antagonist [d(CH 2 ) 5 , D-Ile, 2 Ile, 4 Arg 8 ]-vasopressin (10 −8 to 10 −6 mol/L) did not prevent the potentiation induced by AVP. The dihydropyridine calcium antagonist nifedipine (10 −6 mol/L) did not affect the potentiating effect of AVP. Conclusions —The results suggest that low concentrations of AVP facilitate sympathetic neurotransmission and potentiate constrictor effects of norepinephrine in human saphenous veins. These effects appear to be mediated by V 1 receptor stimulation and are independent of calcium entry through dihydropyridine calcium channels. Thus, AVP may contribute to vascular mechanisms involved in acute ischemic syndromes associated with venous grafts, particularly if the sympathetic nervous system is activated.

1. The aim of the present study was to investigate in rat mesenteric artery rings whether low concentrations of vasopressin could modify the contractile responses to noradrenaline and electrical stimulation of perivascular nerves. 2. Vasopressin (10[10]-10[-7] M) caused concentration-dependent contractions (pD2 = 8.36+/-0.09). The V1-receptor antagonist d(CH2)5Tyr(Me)AVP (10[-9]-10[-8] M) produced parallel rightward shifts of the control curve for vasopressin. Schild analysis yielded a pA2 value of 9.83 with a slope of 1.10+/-0.14. 3. Vasopressin (3 x 10[-10] and 10[-9] M) caused concentration-dependent potentiation of the contractions elicited by electrical stimulation (2-8 Hz; 0.2 ms duration for 30 s) and produced leftward shifts of the concentration-response curve for noradrenaline. The V1-receptor antagonist induced concentration-dependent inhibitions of potentiation induced by vasopressin. The selective V1-receptor agonist [Phe2, Orn8]-vasotocin (3 x 10[10] and 10[-9] M) induced potentiation of electrical stimulation-evoked responses which was also inhibited in the presence of the V1 antagonist (10[-8] M). In contrast, the V2-receptor agonist deamino-8-D-arginine vasopressin (desmopressin 10[-8]-10[-7] M) did not modify the electrical stimulation-induced responses and the V2-receptor antagonist [d(CH2)5, D-Ile2, Ile4, Arg8]-vasopressin (10[-8]-10[-7] M) did not affect the potentiation evoked by vasopressin. 4. In artery rings contracted by 10(-6) M noradrenaline in the presence of 10(-6) M guanethidine and 10(-6) M atropine, electrical stimulation (2, 4 and 8 Hz) produced frequency-dependent relaxations which were unaffected by 10(-9) M vasopressin but abolished by 10(-6) M tetrodotoxin. 5. Vasopressin also potentiated contractions elicited by KCl and contractions induced by addition of CaCl2 to KCl depolarized vessels. The augmenting effects were inhibited by the V1 antagonist. 6. In the presence of the calcium antagonist nifedipine (10[-6] M), vasopressin failed to enhance the contractile responses to electrical stimulation, noradrenaline and KCl. 7. The results demonstrate that low concentrations of vasopressin strongly potentiate the contractions to adrenergic stimulation and KCl depolarization. This effect appears to be mediated by V1 receptor stimulation which brings about an increase in calcium entry through dihydropyridine-sensitive calcium channels.

Purpose: The goal of this study was to determine the effects of vasopressin and the selective V 2 -receptor agonist desmopressin on human saphenous veins, with special emphasis on endothelium-mediated responses. Methods: Human saphenous vein segments were obtained from 35 patients undergoing coronary bypass surgery. Paired segments, one normal and the other deendothelized by gentle rubbing, were mounted for isometric recording of tension in organ baths. Concentration-response curves to vasopressin and desmopressin were determined in the presence and in the absence of either the V,-receptor antagonist d(CH 2 ) 5 Tyr(Me)AVP (10 −6 mol/L), the V 1 -V 2 receptor antagonist desGly-d(CH 2 ) 5 D-Tyr(Et)ValAVP (10 −6 mol/L), indomethacin (10 −6 mol/L), or N G -nitro-L-arginine methyl ester hydrochloride (L-NAME, 10 −4 mol/L). Results: In vein rings under resting tension, vasopressin produced concentration-dependent, endothelium-independent contractions with a concentration of vasopressin producing-half-maximal contractions (EC 50 ) of 3.44 × 10 −8 mol/L. The vasopressin V 1 -receptor antagonist (10 −6 mol/L) displaced the control curve to vasopressin 9.86-fold to the right in a parallel manner. In precontracted vein rings previously treated with the V 1 -antagonist (10 −6 mol/L), vasopressin caused endothelium-dependent relaxations. This relaxation was reduced significantly by indomethacin (10 −6 mol/L) and unaffected by the V 1 -V 2 -receptor antagonist (10 −6 mol/L) or by L-NAME (10 −4 mol/L). Desmopressin caused endothelium-dependent relaxations in precontracted vein rings that were inhibited by the mixed V 1 -V 2 -receptor antagonist and by indomethacin, but not by the V 1 -antagonist or by pretreatment with L-NAME. Conclusions: These observations indicate that vasopressin exerts contractile effects on human saphenous vein by V 1 -receptor stimulation. Vasopressin causes dilatation of human saphenous vein only if V 1 -receptor blockade is present. This relaxation appears to be mediated by the release of relaxant Prostaglandins, probably derived from endothelial cells, and is independent of V 2 -receptor stimulation or release of nitric oxide. Desmopressin elicits relaxation that is largely dependent on V 2 -receptor stimulation, which may bring about the release of dilating Prostaglandins from the endothelial cells.

