Little is known about the in vivo influence of the blockade of the growth hormone secretagogue receptor Ia (GHS-R1a) on the gut structure. Data obtained in in vitro studies can be misinterpreted and can generate a confusing picture of the effects of ghrelin on the gastrointestinal structure. In a living organism the remodeling processes in the gastrointestinal tract is affected by complex regulatory mechanisms governed by locally produced hormones and peptides, as well as by the enteric and central nervous system. To our knowledge, there are as yet no published reports on the influence of ghrelin receptor blockades on the morphology of the alimentary system. The aim of the study was therefore to determine the effect of the GHS-R1a antagonist [D-Lys3]-GHRP-6 on the structure of the gastrointestinal (GI) system in the rat. Studies were performed on 12 male Wistar rats aged approx. 2 months with an initial body mass of approx. 180-200 g. The rats were kept on a 12/12 hour light/dark cycle at a temperature of 22 ± 2°C, and had free access to a standard rat diet and water. The animals were divided into two groups: control and experimental. The control group received physiological saline, and the experimental group were administered 100 nmol/kg b.wt. of [D-Lys3]-GHRP-6, a GHS-R1a antagonist (Peptides International, USA&Canada), intragastrically one dose/day during 4 weeks. The animals were fasted during the night before killing. After euthanasia the GI tract was rapidly removed, and the weight and length of the stomach, pancreas, liver, and small intestine were measured. Samples of the pancreatic tissue, duodenum, jejunum (25%, 50%, 75% of length), and ileum were taken for histological analyses. The paraffin sections were stained with hematoxylin and eosin, and a morphometric analysis was performed with the use of light microscopy. Significant differences in the surface area of pancreatic acinar cells and significantly increased mucosa thickness, villi length and crypt depth in the proximal jejunum were found in the rats intragastrically treated with [D-Lys3]-GHRP-6. However, changes in body weight, weight of the organs, and intestine length were not significant. In conclusion, the blockade of the GHS-R1a by [D-Lys3]-GHRP-6 did not abolish the pro-proliferative effect of endogenous ghrelin on the intestinal mucosa in the proximal jejunum, and increased the surface area of pancreatic acinar cells. The mechanisms behind these changes are not fully understood, and further research is needed for a better understanding of this phenomenon.
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