Aim: The present study was aimed to investigate the developmental patterns of growth hormone receptor (GHr) and somatostatin (SS) mRNA expression in porcine gastric tissue and its relationship with gastric growth and gastric functional development.
Methods: Erhualian and Large White boars were selected randomly and sampled at birth (D0), 3, 20, 30, 90, 120 and 180 days of age respectively, meanwhile the bodyweight and gastric weight were recorded. The single tube semi-quantitative RT-PCR was applied in this experiment to investigate the developmental patterns of gastric GHr and SS mRNA expression, the correlations between the patterns of mRNA expression and the relative gastric weight (ratio of gastric weight to bodyweight) and the pepsin contents in gastric mucous membrane were analyzed. In order to further elucidate the effect of GH on gastric function, the primary cultures of gastric fundic mucosal cells were treated with 2 ng/ml, 20 ng/ml and 200 ng/ml of rpGH for 18 hrs respectively, and the pepsin contents in culture medium were measured.
Results: The expression of GHr mRNA was high at birth, followed by a significant decrease at 3 days of age (D3) in both breeds. In Large White boars, the expression of GHr mRNA reached a peak at D90 and remained a plateau afterward. In Erhualian pigs, however, a slight yet significant increase occurred at D30 reaching a level that was kept constant thereafter. From birth to D30, the expression of GHr mRNA in gastric tissue was higher in Erhualian boars than that in Large White boars, but from D90 to D180, the higher expression of GHr mRNA was found in Large White boars. The gastric GHr mRNA expression was significantly correlated with the relative gastric weight (r=0.541, P<0.05) and pepsin content in gastric mucosa (r=0.625, P<0.05) respectively. The gastric SS mRNA expression was high at birth (Erhualian 1.59, Large White 0.80), but dropped significantly at D3 (Erhualian 0.95, Large White 0.19, P<0.05), a stepwise increase was followed thereafter until a peak at D30 (Erhualian 1.71, Large White 0.95) In general, Erhualian pigs expressed higher levels of SS mRNA in gastric tissue as compared with Large White pigs at the same age (P<0.05). No significant correlations between SS mRNA and relative gastric weight or pepsin content were found. In vitro, 2 ng/ml of rpGH elicited significant increase in pepsin secretion from primary cultures of gastric mucosal cells (P<0.05), and no responses were observed at 20 ng/ml and 200 ng/ml.
Conclusion: The results suggested that: 1, GHr and SS mRNA in porcine stomach are expressed according to strain specific developmental patterns; 2, GH acts directly at the gastric tissue and regulates the structural and functional growth of stomach.