effects of alpha 1adrenergic blockade on pulsatile luteinizing hormone folliclestimulating hormone and prolactin secretion in polycystic ovary syndrome central noradrenergic mechanisms may participate in the regulation of pulsatile gonadotropin secretion in women with the polycystic ovary syndrome pco to examine this possibility we measured serum lh fsh and prl concentrations at 10min intervals and total testosterone and 17 betaestradiol at 60min intervals for 8 h basally and during the infusion of the alpha 1adrenoceptor antagonist thymoxamine 10 microgramskg x min in 10 young women with pco mean and integrated serum lh concentrations as well as lh pulse frequency were not significantly altered p ns during the thymoxamine infusion however we found an increase in lh pulse amplitude as both net p less than 0002 and percent p less than 0002 increment as well as mean lh peak values p less than 005 during alpha 1adrenergic blockade there were no significant changes in pulsatile fsh and prl secretion or gonadal sex steroids during these experimental conditions these data suggest that in pco patients 1 brain noradrenergic mechanisms do not play a stimulatory role in regulating the frequency of pulsatile lh secretion 2 central noradrenergic activity inhibits lh pulse amplitude and 3 prl and fsh pulsatility are not altered by central noradrenergic blockade