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Endothelin-3 was almost equipotent with endothelin-1 (ET-1) in stimulating phosphoinositide hydrolysis, as indicated by [3H]inositol phosphate formation, in cross-chopped slices of guinea-pig cerebellum, rat cerebellum and rat cerebral cortex. The magnitude of [3H]inositol phosphate formation was greatest in guinea-pig cerebellum, approximately 10-fold over basal levels. The similar level of [3H]IP1 accumulation produced by 1 mumol.l-1 ET-1 in rat cerebellum and cerebral cortex (circa 3-fold over basal) did not mirror the large difference in high-affinity [125I]ET-1 binding sites in the two regions. Moreover, the EC50 for ET-induced [3H]IP1 formation differed markedly between the three tissues (7 +/- 2 nmol.l-1 in rat cerebral cortex, 65 +/- 15 nmol.l-1 in guinea-pig cerebellum and greater than 200 nmol.l-1 in rat cerebellum). Only in rat cerebral cortex was the EC50 of the same order as has been reported for peripheral responses to ET-1.

1. The effects of neuropeptide Y on cardiac output, its distribution and organ vascular resistances were determined with tracer microspheres in pithed rats. 2. Neuropeptide Y increased blood pressure by increasing both cardiac output and total peripheral resistance. The increase in cardiac output was due to an increase in stroke volume as heart rate was not changed. Increased vascular resistance in the splenic, renal, testicular, epididymal, skeletal muscle, large intestinal and mesenteric vascular beds contributed to the increase in total peripheral resistance. Vasoconstriction was most pronounced in the mesenteric bed. 3. This study indicates that neuropeptide Y increases blood pressure by increasing cardiac output and total peripheral resistance. The increased cardiac output is possibly due to an increase in venous return, whilst the increased total peripheral resistance was due to regional vasoconstriction, particularly in the mesenteric bed.

1. Pretreatment of rats for 5 days with phenobarbitone (80 mg kg-1 day-1) enhanced the potency enhanced the potency of acetylcholine in opposing noradrenaline-induced vasoconstriction in the isolated perfused superior mesenteric arterial bed; in 10 saline-pretreated control animals the ED50 was 14.0 +/- 3.9 ng whereas it was 3.23 +/- 1.00 ng in 10 phenobarbitone-pretreated animals. 2. In both saline- and phenobarbitone-pretreated rats acetylcholine was ineffective at opposing noradrenaline vasoconstriction after the mesentery had been perfused for 90s with a 0.3% solution of the detergent CHAPS in distilled water (to remove the endothelium), but pressor responses to noradrenaline were unaffected. 3. Pretreatment with phenobarbitone had no effect on the opposition by sodium nitroprusside of noradrenaline pressor responses. Also, the effects of nitroprusside were not affected by perfusion with CHAPS in either control or barbiturate-pretreated groups. 4. Inclusion of indomethacin (10 microM) in the perfusion fluid had no effect on the enhancement by phenobarbitone pretreatment of the endothelium-dependent opposition by acetylcholine of noradrenaline pressor responses; the ED50 values in the absence and presence of indomethacin were, respectively, 2.40 +/- 0.31 ng and 1.87 +/- 0.27 ng (n = 6). 5. The concentration of cytochrome P450 in the microsomal fraction obtained from the mesenteric preparation was increased from 204 +/- 32 (saline-pretreated; n = 7) to 784 +/- 249 pmol g-1 wet wt (n = 7) by the phenobarbitone pretreatment. 6. It is concluded that the increase in potency of acetylcholine as an endothelium-dependent vasodilator by phenobarbitone pretreatment is most probably at the level of the endothelium rather than the vascular smooth muscle.

1. The effects of endothelin-1 and of three analogues in which alanyl residues had been substituted in place of cysteinyl residues were studied in the rat, isolated, Krebs-Henseleit-perfused mesenteric bed and the in situ, blood-perfused, mesenteric and hindquarters circulations of the rat. The effects on the vascular responses to these peptides of removing the endothelium by detergent perfusion or of cyclo-oxygenase inhibition by indomethacin were also determined. 2. In all three preparations, endothelin-1 was a potent vasoconstrictor (ED50 values ranged from 40 to 400 pmol) although it was rather less potent in the hindquarters than in the mesentery. Also, the maximum response was very much smaller in the isolated mesentery (24.7 +/- 2.1 mmHg) than in the in situ mesentery (81.8 +/- 2.6 mmHg) or hindquarters (107 +/- 10 mmHg). 3. Removal of the endothelium by perfusion with detergent significantly enhanced the potency of endothelin as a vasoconstrictor in the in situ messentery, but reduced the maximum response obtained, whereas removal of the endothelium in vitro significantly increased the maximum response without changing the ED50. The presence or absence of indomethacin had no significant effects in the blood-perfused hindquarters preparation or the isolated mesentery but, after administration of 5 mg kg-1 indomethacin to the in situ mesenteric preparation, the maximal response to endothelin-1 was enhanced. 4. When the preparations were preconstricted with alpha 1-adrenoceptor agonists, endothelin-1 had modest vasodilator effects. These vasodilator effects were abolished when the endothelium was destroyed by detergent perfusion. 5. Both [Ala3,11]endothelin-1 and [Ala1,15]endothelin-1 were also vasoconstrictor agents in the mesenteric preparations but they were less potent than endothelin-1 itself; [Ala3,11]endothelin-1 was intermediate in potency between endothelin-1 and [Ala1,15]endothelin-1. In the in situ preparation these analogues gave similar maximal responses to the parent peptide but, in vitro, they gave maximal responses that were much greater than that of endothelin-1 and which were similar to those found with all 3 peptides in the in situ mesentery. Destruction of the endothelium in vitro had no effect on the responses to these 2 analogues and the log dose-response curve for [Ala1,15]endothelin-1 in the isolated mesentery was biphasic. 6. A third analogue possessing no disulphide bridges [( Ala1,3,11,15]endothelin-1) was a partial agonist in the in situ preparations but had no vasoconstrictor effect in the in vitro mesentery. It had no vasorelaxant effect in the hindquarters preparation but it enhanced the responses to endothelin-l when the 2 peptides were administered together in all 3 preparations. 7. It is concluded that it is not essential for the endothelin family of peptides to possess 2 disulphide bridges for them to be vasoconstrictor agents. However, only endothelin-1, of the 4. peptides studied, showed either endothelium-dependent vasorelaxant activity or modulation by the endothelium of its pressor effects. This, together with some differences in the vasoconstrictor log dose-response curves to the peptides and the results of co-administration of [Ala' 3'11"15]endothelin-1 and endothelin-1, suggests that there may be more than one receptor type mediating vascular responses to the peptides studied.

