Variations in plasma growth hormone (GH) and prolactin concentrations were determined during growth (at 20, 33, 56 and 83 d of age) in ad libitum (control) and intermittently (alternate days) fed chicks. 2. In each group of birds the concentration of plasma GH was inversely related to age. The mean prolactin concentration was highest in the youngest (20-d-old) birds. 3. The concentration of plasma GH in the intermittently-fed birds deprived of food for 24 h (depleted birds) was significantly higher than that in the controls at 33, 56 and 83 d of age. The mean GH concentration in the intermittently-fed birds 24 h after refeeding (repleted birds) was less than that in the depleted ones. 4. The overall mean concentration of plasma prolactin in the depleted birds was significantly less than that in the control and repleted birds. 5. These results are consistent with the effects of fasting on GH and prolactin secretion and demonstrate that growth retardation in the intermittently-fed birds was not due to impaired GH secretion.
