THE INFLUENCE OF SURGERY, TIME OF DAY, BLOOD VOLUME REDUCTION AND ANAESTHETICS ON PLASMA PROLACTIN IN OVARIECTOMIZED RATS

SUMMARY Plasma prolactin was measured by double antibody radioimmunoassay in ovariectomized rats bearing indwelling aortic catheters. Samples were obtained during recovery from ovariectomy and catheterization, at various times during the day, after blood volume reduction, and after administration of various anaesthetics. Prolactin levels were stabilized by day 3 after the operation but not by day 1. There was a significant (P < 0·01) increase in plasma prolactin during the afternoon in both ovariectomized rats and ovariectomized rats treated with 1 mg polyoestradiol phosphate. The magnitude of the response was more pronounced in the animals treated with oestrogen. Withdrawal of blood samples without subsequent replacement of fluid volume induced a significant (P < 0·05) decrease in plasma prolactin concentration after removal of only 1·2 ml blood within 20 min. No change was observed, however, when blood was replaced with saline. Ether and the intraperitoneal injection of sodium pentobarbitone produced prolonged increases in plasma prolactin whereas the intra-arterial administration of sodium pentobarbitone produced no change. Urethane and chloral hydrate caused only transient increases in plasma levels of prolactin regardless of the route of administration. Ketamine did not significantly alter plasma levels of prolactin.