VARIATIONS IN PITUITARY RESPONSIVENESS TO LUTEINIZING HORMONE RELEASING FACTOR DURING THE RAT OESTROUS CYCLE

Abstract

Results of experiments using steroid injections or implants have indicated that pituitary gonadotrophin secretion is not only modified by a change in perfusion rate of the releasing factors (RF) of luteinizing hormone (LH) and follicle-stimulating hormone, but that steroid feedback directly at the pituitary level may be involved in the cyclic regulation of gonadotrophin secretion (Ramirez, Abrams & McCann, 1964; Harris & Campbell, 1966; Arimura & Schally, 1971). Consequently, it has been suggested that pituitary responsiveness to LH-RF might change during the oestrous cycle as a result of variation in steroid secretion (Antunes-Rodrigues, Dhariwal & McCann, 1966). This experiment investigates this possibility. Female Sprague—Dawley rats weighing 220–250 g and maintained under a lighting régime of 14 h light: 10 h darkness at a temperature of 21 ± 2 °C were used. Only animals showing at least two consecutive 4-day oestrous cycles were studied. LH-RF-evoked stimulation of LH release was examined