Effects of hyperprolactinemia on toxicological parameters and proliferation of islet cells in male rats.

Prolactin has a wide variety of biological effects. Consequences of hyperprolactinemia on islet B cell proliferation as well as general toxicological parameters were here examined using anterior pituitary-grafted rats. Three or six anterior pituitary glands were implanted under single renal capsules of F344 male rats and left there for 13 weeks afterward. Clinical observation along with measurement of body weight and food consumption was conducted during the observation period, and subsequently hematology, blood biochemistry, gross pathology, organ weights and histopathology were examined. In addition, the proliferation rate of islet B cells was measured by a 5-bromo-2'-deoxy-uridine (BrdU) labeling technique. Serum prolactin concentrations at week 13 were 36, 70, 75 and 105 ng/ml in the sham-operated, 3-pituitary-grafted groups from male or female donors, and 6-pituitary-grafted group from male donors, respectively. Higher cholinesterase and total cholesterol values, lower trigriceride and leutenizing hormones (LH) values, and higher adrenal weights compared to those in the sham-operated group were apparent in the 3- and/or 6-pituitary-grafted groups. Also, the study revealed that mammary gland structure was transformed with change of differentiation from a male to a female acinar pattern. Furthermore a specific increase of islet cell proliferation rate was found, positively correlated with serum prolactin concentration. These findings suggest that elevation of serum prolactin level over 13 weeks induces islet cell proliferation and changes in toxicological parameters, including cholinesterase activity, elements of lipid metabolism and histopathology/morphology of the adrenals and mammary glands in male rats.