THE EFFECT OF OVARIAN STEROIDS ON HYPOTHALAMIC THRESHOLDS FOR OVULATION IN THE FEMALE RAT

• Published in: Journal of endocrinology Vol. 49; no. 3; pp. 421 - 429
• Main Authors: McDonald, P G, Gilmore, D P
• Format: Journal Article
• Language: English
• Published: England BioScientifica 01.03.1971
• Subjects: Animals; Electric Stimulation; Electrodes; Estradiol - pharmacology; Estrus; Fallopian Tubes; Female; Hypothalamus - drug effects; Ovulation - drug effects; Ovum; Pregnancy; Progesterone - pharmacology; Rats
• ISSN: 0022-0795; 1479-6805
• DOI: 10.1677/joe.0.0490421

Electrochemical stimulation of the basal and preoptic hypothalamus, under sodium pentobarbitone anaesthesia, was carried out on the day of pro-oestrus in normal cycling and in ovarian hormone-treated female rats. Control rats ovulated in response to 25, 50 and 100 μA for 60 s in the median eminence and to 10 μA for 60 s in the preoptic area. Oestradiol (1 μg) given 24 h before median eminence stimulation significantly increased the number of rats ovulating. An injection of progesterone (1 mg) 24 h before median eminence stimulation did not affect the number of animals ovulating or the number of ova shed. In contrast, there was a significant reduction in the number of animals ovulating after preoptic stimulation. Stimulation of the median eminence 2–4 h after progesterone administration increased the number of animals ovulating. The results suggest that both oestradiol and progesterone exert a positive feedback effect at or below the level of the median eminence and that the negative feedback effect of progesterone is exerted on the preoptic area.