Ontogeny of gastrin, somatostatin, and the H+/K(+)-ATPase in the ovine fetus

Hypothyroidism impairs development of the gastrointestinal tract in the ovine fetus

Growth and maturation of the fetal gastrointestinal tract near term prepares the offspring for the onset of enteral nutrition at birth. Structural and functional changes are regulated by the prepartum rise in cortisol in the fetal circulation, although the role of the coincident rise in plasma tri-iodothyronine (T3) is unknown. This study examined the effect of hypothyroidism on the structural development of the gastrointestinal tract and the activity of brush-border digestive enzymes in the ovine fetus near term. In intact fetuses studied between 100 and 144 days of gestation (dGA; term ∼145 days), plasma concentrations of T3, cortisol and gastrin; the mucosal thickness in the abomasum, duodenum, jejunum and ileum; and intestinal villus height and crypt depth increased with gestational age. Removal of the fetal thyroid gland at 105-110 dGA suppressed plasma thyroxine (T4) and T3 concentrations to the limit of assay detection in fetuses studied at 130 and 144 dGA, and decreased plasma cortisol and gastrin near term, compared to age-matched intact fetuses. Hypothyroidism was associated with reductions in the relative weights of the stomach compartments and small intestines, the outer perimeter of the intestines, the thickness of the gastric and intestinal mucosa, villus height and width, and crypt depth. The thickness of the mucosal epithelial cell layer and muscularis propria in the small intestines were not affected by gestational age or treatment. Activities of the brush border enzymes varied with gestational age in a manner that depended on the enzyme and region of the small intestines studied. In the ileum, maltase and dipeptidyl peptidase IV (DPPIV) activities were lower, and aminopeptidase N (ApN) were higher, in the hypothyroid compared to intact fetuses near term. These findings highlight the importance of thyroid hormones in the structural and functional development of the gastrointestinal tract near term, and indicate how hypothyroidism in utero may impair the transition to enteral nutrition and increase the risk of gastrointestinal disorders in the neonate.

Cysteamine increases expression and activity of H+-K+-ATPase of gastric mucosal cells in weaning piglets

AIM: To determine the in vivo and in vivo effects of cysteamine (CS) on expression and activity of H⁺-K⁺-ATPase of gastric mucosal cells in weaning piglets.

METHODS: Eighteen litters of newborn Xinhuai piglets were employed in the in vivo experiment and allocated to control and treatment groups. From 12 d of age (D12), piglets in control group were fed basal diet, while the treatment group received basal diet supplemented with 120 mg/kg CS. Piglets were weaned on D35 in both groups. Six piglets from each group (n = 6) were slaughtered on D28 (one week before weaning), D35 (weaning), D36.5, D38, D42, and D45 (36 h, 72 h, one week and 10 d after weaning), respectively. Semi-quantitative RT-PCR was performed to determine the levels of H⁺-K⁺-ATPase mRNA in gastric mucosa. H⁺-K⁺-ATPase activity in gastric mucosa homogenate was also determined. Gastric mucosal epithelial cells from piglets through primary cultures were used to further elucidate the effect of CS on expression and activity of H⁺-K⁺-ATPase in vivo. Cells were treated for 20 h with 0.001, 0.01, and 0.1 mg/mL of CS (n = 4), respectively. The mRNA expression of H⁺-K⁺-ATPase and somatostatin (SS) as well as the H⁺-K⁺-ATPase activity were determined.

RESULTS: in vivo, both mRNA expression and activity of H⁺-K⁺-ATPase in gastric mucosa of control group exhibited a trend to increase from D28 to D45, reaching a peak on D45, but did not show significant age differences. Furthermore, neither the mRNA expression nor the activity of H⁺-K⁺-ATPase was affected significantly by weaning. CS increased the mRNA expression of H⁺-K⁺-ATPase by 73%, 53%, 30% and 39% on D28 (P = 0.014), D35 (P = 0.017), D42 (P = 0.013) and D45 (P = 0.046), respectively. In accordance with the mRNA expression, H⁺-K⁺-ATPase activities were significantly higher in treatment group than in control group on D35 (P = 0.043) and D45 (P = 0.040). In vivo, CS exhibited a dose-dependent effect on mRNA expression and activity of H⁺-K⁺-ATPase. Both H⁺-K⁺-ATPase mRNA expression and activity in gastric mucosal epithelial cells were significantly elevated after 20 h of exposure to the moderate (H⁺-K⁺-ATPase expression: P=0.03; H⁺-K⁺-ATPase activity: P = 0.014) and high concentrations (H⁺-K⁺-ATPase expression: P=0.017; H⁺-K⁺-ATPase activity: P = 0.022) of CS. Significant increases in SS mRNA expression were observed to accompany the elevation of H⁺-K⁺-ATPase expression and activity induced by the moderate (P = 0.024) and high concentrations (P = 0.022) of CS. Low concentration of CS exerted no effects either on expression and activity of H⁺-K⁺-ATPase or on SS mRNA expression in cultured gastric mucosal epithelial cells.

CONCLUSION: No significant changes are observed in mRNA expression and activity of H⁺-K⁺-ATPase in gastric mucosa of piglets around weaning from D28 to D45. CS increases expression and activity of gastric H⁺-K⁺-ATPase in vivo and in vivo. SS is involved in mediating the effect of CS on gastric H⁺-K⁺-ATPase expression and activity in weaning piglets.

Developmental expression and biological activity of gastrin-releasing peptide and its receptors in the kidney

Mammalian gastrin-releasing peptide (GRP) has a widespread distribution and multiple stimulating effects on metabolism, release of regulatory peptides, gastrointestinal and pancreatic secretions, and behavior. GRP is a potent mitogen for a number of tumor types, including colon and lung. Although GRP is known to stimulate the growth of renal tumors, little is known of its synthesis, distribution, and receptors in the developing and mature kidney. Both Northern blot analysis and RT-PCR revealed the presence of GRP mRNA in ovine kidney from midgestation through to adulthood. GRP mRNA was detected in rat kidney from embryonic day 19 to postnatal day 30 by RT-PCR. Sequence-specific radioimmunoassay demonstrated the presence of substantial amounts of fully processed amidated GRP in the ovine renal cortex and medulla. The mRNA for the major receptor subtype, GRP-R, was present in fetal and adult sheep and rat kidneys. The mRNA for the low-affinity GRP receptor, bombesin receptor subtype-3 (BRS-3), was only detected in the rat kidney. In the ovine kidney, immunohistochemistry localized GRP predominantly to the thick ascending limb of the loop of Henle. mRNAs for GRP, GRP-R, and BRS-3 were detected in the human embryonic kidney cell line HEK293, and radioimmunoassay of cell extracts and conditioned media revealed the presence of proGRP but not the amidated form. However, amidated GRP did stimulate the proliferation of these cells. These studies demonstrate that the developing and mature kidney may be previously unidentified sites of autocrine or paracrine action for GRP.

Developmental patterns of GHr and SS mRNA expression in porcine gastric tissue

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.