Influence of temperature on stimulus-secretion coupling in the sympathetic nerves and on neuromuscular transmission, in guinea-pig vas deferens.

UNLABELLED

In guinea-pig isolated vas deferens moderate cooling (within the range 16-41 degrees C) improved, while further cooling depressed, sympathetic neuromuscular transmission. Moderate cooling: (a) enhanced the contractile responses both to electrical nerve stimulation and (although less strongly) to exogenous noradrenaline or to the adenosine 5'-triphosphate (ATP) analogue, alpha, beta-methylene ATP; (b) enhanced the overflow of [3H]noradrenaline evoked by electrical nerve stimulation at 1-8 Hz, but not that caused by direct depolarization of varicosities with 80 mM potassium; (c) reduced the depressing effect of exogenous noradrenaline, as well as the enhancing effect of the alpha-adrenoceptor blocking agent phentolamine, on the secretory responses to electrical nerve stimulation; (d) while not altering the maximal secretion of tracer noradrenaline at infinitely high frequency or external calcium, lowered the frequency or calcium concentration required for half-maximal secretion, both in the absence and in the presence of phentolamine.

IN CONCLUSION

moderate cooling improves sympathetic neuromuscular transmission in guinea-pig vas deferens, both prejunctionally, by enhancing transmitter secretion, and post-junctionally, by increasing the responsiveness of the smooth muscle to transmitter.