Mean (±sem) GH concentrations monitored every 10 min for 5 h in young men (n = 8) and women in the early follicular phase of the menstrual cycle (n = 6) during iv infusion of saline (top left) or the paired secretagogues: l-arginine/GHRP-2 (top right), L-arginine/GHRH (bottom left), and GHRH/ GHRP-2 (bottom right). l-Arginine and peptide delivery began at, respectively, 100 and 130 min (x-axis, where zero min is 0800 h).