Serum insulin and lipogenesis in the suckling 'fatty' fa/fa rat.

Preobese 'fatty' fa/fa rats identified by their decreased rectal temperature were either given access to high carbohydrate chow or maintained on a suckling only diet til 20 days of age. Serum insulin, hepatic and adipose tissue fatty acid synthesis and lipogenic enzyme activities were low in suckling preobese fa/fa. In animals with access to chow diet, hepatic lipogenesis was unaltered, serum insulin rose to similar levels in lean and preobese fa/fa (lean 62 +/- 5; preobese 69 +/- 4 microU/ml), but adipose tissue lipogenesis was increased to higher levels in the preobese than lean rats (lean 0.56 +/- 0.12; preobese 1.80 +/- 0.22 mumol. tissue-1. h-1). The activities of glucose-6-phosphate dehydrogenase, acetyl coenzyme A carboxylase and fatty acid synthetase were increased in adipose tissue of preobese fa/fa rats. Neither streptozotocin treatment nor pretreatment with Triton WR 1339 abolished the difference in adipose tissue lipogenesis between lean and preobese fa/fa rats. Preobese fa/fa rats showed an enhanced insulin secretory response to a glucose load.