Effects on rat fetuses of intrauterine injections of insulin

The effects on rat fetuses of a single intrauterine injection of long-acting insulin with respect to length, body and organ weights, total lipids, phospholipids, cholesterol, neutral fat, total nitrogen and water content were investigated. At the age of 498 hours the fetuses were injected in utero with 2 IU of long-acting insulin or a control solution. Twenty-four hours after the injections the insulin-treated fetuses weighed about 10 per cent more than the control fetuses, 5.32 +/- 0.05 g (75 fetuses) and 4.85 +/- 0.05 (73 fetuses) respectively (p less than 0.001). The body lengths were 54.1 +/- 0.2 mm and 52.9 +/- 0.2 mm respectively (p less than 0.001). The insulin-treated fetuses had higher organ weights and higher content of total lipids, phospholipids and neutral fat. The amount of total lipids was higher in insulin-treated fetuses even after taking into account differences in body weight, suggesting that the insulin-treated fetuses were obese. The finding of significantly lower water content in insulin-treated fetuses at equal body weight is consistent with the higher fat content. There was no increase in total nitrogen or length in the fetuses in the insulin-treated group compared to control fetuses at equal body weight indicating that the administered insulin mobilized maternal proteins and that protein, as well as length, increased proportionately to overweight. For quantitative analysis of morphological and biochemical variables dependent upon body weight, as in this investigation, multivariate analysis is indispensable.