Abstract
Simple SummaryThe semi-natural pastures in the Apennines represent the feed source for ovine, whose grazing activity helps to preserve the grassland’s biodiversity. Summer drought stress decreases the grassland pastoral value and affects the morpho-functional features of sheep’s digestive systems. A better knowledge of the gastrointestinal system of sheep may contribute to guaranteeing their welfare, a prerequisite for the sustainability of livestock production. This study aimed to immune-localize the apelinergic system in the abomasum and duodenum of sheep grazing on semi-natural pasture during the spring–summer season and to compare its behavior among animal groups fed with or without supplementation. The apelinergic system, composed of apelin and its receptor, is involved in foodintake and the secretion and absorption activities of the digestive apparatus. Apelinergic system molecules were localized at the abomasum lining epithelium and fundic glands level and at the duodenum lining and crypt epithelium, in addition to the neuroendocrine cells. Variations in reactivity were observed in the different feed groups; feed supplementation seemed to maintain the functionality of the apelinergic system in the organs near the status related to the better pasture phase, suggesting that it may be a suitable solution able to counteract the harmful effects of summer drought stress.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 × Appenninica adult sheep reared in a semi-natural pasture. Organ samples were collected after maximum pasture flowering (M × F group) and after maximum pasture dryness (M × D group); the experimental group (E × p group) received a feed supplementation of 600 grams/day/head of barley and corn in addition to M × 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 × F and E × p groups, while the M × 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 × p group presents a picture quite overlapped with M × F and suggest that food supplementation has a maintaining effect on the apelinergic system expression in the investigated digestive tracts of the sheep.
Highlights
Adipose tissue acts as an organ producer of adipokines [1], such as apelin (APLN)
The positive cells were found in the mucous layer, especially in the lining epithelium (Figure 1a,d), and in the lower region of fundic glands (Figure 1b,e) where the immunohistochemical staining was appreciated in the chief cell cytoplasm and supranuclear region
Double-label immunohistochemistry showed that neuroendocrine cells, positive to serotonin, did not stain with APLN nor APLNR (Figure 1c,f)
Summary
Adipose tissue acts as an organ producer of adipokines [1], such as apelin (APLN). A sort of feedback takes placebetween APLN and insulin since this adipokine regulates the secretion of insulin through the APLNR expression in pancreatic islet β-cells [5]. It inhibits glucose-stimulated insulin secretion in mice and in isolated islets of Langerhans [6,7]. APLN expression and plasmatic level are inhibited by fasting and recovered after refeeding [8]. APLN expression increases during adipogenesis so that the APLN plasmatic level positively correlates with body mass index in humans [9] and it is increased further in obese patients [8,10]
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