Modulation of microvascular permeability in the preovulatory rat ovary by an ovulatory gonadotropin stimulus

Abstract

To characterize the size selectivity of the rat ovarian vasculature and its changes after gonadotropin induction of ovulation. Experimental study. Obstetrics and Gynecology Department. Immature, female Sprague-Dawley rats. Rats were pretreated with equine chorionic gonadotropin, and ovaries were retrieved either 48 hours later or at any of several time points during ovulation induced by hCG. Fluorescein isothiocyanate-labeled Ficoll was injected 10 minutes before ovarian sampling, and the distribution of Ficoll was measured in plasma and ovarian extracts. The Ficoll data were analyzed according to a two-pore model to acquire information on small (rS) and large (rL) pore radii as well as the number of large pores reflected by the large pore fraction of the hydraulic conductance (LpS%) at each periovulatory time interval. Before hCG, rS and rL were 54.7 ± 1.2 Å (mean ± SEM) and 149.3 ± 5.3 Å, respectively. At this preovulatory stage, LpS% was 7.1% ± 3.2%. Stimulation with hCG caused close to a three-fold increase in LpS% at 2 and 4 hours (20.9% ± 1.8% and 20.7% ± 2.5%, respectively) and approximately 15% enlargements of rS and rL. Thus, the change in LpS% represents a dramatic increase in the number of large pores and not an increased size of preexisting large pores, since the small and large pore radii changed in parallel. These results indicate that capillary permeability of the ovarian blood-follicle barrier is modulated by gonadotropin, mainly through increased numbers of large pores, similar to a classical inflammatory response.