beta-Endorphin plasma levels after intravenous administration of GnRH in female rats.

Objective: The study investigates the effects of intravenously administered GnRH on plasma beta-endorphin levels in female proestrous rats.

Study Design: Sixteen adult female proestrous Wistar rats, 220-250 g, were implanted with two indwelling catheters, one intracarotid and one intrajugular. Ten ng GnRH/100 microl distilled water or 100 microl saline (control) were infused in eight animals per group every 20 min from 12:30 to 14:30 h. Blood was withdrawn through the intracarotid catheter just before the initial infusion (12:30 h) and at 14:00, 15:30, 16:30 and 17:30 h for the determination of plasma beta-endorphin levels. The Mann-Whitney test was used for comparison between GnRH-treated and control rats and the Wilcoxon test within each treatment group.

Results: beta-Endorphin levels of GnRH-treated rats were not significantly different at any sampling moment neither compared to preinfusion time nor to the corresponding controls.

Conclusions: Intravenously administered GnRH was not sufficient for any possible effect on the secretion of beta-endorphin from rat pituitary and further investigation is needed to demonstrate if a different experimental model would have any significant effect.