Effects of (-)-tertatolol, (-)-penbutolol and (+/-)-pindolol in combination with paroxetine on presynaptic 5-HT function: an in vivo microdialysis and electrophysiological study.
The antidepressant efficacy of selective serotonin reuptake inhibitors (SSRIs) might be enhanced by co-administration of 5-HT1A receptor antagonists. Thus, we have recently shown that the selective 5-HT1A receptor antagonist, WAY 100635, blocks the inhibitory effect of an SSRI on 5-HT cell firing, and enhances its ability to elevate extracellular 5-HT in the forebrain. Here we determined whether the beta-adrenoceptor/5-HT1A receptor ligands (+/-)-pindolol, (-)-tertatolol and (-)-penbutolol, interact with paroxetine in a similar manner. Both (-)-tertatolol (2.4 mg kg(-1) i.v.) and (-)-penbutolol (2.4 mg kg(-1) i.v.) enhanced the effect of paroxetine (0.8 mg kg(-1) i.v.) on extracellular 5-HT in the frontal cortex, whilst (+/-)-pindolol (4 mg kg(-1) i.v.) did not. (-)-Tertatolol (2.4 mg kg(-1) i.v.) alone caused a slight increase in 5-HT however, (-)-penbutolol (2.4 mg kg(-1) i.v.) alone had no effect. In electrophysiological studies (-)-tertatolol (2.4 mg kg(-1) i.v.) alone had no effect on 5-HT cell firing but blocked the inhibitory effect of paroxetine. In contrast, (-)-penbutolol (0.1-0.8 mg kg(-1) i.v.) itself inhibited 5-HT cell firing, and this effect was reversed by WAY 100635 (0.1 mg kg(-1) i.v.). We have recently shown that (+/-)-pindolol inhibits 5-HT cell firing via a WAY 100635-sensitive mechanism. Our data suggest that (-)-tertatolol enhances the effect of paroxetine on forebrain 5-HT via blockade of 5-HT1A autoreceptors which mediate paroxetine-induced inhibition of 5-HT cell firing. In comparison, the mechanisms by which (-)-penbutolol enhances the effect of paroxetine on extracellular 5-HT is unclear, since (-)-penbutolol itself appears to have agonist properties at the 5-HT1A autoreceptor. Indeed, the agonist action of (+/-)-pindolol at 5-HT1A autoreceptors probably explains its inability to enhance the effect of paroxetine on 5-HT in the frontal cortex. Overall, our data suggest that both (-)-tertatolol and (-)-penbutolol are superior to (+/-)-pindolol in terms of enhancing the effect of an SSRI on extracellular 5-HT. Both (-)-tertatolol and (-)-penbutolol are worthy of investigation for use as adjuncts to SSRIs in the treatment of major depression. (+info)
beta-blocker binding to human 5-HT(1A) receptors in vivo and in vitro: implications for antidepressant therapy.
A novel strategy for improving the treatment of depressive illness is augmentation of antidepressants with a 5-HT1(1A) autoreceptor antagonist. However, trials using the 5-HT1(1A)/beta-blocker pindolol are proving inconsistent. We report how positron emission tomography (PET) and in vitro autoradiography can inform trials of antidepressant augmentation. We show that in healthy volunteers, in vivo, pindolol (n = 10) and penbutolol (n = 4), but not tertatolol (n = 4) occupy the human 5-HT(1A) receptors, at clinical doses. Pindolol, as well as the beta-blockers penbutolol and tertatolol, has high affinity for human 5-HT(1A) receptors in post-mortem brain slices (n = 4). Pindolol shows preference for 5-HT(1A) autoreceptors versus the post-synaptic receptors both in vitro and in vivo. Our data reveal that pindolol doses used in antidepressant trials so far are suboptimal for significant occupancy at the 5-HT(1A) autoreceptor. Penbutolol or higher doses of pindolol are candidates for testing as antidepressant augmenting regimes in future clinical trials. (+info)
Comparison of the effects of penbutolol and propranolol on glomerular filtration rate in hypertensive patients with impaired renal function.
Penbutolol and propranolol were administered orally in a dosage of 40 mg once daily and 80 mg twice daily, respectively to 12 patients with hypertension and impaired renal function. Both drugs caused a significant decrease in mean arterial pressure and heart rate. Serum creatinine concentration increased significantly by 10% during therapy with propranolol without concomitant decrease in creatinine clearance. No such effect was seen with penbutolol. GFR measured with [125I]-iothalamate showed no significant changes with both drugs. (+info)
Penbutolol and propranolol: a comparison of their effects on antipyrine clearance in man.
