In dairy goats, the hormone ghrelin and its receptor are found in the mammary gland, especially when milk production is highest. In lab tests, adding ghrelin made the cells produce more milk protein (beta‑casein) and divide more, and these effects were stopped by a blocker that blocks the ghrelin receptor.

Recent studies have implicated the peripheral actions of ghrelin in reproductive tissues. The present study provides novel evidence for the expression of ghrelin and its functional receptor (GHSR-1a) in the mammary glands of dairy goat during lactation and the effects of ghrelin on regulation of mammary function in vitro. Ghrelin and GHSR-1a mRNA and protein were persistently detected in goat mammary glands throughout the lactation, and patterns of expression of ghrelin, GHSR-1a and β-casein were generally similar, with highest levels during peak milk yield (day 60-120 of lactation) and lower levels during late (day 180) of lactation. The distribution of ghrelin and GHSR-1a in the mammary glands were substantiated by immunohistochemical method, alveolar and ductal epithelial cells showed distinct immunoreactivity at the different stages of lactation, strong reactivity was seen in most epithelial cells during peak stage, in some alveoli, the vast majority of the epithelial cells were immunoreactivity. Ghrelin and GHSR-1a mRNA expression were demonstrated in cultured primary mammary epithelial cells (MECs). In addition, the results showed that ghrelin could induce a dose-dependent promotion on β-casein expression in cultured mammary tissues and MECs, and the stimulative effects on β-casein expression were blocked by D-Lys3-GHRP6 (a GHSR-1a antagonist). Additionally, ghrelin induced a dose-dependent promotion on cell proliferation. Our present findings suggest that ghrelin may play an important role in regulation of mammary function in lactating dairy goats via GHSR-1a.