THE EFFECTS OF ESTROUS CYCLE AND OESTROGEN ON PLASMA AND ANTRAL GASTRIN ACTIVITY IN MAMMALS

Abstract

Abstract The possible relationship between estrous cycle, oestrogen load and pregnancy on the one hand and antral-gastrin content, circulating plasma gastrin, parietal cell concentration and gastric acid secretion was investigated. Mostly albino rats of the Wistar strain weighing between 170 and 300gms and a few rabbits were used for this study. Gonadectomy was performed on the animals before loading them with known amounts of stilboesterol administered orally and 17B estradiol administered parentally. The oestrogen treated animals were given short-term (4 days) and long-term (10 days) treatments. Vaginal smears were taken and stained to confirm the estrous stage and for the purpose of grouping the animals into definite phases of the estrous cycle. The rats were mated in the laboratory and vaginal smears were taken each day for examination. The first sign of sperms in the smears was takan day 1 of pregnancy. The pregnant rats were arbitrarily divided into three groups namely, early pregnancy (day2-3), mid pregnancy (day 12 - 14) and late pregnancy (day 18 - 20). Gastrin was extracted from the antral mucosa of each rat by a modification of the method used by Brown In 1869, and the extracted gastrin solution assayed for gastrin activity using the perfused rat stomach, The circulating plasma gastrin was estimated by radioimmunoassay and the level expressed in picogramme per ml. Parietal cell estimation was carried out by a special staining technique. The different categories of rats used were studied for their response to basal and induced gastric acid secretion. The results showed some variations in the antral gastrin content of the various categories of animals studied. Antral gastrin content was highest in di-estrous and lowest in pro-estrous. (Di-estrous > estrous P <0.001; Estrus> pro-estrous, p> 0.6). The gastrin yield was highest in early pregnancy and lowest in late pregnancy (Early > mid, P <0.001; mid > late, p<0.01). Castrated male rats had less antral gastrin than uncastrated male rats (P< 0.001). The oestrogen loaded rats had less antral gastrin than the untreated rats. In the rabbit, the crude gastrin from the treated animals were less active than the crude gastrin from the intact male or the castrated untreated rabbits. Plasma circulating gastrin was highest in late pregnancy than in either early or mid-pregnancy. The level of plasma gastrin was highest in rats at pro-estrous than at estrus or di-estrus, but the level at di- estrous was slightly higher than in early pregnancy. The level recorded for the intact male rat was higher than the level obtained for any phase of the estrous cycle. It was not possible to measure the level for the oestrogen loaded animals as most of the values obtained for the bound plasma gastrin fell outside the standard curve. The parietal cell estimation showed a value highest in pro-estrous. It was also highest in late pregnancy than early or mid-pregnancy. Higher values were recorded for the oestrogen loaded rats. The acid gastric secretion is highest during pro-estrous and lowest at estrus. Basal and induced acid secretions were highest in late pregnancy and the values for basal secretions during early and mid-pregnancy were lower than that for non-pregnant female rats. There appears to be some correlation between the parietal cell concentration and the gastric acid secretion on the one hand and plasma level gastrin and acid gastric secretion on the other. It would appear that there was no correlation between antral gastrin content and the plasma level gastrin or the pattern of gastric acid secretion. There is definitely a physiological role of oestrogen in the mechanism of acid secretion from the results obtained.