Prenatal melatonin exposure influences the maturation of gonadotropin and prolactin estradiol-benzoate feedback system

Gonadotropin and prolactin response to estrogen feedback in female rat offs pring of control and melatonin treated (150 mu g/100 g BW) mother rats duri ng pregnancy (MEL-offspring) were studied at these periods: infantile, prep ubertal and pubertal. In controls negative or absent LH feedback developed after estradiol benzoate (EB) injection up to 30 days of age indicating tha t the onset of puberty had not occurred. The positive feedback was establis hed from day 33 on. However, in MEL-offspring the first activation of gonad otropin secretion during afternoon, 31 h after EB, was observed at 25 days of age, representing the first neuroendocrine sign of the onset of puberty. This positive response disappeared on day 30 in MEL-offspring. At 33 days of age, the LH positive response to EB was found in both groups, indicating a more advanced sexual development. In controls, this response increased a t 35 days of age while in MEL-offspring it was highly depressed. FSH secret ion in response to EB showed a negative feedback effect from infantile to t he end of prepubertal period in both groups. The positive feedback was obse rved earlier in MEL-offspring (at 33 days of age) than in controls (at 35 d ays of age), but at this age it was absent in MEL-offspring. A positive pro lactin response to EB at all ages in controls was observed. The typical pul satility with higher values in the afternoon appeared by the first time at 30 days of age. However, in MEL-offspring no pulsatile response was observe d throughout any age. These data suggest that prenatal melatonin administra tion altered gonadotropin and prolactin response to EB inducing precocious sensitivity during prepubertal period but depressed response during the pub ertal period. (C) 1999 Elsevier Science Ltd. All rights reserved.