ROLE OF ENDOTHELIUM IN THE VASODILATING EFFECT OF PROGESTINS AND ANDROGENS ON THE RAT THORACIC AORTA

1. In the rat thoracic aorta, contractions induced by noradrenaline we re inhibited by the steroids progesterone, pregnanolone, testosterone and 5 alpha and 5 beta dihydrotestosterone. 2. Removal of endothelium did not prevent relaxation to the steroids, suggesting that the vasodi lating effect of steroids occurred on the smooth muscle cells. 3. gamm a-Aminobutyric acid (GABA) did not modify noradrenaline-induced contra ction. Thus, the vasodilation elicited by steroids is not apparently m ediated by GABA receptors. 4. On the basis that noradrenaline opens re ceptor operated calcium channels to induce contraction, we suggest tha t relaxation by steroids involves a blockade of this type of channels.