Genistein-induced pituitary prolactin gene expression and prolactin release in ovariectomized ewes following a series of intracerebroventricular infusions.

The aim of the study was to evaluate whether genistein, a phytoestrogen commonly present in feed plants, affects prolactin release and its gene expression in the pituitary gland. In the experimental model, genistein was infused into the third ventricle (IIIv) of the brain in ewes during the short-daylight period (November-December), when the physiological plasma level of prolactin is low. Animals were ovariectomized six weeks before the experiment, to remove the main source of endogenous estrogens, and three weeks later a stainless steel guide cannula was implanted into IIIv. Genistein (10 ng/100 microl/h, n=5) or vehicle (control, n=5) were infused in a series of four one-hour infusions at 30-min intervals (from 16:30 to 22:00). Plasma samples were collected at 15-min intervals from 14:00 to 22:00 through a catheter inserted into the jugular vein and after the experiment ewes were slaughtered. Northern blot analysis revealed that pituitary prolactin mRNA content increased significantly in response to genistein, compared to the vehicle-infused ewes (p<0.05). Prolactin concentration in plasma rose significantly during the periods of genistein infusion, as compared to the values found before infusion (p<0.05-p<0.01) as well as to the values of the concomitant periods in vehicle-infused ewes (p<0.001). Our results show an effective estrogenic action of genistein on prolactin synthesis and release in ovariectomized ewes that might in part be exerted at the central nervous system level.