Effects of isoxuprine and nylidrin on adrenoreceptors in rat vas deferens.
The interaction of isoxuprine and nylidrin with alpha 1- and beta 2-adrenoreceptors in rat vas deferens was examined using radioligand binding assays and physiological studies in vitro. Isoxuprine and nylidrin have a greater affinity for binding to alpha 1 (isoxuprine KD = 59 +/- 15 nM; nylidrin KD = 41 +/- 3 nM) than beta 2-(isoxuprine KD = 3,900 +/- 500 nM; nylidrin KD = 900 +/- 50 nM) adrenoreceptors in rat vas deferens. Vas deferens from rats pretreated for 16-24 h with reserpine (3 mg/kg i.p.) were exposed to 10 microM phenoxybenzamine for 15 min to inactivate alpha-adrenoreceptors. Under these conditions high concentrations of both isoxuprine and nylidrin relaxed vas deferens contracted with 55 mM K+, however the relaxation was not blocked by the beta-adrenoreceptor antagonist propranolol (10 microM). Both isoxuprine and nylidrin were potent competitive antagonists of alpha 1-adrenoreceptor mediated contraction of vas deferens. pA2 values for isoxuprine (6.9 +/- .05) and nylidrin (7.1 +/- .08) agreed well with KD values for binding to alpha 1-adrenoreceptors in vas deferens. The greater potency of isoxuprine and nylidrin in inhibiting alpha 1-adrenoreceptors than binding to beta 2-adrenoreceptors or causing nonspecific relaxation suggest that alpha-adrenoreceptor antagonist actions of these drugs may be important in their ability to inhibit smooth muscle tone.[1]References
- Effects of isoxuprine and nylidrin on adrenoreceptors in rat vas deferens. Abel, P.W., Fox, A.W., Minneman, K.P. Journal of autonomic pharmacology. (1985) [Pubmed]
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