[125I]Endothelin binding sites occurred in glomeruli of human, monkey, rat and dog kidney but not rabbit glomeruli. The renal medulla had more binding sites in all species, with the greatest densities of all in the rat and monkey renal papillas. Binding in rat kidney was inhibited by [Ala3,11]endothelin with lower potency than endothelin but not by unrelated peptides. These binding sites may represent the endothelin receptors and suggest actions for endothelin on renal function.

Cardiac output and its regional distribution were determined with radioactive microspheres in pentobarbitone anaesthetised rats 16 h and 5 days after sympathectomy with 6-hydroxydopamine (150 mg/kg i.p. over 24 h). Distribution was not different at either time in sympathectomised animals compared to controls given i.p. saline/ascorbic acid. Cardiac output was 12% greater 16 h after sympathectomy than in the controls but heart rate and blood pressure were 20% lower. Stroke volume was 43% greater in animals given 6-hydroxydopamine and total peripheral resistance 29% lower than in sham-sympathectomised rats. Five days after sympathectomy, blood pressure and heart rate were still lower in sympathectomised rats, but cardiac output and total peripheral resistance were not significantly different from control. It is concluded that basal sympathetic tone does not determine the distribution of cardiac output at rest and that its primary effect on the heart is to maintain heart rate rather than contractility.

1. Pithed rats were respired at a fixed rate of 54 cycles min-1 and with a ventilation volume of either 20 (control) or 10 ml kg-1. In these two preparations, the dose-response relationships for the systemic blood pressure responses to endothelin-1, administered i.v., were examined. Also, cardiac output, its distribution, tissue blood flows and vascular resistances were determined at both respiratory volumes in pithed rats given saline or during pressor responses to endothelin-1 (750 ng, i.v.). Finally, a comparison was made of the pressor responses to endothelin-1 in the blood perfused superior mesenteric arterial bed of pithed rats respired at 10 or 20 ml kg-1. 2. In control rats the systemic blood pressure responses to i.v. endothelin-1 were biphasic with an initial, transient (30 s) decrease in blood pressure followed by a well sustained pressor response. These responses were dose-dependent (the ED50 for the pressor response being 0.27 +/- 0.04 micrograms). The pressor effect of endothelin-1 was due to an increase in total peripheral resistance with no change in heart rate or cardiac output. This increased total peripheral resistance was due to vasoconstriction of the spleen, stomach, large intestine, small intestine and the pancreas/mesentery (in which it was most severe). Endothelin-1 also increased blood flow through the heart, lungs, liver, epididimides, fat and skin through redistribution of cardiac output to these vascular beds. 3. At the lower ventilation volume there was moderate acidosis, hypoxia and hypercapnia relative to those rats respired at 20 ml kg-1. With respiration at 10 ml kg-1, the pressor response to endothelin-1 was not sustained and, after oscillations in both blood pressure and heart rate, death occurred 15-20 min after administration. The pressor effect resulted from increases in cardiac output (due to increased stroke volume) and total peripheral resistance: the latter was caused by vasoconstriction in the stomach, small intestine, large intestine and pancreas/mesentery. Endothelin-1 increased blood flow through the heart, lungs, liver, kidneys, testes, fat and skin due to either an increase in cardiac output, redistribution of cardiac output or both. 4. Endothelin-1 induced dose-dependent pressor responses in the mesenteric bed in situ. At the lower ventilation volume the potency of endothelin-1 in this vascular bed was increased approximately two fold with the ED50 being 68 +/- 7 pmol compared to 113 +/- 15 pmol in the rats respired at 20 ml kg-1. 5. This study indicates that, in normoxic control pithed rats, the pressor response to endothelin-1 was due largely to vasoconstriction of the splanchnic vascular bed. In rats with moderate hypoxia, hypercapnia and acidosis, the pressor response was due to vasoconstriction of the gastrointestinal tract as well as an increase in cardiac output. Endothelin-1 induced profound vasoconstriction in the mesenteric bed of the pithed rat both in vivo and in situ. The potency of endothelin-1 on this bed in situ was doubled by lowering the ventilation volume. An increase in cardiac contractility and severe gastrointestinal vasoconstriction may be the initial events leading to the eventual toxic effect of endothelin-1 in the hypoxic pithed rat.

