Pulsatile luteinizing hormone release, and the inhibitory effect of estradiol-17 beta in gonadectomized male and female rats: effects of neonatal androgen or exposure to constant light.

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The characteristics of pulsatile LH release and the acute inhibition of LH release by estradiol-17 beta (E2) were studied in long term (21 days) gonadectomized female and male Wistar rats. Three groups of female rats were examined; animals exposed either to summer lighting (14-h on; 10-h off; LD) or continuous illumination (LL) and animals treated neonatally with testosterone propionate (TP) and exposed to LD. The mean plasma LH concentrations and interpulse intervals were similar in both male and LD female rats. However, treatment of female rats with TP or exposure to LL reduced the mean plasma LH concentration in female rats and increased the interpulse interval when compared with LD female or male rats. The amplitude of the LH pulses was significantly greater in the LD female rats compared with those in the male rats; since pituitary responsiveness to a single iv injection of 50 ng LHRH/100 g BW was similar in the two groups, this suggests that the amount of LHRH released per pulse of LH is greater in the female than in the male. The greater amplitude but similar frequency of LH pulses in the LD female compared with the LD male suggest that the MCR of LH may be greater in the female. The pulse amplitude in the TP-treated rats was similar to that in the rats exposed to LL and since pituitary responsiveness to LHRH was significantly greater in the TP rats, there was probably more LHRH released per pulse of LH in the LL-treated rats. Pituitary responsiveness to LHRH was significantly lower in the LL- and TP-treated rats compared with males and LD females. The timing of the inhibition of LH secretion by E2 was similar in all four groups of animals, and in LD females was not affected by a 92% depletion of serotonin, 100% depletion of 5-hydroxyindoleacetic acid, or a 33% depletion of dopamine in the hypothalamus produced by the administration of parachlorophenylalanine.(ABSTRACT TRUNCATED AT 400 WORDS)