Prolactin and the small intestine. Effect of hyperprolactinaemia on mucosal structure in the rat.

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Abstract
To study the mechanism for the adaptive mucosal hyperplasia which occurs independent of luminal nutrition and pancreatico-biliary secretions in isolated Thiry-Vella segments of intestine from lactating rats, and to examine the effects of prolactin on small bowel mucosal structure in the rat, 2 models of experimental hyperprolactinemia were used. Quantitative histology and several markers of mucosal mass were compared in jejunum and ileum from control rats and from test and lactating animals. Hyperprolactinemia, induced by perphenazine injections (5 mg/kg per day for 2 or 7 wk) or transplantation of 4 pituitary glands from donor animals to beneath the renal capsule in the recipient, was confirmed by radioimmunoassay. Proof of its biological activity was obtained by weighing the mammary pads and by demonstrating true breast hyperplasia on histological section. Median serum prolactin levels increased from 50 ng/ml in the controls to 570 ng/ml in the perphanzine treated animals to 600 ng/ml in the pituitary transplanted rats, level comparable with those seen in lactation (870 ng/ml). In the lactating rats, there was striking mucosal hyperplasia of both jejunum and ileum but, despite the hyperprolactinemia, there were no such changes in villus height, crypt depth or in mucosal wet weight, protein or DNA/unit length intestine in the perphenazine-injected or pituitary-transplanted animals. Prolactin evidently is not trophic to the intestine in rats and hyperprolactinemia cannot explain the intestinal adaptive changes of lactation.