The distribution of cardiac output was determined by 15 micron radioactive microspheres in all the major organs of spontaneous, DOCA/NaCl and one kidney Goldblatt hypertensive rats and compared to normotensive Wistar rats. Although there were alterations in cardiac output distribution which were characteristic of each model of hypertension significant changes were common to all three were an increased distribution to skeletal muscle with decreases to the lungs, spleen and hepatosplanchnic tissues. The results suggest that alterations in peripheral resistance induced by hypertension are of unequal importance in the different vascular beds with certain vascular resistance changes occurring irrespective of the origin of the hypertension.

Interactions between alpha 2-agonists and noradrenaline vasoconstrictor responses were studied in the superior mesenteric arterial bed of the rat by use of perfusion both in situ with blood and in vitro with Krebs-Henseleit solution. Xylazine (1.9 X 10(-6) mol) administered into the perfusion circuit reduced the maximum response to noradrenaline in the in situ preparation by 35% and decreased the pD50 for noradrenaline from 8.5 +/- 0.01 to 7.9 +/- 0.13 (n = 7). Yohimbine (1 mg kg-1, i.v.) gave a small parallel shift in the noradrenaline log dose-response curve and prevented the reduction in the maximum response by subsequent administration of xylazine. In vitro, xylazine (1.9 X 10(-6) mol) also gave a long-lasting reduction of 37% in the maximum response but did not affect the mid-point sensitivity to noradrenaline. Yohimbine (10(-6) M) did not change either of these effects. Clonidine (1.9 X 10(-6) mol) did not affect the maximum response to noradrenaline in vitro but did reduce the pD50 from 7.72 +/- 0.17 to 6.9 +/- 0.17 (n = 6). Yohimbine did not change these effects. Guanfacine (1.8 X 10(-6) mol) had no effect on the sensitivity of the in vitro preparation to noradrenaline but did reduce the maximum response by 20%. Yohimbine (10(-6)M) prevented the depression of the maximum response. It is concluded xylazine and clonidine interfere with noradrenaline induced vasoconstriction only to a limited extent through their interaction with alpha 2-adrenoceptors and that some other, as yet uncharacterized mechanism which may be activated by their aryl amidine structure, is responsible for their in vitro effects.

Cardiac output, its distribution and tissue blood flows were determined with tracer microspheres in pithed rats during pressor responses elicited by either alpha 1-adrenoceptor agonists (cirazoline, phenylephrine) or alpha 2-adrenoceptor agonists (xylaxine, B-HT 933). Two doses were used for each of cirazoline and B-HT 933 and phenylephrine was investigated in the presence of propranolol (3 mg kg-1). The rats were pithed under halothane anaesthesia. Cardiac output was increased by xylazine, the higher dose of B-HT 933 and phenylephrine. Heart rate was increased by phenylephrine and the higher doses of both cirazoline and B-HT 933. Stroke volume was greater in those groups given xylazine, phenylephrine and the higher dose of B-HT 933 but was decreased in those animals given the higher dose of cirazoline. Both alpha 2-adrenoceptor agonists increased the number of microspheres trapped in the lungs and the proportion of the cardiac output passing through the hepatic artery but decreased that flowing through the spleen and gastrointestinal tract. The higher dose of B-HT 933 also decreased the fraction of cardiac output flowing to the kidneys but kidney blood flow was maintained as a result of the increased cardiac output. Also, this treatment reduced blood flow in the epididimal fat pads. Both alpha 1-adrenoceptor agonists increased the fraction of cardiac output received by the coronary vasculature but the only other effect on distribution common to these agents was an increase in the percentage of the cardiac output passing to the hepatic artery. Cirazoline decreased the proportion of cardiac output distributed to the gastrointestinal tract and spleen but the total fraction of cardiac output passing to the hepatosplanchnic region was maintained as a result of the increase to the hepatic artery. Cirazoline markedly reduced the proportion of the cardiac output received by the kidneys and absolute flow in these organs was only 1.4% of control after the higher dose of this agonist but flow at the lower dose was maintained by the higher cardiac output. It is concluded that there is a significant contribution to the pressor responses elicited by alpha-agonists resulting from an alpha-adrenoceptor-mediated increase in cardiac output that may result from greater heart rates or stroke volumes. Also, there is a differential distribution of alpha-receptor subtypes throughout the vasculature which is especially noticeable in the kidneys.

Cardiac output distribution in the rat was found to be affected by age. Cardiac index and blood flow to the liver, kidneys, skin and skeletal muscle were lower in 11-12 month compared to 3-4 month old rats.

