Evaluation of the alpha-1 and alpha-2 adrenoceptor-mediated effects of a series of dimethoxy-substituted tolazoline derivatives in the cardiovascular system of the pithed rat.
The alpha-1 and alpha-2 adrenoceptor-mediated effects of a series of dimethoxy-substituted tolazoline derivatives were investigated in the cardiovascular system of the pithed rat. The 2,5- and 3,5-dimethoxy-substituted tolazoline derivatives produced vasopressor responses that were inhibited by the alpha-1 adrenoceptor antagonist, prazosin (0.1 mg/kg i.v.), and were not affected by the alpha-2 adrenoceptor antagonist, yohimbine (1 mg/kg i.v.), suggesting that these derivatives selectively activate postsynaptic vascular alpha-1 adrenoceptors. The 2,5- and 3,5-dimethoxy-substituted derivatives of tolazoline did not produce an alpha-2 adrenoceptor-mediated inhibition of neurogenic tachycardia in cord-stimulated pithed rats and were therefore presumed to be devoid of alpha-2 adrenoceptor agonist activity. In contrast, 2,3-dimethoxytolazoline produced a vasopressor effect that was inhibited by yohimbine but not by prazosin, suggesting selective activation of postsynaptic vascular alpha-2 adrenoceptors. Consistent with this observation is the fact that 2,3-dimethoxytolazoline elicited a dose-dependent, alpha-2 adrenoceptor-mediated inhibition of neurogenic tachycardia in cord-stimulated pithed rat. 3,4-Dimethoxytolazoline was a weak alpha-1 adrenoceptor agonist in the vasculature of the pithed rat and was devoid of agonist activity at alpha-2 adrenoceptors. However, 3,4-dimethoxytolazoline was found to be an alpha-2 adrenoceptor antagonist of similar potency as yohimbine. The results of the present study indicate that dimethoxy-substituted derivatives of tolazoline possess different activities and selectivities at alpha-1 and alpha-2 adrenoceptors depending upon the positions of substitution.(ABSTRACT TRUNCATED AT 250 WORDS)
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D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D000068438:Brimonidine Tartrate; D003000:Clonidine / Q000494:pharmacology; D003655:Decerebrate State; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D013116:Spinal Cord / Q000502:physiology*; D014043:Tolazoline / Q000031:analogs & derivatives*; D015016:Yohimbine / Q000494:pharmacology
D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D014043:Tolazoline; D003000:Clonidine; D011224:Prazosin