Development of pancreatic and plasma insulin in prenatal and suckling Zucker rats.

Pancreatic and plasma insulin concentrations in preobese and lean Zucker rats were determined during three developmental periods: 1) gestation, 2) suckling, and 3) postweaning. Individual fetal samples were derived from two types of matings: 1) homozygous obese males (fafa) with heterozygous females (Fafa), and 2) homozygous lean males and females (FaFa). Suckling and postweaned pups from similar matings were partially pancreatectomized, tail bled, and identified retrospectively. In 21-day-old fetuses bearing the fa gene, plasma insulin concentration was elevated (P less than 0.001) and pancreatic concentration was slightly lower (P less than 0.05) compared to homozygous lean fetuses. Neither pancreatic nor plasma insulin concentration differed between preobese and lean pups during suckling, except that pancreatic concentration became elevated in preobese pups on postnatal day 20 (P less than 0.05). Plasma insulin concentration was elevated 24 h postweaning (P less than 0.01). These data support the hypothesis that the fa gene initiates metabolic changes during gestation that are modulated during suckling, but reappear at weaning. The data also establish that increased adipocyte size and lipoprotein lipase activity in 7- to 12-day-old preobese pups are not dependent on concomitant hyperinsulinemia.