Effects of intra-gastric beta-casomorphin-7 on somatostatin and gastrin gene expression in rat gastric mucosa

Abstract

Aim: To investigate the in vivo effect of beta-casomorphin-7 on the regulation of gastric somatostatin and gastrin messenger RNA in rat gastric mucosa.

Methods: Somatostatin and gastrin mRNA were quantified by RT-PCR and in situ hybridization (ISH) in 24 rats. The rats were divided into three treatment groups: basal diet + physiological saline (n=8), basal diet + beta-casomorphin-7 (7.5 x 10(-7)mol) (n=8), and basal diet + poly-Gly-7 (containing equal mol of N with 7.5 x 10(-7) mol beta-casomorphin-7) (n=8). After oral administration for 30 days, rats were killed by exsanguinations.

Results: After intra-gastric administration of beta-casomorphin-7 for 30 d, gastrin mRNA increased by 52.8% (P<0.05, n=8), and somatostatin mRNA levels decreased by 30.7% compared with the controls (P<0.01, n=8). No significant differences in the expression of the two genes were observed in the poly-Gly-treated group, although gastrin mRNA expression was elevated by 35.6% as against the control group (P=0.15, n=8). The long-term oral administration of a casomorphin solution significantly decreased the even gray of D-cells, but did not lower the number of D-cells both in the antrum and fundus. Interestingly, the number of G-cells increased in the antrum and fundus, but its average density was augmented only in the antrum.

Conclusion: Beta-casomorphin-7 is capable of modulating gene expression of the regulatory peptides from G and D cells. Data from in situ hybridization studies indicate that beta-casomorphin-7 affects gastrin gene expression indirectly by means of the paracrine action of somatostatin, and depends on its intrinsic molecular function.

Figure 1

Effect of beta-casomorphin-7 on gastrin and somatostatin mRNA expression by RT-PCR. (A) and (B): graphs of RT-PCR analysis. (C) and (D): densitometric analysis of somatostatin and gastrin signals over beta-actin signals. The vertical lines indicate the mean ± SE of three different experiments. ^aP < 0.05 vs control group, ^bP < 0.01 vs control group.

Figure 2

In situ hybridization for gastrin and somatostatin mRNA in rat gastric mu-cosa. The oligonucleotide probes were labeled with digoxigenin. A: gastrin, corpus; B: gastrin, antrum; C: somatostatin, corpus; D: somatostatin, antrum. All of the sections magnify at 100 (10 × 10) and stained with DAB. The positive cells show brown precipitate at the site of digoxigenin-probe hybridization (black arrows).