The effects of vasopressin were studied in isolated rings from branches (2-3 mm in external diameter) of human renal arteries obtained from 18 patients undergoing nephrectomy for non-obstructive neoplasia. In arterial rings under resting tension, vasopressin produced concentration-dependent and endothelium-independent contractions with an EC 50 of 9.1 x 10 -10 mol L -1 . The vasopressin V 1 receptor antagonist d(CH 2 ) 5 Tyr(Me)AVP (10 -6 mol L -1 ) displaced the control curve to vasopressin 564-fold to the right in a parallel manner. In precontracted arterial rings and previously treated with the V 1 antagonist (10 -6 mol L -1 ) vasopressin caused endothelium-independent relaxation. The relaxation to vasopressin was reduced significantly by indomethacin (10 -6 mol L -1 ) and unaffected by the V 1 /V 2 receptor antagonist desGly d(CH 2 ) 5 -D-Tyr(Et)ValAVP (10 -6 mol L -1 ) or by N G -nitro-L-arginine methyl ester (10 -4 mol L -1 ). These observations indicate that vasopressin is primarily a constrictor of human renal arteries by V 1 -receptor stimulation. Vasopressin causes prostaglandin-mediated dilatation of human renal arteries only if V 1 -receptor blockade is present. The effects of vasopressin on human renal arteries may be relevant in those clinical situations characterized by increased plasma vasopressin levels.

The present study was designed to investigate the influence of the endothelium and that of the L-arginine pathway on the contractile responses of isolated human cerebral arteries to electrical field stimulation (EFS) and norepinephrine. Rings of human middle cerebral artery were obtained during autopsy of 19 patients who had died 3–8 h before. EFS (1–8 Hz) induced frequency-dependent contractions that were abolished by tetrodotoxin, prazosin, and guanethidine (all at 10-6 M). The increases in tension were of greater magnitude in arteries denuded of endothelium. NG-monomethyl L-arginine (L-NMMA 10-4 M) potentiated the contractile response to EFS in artery rings with endothelium but did not influence responses of endothelium-denuded arteries. L-arginine (10-4 M) reversed the potentiating effects of L-NMMA on EFS-induced contractions. Norepinephrine induced concentration-dependent contractions, which were similar in arteries with and without endothelium or in arteries treated with L-NMMA. Indomethacin (3 × 10−6 M) had no significant effect on the contractile response to EFS or on the inhibition by L-NMMA of acetylcholine-induced relaxation. These results suggest that the contractile response of human cerebral arteries to EFS is modulated by nitric oxide mainly derived from endothelial cells; although adrenergic nerves appear to be responsible for the contraction, the transmitter involved in the release of nitric oxide does not appear to be norepinephrine. The effects of L-NMMA in this preparation appear to be due to inhibition of nitric oxide formation rather than caused by cyclooxygenase activation.

We studied the effects of vasopressin on isolated rings of human deferential artery and vas deferens (prostatic portion) obtained from patients undergoing radical cystectomy (n = 11) or prostatectomy (n = 10). Ring segments of artery or vas deferens were studied in organ bath experiments at optimal resting tension. In artery rings, vasopressin produced concentration-dependent, endothelium-independent contractions with an EC50 of 4.5 x 10(-10) M. The presence of NG-nitro-L-arginine methyl ester hydrochloride (10(-4) M), an inhibitor of nitric oxide synthase, did not change significantly (P > 0.05) the vasopressin-induced contraction. In ring preparations of the prostatic part of the vas deferens, vasopressin induced phasic contractions with an EC50 of 7.0 x 10(-9) M. The vasopressin V1 receptor antagonist, d(CH2)5Tyr(Me)AVP (10(-8) and 10(-6)), displaced to the right in parallel the control curve to vasopressin in artery and vas deferens rings. These results indicate that vasopressin exerts a powerful constrictor action on human deferential artery and vas deferens by direct stimulation of V1 receptors. It is concluded that the deferential artery may dampen the passage of blood to the vas deferens in circumstances characterized by increased plasma vasopressin levels.

