Immunohistochemical distributions of leptin, ghrelin and obestatin hormones in bull and ram abomasum

In most mammals, leptin plays central and peripheral roles in a wide range of metabolic activities including feed consumption and digestion, energy expenditure and the regulation of carbohydrate-fat accumulation. Ghrelin is a strong appetite-stimulating hormone, while obestatin has the opposite effect of ghrelin. The latter is released during feeding, causing a sense of satiety. This study aimed to reveal if the metabolic hormones, as well as OB-R and GHS-R, were present in bull and ram abomasums. Streptavidin-biotin peroxidase method was implemented to determine the expressions and localizations of metabolic hormones and their receptors, and obestatin. Immunoreactivity for leptin and obestatin was present in the cytoplasms of luminal and glandular cells, while smooth muscle cells were immunoreactant for ghrelin, in both bull and ram abomasums. Immunoreactivity for OB-R was present in luminal and glandular cell, parietal cell cytoplasms, and blood vessels. Immunoreactivity for GHS-R, on the other hand, was found in glandular epithelial cell cytoplasms and parietal cell cytoplasms, in both bull and ram abomasums. Leptin immunoreactivity was detected in the glandular epithelial cells and stroma, and particularly in the parietal cells. Ghrelin immunoreactivity was not observed in glandular epithelial cells. Obestatin immunoreactivity was found intensely in the bull abomasum, while moderate immunoreactivity was observed in the ram abomasums. As such, leptin, ghrelin and obestatin hormones were expressed in bull and ram abomasums, similar to the abomasums of other species. It is believed that these hormones play important roles in the digestive system activities and the regulation of energy in bulls and rams.