The objective of the study was to evaluate the effect of pretreatments such as gonadectomy in male and female rats, and gonadotropin-releasing hormone agonist (GnRHa) administration in female rats, on levels of secretion of melatonin, using an organ culture of pineal glands. Gonadectomy 2 weeks before the animal was killed increased the amount of melatonin secreted into the medium by the pineal glands of female rats but not of male rats. The increase in in vitro melatonin secretion after ovariectomy in female rats was prevented by estrogen replacement. Ovariectomy 3 and 4 weeks before death also significantly increased the amount of melatonin secretion. Administration of GnRHa 2 weeks before decapitation significantly decreased serum estradiol concentrations and significantly increased melatonin secretion by the pineal glands of female rat. GnRHa administration 3 or 4 weeks before decapitation also significantly decreased serum estradiol concentrations, but did not increase pineal secretion of melatonin. The results indicate that ovariectomy increases melatonin secretion from organ-cultured pineal glands and that this increase is suppressed by estrogen in adult female rats. In contrast, orchiectomy in male rats does not influence in vitro secretion of melatonin. These results suggest that the GnRH-gonadotropin system may participate in the regulation of pineal melatonin secretion in adult female rats.
A 56-year-old female with Graves' disease who presented with decreased secretion of gonadotropins is described. She was admitted to hospital because of her being in a state of confusion. One month before admission she had been diagnosed as having Graves' disease and was treated with methimazole since then. Plasma LH and FSH levels were undetectable, and their responses to LH-RH were extremely decreased in spite of undetectable levels of plasma estradiol and estriol. One year after treatment, both basal and stimulated values of LH and FSH reverted to normal as did those of TSH. Reversible suppression of gonadotropins as described herein has never been reported in cases of Graves' disease.
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