1. Cardiac output, its distribution and regional vascular resistances were determined with tracer microspheres in pithed rats in the presence of the angiotensin converting enzyme inhibitor enalapril. The effects of enalapril on the cardiovascular responses elicited by either the alpha 1-adrenoceptor agonist phenylephrine or the alpha 2-adrenoceptor agonist xylazine were determined. 2. Enalapril decreased diastolic and mean blood pressure by decreasing cardiac index and total peripheral resistance. It induced vasodilatation in the kidney, epididimides, epididimidal fat and pancreas/mesentery. Vasoconstriction in the lungs, testes and liver was evident following enalapril administration as well as a decrease in the proportion of cardiac output passing to them, whilst the pancreas and mesentery received a greater proportion of the cardiac output. All the above effects of enalapril were reversed by infusion of angiotensin II at a rate of 75 ng kg-1 min-1. 3. Xylazine increased blood pressure by increasing both cardiac output and total peripheral resistance. Enalapril did not affect the increase in cardiac output caused by xylazine but decreased the effect of the alpha 2-agonist on blood pressure by preventing the increase in total peripheral resistance. Inhibition by enalapril of xylazine-induced vasoconstriction in the kidneys, testes, fat and gastrointestinal tract contributed to the decrease in total peripheral resistance. Enalapril also inhibited xylazine-induced changes in cardiac output distribution to the liver, lungs and heart. All the above effects of enalapril were reversed by infusion of angiotensin II. 4. Enalapril decreased the sustained phase of the pressor response to an infusion of phenylephrine whilst having no effect on the initial peak pressor response to a bolus injection of phenylephrine. Phenylephrine increased both cardiac output and total peripheral resistance and enalapril abolished its effect on total peripheral resistance whilst having no effect on the increase in cardiac output. Enalapril inhibited phenylephrine-induced vasoconstriction in the testes, fat, muscle, spleen and gastrointestinal tract. Enalapril also inhibited phenylephrine-induced changes in cardiac output distribution to the lungs and liver. The infusion of angiotensin II did not fully reverse the inhibitory effect of enalapril either on the phenylephrine-induced increases in diastolic blood pressure or on the vasoconstriction in the fat, spleen and gastrointestinal tract, but did reverse all other effects of enalapril.

In order to determine whether or not glucagon released from the pancreas might have local vascular effects, the actions upon regional haemodynamics in the anaesthetised rat of two doses of glucagon (2 and 10 micrograms kg-1 min-1) infused intrasplenically (and thus into the portal vein) were compared with those of a single dose (2 micrograms kg-1 min-1) infused i.v. Infusion of glucagon i.v. produced a significantly increased heart rate (by 6%) and cardiac output (by 23%) in the experimental animals compared to those receiving saline by the same route. Total peripheral resistance fell by 24%. A greater proportion of the cardiac output passed to the coronary and renal vascular beds and blood flow was increased in the spleen, testes, pectoral skeletal muscle, stomach and small intestine as well as the heart and kidneys. The lower dose infused intrasplenically had no significant effect on cardiac output or total peripheral resistance but significantly increased the proportion of cardiac output passing both to the stomach and the small intestine such that the percentage of cardiac output flowing through the portal vein increased from 19.1 +/- 1.1% to 23.8 +/- 1.7%. Intrasplenic infusion of 10 micrograms kg-1 min-1 significantly increased cardiac output (by 29%) but reduced total peripheral resistance by 37%. Greater fractions of the cardiac output were received by the spleen, small intestine and epididymides. Blood flow was increased in these organs and the skin, kidneys, stomach, large intestine and the mesentery. It is concluded that pharmacologically effective amounts of glucagon only passed into the systemic circulation with the higher dose infused intrasplenically.(ABSTRACT TRUNCATED AT 250 WORDS)

Choline acetyltransferase activity (presynaptic cholinergic system) and high affinity binding of cholinergic antagonists (postsynaptic cholinergic system) were measured in brain tissue removed after death from both mentally normal and demented old people. Muscarinic receptor binding sites in frontal cortex decreased with advancing years only in old people without appreciable morphological evidence of senile degeration. Preliminary data for temporal lobe suggested that also in Pick's disease the density of receptor binding sites is reduced. The markers are not significantly reduced in cases of mixed senile and vascular dementia. However, in non-vascular senile dementia of the Alzheimer type, there were indications that the presynaptic marker is selectively depleted. Therefore, centrally acting anticholinesterases might be beneficial, particularly in the early stages of the disease.

Treatment of guinea-pigs for 24 days with a single daily dose of mepyramine, 5 mg/kg i.p. had no consistent significant effect on the number of histamine H1-receptors, determined from the promethazine-sensitive binding of [3H]mepyramine, in cerebellum, cerebral cortex, hippocampus, hypothalamus or intestinal smooth muscle. Measurement of the time course of the block of H1-mediated blood pressure responses in conscious guinea pigs following a single i.p. injection of mepyramine, 5 mg/kg, suggested that some degree of block persisted for up to 16 h. Treatment of guinea pigs with two daily doses of 5 mg mepyramine/kg, i.p., for 10 days had no consistent effect on the KD or capacity of promethazine-sensitive [3H]mepyramine binding to cerebellum or hypothalamus.

Cardiac output and liver blood flow were measured using 15-micron diameter radioactive microspheres in anaesthetized male rats 12, 24 and 48 h and 7 days after induction of acute renal failure with glycerol. Plasma urea concentration was greatest in those rats studied 48 h after glycerol injection and at 7 days animals could be divided into 'recovering' and 'azotemic' on the basis of plasma urea levels. Cardiac output was significantly lower at 12 h than that found in control rats, but it was significantly greater than control values in azotemic animals at 48n h and in the 'recovering' group of rats at 7 days. Changes in cardiac output did not correlate with alterations in haematocrit. Liver blood flow showed a number of changes in the azotemic animals relative to the control rats; at 12 h it was significantly lower in the glycerol-treated rats whilst it was increased at 48 h and in both groups of animals at 7 days. When the proportion of cardiac output distributed to the liver was determined using 50-micron diameter microspheres, it was not significantly different from that determined using the smaller microspheres at 12 and 48 h after glycerol injection. This indicates that the results with the smaller microspheres were not distorted by incomplete trapping in the hepatic and splanchnic vascular beds. The implications of altered liver blood flow for drug metabolism in renal failure are discussed.

