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Patients with asthma are a target group for medication with beta2-agonists, often in combination with corticosteroids. Salbutamol is commonly marketed as racemate. R-Salbutamol carries beta2-agonistic property whereas S-salbutamol does not. The racemate undergoes stereoselective sulphatisation by sulfotransferases mainly in the gut and liver, so that S-salbutamol rests for a longer time in the body and reaches higher plasma levels than R-salbutamol. Ten patients with mild stable asthma and at present without cortisone medication were given racemic salbutamol as ventoline 4 mg orally. Plasma and urine levels were estimated until 24 hr after ingestion. For comparison healthy volunteers were treated in the same way. The group of asthma patients was then treated with budesonide inhalations 800 microg daily for one week and the initial programme resumed. Non-cortisone-treated asthmatic patients displayed higher levels of both R- and S-salbutamol in plasma than did healthy volunteers after one single ingestion of racemic salbutamol (CMAX both comparisons P<0.05). Plasma levels of salbutamol isomers in cortisone-treated asthmatic patients resembled the levels in volunteers. The most plausible explanation for the discrepancy in values between asthmatic patients and volunteers is a defective metabolic function by asthmatic patients possibly enzymatic in origin.

The cyclic GMP mediated non-adrenergic non-cholinergic (NANC) relaxation in field stimulated bovine mesenteric artery and its modulation by various factors was studied. Electrical field stimulation of precontracted (Phe 2.5 microM or histamine 5 microM) bovine mesenteric arteries resulted in relaxations varying between 10-70% in different preparations. Tetrodotoxin (3 microM) completely blocked the inhibitory NANC response. Preincubation with high concentrations (100 microM-1 mM) of NG-nitro-L-arginine for 15 min. significantly reduced the relaxation induced by electrical field stimulation. Blockade of cyclooxygenases and prostaglandin synthesis by indomethacin had no effect on the relaxatory response to electrical field stimulation. Neither the alpha 2-adrenoceptor selective antagonist yohimbine (1 microM) nor the alpha 2-adrenoceptor selective agonist UK 14,304 (1 microM) had any significant effect on the electrical field stimulation-induced relaxation. Pertussis toxin (100 ng/ml) was without effect on relaxations elicited by electrical field stimulation. GTP in the concentration range 10 microM-1 mM slightly potentiated the relaxant response. N-carboxymethyl-Phe-Leu (an inhibitor of enkephalinase) or aprotinin (an inhibitor of several proteases) had no significant effect on the electrical field stimulation response. Addition of trypsin (100 U/ml) in combination with chymotrypsin (20 U/ml) significantly reduced the electrical field stimulation-induced relaxation. In the present study we have found indications for the involvement of nitric oxide and possibly also peptides in mediating the inhibitory NANC response (relaxation) in bovine mesenteric arteries.

The effect of pertussis toxin (PTX) and the cyclic GMP lowering agent LY83583 on the relaxatory response induced by glyceryl trinitrate (GTN), isosorbide dinitrate (ISDN), isosorbide-5-mononitrate (IS-5-MN) and sodium nitroprusside (SNP) in bovine mesenteric artery (BMA) was investigated. Pretreatment with PTX (100 ng/ml; 2 hr induced a 100-fold right shift of the concentration-effect curve for GTN, while no effect on the relaxatory response elicited by ISDN, IS-5-MN or SNP was seen. The relaxatory effect of all the substances tested was markedly reduced by LY83583 (10 microM). The basal cGMP level as well as the GTN induced increase in cGMP were markedly reduced when BMA was exposed to LY83583. The substance also reduced the activation of soluble guanylate cyclase by SNP. Based on the different sensitivity towards PTX it is suggested that GTN induces vascular smooth muscle relaxation by a partly different mechanism than ISDN, IS-5-MN and SNP. As far as the GTN induced relaxation is concerned the sensitivity towards PTX indicates the involvement of regulatory component, possibly a G-protein. However, cyclic GMP seems to play a crucial role in mediating the relaxatory response of all the substances tested since the cGMP-lowering agent LY83583 markedly inhibited the relaxant response induced by all the vascular relaxant agents investigated.

It was recently observed that the relaxation induced by glyceryl trinitrate (GTN) showed a biphasic concentration-response curve; a high-sensitivity component represented by concentrations less than 1 nM and a low-sensitivity component represented by concentrations greater than 1 nM. The effect of two glyceryl trinitrate concentrations (0.1 nM and 1 microM) were tested on the uptake of 45Ca2+ to tissue pieces of bovine mesenteric arteries (BMA) as well as on the uptake of 45Ca2+ to a microsomal preparation of BMA. The effect of GTN and 8-Br-cGMP was also studied on the IP3-induced release of Ca2+ from the microsomal preparation preloaded with 45Ca2+. The influence of IP3 and GTN on the activity of Ca2(+)-ATPase in the microsomal preparation was tested as well. The phenylephrine-stimulated uptake of Ca2+ to tissue pieces of BMA was significantly reduced by the high GTN-concentration (1 microM) but not by the lower concentration. The uptake of Ca2+ to the microsomal preparation was significantly stimulated by the two GTN-concentrations tested, as well as by 8-Br-cGMP (0.1 mM). The calcium release induced by IP3 (1 microM) from the microsomal preparation was inhibited by both the low and the high GTN-concentration and by 8-Br-cGMP (0.1 mM). The Ca2(+)-ATPase activity was stimulated by both GTN-concentrations tested while it was inhibited by IP3. It is concluded that GTN is able to induce a reduction of the free intracellular Ca2+ by several mechanisms, which are of importance for the relaxation represented by the high-affinity component. The low-affinity component in addition reduces the inflow of Ca2+ over the plasma membrane.

