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The Combined Effects of Dietary Protein and Fat on Prolactin in Female Rats¹

University of Illinois College of Medicine at Urbana-Champaign, Urbana, Illinois 61801

A 3 x 3 factorial experiment was conducted to examine how protein content (8, 16 and 32% of kcals from casein) and fat content (12, 24 and 48% of kcals from corn oil) interact to influence prolactin homeostasis in female rats. Weanling Sprague-Dawley rats were assigned to each of nine diets fed ad libitum. Dietary fat had no effect on the time of vaginal opening although first estrus occurred slightly earlier with high fat diets (P < 0.05). Rats fed diets with protein at 8% of kcal showed a 2-wk delay in vaginal opening and first estrus. After 18–20 wk of feeding, serum and pituitary prolactin concentrations were determined after decapitation during the afternoon of proestrus or diestrus. Although serum prolactin was elevated at proestrus, there were no effects of fat or protein on the serum or pituitary prolactin. Another group of rats were fitted with jugular cannulae and treated with perphenazine, a potent prolactin-stimulating drug. Dietary fat or protein had no effect on prolactin secretion after perphenazine treatment. In the final experiment, rats fed each diet were treated with either i.p. saline or perphenazine followed by decapitation. The pituitary was removed 3 h later for determination of the amount of prolactin depleted from the pituitary. There was no effect of diet on the amount of pituitary prolactin depleted by perphenazine. No evidence was obtained that changes in dietary fat or protein concentration influence serum prolactin or its secretion in response to a provocative stimulus. This study supports the hypothesis that dietary fat enhances mammary carcinogenesis by mechanisms independent of prolactin concentrations in the serum and pituitary prolactin secretion. Previous studies showing an effect of fat on serum prolactin may have been due to a deficiency of essential fatty acids.

KEY WORDS: • dietary protein • casein • dietary fat • corn oil • rats • prolactin • pituitary • perphenazine • breast cancer

¹ Supported by Grant No. HEW PHS R01 AM28026 and Grant No. HEW PHS CA 28629 from the National Cancer Institute.

² Current address: The University of Chicago Medical Center, Department of Medicine, 5841 South Maryland Avenue, Chicago, IL 60637.

³ Current address: Medical College, National Cheng Kong University, Tainan, Taiwan 700, Republic of China.

⁴ To whom reprint requests should be sent.

Manuscript received 19 July 1984.