Putative receptors for endothelin were localised autoradiographically in frozen sections of rat and human brain using [125I]endothelin as a ligand. In the rat brain the highest densities were in the granular layer of the cerebellum, choroid plexus, hippocampus, and habenular nucleus. Similar brain high densities were found in the human cerebellum and hippocampus. The non-vascular pattern of distribution suggests that endothelin may have a function as a modulator of neuronal function in addition to its possible involvement in the regulation of vascular tone.

The in-situ blood perfused rat superior mesenteric arterial and right iliac arterial preparations were used to investigate the effects of pretreatment for 5 days with either phenobarbitone (80 mg kg-1 daily) or 6-methylprednisolone (17 mg kg-1 daily) on regional vascular resistances. The elevation of the regression of perfusion pressure on perfusion rate in the superior mesenteric arterial bed was significantly decreased by both phenobarbitone and 6-methylprednisolone over the range of flow rates used. Neither phenobarbitone nor 6-methylprednisolone had a significant effect on hepatic portal venous pressure nor was there any significant effect on the regression of perfusion pressure on flow rate in the in-situ iliac arterial bed. It is concluded that pretreatment with either phenobarbitone or 6-methylprednisolone lowers vascular resistance in the superior mesenteric arterial by approximately 9 and 8% respectively but does not affect vascular resistance in the iliac arterial bed.

1 The effects of the hypolipidaemic agents ICI 53072 and clofibrate on cardiac output and its distribution to the hepatosplanchnic bed were determined by the use of radioactive microspheres in the rat. The effects of these agents on hepatic DNA content were compared with those of phenobarbitone. Also the effects of ICI 53072 on hepatic microsomal enzymes and bile flow were determined together with the effects of phenobarbitone. 2 ICI 53072 and clofibrate both increased liver size and liver blood flow. A daily dose of 25 mg kg-1 ICI 53072 for 5 days increased liver weight by 55% and liver blood flow by 43%, the latter by enhancing the proportion of cardiac output passing to the hepatosplanchnic bed. The increased liver blood flow with clofibrate (480 mg kg-1 daily for 5 days) was the result of greater cardiac output but the change (35%) was half the increase in liver weight. 3 Phenobarbitone (80 mg kg-1 daily for 5 days) produced a fall in DNA content per unit mass of liver but no change in hepatic DNA relative to body weight. ICI 53072 (25 mg kg-1 daily) increased hepatic DNA relative to body weight but by a lesser extent than it increased liver weight as a proportion of body weight; hence DNA content per unit mass of liver decreased. Clofibrate at three dose levels increased hepatic DNA relative to body weight but only one dose significantly decreased DNA content as a proportion of liver weight. 4 Phenobarbitone (80 mg kg-1 daily) increased bile flow whereas ICI 53072 (25 mg kg-1 daily) had no effect. Both treatments increased hepatic cytochrome P450 content and cytochrome c reductase activity. 5 It is concluded that phenobarbitone increases liver size by hepatocyte enlargement rather than cellular proliferation but that the hepatomegaly produced by the hypolipidaemic agents, at least at some doses, is due to a mixture of both processes. 6 It is further concluded that there is no simple relationship between the mechanism of hepatic enlargement resulting from drug treatment and changes in liver blood flow.

The responses of the nasal capacitance vessels of the cat were recorded following intra-arterial injections of beta-adrenoceptor agonists and histamine H1-and H2-receptor agonists. Isoprenaline evoked vasodilation and propranolol (beta-adrenoceptor antagonist) caused a parallel shift to the right of the isoprenaline log dose-response curve. Histamine, 2-(2-aminoethyl)pyridine (H1-agonist) and 4-methylhistamine (predominantly H2-agonist) all evoked vasodilation. Metiamide (H2-antagonist) produced a further small parallel shift to the right of the histamine log dose-response curve after the administration of mepyramine (H1-antagonist). It is concluded that the nasal capacitance vessels of the cat contain beta 2-adrenoceptors and H1-and H2-histamine receptors.

1. The anti-dopaminergic effects of several dibenzodiazepines were examined on the dopamine-stimulated adenylate cyclase in rat striatal homogenates. The "cis" isomer of clozapine, HF-2046, was the most potent in this respect and perlapine, which is devoid of neuroleptic activity, was the weakest. 2. The anti-muscarinic effects of the same compounds were measured by using the muscarinic affinity label 3H-propylbenzilylcholine mustard. HF-2046 was the most potent and loxapine the least potent of the drugs used. 3. The anti-dopaminergic effects of the drugs correlate well with neuroleptic but not with extrapyramidal effects. The anti-dopaminergic/anti-muscarinic ratio, however, correlates well with extrapyramidal rather than neuroleptic effects.

