Development of gastric somatostatin-like immunoreactivity in response to corticosterone acetate and dietary changes in young rats

Abstract

The effects of dietary changes from breast milk to solid food and corticosterone acetate administration on somatostatin-like immunoreactivity (SLI) in the gastric antrum and corpus were studied in young and adult rats. At 7 days of age, a single dose of corticosterone acetate (250 mg/kg of body weight) was injected in one group of rats, and a single dose of physiological saline was injected in another group. Each group was divided into two subgroups; one was fed only rat breast milk until 25 days of age and the other weaned (solid food alone) at 21 days of age. Gastric antrums and corpora were removed at various ages for assay of SLI concentrations by radioimmunoassay. In non-corticosterone treated rats, antral and corpus SLI increased gradually until 20 days of age, and after changing from breast milk to solid food on day 21 antral SLI increased 2-fold to the adult level, whereas corpus SLI remained constant. In corticosterone\x=req-\ treated rats, antral and corpus SLI on day 11 was 5-fold that on day 7, and thereafter remained constant before changing from breast milk to solid food; after weaning (solid food alone) antral SLI increased again to reach the adult level at 25 days of age whereas corpus SLI remained constant after weaning. Prolonged breast milk feeding alone did not influence antral or corpus SLI levels in either corticosterone-treated or non\x=req-\ treated rats as compared to levels on day 20. Gel filtration of antral and corpus SLI from 15 day old corticosterone-treated and non-treated, and 25 day old weaned (solid food alone) and unweaned (breast milk alone) rats showed almost the same results: only one peak coeluted with synthetic somatostatin-14. The resuits suggest that weaning (solid food alone) and corticosterone administration affect the antral and corpus SLI.Somatostatin is found in the antrum and corpus of the stomach and it has paracrine mechanism in gastric acid secretion (Arimura et al. 1975;Larsson 1981). It has recently been shown that steroid hormone administration in young unweaned rats results in the development of gastrointestinal en¬ zymes and hormones as seen in weaned animals (Furihata et al. 1972;Henning & Sims 1979). Especially in the stomach, the antral gastrin con¬ centration in unweaned rats increased after cor¬ ticosterone acetate administration as it did in weaned rats (Peitsch et al. 1981). Koshimizu has reported that somatostatin-like immunoreactivity (SLI) concentrations in the gastric antrum and corpus of immature rats increased with age up to 21 days of age (time of weaning) (Koshimizu 1983). In this investigastion, we studied the effects of weaning (changes from breast milk to solid food abruptly) and corticosterone acetate on an¬ tral and corpus SLI in young rats. This study differs from Koshimizu's study, particularly in its emphasis on the relationship of this peptide to dietary changes, weaning and breast milk alone until day 25 and to the effect of corticosterone administration.