The human vas deferens receives its blood supply from the deferential artery, a long vessel which usually arises from the superior vesical artery. To date no information is available on the responsiveness of this artery to adrenergic stimulation. In the present work the effects of electrical field stimulation and noradrenaline were studied isometrically in rings of human deferential artery obtained from patients undergoing radical cystectomy (n = 7) or prostatectomy (n = 10). Electrical field stimulation (1–8 Hz, 20 V, 0.25 ms for 30 s) caused frequency-dependent contractions that were abolished by guanethidine, tetrodotoxin or prazosin. Noradrenaline (10−7 – 10−4 M) induced concentration-dependent contractions with an EC50 of 1.3 × 10−5 M. The increases in tension induced by electrical field stimulation and noradrenaline were of greater magnitude in arteries denuded of endothelium. The inhibitor of nitric oxide synthesis, N G - nitro- L -arginine methyl ester (10−4 M), potentiated the responses to electrical field stimulation and noradrenaline in artery rings with endothelium. The results indicate that the human deferential artery has a marked ability to contract in response to adrenergic stimulation; they also suggest that the endothelium may have an inhibitory effect on adrenergic responses due, at least in part, to the release of endothelial nitric oxide. These effects could play an important role in regulating blood flow to the vas deferens.

The present study was designed to investigate the influence of endothelium-derived nitric oxide on the contractile responses of isolated human omental arteries to electrical field stimulation and noradrenaline. We measured isometric tension in artery rings obtained from portions of human omentum during the course of abdominal operations (32 patients). Electrical field stimulation induced frequency-dependent contractions which were abolished by tetrodotoxin (10−6 M) and prazosin (10−6 M), thus indicating that this effect was due to noradrenaline released from adrenergic nerves acting on α1-adrenoceptors. The increases in tension induced by electrical field stimulation were of greater magnitude in arteries denuded of endothelium. N G - Nitro- L -arginine (L-NAME, 10−4 M) potentiated the contractile response to electrical field stimulation in artery rings with endothelium but did not influence the contractile responses of endothelium-denuded arteries. The potentiation induced by L-NAME was completely reversed by L -arginine (10−4 M), but not by D -arginine (10−4 M). Contractile responses to noradrenaline were similar in arteries with and without endothelium. L-NAME (10−4 M) had no significant effect on the contractile responses to noradrenaline. Our results suggest that electrical field stimulation releases endothelium-derived nitric oxide which inhibits the contractile responses of human omental arteries. The constrictor responses to noradrenaline are not modulated by the endothelium.

Objectives The present study was designed to evaluate the role of K + channels in the adrenergic responses of human vas deferens as well as the intervention of dihydropyridine-sensitive Ca 2+ channels on modulation of adrenergic responses by K + channel inhibitors. Methods Ring segments of the epididymal part of the vas deferens were taken from 32 elective vasectomies and mounted in organ baths for isometric recording of tension. We then studied the effects of K + channel blockers on neurogenic and norepinephrine-induced contractile responses. Results Addition of tetraethylammonium (TEA, 10 −3 M), a nonspecific K + channel blocker, or charybdotoxin (10 −7 M), a nonselective inhibitor of large- and intermediate-conductance Ca 2+ -activated K + channel, increased the contractile responses to norepinephrine and electrical field stimulation-induced contractions ( P −7 M), a selective blocker of large-conductance Ca 2+ -activated K + channels, apamin (10 −6 M), a blocker of small-conductance Ca 2+ -activated K + channels, or glibenclamide (10 −5 M), an inhibitor of ATP-sensitive K + channels, were without effect. TEA- and charybdotoxin-induced potentiation of contractions elicited by electrical field stimulation and norepinephrine was blocked by L-type Ca 2+ channel blocker nifedipine (10 −6 M). Conclusions The results suggest that charybdotoxin-sensitive, but iberiotoxin-insensitive, K + channels are activated by stimulation with norepinephrine and electrical field stimulation to counteract the adrenergic-induced contractions of human vas deferens. Thus, inhibition of these channels increases significantly the contraction, an effect that appears to be mediated by an increase in Ca 2+ entry through L-type voltage-dependent Ca 2+ channels.

The effects of endothelin have been studied in isolated arterial segments (0·8–1 mm in external diam.) of human omental arteries obtained during the course of abdominal operations (15 patients, 7 men and 8 women). Paired segments, one normal and the other de-endothelized, were mounted for isometric recording of tension in organ baths. Endothelin produced concentration-dependent contractions with an EC50 value of 5·4 × 10−9 m. Removal of endothelium did not affect significantly endothelin-induced contractions (EC50, 6·7 × 10−9 m). Removal of extracellular calcium or addition of the calcium channel blocker nicardipine (10−6 m) diminished but did not abolish responses to endothelin. These results indicate that endothelin exerts powerful contractile effects on human isolated omental arteries which are independent of the presence of an intact endothelial cell layer; this contraction cannot be explained solely by voltage-dependent calcium channels.

Previous studies have shown that asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and nitric oxide (NO) play a prominent role in liver dysfunction. The objective of this study was to determine whether plasma levels of ADMA, SDMA and NO are altered in patients with chronic hepatitis C.Plasma levels of ADMA, SDMA and NO (nitrite plus nitrate) were measured in 22 patients with chronic hepatitis C and 24 patients with sustained virologic response after treatment with peginterferon plus ribavirin. Seven healthy volunteers served as controls.Plasma levels of ADMA, SDMA and NO were not significantly different between groups: chronic hepatitis C, ADMA 0.55+/-0.06, SDMA 0.22+/-0.03, NO 36.3+/-5.9 micromol/l; treated patients, ADMA 0.60+/-0.15, SDMA 0.31+/-0.05, NO 36.1+/-5.5 micromol/l; controls, ADMA 0.65+/-0.08, SDMA 0.28+/-0.05, NO 40.7+/-8.9 micromol/l).Our results show that plasma NO, ADMA and SDMA concentrations are not changed in patients with chronic hepatitis C without superimposed signs of acute inflammatory activity. Furthermore, no significant differences in plasma values of NO and dimethylarginines were observed between the group of untreated patients and the group of patients treated with interferon plus ribavirin.

