Sensitivity of anterior hypothalamic areas to gonadal steroid implantation in androgenized female rats.

A single injection of 1 mg of a complex of testosterone esters on day 5 of life was used to prepare constantly oestrous rats. Such androgenized female rats were then ovariectomized and submitted to stereotaxical implantation of 1 microgram oestradiol benzoate, 5 microgram testosterone isobutyrate or, as a control, 10 microgram cholesterol in the anterior hypothalamic areas. The effects of the steroids on plasma and pituitary FSH and LH were assessed by radioimmunoassay. As reported previously by us in normal female and male rats, the preoptic-suprachiasmatic area (POA) was able to control synthesis and secretion of both gonadotrophins and did not lose its sensitivity to oestradiol and testosterone in andorgenized rats. Evidence for enhanced prolactin secretion in androgenized rats was derived from immunofluorescence studies of the pituitary gland and from histology of the mammary glands. In this respect the condition of the androgenized females was opposite to that of the males. The present work demonstrated that stimulation of prolactin secretion in androgenized female rats resulted from oestrogen action due to permanent oestrus rather than from impairment of hypothalamo-hypophysial relationships. Indeed, prolactin stimulation was suppressed when the androgenized rats were ovariectomized and restored when they were subsequently implanted with oestradiol in the POA.