title: Effects of verapamil on [3H]norepinephrine release.
abstract: If calcium entry blocking drugs affect norepinephrine release, this may alter their cardiovascular action by modifying the activity of baroreceptor reflexes. We investigated the effect of verapamil on 3H-release in [3H]norepinephrine-incubated rat arteries and guinea pig vas deferens. Superfusion of tail artery with verapamil (10(-6) - 10(-4) M) increased the 3H-overflow induced by transmural stimulation (1 Hz, 2 ms, 10 V) both in Wistar Kyoto and in spontaneously hypertensive rats. The effect was present also in vessels pretreated with cocaine to inhibit neuronal uptake or with yohimbine to block alpha 2-adrenoceptors. The greatest increase in 3H-overflow--around 400% in the various groups--was observed after perfusion with 10(-4) M verapamil. In other experiments, we found that verapamil also enhanced 3H-overflow from vessels not stimulated transmurally; this effect again was dose-related (p less than 0.001). In the vas deferens of the guinea pig, 10(-5) M verapamil increased spontaneous and electrical stimulation-induced 3H-release (p less than 0.001), whereas superfusion of the tissue with 10(-9) and 10(-7) M verapamil was ineffective. The results indicate that verapamil can act on sympathetic nerves to release norepinephrine.
mesh_terms: D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology; D001808:Blood Vessels / Q000187:drug effects* / Q000502:physiology; D003042:Cocaine / Q000494:pharmacology; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D013045:Species Specificity; D013997:Time Factors; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology; D014700:Verapamil / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D015016:Yohimbine; D014700:Verapamil; D003042:Cocaine; D009638:Norepinephrine