Objective: The present experiments were designed to evaluate differences in the effects of cyclooxygenase (COX)-1 and COX-2 inhibition on contractile responses of human gastroepiploic artery and saphenous vein elicited by vasopressin. Design: Laboratory investigation. Setting: University laboratory. Subjects: Rings of human gastroepiploic artery were obtained from 32 patients undergoing gastrectomy, and rings of saphenous vein were obtained from 30 patients undergoing coronary artery bypass surgery. Interventions: The rings were suspended in organ baths for isometric recording of tension. We studied the responses to vasopressin in the absence and in the presence of either the vasopressin V 1 -receptor antagonist d(CH 2 ) 5 Tyr(Me)AVP or the COX inhibitors aspirin, nimesulide, or SC-560. Measurements and Main Results: Vasopressin (10 -11 -10 -6 mol/L) produced concentration-dependent contractions with an EC 50 value of 4.3 x 10 -10 mol/L for gastroepiploic artery and 3.4 x 10 -8 mol/L for saphenous vein. The vasopressin V 1 -receptor antagonist d(CH 2 ) 5 Tyr(Me)AVP (10 -7 mol/L) induced significant shifts (p

The effect of 4-hydroxynonenal (4-HNE), a circulating lipid peroxidation product, on the vascular tone of human mesenteric arteries is studied. 4-HNE promotes relaxation of human mesenteric arterial rings in a concentration-dependent manner. Removal of the endothelium or treatment with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME; 10(-4) M) partially prevented 4-HNE-induced relaxation, thus suggesting the intervention of nitric oxide from endothelial origin in the vascular effects of 4-HNE.

Background We recently reported that endothelium-dependent relaxation is impaired in forearm veins from patients with chronic renal failure. However, assessment of responses to norepinephrine remains controversial. We examined the contractile response to norepinephrine in forearm veins from patients on chronic hemodialysis and the role of nitric oxide (NO), prostanoids, and Ca 2+ -activated K + channels in this response. Methods Isometric contraction curves were obtained in rings of forearm vein from 21 dialyzed patients and 12 multiorgan donors in response to norepinephrine (1 nmol/L to 10 μmol/L) or KCl (5 to 100 mmol/L). Results Veins from uremic patients were markedly less responsive to norepinephrine (7.6 ± 0.6 g) and KCl (6.0 ± 0.3 g) than those from organ donors (12.0 ± 0.7 g and 10.4 ± 0.5 g, respectively, P N G -monomethyl- l -arginine (100 μmol/L), an inhibitor of NO synthase, or indomethacin (10 μmol/L), an inhibitor of prostacyclin synthesis, increased the response to norepinephrine in veins from control subjects but not in veins from dialyzed patients. Additional blockade of Ca 2+ -activated K + channels did not correct the hyporesponsiveness. In veins incubated in Ca 2+ -free solution containing either 100 mmol/L KCl or 1 μmol/L norepinephrine, addition of calcium chloride (0.1 to 30 mmol/L) elicited contractile responses that were significantly lower in veins from dialyzed patients. Conclusions The results demonstrate that norepinephrine-mediated contractions of forearm veins are markedly decreased in dialyzed patients. Endothelium-derived relaxing factors are not involved in this effect. The reduced contractile response is most likely caused by a decreased calcium entry through voltage- and receptor-dependent calcium channels.

Objective: We studied the intervention of nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor (EDHF) in mediating responses to acetylcholine in thyroid arteries from euthyroid and methimazole-treated (MT) patients. Design and methods: Branches of the superior thyroid artery were obtained from 19 euthyroid patients and 17 MT patients (euthyroid at the time of surgery) undergoing total thyroidectomy or hemithyroidectomy. Artery rings were suspended in organ baths for isometric recording of tension. Results and conclusions: Acetylcholine caused endothelium-dependent relaxation of greater magnitude in arteries from MT patients (pD2 (−log EC50) values were 7.68±0.19 in euthyroid and 8.17±0.26 in MT patients, P l-arginine (l-NMMA). This reduction was higher in arteries from MT patients (50±6%) as compared with euthyroid patients (36±6%) (P + channels using apamin combined with charybdotoxin or high K+ solution abolished the relaxation resistance to l-NMMA and indomethacin. The maximal contraction response to noradrenaline (as a percentage of the response to 100 mM KCl) was lower in MT than in euthyroid patients (57±10 and 96±8 respectively, P < 0.05). The hyporesponsiveness to noradrenaline in arteries from MT patients was corrected by l-NMMA. The results indicate that: (i) thyroid arteries from MT patients show an increased relaxation response to acethylcholine and a decreased contraction response to noradrenaline due to overproduction of NO; (ii) EDHF plays a prominent role in acetylcholine-induced relaxation through activation of Ca2+-activated K+ channels; (iii) the abnormal endothelium-dependent responses in arteries from MT patients are not corrected by medical treatment.

