Figure 5.

Discharges of LH, as reflected by circulating concentrations of the gonadotropin (mean ± sem), during the last priming pulse of GnRH (G) (broken black arrow) in agonadal male monkeys were sustained without decrement by an intermittent iv infusion of 2 μg Kp-10 administered as a 1-min pulse every hour for 5 h and initiated at time 0 (open data points) after concomitantly terminating the GnRH-priming infusion. In striking contrast, a similar intermittent iv infusion of senktide (50 μg/pulse) after termination of GnRH priming failed to mimic the action of repetitive Kp-10 administration. Instead, LH levels (closed data points) fell in parallel with those observed during intermittent iv infusion of vehicle (gray data points). The down-regulation of the LH response to repetitive senktide administration, however, did not compromise the GnRH-releasing action of an iv bolus of Kp-10 (K) (black arrow) administered after the last of four pulses of senktide. White block arrows indicate time of hourly intermittent infusions of Kp-10 (K) or senktide (S) or vehicle (V). Black arrow at 240 min indicates time of the last of 5 Kp-10 pulses or of the Kp-10 challenge after the intermittent infusion of either senktide or vehicle. n = 3.