Effect of intracerebroventricular administration of opioid peptides on urinary function in the conscious goat

The effects of methionine(met)-enkephalin, leucine(leu)-enkephalin, beta-endorphin and blocking substances upon renal function were studied in conscious goats. Injections were made through a permanent cannula into the 3rd ventricle. Leu- and met-enkaphalin, as well as beta-endorphin induced an antidiuretic response to the pituitary type. The responses to beta-endorphin were found to be dose-dependent. Pretreatment with naloxone, either into the 3rd ventricle or into the jugular vein, antagonised the antidiuretic responses to injected opioid peptides with the magnitude of the inhibition being dependent upon the dose. Atropine, hexamethonium or phentolamine did not interfere with the antidiuretic activity of beta-endorphin. Injection of naloxone alone into the 3rd ventricle of goats with a normal water balance, induced both a diuretic response and an increase in free water clearance. It is suggested that the opioid peptides are acting selectively on opiate receptors to influence the release of antidiuretic hormone.