Background The objective of this study was to characterize the neurogenic contraction and relaxation of the human gastroepiploic artery and to determine whether the responses are mediated by nitric oxide (NO) from neural or endothelial origin. Methods Rings of human gastroepiploic artery were obtained from 18 patients (12 men, 6 women) undergoing gastrectomy. The rings were suspended in organ baths for isometric recording of tension. We studied the contractile and relaxant responses to electrical field stimulation. Results In arteries under resting conditions, electrical field stimulation (2 to 8 Hz) caused frequency-dependent contractions that were of greater magnitude in arteries denuded of endothelium and blocked by tetrodotoxin (10−6 mol/L). The inhibitor of NO synthesis NG-monomethyl- l -arginine (L-NMMA, 10−4 mol/L) increased contractile responses only in arteries with endothelium. In preparations contracted with norepinephrine in the presence of guanethidine (10−6 mol/L) and atropine (10−6 mol/L), electrical stimulation induced frequency-dependent relaxations. This neurogenic relaxation was prevented by L-NMMA (10−4 mol/L) and tetrodotoxin (10−6 mol/L), but was unaffected by removal of the endothelium. Conclusions The results provide functional evidence that NO is released by autonomic nerves of the human gastroepiploic artery. We hypothesize that the release of NO from both endothelial and neurogenic origin may modulate resistance of the human gastroepiploic artery. Dysfunction in any of these sources of NO should be considered in some form of vasospasm.

Cardiovascular manifestations are frequent findings in patients with thyroid hormone disorders. Nitric oxide (NO) plays a key role in vascular, endothelial-mediated relaxation. NO is synthesized from L-arginine by NO synthase, an enzyme inhibited by endogenous compounds, mainly asymmetric dimethylarginine [asymmetric N(G),N(G)-dimethyl-L-arginine (ADMA)]. The aim of our work was to investigate whether plasma L-arginine and dimethylarginine concentrations and NO production are altered in hypo- and hyperthyroid patients, compared with control subjects. L-arginine, ADMA and symmetric dimethylarginine were analyzed by HPLC. NO was measured as plasma nitrite plus nitrate (NO(x)) concentration by a colorimetric method based on Griess reagent. L-arginine, ADMA, and symmetric dimethylarginine plasma levels in the hypothyroid group were similar to those of the control group; whereas in hyperthyroidism, these values were significantly increased. However, the L-arginine/ADMA ratio was decreased in hyperthyroid patients, resulting in diminished NO(x) production. When all subjects were analyzed together, free T(4) levels were directly correlated with ADMA and inversely correlated with NO(x).

Objective: We investigated the potentiating effect of U-46619, a synthetic analogue of thromboxane A2 (TXA2), on the adrenergic responses in human saphenous vein. Methods: Saphenous vein rings were obtained from 35 patients undergoing coronary artery bypass surgery. The rings were suspended in organ bath chambers for isometric recording of tension. Results: U-46619 (10−10–3×10−7 mol/l) produced concentration-dependent and endothelium-independent contractile responses. U-46619 (10−10 mol/l) potentiated the contractions elicited by electrical stimulation and potassium chloride, and produced leftward shifts of the concentration–response curve for noradrenaline. The TXA2 receptor antagonist SQ-30741 (10−8 mol/l) prevented the potentiation evoked by U-46619. The dihydropyridine calcium antagonist nifedipine (10−6 mol/l) did not affect the potentiation of electrical stimulation and noradrenaline induced by U-46619, but abolished the potentiation of U-46619 on KCl-induced contractions. Conclusions: U-46619 facilitates sympathetic neurotransmission and potentiates constrictor effects of noradrenaline in human saphenous veins through stimulation of TXA2 receptors. These effects are independent of calcium entry through dihydropyridine calcium channels.

Objectives. To investigate the effects of sildenafil on human penile blood vessels and evaluate the interaction of sildenafil with neurogenic-mediated responses. Sildenafil is currently used in the treatment of erectile dysfunction. Methods. Penile dorsal arteries and deep dorsal veins were obtained from 14 multiorgan donors. Vascular rings were suspended in organ bath chambers, and the isometric tension was recorded. We then studied the effects of sildenafil on precontracted vessels and the neurogenic (noradrenergic and nitrergic) responses. Results. Sildenafil (10 −9 to 3 × 10 −6 M) caused concentration-dependent relaxation and amplified the relaxation induced by sodium nitroprusside. Relaxation was unaffected by the inhibitor of nitric oxide synthase N G -monomethyl- l -arginine (10 −4 M). Compared with zaprinast, sildenafil was 8 to 10 times more potent in terms of the median effective concentration (EC 50 ) values. Electrical field stimulation of the vessels under resting tension caused frequency-dependent contractions that were attenuated in the presence of sildenafil. When penile vessels were contracted after blockade of norepinephrine release with guanethidine (10 −6 M), electrical stimulation induced frequency-dependent, nitric oxide-dependent relaxations that were enhanced by sildenafil. Conclusions. These results indicate that the relaxation of human penile arteries and veins induced by sildenafil involves inhibition of noradrenergic contraction, enhancement of neurogenic nitric oxide-mediated relaxation, and inhibition of smooth muscle contraction.

