DIETARY-FAT AFFECTS PLASMA PROLACTIN IN FEMALE F344 RATS UNDER CONDITIONS OF ETHER STRESS

The influence of amount and type of dietary fat on circulating concent rations of prolactin and estradiol-17 beta in female F344 rats from wh ich blood was sampled by decapitation under ether anesthesia was compa red with that in rats from which blood was collected without anesthesi a. The animals were fed isonutrient (adjusted for differences in energ y density) semipurified diets containing 5% or 20% (by weight) sunflow er seed oil or lard. Blood was sampled by decapitation with or without standardized ether anesthesia during the afternoon of proestrus-estru s or the morning of metestrus-diestrus, as determined by examination o f vaginal smears. Plasma hormone concentrations were measured by radio immunoassay. Prolactin levels were lower during proestrus-estrus in ra ts fed a low-fat diet than in animals fed a high-fat diet, statistical ly independent of the type of dietary fat, but only when blood was sam pled by decapitation under ether anesthesia [p = 0.0384, 2-way analysi s of variance (ANOVA)]. No such difference was found in rats decapitat ed without anesthesia. This effect of amount of dietary fat on prolact in in proestrus-estrus animals anesthetized with ether was predominant ly present in animals fed polyunsaturated fat (p < 0.05, 1-way ANOVA a nd Tukey's test) and was statistically not significant in rats fed sat urated fat diets. During metestrus-diestrus, prolactin levels were sig nificantly lower in animals fed a high-saturated fat diet than in thos e fed low-saturated fat, low-unsaturated fat, or high-unsaturated fat diets, independent of the blood sampling conditions (p < 0.05, 2-way A NOVA and Tukey's test). No consistent effects on estradiol-17 beta lev els were found in type or amount of dietary fat or in presence or abse nce of ether anesthesia before decapitation. Growth, apparent digestib ility of fat, and caloric intake were similar in all four dietary grou ps, but food consumption was higher and food conversion efficiency was lower in animals fed low-fat diets than in those fed high-fat diets. This study confirms the hypothesis that effects of dietary fat, partic ularly polyunsaturated fat, on circulating prolactin occur only during (ether) stress. Because stress is a frequent and normal phenomenon, t his observation implies that the mammary glands of animals with a high dietary intake of polyunsaturated fat are frequently exposed to highe r circulating prolactin concentrations than rats fed a low-fat diet, w hich may be a major mechanism by which dietary fat enhances rat mammar y carcinogenesis.