Effects of sodium pentobarbitone on serum gonadotrophin levels and on the incorporation of 35S from methionine into protein in the brain and anterior pituitary during the oestrous cycle of the rat.

Ovulation was delayed for 24 h after the administration of sodium pentobarbitone (Nembutal, 35 mg/kg body weight) at 14.00 h, before the critical period on the afternoon of pro-oestrus. The expected preovulatory surge of serum LH at 18.00 h of pro-oestrus was also delayed until 21.00 h on the following day; however, increased levels (less than 12 ng/ml) were observed in 14 out of 23 animals (killed by decapitation) at 21.00 h on the day of Nembutal administration. The serum FSH rise observed on the morning of expected oestrus was extended after Nembutal treatment, and a further rise was noted 24 h later. Peak levels of incorporation of 35S from methionine into protein of the median eminence area (ME) and of the anterior pituitary (AP) which normally occur about the time of the preovulatory LH surge, were also delayed until 21.00 h on the day following Nembutal administration. Neither ovulation nor the preovulatory gonadotropin rises with their accompanying changes in incorporation in the ME and the AP, were altered by Nembutal administered after the pro-oestrous critical period. Thus Nembutal, while blocking ovulation, inhibits the circadian rhythm of incorporation of 35S from methionine in the brain as well as the peaks of incorporation in the median eminence and the anterior pituitary which accompany the normal preovulatory surges of gonadotrophin.