Vasopressin not only acts directly on blood vessels through V1-receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments in vitro and in vivo. The aim of the present study was to investigate whether subpressor concentrations of vasopressin could modify the constrictor responses to norepinephrine and electrical stimulation of the perivascular nerves in human mesenteric arteries. Human mesenteric artery rings (3-3.5 mm long, 0.8-1.2 mm OD) were obtained from 38 patients undergoing abdominal operations. The arterial rings were suspended in organ bath chambers for isometric recording of tension. Vasopressin (3 x 10(-11) M) enhanced the contractions elicited by electrical stimulation at 2, 4, and 8 Hz (by 100, 100, and 72%, respectively) and produced a leftward shift of the concentration-response curves to norepinephrine (half-maximal effective concentration decreased from 2.2 x 10(-6) to 5.0 x 10(-7) M; P < 0.05) without any alteration in maximal contractions. Vasopressin also potentiated KCl- and calcium-induced contractions. The V1-receptor antagonist 1-[beta-mercapto-beta,beta-cyclopentamethylenepropionic acid-2-O-methyl-tyrosine, 8-arginine]vasopressin (10(-6) M) prevented the potentiation evoked by vasopressin in all cases. The calcium antagonist nifedipine (10(-6) M) did not affect the potentiation of electrical stimulation and norepinephrine induced by vasopressin but abolished KCl-induced contractions. The results suggest that vasopressin, in addition to its direct vasoconstrictor effect, strongly potentiates the responses to adrenergic stimulation and KCl depolarization. Both the direct and indirect effects of vasopressin appear to be mediated by V1-receptor stimulation. The amplifying effect of vasopressin on constrictor responses may be relevant in those clinical situations characterized by increased plasma vasopressin levels.

1. The effects of noradrenaline, endothelin-1, acetylcholine and sodium nitroprusside were studied in isolated pulmonary arteries obtained from 14 patients undergoing lobectomy for lung carcinoma. Seven patients had shown increased response to a bronchodilator test prior to operation. In the remaining patients (control) the bronchodilator test was negative. 2. Artery rings from patients with a positive bronchodilator response showed greater contraction to noradrenaline (pD2 = 6.44 +/- 0.1; Emax = 93 +/- 9% of response to 100 mM KCl) and endothelin-1 (pD2 = 8.92 +/- 0.1; Emax = 130 +/- 16%) than the rings from control patients (pD2 = 6.04 +/- 0.08; Emax = 56 +/- 8% for noradrenaline; pD2 = 8.29 +/- 0.1; Emax = 78 +/- 10% for endothelin-1). There was no significant difference in the contractile responses to 100 mM KCl between arteries from either group of patients. 3. Arterial rings from patients with a positive bronchodilator test achieved 96 +/- 3% of maximal relaxation in response to acetylcholine, whereas rings from control patients achieved a maximal relaxation of 72 +/- 5%. Rings from both the controls and the patients with a positive bronchodilator test achieved complete relaxation in response to sodium nitroprusside but pD2 values were significantly higher in patients with a positive bronchodilator test. 4. Removal of endothelium or treatment with NG-nitro-L-arginine methyl ester of artery rings from both the control and the patients with a positive bronchodilator test reduced the relaxation to acetylcholine (P < 0.05) but did not modify relaxation to sodium nitroprusside. 5. It is concluded that responsiveness of pulmonary arterial smooth muscle to dilator and constrictor agents is increased in patients showing reversibility of airway constriction. Thus hyperresponsiveness of airway smooth muscle may be associated with a similar phenomenon in the surrounding vascular smooth muscle.

The present study was designed to investigate the contribution of the endothelium and that of the L-arginine pathway on the contractile responses of isolated human pulmonary arteries to electrical field stimulation (EFS) and noradrenaline. Isometric tension was measured in artery rings obtained from portions of human lung after thoracic surgery for removal of lung carcinoma (18 patients). Electrical field stimulation (EFS) induced frequency-dependent contractions of isolated human pulmonary arteries which were abolished by tetrodotoxin, guanethidine and prazosin (all at 10(-6) M). The increases in tension were of greater magnitude in arteries denuded of endothelium. NG-nitro-L-arginine methyl ester (L-NAME) (10(-4) M) potentiated the contractile response to EFS in artery rings with endothelium but not in endothelium-denuded arteries. The potentiation induced by L-NAME was completely reversed by L-arginine (10(-4) M) but not by D-arginine (10(-4) M). Indomethacin (3 x 10(-6) M) had no significant effect on the contractile response to EFS. Contractile responses to noradrenaline were similar in arteries with and without endothelium. Our results suggest that electrical field stimulation releases endothelium-derived nitric oxide, which inhibits the contractile responses of human pulmonary arteries. Although adrenergic nerves seem to be responsible for the contraction, the transmitter involved in the release of nitric oxide does not appear to be noradrenaline.

