Pharmacological studies on stress-induced renin and prolactin secretion: effects of benzodiazepines, naloxone, propranolol and diisopropyl fluorophosphate.

Stress-induced renin and prolactin secretion was investigated using a conditioned emotional response paradigm. Three minutes after placement in a chamber the rats received an electric shock to their feet via the grid floor, then were immediately returned to their home cage. This procedure was repeated for 3 consecutive days. On the fourth day, instead of receiving an electric shock, they were removed after 3 min and sacrificed by decapitation. Control rats were treated identically with the exception that shock was not administered at any time. There was a significant increase in plasma renin activity and prolactin level in the stressed rats. The administration of the antianxiety drugs chlordiazepoxide (10 mg/kg i.p.) or midazolam (0.125-2 mg/kg i.p.) blocked the stress-induced increase in prolactin levels but not the stress-induced rise in plasma renin activity. Administration of the beta-blocker propranolol (1 mg/kg i.p.) inhibited, but did not completely block, stress-induced rise in plasma-renin activity and had no effect on stress-induced prolactin secretion. The opiate antagonist naloxone (0.1-10 mg/kg i.p.) and the acetylcholinesterase inhibitor diisopropyl fluorophosphate (0.5 mg/kg i.p.) did not block stress-induced renin or prolactin secretion. It is concluded that stress-induced prolactin secretion is regulated by a benzodiazepine-mediated mechanism and that stress-induced renin but not prolactin secretion is mediated in part via beta-receptors.