INFLUENCE OF ANAESTHETICS, MATING, PREMATURE DELIVERY, THE TIME OF DAY OF BLOOD SAMPLING, AND SUCKLING ON PLASMA LEVELS OF LUTEINIZING HORMONE IN HAMSTERS

Abstract

SUMMARY: The influence of several factors on immunoreactive LH levels in peripheral plasma of female hamsters was investigated. The LH values for animals anaesthetized with either sodium pentobarbitone or chloral hydrate were significantly lower (P < 0-01) than those values obtained for hamsters sampled under ether anaesthesia. Mating on the night of pro-oestrus resulted in increased LH levels (P < 0-01) the following morning as compared with the levels in control females not caged with males. The LH levels were relatively low (13 ± 2 (s.e.m.) ng/ml) on the afternoon (16.00–18.00 h) of day 15 of pregnancy and also on the morning (09.00– 10.00 h) of day 16 before (7 ± 1 ng/ml) and after parturition (4 ± 0·2 ng/ml), but rose severalfold (561 ± 201 ng/ml) on the afternoon post partum. When premature delivery was induced on day 15 of pregnancy by administration of prostaglandin E2 the LH levels did not rise on the afternoon of this day (29± 11 ng/ml), but did so on the following afternoon (213± 115 ng/ml), at the same interval post coitum as in normal delivery. Marked increases in the concentration of LH in plasma were observed on the afternoon of each of days 0–6 post partum. The levels were comparable to those found on the afternoon of pro-oestrus in cyclic hamsters and could be blocked by administration of sodium phenobarbitone at 13.00 h. Similar afternoon surges of LH were not observed during dioestrus. In the morning, the LH levels were significantly higher (P < 0-001) in the non-suckled dams (95 ± 4 ng/ml) than those in mothers allowed to nurse their young (13± 4 ng/ml). In contrast, the levels in the afternoon were unaffected by the suckling stimulus (suckled, 495 ± 76 v. non-suckled, 744± 165 ng/ml; P > 0-05).