THE POSSIBLE ROLE OF ADENOSINE TRIPHOSPHATE IN CHEMICAL TRANSMISSION BETWEEN THE HYPOGASTRIC NERVE TERMINAL AND SEMINAL VESICLE IN THE GUINEA-PIG

Abstract

The study was designed to confirm the hypothesis that adenosine 5' triphosphate (ATP), in addition to Norepinephrine (NE) is involved in the excitatory transmission between the hypogastric nerve terminal and seminal vesicle in the guineapig. ATP produced a contraction in the isolated seminal vesicle. The pattern of contraction in response to exogenously administered ATP resembled that of nervemediated contraction in respect of short latency, rapid rising phase and short duration. The contractions in response to both post-ganglionic hypogastric nerve stimulation and exogenously administered ATP were remarkably enhanced in the presence of NE. The potentiating effect of NE on both responses was depressed with the pre-treatment of adrenergic α-blocking agents such as tolazoline, phenoxybenzamine, yohimbine and hydergine. The contractile responses to both hypogastric nerve stimulation and exogenously administered ATP were affected by pre-treatment with various adrenergic α-blocking agents; tolazoline augmented both responses; phenoxybenzamine had a variable effect on both responses; yohimbine and hydergine depressed both responses. The contractile response to NE was depressed or abolished by these adrenergic α-blocking agents. The contractile responses to both hypogastric nerve stimulation and exogenously administered ATP were also modified by cholinergic drugs; acetylcholine (ACh) enhanced both responses; physostigminc enhanced both responses as well as the response to ACh. Atropine slightly depressed both responses and abolished the response to ACh. Atropine also slightly depressed the nervemediated contraction in the reserpinized preparation. A relatively longer period of hypogastric nerve stimulation caused a biphasic contraction of the seminal vesicle. The initial “twitch” like contraction was resistant to reserpine-pretreatment, while the second slow rising contraction was abolished. The potentiating effect of NE on contractile responses to both hypogastric nerve stimulation and exogenously administered ATP was observed even in the reserpinized preparation. The sensitivity to NE was increased after denervation, while that to ATP was almost unaltered. The potentiating effect of NE on ATP-induced contraction was still observed in the denervated preparation. These findings are consistent with the hypothesis that ATP is involved in excitatory transmission between the hypogastric nerve and seminal vesicle in the guinea-pig. Possible role of ATP in the transmission-mechanism was discussed herein.