Abstract
The influences of dose, age and sex on the growth hormone (GH) secretion in response to a GH-releasing factor, synthetic human pancreatic GH-releasing factor-44 (hpGRF-44), were investigated in goats and sheep. Blood samples were collected before, and for 90min after intravenous (iv) injection of hpGRF-44 from an indwelling catheter previously inserted into one of the external jugular veins, or by venipuncture. The plasma GH concentration was measured by radioimmunoassay. 1) In Saanen female goats, 14 months of age, iv injection of 0.1, 0.25 and 0.5μg of hpGRF-44 per kg of body weight (bw) caused a significant increase in the plasma GH concentration; the peak value was obtained after 5 to 10min. The peak value of GH increased proportionally to the dose of hpGRF-44 injected. 2) The plasma GH concentration in female sheep of 2, 13 and 40 months of age increased significantly after iv injection of hpGRF-44 (0.25μg per kg of bw) and reached a peak 5 to 10min later. In Japanese native meat-type (Shiba) female goats of 5 and 14 months of age, the plasma GH concentration also significantly in creased after 0.25μg of hpGRF-44 per kg of bw injection, and the peak value was obtained after 5min. The peak value of GH decreased with advancing age. 3) In Shiba male and female kids of 1 month and lambs of 2 months of age, iv injection of 0.25μg of hpGRF-44 per kg of bw caused a significant increase in plasma GH concentration and reached a peak after 5 to 10min. The mean peak value of GH in the male animals was higher than that in the female animals. We conclude that the plasma GH response to hpGRF-44 in goats and sheep is dose dependent and decreases with advancing age. The results also suggest that the response in male animals is higher than that in females.