The effects of two beta-adrenoceptor antagonists, penbutolol (administered on separate occasions as (+/-)- and (-)-forms) and propranolol, on the kinetics of antipyrine were studied in eight normal subjects. At the same degree of beta-adrenoceptor blockade, as assessed by the lowering of exercise tachycardia, propranolol decreased antipyrine clearance by 31 +/- 11 s.d.% (P less than 0.001) whereas neither of the two penbutolol formulations had a significant effect. The volume of distribution of antipyrine was unchanged following any of the beta-adrenoceptor antagonist treatments. The lack of effect of penbutolol on oxidative drug metabolism is not consistent with in vitro data suggesting a relationship between the lipid solubility of beta-adrenoceptor antagonists and inhibition of metabolism. (+info)
The interaction between H2-receptor antagonists and beta-adrenoceptor blockers.
The degrees of interactions between the H2-receptor antagonists, cimetidine and ranitidine, and several beta-adrenoceptor blockers were investigated in healthy volunteers following 7 days of oral monotherapy with penbutolol, propranolol, metoprolol, pindolol and atenolol, and after co-administration with each of the H2-receptor antagonists. The kinetic parameters of unmetabolised penbutolol and penbutolol glucuronide were unaffected, whereas the levels of 4-hydroxypenbutolol and 4-hydroxypenbutolol glucuronide were significantly reduced. Furthermore, cimetidine led to a marked increase in propranolol and metoprolol plasma levels. During co-administration with cimetidine, pindolol plasma levels were only slightly raised, whereas the pharmacokinetics of atenolol were not affected. With regard to pharmacodynamics, the inhibition of exercise-induced tachycardia by each of the beta-adrenoceptor blockers was not affected by cimetidine. Ranitidine did not alter atenolol plasma levels, but did raise the peak plasma concentration of metoprolol by about 30%. It is concluded that cimetidine interactions do occur and can be predicted for substances metabolised by the cytochrome P-450 pathway. (+info)
Haemodynamic dose-response effects of i.v. penbutolol in angina pectoris.
The haemodynamic dose-response effects of intravenous penbutolol, a newer beta-adrenoceptor antagonist with intrinsic sympathomimetic activity but without cardioselectivity, were evaluated in 10 patients with angiographically documented coronary artery disease. Following four logarithmetically cumulative i.v. boluses (0.5-4 mg dosage range) there was a log linear increase in plasma penbutolol concentration; the levels achieved (51 +/- 8 to 219 +/- 19 ng/ml) were in the therapeutic range (12 to 250 ng/ml). Penbutolol resulted in a linear decrease in heart rate (maximum delta HR - 4 beats/min; P less than 0.01); there was a small increase in pulmonary artery occluded pressure which reached its maximum at the lower doses (maximum delta PAOP + 1 mm Hg; P less than 0.01). The resting cardiac output, blood pressure and calculated systemic vascular resistance were unchanged. During 4 min steady-state supine bicycle exercise there was attenuation of exercise cardiac output (delta C.I. - 0.6 1 min-1 m-2; P less than 0.01) and systolic pressor response (delta SBP - 13 mm Hg; P less than 0.01) compared with control observations without change in other measured or derived variables. The haemodynamic profile of penbutolol compared favourably with other beta-adrenoceptor antagonists previously evaluated under similar conditions in patients with ischaemic heart disease. Over the i.v. dose-range evaluated penbutolol attenuated exercise-induced angina with a relatively modest depression of cardiac performance; the small change induced in resting haemodynamic variables may, in part, have been contributed to by the intrinsic sympathomimetic activity of penbutolol. (+info)
A comparison of a combination of penbutolol and frusemide with the two compounds individually in the treatment of hypertension.
Forty-one patients completed a randomized, double-blind, between-group comparison of a combination of penbutolol and frusemide, with penbutolol alone, and frusemide alone in the management of mild to moderate essential hypertension. The results suggest that the combination caused a superior reduction in systolic and diastolic pressure compared with penbutolol and a superior reduction in systolic blood pressure compared with frusemide. (+info)
Liquid-chromatographic determination of penbutolol and its principal metabolites in plasma and urine.
We describe a sensitive, specific liquid-chromatographic determination of penbutolol and its 4-hydroxy metabolite in plasma and urine. The method involves a simple organic extraction, evaporation of the solvent, reconstitution in methanol/water, and injection into the chromatograph. Penbutolol, its metabolites, and the internal standard, propranolol, are resolved on a CN reversed-phase column and detected fluorometrically. Conjugates of penbutolol and its 4-hydroxy metabolite may be determined after a 2-h enzymic hydrolysis. Detection limits are in the range of 3 to 12 micrograms/L of plasma. The assay is reproducible and nearly free of interferences. Representative concentrations in blood and urine of normal volunteers are reported. (+info)