Acute modulation of the hypothalamic-pituitary axis by intravenous testosterone in normal women.

Intravenous testosterone was infused for 6 hours in 23 ovulatory women, divided into five groups according to dose, to assess the effects of testosterone on gonadotropin secretion. Serum testosterone increased from 0.24 +/- 0.08 to steady-state levels of 1.63 +/- 0.18 ng/ml in the lowest-dose group (1) and to 42.1 +/- 3.3 ng/ml in the highest-dose group (4). In another group (5), patients were pretreated with testolactone, which prevented the estradiol rise associated with testosterone infusion. All groups except group 1 exhibited significant reductions in the delta maximum responses of luteinizing hormone to gonadotropin-releasing hormone during testosterone infusion compared with pretreatment levels (p less than 0.01). This was also evident for the testolactone group (5). There were no observed changes in serum follicle-stimulating hormone. Luteinizing hormone pulse frequency was decreased (p less than 0.05) with testosterone concentrations of 27.2 +/- 0.77 and 42.1 +/- 3.3 ng/ml (groups 3 and 4), but only in the highest group (4) was there a decrease in pulse amplitude (p less than 0.05). No luteinizing hormone pulse changes were observed with lower concentrations of testosterone. Plasma immunoreactive gonadotropin-releasing hormone levels remained undetectable or low in some of the groups sampled. These data suggest that short-term infusions of testosterone inhibit hypothalamic-pituitary function of normal women when high doses are used, and this effect may be independent of aromatization to estrogen.