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Clinical relevance of intrinsic sympathomimetic activity of beta blockers.

beta-Blockers are effective in the symptomatic relief of angina pectoris by decreasing myocardial oxygen demand during effort and emotional stress. Agents with ISA such as pindolol produce effective beta-blockade during effort or emotional stress while conferring significant protection from myocardial depression and bradycardia at rest. In addition, agents with ISA have been shown to depress respiratory function to a lesser extent and to induce fewer peripheral vascular side effects than compounds devoid of this property. These potential effects of ISA may be counterbalanced by the consideration that ISA may be undesirable in angina occurring at rest or at low exercise levels. Additional well-controlled trials in patients with angina and resting bradycardia or impaired left ventricular function are needed to further document the clinical importance of ISA.

Adrenergic beta-Agonists↗

Spirotetrahydronaphthalene analogues of sympathomimetic catecholamines. Synthesis and adrenergic activity of 5,6- and 6,7-dihydroxy-3,4-dihydrospiro[naphthalen-1 (2H)-3'-piperidines].

The 5,6- (5a) and 6,7-dihydroxy-3,4-dihydrospiro[naphthalen-1 (2H)-3'-piperidine] (6a) and their N-isopropyl derivatives (5b and 6b), DDSNPs, were synthesized. These compounds can be viewed as the result of the combination of the structure of the 3-(3,4-dihydroxyphenyl)-piperidine 2a or 2b, with the structure of the corresponding 1-(aminomethyl)-5,6-dihydroxy-(3a or 3b) or 1-(aminomethyl)-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (4a or 4b), 1-AMDTNs. The new compounds (5a, b and 6a, b) were assayed for their alpha and beta adrenergic properties by means of binding experiments and functional tests and the results were compared with those obtained for catecholamines 1a, b and the previously described 3-(3,4-dihydroxyphenyl)piperidine (3-DPP; 2) and 1-AMDTNs (3, 4). Comparison of the affinity and activity data of novel derivatives with those of reference compounds 2, 3 and 4 shows a general low ability of DDSNPs 5 and 6 to interact with both alpha and beta- adrenoceptors.

Animals↗

[Mode of action of clonidine, a central hypotensive agent, analyzed by the interaction with various sympathomimetic agents].

Injection of a low dose of clonidine showed the biphasic blood pressure response which comprises a delayed onset of long lasting hypotension and a quick onset of hypertension of short duration followed by the former, in the alpha-chloralose-urethanized rat. A second injection of low dose of clonidine administered 90 min after the first showed only two peaks of pressor response, no longer a depressor one, and tachyphylaxis occurred with repeated injections of the same dose of clonidine, together with a gradual elevation of blood pressure level. Furthermore, the depressor action was inhibited by pretreatment with cocaine or imipramine. In contrast, injection of a high dose of clonidine exhibited pressor response with only two peaks, duration of which was markedly potentiated by pretreatment with cocaine or imipramine, and also by guanethidine, but inhibited in reserpinized and spinal rats. While the blood pressure was sustained at a high level after the injection of a high dose os clonidine, blood pressure reversal was produced by tyramine, due to possible beta-mimetic action of much greater amounts of catecholamines released by tyramine. The isolated guinea-pig vas deferens contracted when treated with clonidine, and this contraction was inhibited in the reserpinized preparation. This inhibition was recovered by incubation with norepinephrine. Interaction between tyramine and clonidine was also seen in vitro, but it disappeared in the reserpinized, denervated or propranolol-pretreated guinea-pig vas deferens. The contraction of the vas deferens induced by clonidine was potentiated by pretreatment with cocaine, but not by pretreatment with guanethidine, ans was inhibited by treatment with alpha-adrenergic blocking agents phentolamine and phentolame and phenoxybenzamine, but not by tolazoline.

Animals↗