| Research Abstract |
Leptin is an adipocyte-derived hormone serving as an appetite-regulating factor, and furthermore regulates various neuroendocrine functions linking nutrition and endocrine systems. The present research project led to the following novel, data.
1.Mechanism underlying the. sex-related difference in plasma leptin concentrations. It is well known that females have higher leptin levels than males in humans and also other mammals, but its underlying mechanism remains elucidated. The present study suggests that the neonatal exposure to androgens in male rats mediates, at least in part, the male-type lower leptin concentrations.
2.Mechanism of leptin-induced prolactin secretion. This subject was examined in the present study, and the. following data were obtained. Stimulation of prolactin secretion by leptin is mediated by none of dopamine, serotonin, vasoactive intestinal peptide, prolactin-releasing peptide, or beta-endorphin, and only alpha-melanocyte-stimulating hormone seems to play a signi
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ficant intermediary role by way of the melanocortin 4 receptor in the brain.
3.Mechanism of the suppression of the hypothalamo-pituitary-gonadal axis by inflammatory cytokines. It is well established that endotoxemia in bacterial infections induces the suppression of the hypothalamo-pituitary-gonadal axis, but the details of cytokines' roles in this phenomenon are not fully understood. The present study demonstrates that interleukin-1beta and tumor necrosis factor-alpha are almost equipotent in suppressing the release of gonadotropin-releasing hormone from rat hypothalamus, but the involvement of interleukin-6 is insignificant in this regard.
4.Role of melanocortin receptors in leptin-induced growth hormone secretion. It has been reported that the melanocortin 4 receptor in the brain mediates the actions of leptin on the hypothalamo-pituitary-thyroid/gonadal/adrenal axes. This study demonstrated that leptin-induced stimulation of growth hormone release is not mediated by either the melanocortin 3 or 4 receptor. Less
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