Contractile responses of isolated guinea-pig vas deferens to trains of electrical stimuli and influence of prostaglandin E 2

Abstract

The contractile responses of isolated guinea-pig vas deferens to long trains of 300 stimuli (0.3 ms, 90 V) applied at a frequency of 8 Hz or 20 Hz were diphasic contractions comprising a non-adrenergic, probably ATP-mediated component (phase I) and an adrenergic component (phase II). Stimulation with short trains of 10 stimuli (1 ms, 90 V) at a frequency of 10 Hz elicited monophasic responses. The contractions evoked by either long or short trains of stimuli were due to excitation of sympathetic nerve terminals without, however, being purely adrenergic ones. Prostaglandin E2 (PGE2) in increasing concentrations of 1 nmol/l to 100 nmol/l reduced phase I of the responses to long trains of stimuli at a frequency of 8 Hz, as well as the monophasic responses to short trains of stimuli. Both phases of the contractions evoked by long trains of stimuli at a frequency of 20 Hz were reduced by the lowest and potentiated by the highest concentrations of PGE2. The high concentration of PGE2 also potentiated phase II of the responses to long trains of stimuli at a frequency of 8 Hz and the diphasic contractions, resulting from the simultaneous application of ATP and noradrenaline. The results suggest that in guinea-pig vas deferens, PGE2 in low concentrations presynaptically inhibits the non-adrenergic components of the contractile responses to electrical stimulation of the sympathetic nerve terminals, while in high concentrations postsynaptically potentiates mainly the adrenergic components of these responses.