1. The effects of vasopressin and deamino-8-D-arginine vasopressin (DDAVP, desmopressin) were studied in artery rings (0.8-1 mm in external diameter) obtained from portions of human omentum during the course of abdominal operations (27 patients). 2. In arterial rings under resting tension, vasopressin produced concentration-dependent, endothelium-independent contractions with an EC50 of 0.59 +/- 0.12 nM. The V1 antagonist d(CH2)5Tyr(Me)AVP (1 microM) and the mixed V1-V2 antagonist desGly-d(CH2)5D-Tyr(Et)ValAVP (0.01 microM) displaced the control curve to vasopressin to the right in a parallel manner without differences in the maximal responses. In the presence of indomethacin (1 microM) the contractile response to vasopressin was significantly increased (P < 0.01). 3. In precontracted arterial rings, previously treated with the V1 antagonist, d(CH2)5Tyr(Me)AVP (1 microM), vasopressin produced endothelium-dependent relaxation. This relaxation was reduced significantly (P < 0.05) by indomethacin (1 microM) and unaffected by the V1-V2 receptor antagonist desGly-d(CH2)5D-Tyr(Et)ValAVP (1 microM) or by NG-nitro-L-arginine methyl ester (L-NAME, 0.1 mM). 4. The selective V2 receptor agonist, DDAVP, caused endothelium-independent, concentration-dependent relaxations in precontracted arterial rings that were inhibited by the mixed V1-V2 receptor antagonist, but not by the V1 receptor antagonist or by pretreatment with indomethacin or L-NAME. 5. Results from this study suggest that vasopressin is primarily a constrictor of human mesenteric arteries by V1 receptor stimulation; vasopressin causes dilatation only during V1 receptor blockade. The relaxation appears to be mediated by the release of vasodilator prostaglandins from the endothelial cell layer and is independent of V2 receptor stimulation or release of nitric oxide. In contrast, the relaxation induced by DDAVP is largely dependent on stimulation of V2 receptors.

The L-arginine analogues NG-monomethyl-l-arginine (l-NMMA, 10−4 m) and NG-nitro-L-arginine methyl ester (l-NAME, 10−4 m), which specifically inhibit the synthesis of nitric oxide from l-arginine, significantly reduced acetylcholine-induced endothelium-dependent relaxations in rings of human omental arteries. The inhibitory potency of l-NMMA and l-NAME was similar. Addition of l-NMMA or l-NAME to the organ bath did not induce any significant changes in the resting tension of the tissues. The effects of l-NMMA were reversed by l-arginine (3 × 10−4 m). The l-NMMA enantiomer, d-NMMA (10−4 m), did not influence either the basal tone of the preparation or the relaxing effects of acetylcholine. Arterial relaxations induced by sodium nitroprusside (10−6 m) were not influenced by incubation with l-NMMA or l-NAME. These results suggest that endothelium-dependent relaxations in human omental arteries are mediated by the endogenous and substrate-specific generation of nitric oxide from l-arginine.

We studied the effects of vasopressin in isolated segments from branches (500-700 micrograms in external diameter) of human middle cerebral arteries obtained during autopsy of 15 patients who had died 3-8 hours before. Paired segments, one normal and the other de-endothelized by gentle rubbing, were mounted for isometric recording of tension in organ baths. In 11 normal segments, vasopressin produced concentration-dependent contractions with an EC50 of 7.0 X 10(-10) M. Removal of the endothelium from 12 segments did not significantly affect vasopressin-induced contractions. Vasopressin produced further contractions in arterial segments with (n = 4) or without (n = 5) endothelium precontracted with KCl. In segments precontracted with prostaglandin F2 alpha, acetylcholine choline caused relaxation only of those with endothelium. At 10(-8) M (n = 11), the vasopressin V-1 receptor antagonist d(CH2)5Tyr(Me)AVP produced a 60-fold shift to the right of the control response curve for vasopressin. Increasing the concentration of the receptor antagonist to 10(-6) M (n = 7) further displaced the control curve in a parallel manner. These results indicate that vasopressin exerts a powerful constrictor action on isolated human cerebral arteries by direct stimulation of V-1 receptors located predominantly on smooth muscle cells. It appears that this contractile response is not modulated by the presence of an intact endothelial cell layer.

5-Hydroxytryptamine (5-HT), norepinephrine (NE), histamine (H) and potassium (K+) chloride induce dose-dependent changes in tension of the isolated middle cerebral artery of the goat. Vasopressin produces highly variable responses followed by tachyphylaxis; angiotensin II is ineffective over a wide dose range. The order of potencies of these vasoactive agents is 5-HT > NE > H > K+. With regard to their ability to induce maximal contractile responses, the order is: H > 5-HT, K+ > NE. Lysergic acid diethylamide (LSD) antagonizes the actions of 5-HT in a manner which progresses from surmountability to unsurmountability of the blockade depending on the concentration of LSD. The blockade exerted by LSD is reversed by washing. Phentolamine and diphenhydramine competitively antagonize the actions of NE and H, respectively. The potency of phentolamine and diphenhydramine in the cerebral arteries of the goat is similar to that determined in different tissues obtained from a variety of animal species. It is concluded that the cerebral arteries of the goat possess receptors for biogenic amines, the most effective of which is 5-HT; receptors for vasoactive peptides are ill defined.

