The Apelinergic System Immuno-Detection in the Abomasum and Duodenum of Sheep Grazing on Semi-Natural Pasture

Apelin (APLN) is an adipokine mainly produced by adipose tissue and related to an individual's nutritional status as well as digestive apparatus functions. In this work, APLN and its receptor (APLNR) were investigated, by immunohistochemistry, in the abomasum and duodenum of 15 Comisana x Appenninica adult sheep reared in a semi-natural pasture. Organ samples were collected after maximum pasture flowering (M x F group) and after maximum pasture dryness (M x D group); the experimental group (E x p group) received a feed supplementation of 600 grams/day/head of barley and corn in addition to M x D group feeding. APLN and APLNR were identified in the lining epithelium and the fundic gland chief cells of the abomasum. APLNR was observed in the lining epithelium, in the crypts and the serotonin secreting cells of the duodenum. Similar reactivity was observed between the M x F and E x p groups, while the M x D group showed a lower intensity of immunostaining for both APLN and APLNR in all positive structures but the duodenal serotonin neuroendocrine cells. Hence, our findings show that the E x p group presents a picture quite overlapped with M x F and suggest that food supplementation has a maintaining effect on the apelinergic system expression in the investigated digestive tracts of the sheep.