Expression analysis of key somatotropic axis and liporegulatory genes in ghrelin- and obestatin-infused dairy cows

Abstract

Ghrelin, an orexigenic hormone, is the endogenous ligand for the growth hormone secretagogue receptor (GHSR). Obestatin is produced from the same precursor peptide as ghrelin, and although obestatin was initially thought to promote actions opposite to those of ghrelin, many studies have failed to confirm this hypothesis. In the current study, multiparous cows were continuously infused with ghrelin (n = 10) or obestatin (n = 10) for 8 wk and compared to an untreated group (n = 10) to examine the effects of these hormones on somatotropic and liporegulatory gene expression. The expression of key genes was measured by quantitative real-time polymerase chain reaction. Growth hormone secretagogue receptor mRNA expression was altered in ghrelin- and obestatin-infused cows in a similar manner, as expression was increased at 4 wk, however it had decreased by 8 wk. Obestatin-infused cows presented with a significant decrease in the expression of ATP-binding cassette A1 (ABCA1) in adipose tissue, suggesting changes in cholesterol transport. Liver insulin-like growth factor (IGF) binding protein-3 mRNA displayed a week-by-treatment interaction, as expression was increased in control and obestatin-infused cows; however, expression decreased in ghrelin-infused cows. Adipose expression of hormone sensitive lipase (LIPE) mRNA was not altered by treatment or time, suggesting hormone infusion is not initiating lipolysis. The expression of lipogenic genes in adipose tissue increased with time in all groups, consistent with the general lactational profile of lipogenesis in dairy cows. These data indicate that continuous infusion of ghrelin or obestatin does not alter the expression of key somatotropic or liporegulatory genes in the lactating dairy cow, although obestatin infusion may alter cholesterol transport.