This study has investigated the effects of 6.2, 12.5, 25, 50 and 100 ng/kg/min/60 min of NE infused to normal men. Blood samples were obtained every 10 min, before, during and after drug administration for 3 consecutive h. Plasma levels on NE, LH, FSH, PRL, and GH were measured in all samples. The administration of 12.5 ng/kg/min over 60 min of NE induced a significant increase (p less than 0.001) in plasma NE levels (n = 5) from a mean (+/- SE) baseline of 239 +/- 14 ng/L to 706 +/- 54 ng/L which peaked and plateaued at 40 min. The calculated area under the curve was 18562 +/- 3537 ng/L/h of NE and significantly higher (p less than 0.001) than during the h before the infusion (2358 +/- 780 ng/L/h). This increase in plasma NE correlated well with the rise in plasma LH which showed a steady increase from baseline of 7.4 +/- 1.3 mIU/ml to a significant (p less than 0.05) peak of 11 +/- 1.9 mIU/ml at the end of the infusion. Furthermore, analysis of the area under the curve revealed a greater (p less than 0.05) LH release during the NE infusion (180 +/- 18 mIU/ml/h) than before the infusion (92 +/- 17 mIU/ml/h). With the exception of the studies utilizing 12.5 ng/kg/min/60 min, all other doses of NE resulted in no significant and/or consistent changes in plasma concentration of LH, FSH, GH and PRL. Thus, the direct participation of NE in the control of LH secretion in humans seems to occur in a very narrow window.