Quantitative and qualitative changes in serum luteinizing hormone after injectable testosterone undecanoate treatment in hypogonadal men

To clarify the immune-active LH (i-LH) and bioactive LH (b-LH) responses an d qualitative changes in the circulating LH to testosterone undecanoate (TU ) injection. Methods: Eight men with Klinefelter's syndrome were recruited for the study. They received crossover injections of TU at doses of 500 and 1000 mg. Serum i-LH and b-LH levels before and at various time intervals a fter TU injection were measured and the serum i-LH, b-LH, b-LH/i-LH (B/I) a nd testosterone/sex hormone-binding globulin (T/SHBG) ratio in LH-responder s and LH non-responders were compared. Results: A parallel suppression of s erum I-LH and b-LH was consistent with their overall high correlation betwe en each other (r=0.84, P <0.001). Mean serum i-FSH levels were decreased by TU injection at both doses without dose-response effects. LH-responders ha d lower baseline serum i-LH and b-LH, and higher E-2 levels and T/ SHBG rat io. There was a quantitative change in serum LH as induced by TU without qu alitative change within LH-responders os LH-non-responders. Conclusion: A h igh loading dose (1000 mg) of TU is important for the initial suppression o f LH. With the lower dose (500 mg), repeated injections will be required to attain such LH suppression for the purpose of fertility regulation. The lo wer baseline serum i-LH level may be an intrinsic characteristic of LH-resp onders.