Reduction in maternal circulating ouabain impairs offspring growth and kidney development

Ouabain, a steroid present in the circulation and in various tissues, was shown to affect the growth and viability of various cells in culture. To test for the possible influence of this steroid on growth and viability in vivo, we investigated the involvement of maternal circulating ouabain in the regulation of fetal growth and organ development. We show that intraperitoneal administration of anti-ouabain antibodies to pregnant mice resulted in a >80% decline in the circulating ouabain level. This reduction caused a significant decrease in offspring body weight, accompanied by enlargement of the offspring heart and inhibition of kidney and liver growth. Kidney growth inhibition was manifested by a decrease in the size and number of nephrons. After the reduction in maternal circulating ouabain, kidney expression of cyclin D1 was reduced and the expression of the α1 isoform of the Na⁺, K⁺-ATPase was increased. In addition, the elevation of proliferation signals including ERK1/2, p-90RSK, Akt, PCNA, and Ki-67, and a reduction in apoptotic factors such as Bax, caspase-3, and TUNEL were detected. During human pregnancy, the circulating maternal ouabain level increased and the highest concentration of the steroid was found in the placenta. Furthermore, circulating ouabain levels in women with small-for-gestational age neonates were significantly lower than the levels in women with normal-for-gestational age newborns. These results support the notion that ouabain is a growth factor and suggest that a reduction in the concentration of this hormone during pregnancy may increase the risk of impaired growth and kidney development.