Selective ligation of uterine artery branches accelerates fetal growth in the rat.

We determined if reducing litter number by selective fetal ablation (A) might enhance the growth of the surviving fetuses. On day 14 of the rat's 21.5-day gestation, we ligated branches of the uterine artery at their secondary division. Each of these branches supplies a placenta and its fetus, and ligation kills them. Every other fetus in litters of eight to 14 fetuses was ablated. Each A maternal rat was matched to a control with an equal number of fetuses. Ablation reduced fetal number (from 8-14 to 4-7) and increased fetal growth (birth weight 5.84 +/- 0.05 versus 5.20 +/- 0.05 g, p less than 0.001). In the A but not control litters, newborn body mass was negatively related to litter number. Fetuses of A litters had increased carcass, liver, and brain mass. On days 18 and 19, fetal plasma glucose concentrations, fetal/maternal glucose ratios, insulin concentrations, and hepatic glycogen concentrations were increased suggesting that A increases glucose provision to the surviving fetuses. Although these observations imply that A enhances glucose provision resulting in stimulated growth of insulin-sensitive tissues, the growth of the brain, purportedly a tissue not sensitive to insulin, was also increased. In addition, the growth rate of A fetuses continued to be increased on days 20 and 21 despite normal fetal plasma glucose and insulin. These observations indicate that with A, factors other than insulin also stimulated growth. Of note, newborn A pups developed hypoglycemia at 20 and 60 min as a result of increased insulin secretion.