Effect of TRH on plasma levels of LH, estrogen, and progestin following LH release: in relation to luteinization during the early luteal phase (Japanese)

Recently it has been observed that biphasic (former and later) elevation of peripheral LH levels with increment of plasma estrogen and progestin is induced by LH-RH injection in the baboon, and it is inferred that elevation of circulating estrogen and progestin exerts its effect on hypothalamus and/or pituitary as to the later LH release. This study was performed to investigate the effect of TRH, following LH-RH injection, on the pituitary-gonadal system in relation to LH release and plasma levels of ovarian hormones. 100 μg of LH-RH was injected s.c. during the early luteal phase (2 to 5 days after ovulation) in 5 normal menstruating baboons. Blood samples collected every 15 minutes for the first hour and every 30 minutes for the next 2 hours were assayed for LH, estrogen and progestin. A plasma LH peak appeared within 30 minutes; in addition, another LH release appeared within 90 to 150 minutes after injection. Plasma levels of estrogen and progestin were elevated within 30 to 45 minutes after injection. In the next early luteal phase of the same 5 baboons, 40 μg of TRH following 100 μg of LH-RH was injected s.c. twice at 30 minute-intervals and blood samples were collected in the same manner. An increment of plasma progestin and no changes of plasma LH and estrogen were observed after TRH injection as compared to control levels obtained by only LH-RH injection. This result suggests that TRH may be involved in the regulation of luteinization. The following study was therefore performed as a preliminary experiment. In 3 baboons, 40 μg of TRH was administered s.c. every day for 4 days from the day after ovulation and blood samples collected every other day from the last day of TRH injection to menstruation were assayed for progestin. An increment of plasma progestin was observed after TRH injection as compared to the plasma progestin level during a control period in the same subjects. The findings suggest that TRH may have a luteotropic action during the early luteal phase of the menstrual cycle in the baboon.