Obesity and type 2 diabetes are worldwide health issues. The present paper investigates prenatal and postnatal pathways to obesity, identifying different metabolic outcomes with different effects on insulin sensitivity and different underlying mechanisms involving key components of insulin receptor signalling pathways.

Pregnant Wistar rats were fed either chow ad libitum or were undernourished throughout pregnancy generating either control or intrauterine growth restricted (IUGR) offspring. Male offspring were fed either standard chow or a high-fat diet from weaning. At 260 days of age whole-body insulin sensitivity was assessed by hyperinsulinaemic-euglycaemic clamp, and other metabolic parameters were measured.

As expected, high-fat feeding caused diet-induced obesity (DIO) and insulin resistance. Importantly, the insulin sensitivity of IUGR offspring was similar to that of control offspring, despite fasting insulin hypersecretion and increased adiposity, irrespective of postnatal nutrition. Real-time PCR and Western blot analyses of key markers of insulin sensitivity, and metabolic regulation showed that IUGR offspring had increased hepatic levels of atypical protein kinase C (PKC ) and increased expression of fatty acid synthase (FAS) mRNA. In contrast, DIO led to decreased expression of FAS mRNA and hepatic steatosis. The decrease in hepatic PKC with DIO may explain, at least in part, the insulin resistance.

Our data suggest that the mechanisms of obesity induced by prenatal events are fundamentally different from those of obesity induced by postnatal high-fat nutrition. The origin of insulin hypersecretion in IUGR offspring may be independent of the mechanistic events that trigger the insulin resistance commonly observed in DIO.