Comparison of the somatogenic action of 20 kDa- and 22 kDa-human growth hormones in spontaneous dwarf rats.

The somatogenic action of the 20 kilodalton human growth hormone (20 K) was studied using the spontaneous dwarf rat (SDR), which has an isolated GH deficiency. Saline or 2.5 microg, 10 microg, or 100 microg/rat/day of recombinant 20 K or 22 K was administered to prepubertal male and female SDRs for 10 days. Their body weights, serum IGF-I, glucose and insulin were measured, and their body composition was determined. Body weights and serum IGF-I increased dose-dependently in both the 20 K- and 22 K-treated groups. There was no significant difference in body weights and serum IGF-I between the 20 K- and 22 K-treated groups except at the dose of 100 microg/rat, in which the IGF-I concentrations were higher in the 22 K-treated male SDRs (P< 0.05: 20 K vs 22 K). Blood glucose was not significantly different between the Spague-Dawley (SD) normal rats and the SDR control groups; however, serum insulin levels of the SDR were higher than those of the SD control group (P< 0.05). Additionally, there was a tendency for serum insulin and glucose levels to increase following 22 K treatment, but the differences were not significant. The percentage of body fat decreased with hGH treatment in both groups (P< 0.01: GH 10, 100 microg/rat group vs SDR control group), however, no significant differences were observed in body composition between the 20 K and 22 K treatment groups. In summary, the 20 K-hGH showed almost the same somatogenic activity as the 22 K-hGH in prepubertal male and female SDRs.