Adipose tissue hyperplasia and hyperinsulinemia on Zucker obese female rats: a developmental study.

Obese female Zucker rats show persistent increases in fat cell number compared to lean female Zucker rats from 5 to 52 wk of age. The hyperplastic obesity of the Zucker rat is also accompanied by fat cell hypertrophy and elevated plasma immunoreactive insulin (IRI). Average adipocyte size reaches a peak value at 14 wk of age in the subcutaneous, retroperitoneal and parametrial depots of the female obese rat. Plasma IRI also shows a peak at 14 wk of age. In addition, at this age thymidine kinase activity, a measure of proliferative capacity in tissue, is elevated in obese compared to lean rats, and at 15 1/2 wk of age a bimodal distribution of adipocytes is present in obese rat adipose tissue. The data suggest that attainment of a critical adipocyte size accompanied by maximum levels of plasma IRI may act in concert to potentiate fat cell hyperplasia in Zucker obese rats.