Developmental, dietary, and hormonal regulation of leptin synthesis, secretion, and action in cattle

摘要

Hypotheses to examine the developmental, dietary, and hormonal relationships of leptin to reproductive processes in cattle were investigated in three studies. In the first study, circulating concentrations of leptin, adipocyte leptin gene expression, serum binding of [125I]ovine leptin during pubertal development, as well as leptin gene expression and serum leptin during the estrous cycle and different calendar seasons were investigated. Serum leptin and leptin gene expression increased (P < 0.05) as puberty approached in heifers. No differences in the magnitude of increases in serum leptin were detected in heifers attaining puberty in the spring or late summer months, indicating that the pubertal increase was independent of seasonal day lengths. No evidence of leptin binding proteins in serum from developing heifers was found. In mature heifers and cows, serum leptin tended (P = 0.10) to decrease during the late luteal/early follicular phase of the estrous cycle, which corresponded to a reduction (P < 0.03) in adipocyte leptin gene expression. In mature ovariectomized cows, serum leptin increased (P < 0.0001) by 34% from early winter to the summer solstice, and remained unchanged until the winter solstice. A second study was conducted to examine the effects of high linoleic acid diets on adiposity, serum leptin, and age at puberty in young heifer calves. We hypothesized that diets high in linoleic acid would increase conjugated linoleic acid (CLA) tissue content, an inhibitor of pre-adipocyte differentiation and proliferation, reduce serum leptin, and increase age at puberty. Although tissue content of CLA was higher (P < 0.03) in linoleic acid-supplemented heifers, total carcass fat, serum leptin, and age at puberty were not affected by diet. A third experiment examined the ability of leptin to attenuate simulated post-secretory effects of neuropeptide Y (NPY) on gonadotropin and somatotropin secretion in ovanectomized cows. Treatment with leptin prior to intracerebroventncular administration of NPY did not alter the ability of NPY to suppress LH secretion; however, leptin pre-treatment attenuated the stimulatory effects of NPY on GH secretion. These studies verify functional interrelationships between leptin, pubertal development, and neuroendocrine function in cattle, similar to those reported in other species.