Effect of naloxone on the basal 3H-noradrenaline outflow from adrenal gland slices of normotensive and spontaneously hypertensive rats.

The adrenal medulla provides one of the most convenient preparations for studying the mechanism and control of neurosecretion. It has been suggested that neuropeptides including opioid peptides control the catecholamine secretion from adrenals and may play an important role in the maintenance of hypertension. In the present study the basal outflow of 3H-noradrenaline (3H-NA) from adrenal gland slices of normotensive and spontaneously hypertensive (SH) rats in the presence and without naloxone was examined. The amount of the basal 3H-NA outflow from adrenal gland slices of SH-rats was significantly higher compared with WKY-rats, whereas the outflow on slices of Wistar-rats was significantly lower compared with WKY-rats. Naloxone reduced the elevation of the basal 3H-NA outflow in a concentration-dependent manner, both in SH- and WKY-rats, but the absolute reduction was dependent from the level of elevation. These data suggest a functional interaction between opioid peptides and the basal catecholamine outflow during maintenance of hypertension.