Plasma gonadotropin patterns characterizing the development of polycystic ovaries in the estradiol valerate treated rat

Polycystic ovaries (PCO) develop in female rats within 4 weeks of an injection of estradiol valerate (EV). The final morphological transition from a noncystic to a cystic state occurs in the presence of estrous (control) mean serum gonadotropin concentrations, suggesting that gonadotropin patterns rather than mean concentrations are causal to PCO. We have examined plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) patterns in female rats at estrus and on days 5, 11, 16, and 21 following EV treatment. Estrous animals displayed large amplitude LH pulses of short duration, interspersed among frequent, low amplitude pulses of similar duration, and infrequent, broad-based LH episodes. Following EV treatment, there was a progressive decline in the frequency and magnitude of the large amplitude LH pulses, such that by day 16, they ceased altogether. Conversely, the frequency of the low amplitude pulses increased such that the total pulse frequency remained constant. The onset of this pattern coincides with the wave of atresia that precedes the emergence of cystic follicles. The pulsatile plasma pattern of FSH seen at estrus remained unaltered at all time intervals examined after EV treatment. We conclude that there is a specific LH pattern responsible for the generation and maintenance of the PCO condition.