The role of leptin in development of mammary gland secretory function was studied during the periparturient period in dairy goats. Changes in mammary leptin and leptin receptor (short cytoplasmic form) expression were evaluated by real-time RT-PCR and related to changes in milk and plasma leptin concentrations from 5 weeks pre-partum to 7 weeks post-partum. It was further investigated if systemic leptin concentration in the neonate is affected by milk leptin intake.
We found no evidence of accumulation of leptin in colostrum pre-partum. Pre- and post-partum milk leptin concentrations were similar, but interestingly, leptin increased markedly post-partum to reach a peak 2 days after parturition (P=0.01). Plasma leptin concentrations were higher pre-partum than post-partum (P<0.05), decreased at parturition and arterio-venous differences for leptin across the mammary gland were at no time significantly different from zero. Plasma leptin does thus not appear to be involved in regulation of milk leptin.
Both leptin and the short cytoplasmic form of its receptor were expressed in the mammary gland. The highest leptin receptor expression was observed pre-partum and decreased post-partum. Expression of leptin was relatively constant except for an increase in the last week prior to parturition. Our results can neither confirm nor exclude that increased leptin and/or leptin receptor synthesis is responsible for regulation of milk leptin in the early post-partum period. The physiological significance of the distinct peak in milk leptin 2 days post-partum needs to be understood. We did not find evidence that milk leptin can be absorbed, and thus play a role in systemic regulation, of the neonatal goat.