Growth hormone during catch-up growth and failure of catch-up growth in rats

Male Long-Evans rats were fasted or given cortisone injections beginning at 37 days of age in order to produce growth retardation. They were then allowed to recover for periods of up to 28 days. GH concentration was measured in trunk blood plasma of rats decapitated after minimal stress. During the recovery period there was a significant increase in plasma GH in both experimental groups. Organ weight/body weight ratios for liver and heart, protein/tissue, DNA/tissue, and DNA/protein ratios of liver, heart, and skeletal muscle were found to remain normal or to return to normal values during the recovery periods in both experimental groups. DNA content was reduced in both liver and heart at 14 days. At later recovery periods no significant differences from controls were observed. The findings indicate that increased GH release is common to the growth recovery period after both fasting or cortisone treatment. GH concentration in plasma does not correlate with presence or absence of catch-up growth. The organ weight/body weight ratios correlate with previous findings showing prompt return to normal proportions of body weight to tail length in both the cortisone and fast models irrespective of presence or absence of catch-up growth. The results indicate that failure of catch-up growth after cortisone treatment is not the result of decreased pituitary GH secretion. It is probable that multiple factors working in concert are responsible for recovery after transient growth retardation.