Developmental Changes in the Luteinizing Hormone Secretory Pattern in Peripubertal Female Rhesus Monkeys: Comparisons between Gonadally Intact and Ovariectomized Animals*

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Abstract
Developmental changes in LH [luteinizing hormone] release patterns were observed longitudinally in female rhesus monkeys at 10-65 months of age. The average ages of menarche and first ovulation in this experiment (n = 14) were 31.1 .+-. 2.6 and 47.0 .+-. 2.6 mo. (mean .+-. SE), respectively. To assess the ovarian influence on developmental changes in LH, data were simultaneously obtained from neonatally ovariectomized animals at similar ages. The estimation of circulating LH was made with RIA [radioimmunoassay] as well as biological assay. During the prepubertal period (10-20 mo. of age), basal LH was very low, and there was no circadian fluctuation of LH in gonadally intact monkeys. During the early pubertal stage (20-30 mo. of age), before menarche, basal LH levels started to increase, and a circadian LH rhythm (nocturnal increases) appeared. At the midpubertal stage (30-50 mo. of age), a period between menarche and first ovulation, basal LH levels further increased, and the circadian LH rhythm was maximal. At the late pubertal stage (50-60 mo. of age), a period after the first ovulation during which the animals were not able to reproduce fully as adults, basal LH declined and the circadian rhythm diminished. Similar but more exaggerated developmental changes in basal LH and the circadian fluctuation of LH were observed in females ovariectomized neonatally. Basal LH levels at 10-20 mo. were as low as those in intact animals with no circadian rhythm present. During the early pubertal period, a circadian fluctuation appeared at the time when a slight increase in the basal LH level occurred. Furthermore, the amplitude of circadian fluctuation (the difference between morning and evening LH values) increased linearly with the increase in basal LH during the midpubertal stage. These LH parameters in ovariectomized animals reached their peaks at 40-44 mo., an age before the 1st ovulation in intact animals. As basal LH levels declined during the late pubertal stage to postpubertal stage, circadian fluctuation disappeared. The increase in LH output and concomitant circadian fluctuations occur in close association with the pubertal process, and this change in LH release is not dependent on the presence of the ovary. Alteration of the LHRH release pattern during maturation, as reflected by LH release, rather than resetting of the gonadostat, apparently is the key factor involved in the mechanism of the onset of puberty.