Posterior hypothalamic lesions advance the time of the pubertal changes in luteinizing hormone release in ovariectomized female rhesus monkeys.

Abstract

To examine further the relationship between developmental changes in LH release and the onset of puberty, effects of posterior hypothalamic lesions were tested in ovariectomized (OVX), sexually immature female monkeys. In OVX females (n = 3) with sham hypothalamic lesions basal LH levels were suppressed during the prepubertal period until 25 months of age, when LH levels started to increase. The increase in basal LH continued; a 100% elevation from prepubertal levels was attained at 26.0 +/- 0 months of age, and a 200% elevation was attained at 31.0 +/- 3.2 months of age. A consistent appearance of LH circadian fluctuation (nocturnal LH increase) with a large amplitude accompanied the initial LH increase. Lesions of the posterior hypothalamus (PH) in OVX animals (n = 6) at 17-18 months of age, which we previously reported to be effective in advancing the onset of puberty by several months in ovarian intact monkeys, resulted in an early 100% increase in basal LH levels and the circadian LH fluctuation (19.5 +/- 1.0 months of age). Basal LH levels in these animals further increased, reaching a 200% elevation of prelesion levels at 24.2 +/- 0.7 months of age. All of these LH changes with PH lesions occurred significantly (P less than 0.01) earlier than those in sham-lesioned animals. Lesion of the PH in OVX animals (n = 4) at 13-14 months of age resulted in an increase in LH and the circadian LH fluctuation within 1 month postoperatively. However, 100% and 200% LH elevations did not occur until 20.8 +/- 1.0 and 24.8 +/- 1.4 months of age, respectively. These ages were similar to those of animals receiving lesions at 17-18 months of age, but much younger than those of sham controls (P less than 0.01). PH lesions in animals at 13-14 months of age also advanced the time of the first positive feedback effects of estrogen. In animals (n = 4) with PH lesions, estradiol benzoate induced a first LH response at 21.5 +/- 1.6 months of age, when basal LH was 276 +/- 83% increased from prelesion levels. This age was significantly (P less than 0.05) younger than that (29.3 +/- 1.9 months; n = 6) of the first LH surge induced by estrogen in control animals when basal LH levels attained 248 +/- 18% of prepubertal levels.(ABSTRACT TRUNCATED AT 400 WORDS)