Lack of Effect of Chronic Hyperinsulinaemia on Growth and Body Composition in the Fetal Pig

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Abstract
Chronic hyperinsulinaemia in the presence of euglycaemia was obtained in pig fetuses using implanted osmotic minipumps to deliver 3 U of insulin per day over 14 days (90–104 days gestational age); term is 114 days. Total body growth (length and weight) was unaffected by insulin administration, although some changes in organ weights were observed. There was a significant retardation of lung growth (apparently as a result of operative stress) and, in the insulin-treated fetuses, an increase in liver weight which was attributable to enhanced glycogen deposition. Two of the insulin-treated fetuses appeared to have an increase in subcutaneous fat at delivery, but overall there was no statistically significant change in body fat, water, or protein content of the carcases. Growth hormone levels in all the fetuses were high, but there were no differences between treatment groups. Bioassayable plasma somatomedin activity was increased in the insulin-treated fetuses. It is proposed that this increase may be a result of insulin-induced enhancement of liver growth hormone receptors. From these data we conclude that a 14-day period of hyperinsulinaemia towards the end of gestation does not stimulate growth of the pig fetus despite producing an increase in somatomedin activity. The growth enhancement seen in offspring from diabetic mothers is probably due to increased nutrient availability rather than a direct effect of fetal insulin. Insulin does, however, significantly increase glycogen deposition in the fetus.