Studies on the growth of the fetal guinea pig. The effects of nutritional manipulation on prenatal growth and plasma somatomedin activity and insulin-like growth factor concentrations.

In guinea pigs between days 41-46 of pregnancy prenatal growth has been manipulated by alteration of nutritional state. Three methods were used. Uterine artery ligation at day 30 of pregnancy depressed fetal growth rate by greater than 50% and was associated with falls in plasma insulin, IGF-1, cortisol, thyroid hormone, glucose, acetate and free fatty acid concentrations and rises in that of IGF-2, glucagon and amino acids. Fetal plasma was inhibitory to sulphate incorporation into pig costal cartilage. Complete food withdrawal from pregnant guinea pigs for 2 days at days 43-44 of pregnancy caused mild fetal growth retardation and similar changes in plasma constituents, except in that plasma IGF-2 concentrations were now depressed and plasma was not inhibitory to sulphate incorporation into pig costal cartilage. Production of hypoglycaemia by 4-times-daily maternal injections of glucose between days 41-46 of pregnancy accelerated fetal growth rate. It also elevated fetal plasma concentrations of insulin, IGF-1, IGF-2, sulphation-promoting activity, thyroid hormones, glucose and free fatty acids and depressed that of glucagon and amino acids. Fetal growth rate during the experimental period showed a good correlation with plasma glucose, insulin and IGF-1 and, to a certain extent, with sulphation-promoting activity. It did not correlate closely with fetal plasma IGF-2 concentration. Hepatic glycogen concentrations showed a good correlation with plasma IGF-2 levels.