Veldhuis JD, Liu PY, Keenan DM, Takahashi PY. Older men exhibit reduced efficacy of and heightened potency downregulation by intravenous pulses of recombinant human LH: a study in 92 healthy men. American Journal of Physiology-Endocrinology and Metabolism. 2012 Jan 01;302(1):E117–22. doi: 10.1152/ajpendo.00450.2011.