Effect of ovarian hormones, pregnancy and lactation on somatostatin and substance P in the alimentary tract of mice

Immunoreactive somatostatin and substance P were determined in extracts of alimentary tract (stomach to colon) from the following groups of adult female mice: intact control, ovariectomized, ovariectomized and treated with oestradiol (50 μg/kg per day) and/or progesterone (2 mg/kg per day) for 30 days, 19-day-pregnant, and 10-day-postpartum lactating. Ovariectomy increased the somatostatin concentration of the stomach (by 52%, P < 0.05), jejunum (by 116%, P < 0.01) and caecum (by 114%, P < 0.01). These effects were partially or totally prevented by the oestradiol and progesterone treatments, especially the oestradiol-progesterone combination, except for an increase (by 126%, P < 0.01) in gastric somatostatin after treatment with oestradiol alone. Lactation also increased gastric somatostatin (by 108%, P < 0.001), but the somatostatin concentration of other regions of the alimentary tract (jejunum to colon) was reduced (by 21-55%, P < 0.05) in pregnant and lactating mice. The concentration of substance P was increased by ovariectomy in stomach (by 69%, P < 0.01), duodenum (by 84%, P < 0.05), ileum (by 163%, P < 0.001) and caecum (by 57%, P < 0.01). This effect was partially or totally prevented by treatment with progesterone alone and by the oestradiol-progesterone combination, but not by oestradiol alone. Pregnancy and lactation increased gastric substance P by 46% (P < 0.01) and 61% (P < 0.001) respectively, but substance P concentrations in other regions of the alimentary tract were not significantly altered. The results suggest that ovarian oestrogens and progestogens are important in the maintenance of normal concentrations of somatostatin and substance P in the gastrointestinal tract of female mice.