1. Field electrical stimulation of perfused segments (15 mm long) of the goat saphenous artery caused frequency-dependent increases in perfusion pressure which were blocked by tetrodotoxin, phentolamine or prazosin. 2. Mechanical removal of the endothelium augmented both resting perfusion pressure and responses to electrical stimulation. 3. Methylene blue enhanced responses with intact endothelium only. It is likely that the endothelium exerts part of its inhibitory influence through the activation of guanylate cyclase.

Chlorpromazine injections, 200–700 μg, and infusions released histamine, free fatty acids and glycerol from blood-perfused canine subcutaneous adipose tissue; concomitantly there was vasodilatation. In addition, chlorpromazine inhibited vasoconstriction induced by sympathetic nerve stimulation. The results demonstrate that chlorpromazine is lipolytic in adipose tissue and suggest that release of endogenous histamine is one mechanism of action.

The following experiments have been carried out in order to establish the validity of the hypothesis that the cardiac stimulatory effects of 5-hydroxytryptamine (5-HT) are mediated by catecholamines. Release of cardiac noradrenaline (NA) has been observed after administration of 5-HT either intravenously or intracoronarily. After labelling the heart with 3H-5-HT, it was possible to release this amine by cardioaccelerator nerve stimulation even after treatment with an adrenergic β blocker. It is concluded that the cardiac stimulatory effects of 5-HT are mediated by NA; this NA is mainly derived from sympathetic nerve endings by intra-neuronal exchange for 5-HT.

Tyramine induces dose-dependent changes in tension of the isolated middle cerebral artery of the goat. Cocaine, phentolamine and reserpine reduce the sensitivity of the tissue to tyramine by factors of 2.8, 3.7 and 3.7, respectively. The norepinephrine (NE) concentration of the arteries of the circle of Willis is 2.10 µg per gram and the corresponding value for the right atria is 1.25 µ per gram. Reserpine pretreatment (0.02 mg/kg/day for three days) reduces the NE concentration of the cerebral arteries to undetectable levels and that of the right atria to 2.4% of the control value. The relatively high concentration of NE of the cerebral arteries of the goat suggests that this tissue receives considerable sympathetic innervation. It is likely that part of the contractile response to tyramine is due to release of endogenous NE from sympathetic stores in the artery. However, some contractile response to tyramine remains after α-adrenergic blockade, reserpine pretreatment and in the presence of cocaine, suggesting that in addition to an indirect action (release of NE) tyramine also possesses a direct stimulatory effect in cerebral arteries.

Despite considerable research, the question of whether adrenergic drugs exert direct effects on the cerebral circulation has remained unresolved. With the development of a method for monitoring continuously the entire blood flow to one hemisphere in the unanesthetized goat, we have been able to study this problem directly. The effects of epinephrine, norepinephrine, and isoproterenol administered by close intra-arterial injection were investigated in 15 goats in which an electromagnetic flowmeter had been implanted previously on the internal maxillary artery, which, in this animal, provides the sole blood supply to a hemisphere. Both epinephrine and norepinephrine (0.1 to 5.0 µg) produced dose-dependent reductions in cerebral blood flow, a decrease of 55 ± 3% (SEM) occurring with the highest dose. Alpha receptor blockade of the ipsilateral hemisphere with phenoxybenzamine totally or partially abolished this cerebral vasoconstriction. Isoproterenol (0.01 to 1.0 µg) produced dose-dependent increases in cerebral blood flow, an increment of 75 ± 6% occurring with the highest dose. Beta blockade with propranolol totally or partially abolished the cerebral vasodilation induced by isoproterenol. Thus, epinephrine, norepinephrine, and isoproterenol exert powerful direct effects on the cerebral circulation of the unanesthetized goat, and these effects appear to be mediated by alpha and beta receptors.

An animal model has been developed for the continuous measurement of total cerebral blood flow in the unanesthetized, unrestrained goat. We selected the goat because each internal maxillary artery, a branch of the external carotid artery, provides the total blood flow to each hemisphere via the rete mirabile. After the occlusion of the extracerebral vessels of the internal maxillary artery with thrombin, an electromagnetic flow transducer was chronically implanted on this artery, distal to the temporal artery, to measure hemispheric blood flow. Reproducible measurements of cerebral blood flow were obtained in ten unanesthetized goats for periods ranging between two weeks and five months. The mean cerebral blood flow for the ten goats was 133 ± 5 ml/min/100 gm tissue at an average mean aortic pressure of 91 ± 3 mm Hg, heart rate of 79 ± 3 beats/min, arterial P CO CO2 of 31.4 ± 1.0 mm Hg, P 0 02 of 76.6 ± 1.7 mm Hg, and pH of 7.48 ± 0.02. The present experimental preparation allows cerebrovascular hemodynamics to be evaluated under near-normal conditions and is suitable for physiological and pharmacological studies in normal and abnormal states.