Low concentrations (less than 1 nM) of glyceryl trinitrate (GTN) induced a considerable relaxation of bovine mesenteric arteries (BMA) brought to sustained contraction by the addition of phenylephrine. The concentration-response curve of GTN showed a biphasic pattern with a high and a low affinity component. Pretreatment with pertussis toxin (IAP) attenuated the high affinity relaxant component, but not the low affinity component or the relaxation induced by NaNO2. A polyclonal antibody to IAP counteracted the effect of the toxin on the GTN-response. Low concentrations of GTN increased the cGMP level in BMA via activation of the high affinity pathway. This effect was also inhibited in preparations pretreated with IAP. It is suggested from the present study that GTN induces relaxation of vascular smooth muscle via two separate pathways, the high affinity pathway might involve a receptor-complex interaction with a regulatory protein.

In the present study the possible existence of cross-tolerance between GTN, atrial natriuretic peptide and the endothelium-dependent vasodilators acetylcholine and calcium ionophore A23187 was investigated. Pretreatment of bovine mesenteric arteries (BMA) with GTN (0.44 mM) for 2 hrs caused a significant (P less than 0.001) right-shift of the concentration-effect curve for GTN as compared to controls (pD2 = 6.96 +/- 0.208 and 4.57 +/- 0.148 in controls and GTN treated vessels, respectively), thus indicating the development of tolerance. Cross-tolerance between GTN and the endothelium-dependent vasodilators acetylcholine and calcium ionophore A23187 was found as judged from cumulative concentration-effect curves. The cGMP response evoked by 1 microM GTN was markedly blunted in the GTN-pretreated vessels (P = 0.0056). Similarly the cGMP elevation induced by 10 microM acetylcholine and 0.1 microM calcium ionophore A 23187 was significantly reduced in GTN-pretreated muscle specimens (P = 0.0475 and P = 0.0103, respectively). No cross-tolerance between GTN and atrial natriuretic peptide (ANP) could be established from tension studies. Furthermore, the cGMP response induced by atrial natriuretic peptide was not significantly different in GTN-tolerant vessels as compared to in controls (P = 0.2097). BMA specimens were also incubated with acetylcholine and ANP (2 hrs and 6 hrs, respectively) and the vessels were thereafter tested for their responsiveness to acetylcholine, ANP and GTN. Preincubation with acetylcholine (10 microM) for 2 hrs did not affect the relaxant response to a subsequent challenge with acetylcholine or GTN. Preincubation of BMA with ANP (0.1 microM) for 6 hrs was also without effect on the responsiveness to ANP or GTN.(ABSTRACT TRUNCATED AT 250 WORDS)

The present study compares the relaxant effect of glyceryl trinitrate (GTN) on isolated bovine mesenteric artery in commonly used organ baths made of glass and in disposable vials made of polyethylene, a material known to be inert to GTN. It is shown that the EC50-value for the GTN-induced relaxation is about 1000-fold lower when polyethylene vials are used. The study also shows that the reason for this is that the materials previously used in the experimental equipment retain and subsequently liberate GTN at re-use. In organ baths of glass with holders of acrylics, GTN concentrations of about 20 nM were found during equilibration, i.e. before start of the experiment. The vessel specimens become partly tolerant during equilibration in such organ baths and thus the vessels are less sensitive to GTN. The findings may explain the discrepancy between previous in vitro and in vivo studies. Low concentrations known to be effective in vivo have not been demonstrated to have a relaxant effect in earlier in vitro studies.

The density of beta- adrenoceptors has been determined on membranes prepared from rat myocardium. Long-term administration of prenalterol resulted in an increase in the density of receptors, without any change in affinity. The average heart rate increase induced by intravenous prenalterol administration to denervated rats was, however, similar in the prenalterol pretreated and the control groups. We conclude that long-term treatment with a partial beta1-adrenoceptor agonist lead to an increased beta-adrenoceptor density in the myocardium.

In order to study distribution in tissue, rats were treated subcutaneously with glyceryl trinitrate, GTN, (50 mg/kg). The concentrations of GTN were measured in plasma, brain, heart, adipose tissue and aortic tissue at different sampling times by a gas chromatographic method with electron-capture detection. The peak GTN-concentration was reached after 2 hours in all tissues examined. The highest concentration of GTN was found in adipose tissue, where the level was approximately forty times higher than in plasma. The concentration of GTN in brain, heart and aortic tissue was about 2-3 times as high as in plasma. The cGMP level was measured in heart and brain. An increase of the cGMP level was found in brain 2 hours after GTN administration. No cGMP increase was found in heart tissue. The results indicate a substantial distribution of GTN to tissue, and an increase of cGMP in brain. The distribution of the substance in the tissues as shown, might have both pharmacokinetic and pharmacodynamic implications.