1. The effect of varying artificial respiratory volume (at a fixed rate of 54 min-1) on cardiac output, its distribution and tissue blood flows were determined with tracer microspheres in control pithed rats or during pressor responses to either the alpha 1-adrenoceptor agonist phenylephrine or the alpha 2-agonist xylazine. Phenylephrine was investigated in the presence of propranolol (3 mg kg-1). The rats were pithed under halothane anaesthesia. 2. A respiratory volume of 15 ml kg-1 produced modest hypercapnia (PaCO2 = 47 mmHg), hypoxia (PaO2 = 60 mmHg) and acidosis (pH = 7.35) relative to control animals respired at 20 ml kg-1 (PaCO2 = 32 mmHg; PaO2 = 77 mmHg; pH = 7.47). In rats respired at 15 ml kg-1, total peripheral resistance was lower, and cardiac output greater (due to increased stroke volume), than in the controls. Lowering respiratory volume reduced distribution of cardiac output to the kidneys, increased it to the large intestine and also increased blood flow through the gastrointestinal tract, skin and spleen. A respiratory volume of 30 ml kg-1 gave mild hypocapnia (PaCO2 = 19 mmHg), hyperoxia (PaO2 = 101 mmHg) and alkalosis (pH = 7.59) compared to 20 ml kg-1 but had no effect on cardiac output distribution or organ blood flow although heart rate was 29% greater at 30 ml kg-1. 3. Xylazine (500 micrograms bolus followed by 100 micrograms min-1 infusion) at all three respiratory volumes gave well-sustained mean pressor responses of 62-64 mmHg by increasing both total peripheral resistance and cardiac output (resulting from increased stroke volume). It increased the proportion of cardiac output passing to the liver, reduced that going to the spleen and gastrointestinal tract and increased cardiac, renal and hepatosplanchnic blood flows. 4. The secondary, relatively sustained, pressor effect of phenylephrine (5 micrograms bolus followed by 0.4 micrograms min-1 infusion, i.v.) varied at the 3 respiratory volumes with mean values from 32 to 53 mmHg. This response was due to both increased total peripheral resistance and cardiac output (resulting from greater stroke volumes and/or heart rates). Phenylephrine increased the proportion of cardiac output passing to the gastrointestinal tract, heart, kidneys and hepatosplanchnic bed and increased cardiac, hepatosplanchnic, renal and gastrointestinal blood flows. 5. Respiratory volume had no effect on the cardiovascular effects of xylazine. However, respiratory volume modified the effects of phenylephrine on heart rate and changed the relative contributions of stroke volume and heart rate to the increased cardiac output. It also influenced the effects of phenylephrine on cardiac output distribution to the liver, epididimides and hepatosplanchnic bed and on blood flow through skeletal muscle and the large intestine. 6. Changes in respiratory volume of air ventilated pithed rats thus influence cardiac output, its distribution and regional blood flows. Such changes can also differently influence the responses of various vascular beds to phenylephrine whilst having no effect on their responses to xylazine.

The nature of the adrenoceptors and dopamine receptors mediating vascular responses in the in-situ blood perfused superior mesenteric arterial bed of the rat have been studied. alpha 1-Adrenoceptor agonists produced vasoconstriction but alpha 2-agonists had no significant effect on vascular resistance. The vasoconstrictor effects of noradrenaline were antagonized by low doses of prazosin (26 nmol kg-1 i.v.). Isoprenaline and salbutamol produced vasodilation when the vasculature was preconstricted with arginine vasopressin. The responses to isoprenaline were potently antagonized by propranolol (1.69 mumol kg-1 i.v.) and weakly but significantly reduced by practolol (3.75 mumol kg-1 i.v.) whereas the responses to salbutamol were unaffected by the same dose of practolol. After preconstriction of the vasculature and alpha-adrenoceptor blockade, dopamine and apomorphine produced dilator responses with both compounds producing the same maximal response and apomorphine being 1.8 times more potent than dopamine. The dopamine responses were present after the animals had been pithed and were resistant to spiperone (506 nmol kg-1 i.v.) but were antagonized by cis-alpha-flupenthixol (460 nmol kg-1 i.v.). These results suggest that this vascular bed possesses vasoconstrictor alpha 1- but not alpha 2-adrenoceptors, vasodilator beta 1- and beta 2-adrenoceptors and vasodilator dopamine receptors which appear similar to the D1-type found centrally.

The cardiovascular effects of intracerebroventricular (i.c.v.) bradykinin and melittin were investigated in the anaesthetized rat. Bradykinin, 30 micrograms, increased mean arterial pressure by 15 mmHg and this was the result of an increase in peripheral resistance; heart rate and cardiac output were unchanged. Tissue blood flow was lower in the skin and spleen in the animals given bradykinin than the controls. Significant increases in tissue vascular resistance occurred in the skin and several organs of the splanchnic region, the spleen, stomach, large intestine and the pancreas/mesentery. Melittin infusion gave a biphasic response in systemic blood pressure in which a depressor response was followed by a pressor phase; the pressor stage was accompanied by an increase in heart rate. Since melittin is a stimulant of membrane bound kallikrein, the results lend limited support to the hypothesis that there is a kallikrein-kinin system endogenous to the central nervous system which is involved in cardiovascular regulation.

