Abstract
In a previous communication (1) we reported that 7,12-dimethylbenz (a) anthracene (DMBA)-treated rats fed a 20% fat semisynthetic diet exhibited a higher mean mammary tumor incidence (56%) than rats fed a 0.5% fat diet (34%), thus confirming the earlier studies of Carroll and coworkers (2, 3). Also, on the basis of experiments using hormone antagonists we tentatively concluded that the high fat effect was mediated through elevated serum prolactin and that changes in the estrogen-receptor system were probably not involved.
We now submit direct evidence, based on the radioimmunoassay of serum prolactin, that animals maintained on high-fat diets (HF) exhibit significantly higher serum prolactin levels during the proestrus-estrus period than animals fed low fat diets (LF).
Materials and Methods. Forty virgin female Sprague-Dawley rats (ARS/Sprague-Dawley, Madison, WI) were housed five in a cage in a temperature (24° ± 1°), humidity (50%) and light controlled (12 hr/ day) room and fed Purina Lab Chow and water ad libitum. When 50 days old, the rats were separated into two groups of 20 each and fed a high (20%) lard semisynthetic diet, as described previously (1), or a low (0.5 %) lard diet. After 2 and 5 mo on the diets, tail blood was taken once a week for 3 wk and the serum separated and stored at —20°. Bleeding was carried out under ether anesthesia at 4:00 pm and completed within 2 min. Also, during these 3 wk, vaginal smears were taken daily at 4:30 pm to determine the estrous stage. Radioimmunoassay of serum prolactin from cycling rats was carried out using reagents and methods supplied by the Hormone Distribution Program, National Institutes of Arthritis, Metabolic and Digestive Diseases, Bethesda, MD. Rat prolactin was iodinated with 125I obtained from Cambridge Nuclear Corp., Billerica, MA.
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