In miniature Japanese goats, growth hormone (GH) is released in regular 5‑hour pulses. Removing the testes (and thus testosterone) makes those pulses taller but shorter, while a drug called KP102 can trigger a strong GH burst and reset the pulse timing. The study shows that both sex hormones and GH‑releasing compounds shape how GH is secreted.

The present study was conducted in order to characterize the secretory pattern of GH in the Shiba goat, a native Japanese miniature goat, and to examine the effects of castration and KP102, a GH secretagogue, on this pattern. Blood samples were taken from an indwelling jugular catheter every 15 min for 24 h, and plasma GH was measured by radioimmunoassay. In intact males, GH was secreted in a pulsatile manner with very regular 5-h periodicity, which consisted of a distinctive GH pulse and a trough of virtually no GH secretion. Postpubertal castration increased the height and decreased the width of GH pulses, though it did not affect the interpulse interval and area under the curve. Modification of the shape of each GH pulse by testicular androgen might play a role in the expression of GH action in the male. KP102 (10 microg/kg, i.v.) immediately induced a robust GH pulse, which was followed by a spontaneous GH pulse of normal characteristics at regular intervals, suggesting that the clock generating GH pulses was reset by KP102. From these observations, we concluded that the Shiba goat is a very suitable experimental model for elucidating the mechanisms underlying GH pulse generation, and in particular, the involvement of androgen and GH secretagogues.