Abstract
1. The hGH20K variant accounts for 10-15% of the hGH in the pituitary gland and is, therefore, the second most abundant hormone in the gland.
2. Although no specific RIA exists for hGH20K, which must be measured by a combination of electrophoretic and immunological techniques, the following conclusions appear warranted. During provocative in vivo secretion, the ratio of hGH20K to hGH22K in blood is similar to that found in the pituitary gland. During basal in vivo secretion of hGH, the ratio of hGH22K to hGH20K can be quite different. A differential secretion rate for hGH22K and hGH20K was noted during in vitro stimulation of pituitary cells with GHRH. A six-fold rise in hGH 20K contrasted with only a twofold rise in hGH22K.
3. The 20K dalton variant has full growth promoting activity and stimulates production of somatomedins even though binding hGH 20K to membrane receptors for hGH is lower than that observed with hGH22K.
4. In vitro insulin-like activity of hGH20K on adipose tissue is either absent or at best 10-15% of that seen with hGH22K, whereas in vivo insulin-like activity of hGH 20K is 30-40% of that observed with hGH22K.
5. At high doses, hGH 20K exhibits about the same anti-insulin activity as does hGH22K.
