Plasma gonadotropin concentrations in the cyclic female brushtail possum (Trichosurus vulpecula)

Changes in plasma concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and their relationship to antral follicle develop ment and ovulation, were determined in female brushtail possums (Trichosuru s vulpecula) in experiments in which pouch young were removed (RPY) from la ctating females to promote ovarian activity. In Experiment 1 (n = 8), the d evelopment of preovulatory follicles and ovulation was monitored by laparos copy. In Experiment 2 (n = 15) estrus and mating were monitored by cytology of urine. Ovulation occurred in 4/8 (Experiment 1) and 9/16 (Experiment 2) possums, and in these animals, plasma FSH concentrations fell progressivel y over the period of preovulatory follicle development and returned to pret reatment levels after ovulation. With the exception of samples taken at the time of the preovulatory gonadotropin surge, mean plasma LH levels remaine d basal. In those possums that failed to ovulate, plasma FSH concentrations were elevated while plasma LH concentrations were low; these patterns rema ined unchanged throughout the sampling period. It was not possible to disti nguish between animals that would ovulate and those that would not ovulate after RPY on the basis of gonadotropin profiles at the time of RPY. A furth er group of possums (Experiment 3, n = 10) were blood-sampled at hourly int ervals for 48 h to characterize preovulatory gonadotropin surges, using lap aroscopy to monitor preovulatory follicular development and predict ovulati on. A preovulatory LH surge (max. cone. 10.2-43.5 ng/ml, duration 7-9 h) wa s recorded in 4 animals, with a coincident preovulatory FSH surge (max. con e. 1.4-21.4 ng/ml, duration 3-11 h) observed in 3 of these possums. The pat terns of gonadotropin secretion in the cycling brushtail possum conform to those reported for eutherians that ovulate spontaneously and appear to be r egulated by similar mechanisms. (C) 1999 Academic Press.