1. The autoperfused superior mesenteric arterial bed of the rat was used to study the opposition by carbachol of pressor responses to noradrenaline and the effects of methylene blue, the detergent CHAPS and indomethacin on pressure/flow relations. 2. Carbachol (1 ng-3 micrograms) reduced the pressor response to 1 microgram noradrenaline in a dose-dependent manner with an ED50 = 25.5 +/- 6.0 ng and a maximum inhibition of 51.8 +/- 1.9%. Perfusion of the mesenteric bed with 0.3% CHAPS in saline for 150s abolished the reduction by carbachol of the noradrenaline pressor response. The effect of carbachol was also abolished by infusion of 1% methylene blue into the mesenteric vascular bed. Indomethacin (5 mg kg-1) was without significant effect on the carbachol opposition of noradrenaline pressor responses. None of the 3 treatments had any effect on the response to 1 microgram noradrenaline. 3. Perfusion with CHAPS before determination of pressure/flow relations, or infusion of methylene blue during their determination, steepened the regression of pressure upon flow to the same extent; at all the flow rates used (0.4-3.54 ml min-1) pressure was greater as a result of the treatment than in control animals. Pretreatment with indomethacin had no effect on pressure/flow relations. 4. It is concluded that carbachol opposition to noradrenaline pressor responses in the blood perfused superior mesenteric arterial bed of the rat shows the characteristics of being mediated by endothelium-dependent relaxing factor (EDRF). Since vascular resistance increases more rapidly than in controls when the endothelium is functionally inhibited by treatment with CHAPS or perfusion with methylene blue, it appears that EDRF has a role in vivo in the modulation of myogenic vascular tone.

[3H]quinuclidinyl benzilate ([3H]QNB) was used to investigate the effects of administration of cycloheximide to mice on the concentration of muscarinic receptors in the cerebral cortex. A single subcutaneous (s.c.) injection of cycloheximide (3.5 mg/kg) reduced receptor concentration by 18% afer an apparent latency of 1 hr. A single intraperitoneal (i.p.) injection of 3.5 mg/kg produced a 14% reduction in muscarinic receptor concentration 20 min after injection. After both s.c. and i.p. administration the effects of cycloheximide were reversible, dose-related and maximal at a dose of 3.5 mg/kg. The maximum reductions in receptor concentrations obtained were 13-18%. Multiple doses of cycloheximide did not produce greater falls in receptor concentration than single doses and did not prevent its return towards control levels. Treatment of mice for 10 day with cycloheximide reduced muscarinic receptor concentration to 71% of the control at 3 days after stopping administration; receptor levels returned to control values 35 days after the last dose of cycloheximide. Treatment of mice with cycloheximide had no effect on the affinity of [3H]QNB for the receptor and, in vitro, 10(-4)M cycloheximide did not have any significant effect on the binding of the radiolabel.

1. Pressor responses to arginine vasopressin (AVP) were determined in the rat isolated superior mesenteric arterial bed perfused with Krebs-Henseleit solution and compared with those to noradrenaline. 2. In control preparations the maximum pressor response to the peptide was 34 +/- 3 mmHg and the ED50 was 21 +/- 4 mu (n = 11). The maximal pressor response to noradrenaline (30 micrograms) was 100 +/- 6 mmHg (n = 8). After removal of the functional endothelium with the detergent CHAPS, the maximum pressor response to AVP increased to 64 +/- 4 mmHg and the ED50 decreased to 7.7 +/- 2.0 mu (n = 11) but the response to 10 micrograms noradrenaline was unaffected. 3. Nordihydroguaiaretic acid (2.5 microM) significantly increased the maximum pressor response to AVP from 41 +/- 2 mmHg to 86 +/- 8 mmHg (n = 9); the ED50 was unchanged. Methylene blue (50 microM) also increased the maximum response from 41 +/- 3 mmHg to 87 +/- 13 mmHg (n = 8) without affecting the ED50. Neither treatment significantly affected the response to 10 micrograms noradrenaline. 4. Neither indomethacin (10 microM) nor BW755C (10 microM) had significant effects upon either the maximal response or ED50 for AVP nor did they affect the response to 10 micrograms noradrenaline. 5. In 6 preparations SKF-525A significantly increased both the ED50, from 9.8 +/- 2.1 to 22 +/- 2 mu, and the maximum response, from 36 +/- 2 to 70 +/- 3 mmHg. 6. It is concluded that the pressor response to AVP in this vascular bed is modulated, in the presence of functional endothelium, by the simultaneous release of endothelium-derived relaxing factor.

The binding of one irreversible and two reversible radioactive antagonists to muscarinic receptors in synaptosome preparations of rat cerebral cortex has been studied. The ligands all bind to the same receptor pool and directly and competitively yield self-consistent binding constants closely similar to those obtained by pharmacological methods on intact smooth muscle. The binding process for antagonists seems to be a simple mass action-determined process with a Hill slope of 1.0. The quantitative correlations strongly support the view that the receptor studied by ligand binding corresponds to the receptor studied by pharmacological methods. Inhibition of antagonist binding by most agonists shows a reduced Hill slope which also applies to direct binding studies of [3H] acetylcholine. Mechansims that might account for the behavior of agonists are discussed but do not conclusively point to any single mechanism.

