The time-course of contractions induced by acetylcholine and barium in the vas deferens of normal and castrated guinea-pigs.
1. The influence of castration on contraction of the guinea pig vas deferens induced by acetylcholine was investigated regarding facilitation of endogenous neurotransmitter release, changes in post-synaptic events and modification in acetylcholine metabolization. 2. Castration prolonged the duration of the isometric contraction of the vas deferens induced by acetylcholine (3 mM) but not the duration of that induced by barium chloride (10 mM). 3. Reserpinization (0.5 mg/kg) of normal and castrated guinea pigs did not change the time-course of acetylcholine-induced contraction in the vas deferens. 4. 4-Aminopyridine (0.05 mM) prolonged the contraction induced by acetylcholine and barium chloride. This effect was blocked by reserpine pretreatment, indicating that in the presence of 4-AP, both acetylcholine and barium release endogenous noradrenaline. Since there was no difference between the effects of 4-AP on organs from normal and castrated animals, prolongation of the acetylcholine-induced contraction is not related to an increase in neutransmitter release. 5. Total cholinesterase and acetylcholinesterase activities were reduced after castration and the time-course of carbachol contraction was not changed. Thus, this decrease in enzyme activity appears to play a relevant role in the prolongation of acetylcholine-induced contraction.
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D017609:Barium Compounds; D002217:Carbachol / Q000494:pharmacology; D002369:Castration; D002712:Chlorides; D006168:Guinea Pigs; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D009638:Norepinephrine / Q000378:metabolism; D014649:Vas Deferens / Q000187:drug effects* / Q000502:physiology
D017609:Barium Compounds; D002712:Chlorides; C024986:barium chloride; D001464:Barium; D002217:Carbachol; D000109:Acetylcholine; D009638:Norepinephrine