Diurnal variation in the effect of potassium depolarization on vasoactive intestinal polypeptide release from rat hypothalamus: a possible role for adrenaline

Publisher Website
Google Scholar
Abstract
We have previously reported a lack of effect of a depolarizing concentration of K+ on the release of vasoactive intestinal polypeptide (VIP) from the perifused rat hypothalamus, and suggested that this was due to the presence of an endogenous inhibitor of the release of VIP. In this study we report that the VIP response to K+ was restored if the hypothalami were obtained from animals killed during the dark phase of the light–dark cycle. Adrenaline blocked the K+-stimulated release of VIP when used at a concentration of 0·1 μmol/l; however, at a higher concentration (10 μmol/l) adrenaline stimulated the basal release of VIP. The use of specific receptor antagonists indicated that this dual effect of adrenaline was mediated through two distinct receptors, a stimulatory β-receptor and an inhibitory α2-receptor. The suggestion that adrenaline might be the endogenous inhibitor of the release of VIP, mediating the diurnal variation in the effect of K+, was supported by studies where 50 mmol K+/l was perifused concomitantly with an α2-antagonist, restoring the VIP response to K+ in light-phase hypothalami. In conclusion, adrenaline has a dual role in the control of VIP release and may function to inhibit the K+-stimulated release of VIP in our system. J. Endocr. (1988) 116, 335–341