Human/porcine endothelin-1 (ET-1) dose-dependently increased perfusion pressure in both Krebs-Henseleit and blood-perfused superior mesenteric arterial bed preparations of the rat. In vitro, it was a partial agonist relative to two analogs, [Ala1,15]- and [Ala3,11]-ET-1, and the maximum response was increased by removal of the endothelium. Endothelial destruction had no effect on the responses to either [Ala1,15]- or [Ala3,11]-ET-1. [Ala1,3,11,15]-ET-1 was not an agonist in vitro but was a partial agonist relative to ET-1 and [Ala1,15]- and [Ala3,11]-ET-1 in vivo. Also, the responses to [Ala1,15]-ET-1 in the blood-perfused preparation were best described by a two-site model. These results suggest that there may be two types of receptor for these peptides. In vivo, 5 mg/kg of indomethacin potentiated the maximum response to ET-1, suggesting that its actions may be opposed by vasodilator cyclo-oxygenase products.

1 The reaction of tritiated propylbenzilylcholine mustard ([(3)H]-PrBCM; N-2'-chloroethyl-N-[2'',3''-(3)H(2)] -propyl-2-aminoethylbenzilate) with homogenates of mammalian brain has been studied.2 The uptake can be divided into an atropine-sensitive component of fixed capacity (380 pmol/g protein in the rat) and an atropine-insensitive part.3 The atropine-sensitive portion is identified as muscarinic receptor by its insensitivity to nicotinic antagonists and anticholinesterases and its sensitivity to a range of muscarinic antagonists.4 The uptake of [(3)H]-PrBCM is also inhibited by muscarinic agonists and there is reasonable quantitative agreement between the affinities of agonists estimated in this way and in intact tissues by physiological responses.5 The fraction of [(3)H]-PrBCM uptake inhibited by muscarinic antagonists and agonists is the same.6 The amount of receptor found in six mammalian species was inversely related to the size of the brain, but the rates of alkylation and the sensitivity to atropine were not dissimilar.

1. Blood pressure responses to single and multiple bolus doses of the alpha 2-adrenoceptor agonist B-HT 933 were analysed in intact anaesthetized rats which were either normotensive or hypotensive as a result of haemorrhage. Single bolus doses of B-HT 933 in normotensive rats induced a fall in blood pressure, whilst further doses induced dose-dependent pressor responses which were inhibited by the alpha 2-adrenoceptor antagonist yohimbine and unaffected by the alpha 1-adrenoceptor agonist prazosin. In the haemorrhagic, hypotensive animals, single bolus doses of B-HT 933 induced immediate dose-dependent pressor responses; the maximum pressor responses to the bolus of B-HT 933 and its ED50 values were the same in both the normotensive and hypotensive, haemorrhagic animals. 2. Cardiac output, its distribution and tissue blood flows were determined with tracer microspheres in intact anaesthetized normotensive and haemorrhagic, hypotensive rats during depressor (normotensive) and pressor (normotensive and hypotensive) responses to B-HT 933. Haemodynamics were also determined during pressor responses to the alpha 1-adrenoceptor agonist amidephrine. 3. In control normotensive rats, a single dose of B-HT 933 (1 mg kg-1) reduced blood pressure by reducing cardiac output (through a decrease in heart rate). It increased the fractional distribution of cardiac output to the spleen and stomach, reduced it to the heart and liver and reduced cardiac and hepatic blood flow. A further dose of B-HT 933 (1 mg kg-1 bolus followed by 100 micrograms min-1 infusion) increased blood pressure by increasing total peripheral resistance, which was accompanied by decreased proportions of cardiac output passing to the heart, liver and testes. There was also increased fractional distribution of cardiac output to the lungs, spleen, kidneys and stomach but blood flows through the liver and testes were reduced. Amidephrine (6 micrograms kg-1 bolus followed by 0.5 micrograms min-1 infusion) increased blood pressure by increasing cardiac output through an increased stroke volume. It increased cardiac output distribution to the kidneys and brain, increasing blood flow through the heart, lungs, brain, testes, epididimides, skin and large intestine. 4. Haemorrhage caused a fall in blood pressure which resulted from decreased total peripheral resistance and cardiac output (the latter due to decreases in both heart rate and stroke volume). It reduced the proportion of cardiac output distributed to the lungs, spleen, kidneys, testes and pancreas/mesentery and decreased blood flow through these organs as well as through the heart, liver, brain, epididimides, skin and the gastrointestinal tract.4

The effect of urethane and pentobarbital anaesthesia and hepatic portal vein catheterization on liver blood flow was investigated in the rat. Liver blood flow with pentobarbital anaesthesia was 40% greater than with urethane. Hepatic portal vein catheterization had no effect under pentobarbital anaesthesia whereas it produced an 18% fall in liver blood flow with urethane.

1 The synthesis of tritium labelled propylbenzilylcholine mustard ([(3)H]-PrBCM; N-2'-chloroethyl-N-[2'', 3''-(3)H(2)] propyl-2-aminoethyl benzilate) is described.2 The uptake by muscle strips was measured and shown to be considerably increased by previous immersion of the muscle in distilled water.3 A considerable part of the uptake is inhibited selectively by atropine, but not by nicotinic antagonists. A number of muscarinic agonists also inhibit uptake and their apparent affinity constants have been determined.4 The uptake by atropine-sensitive sites is temperature-insensitive, whereas the other sites are temperature-sensitive. Recovery is highly temperature-sensitive and there is good agreement between recovery of sensitivity to agonists and loss of radioactivity from the muscle.