GTP-dependent protein(Gs) activity in preterm infants.

In a previous study, we showed a renal resistance to PTH in preterm infants during their 1st week of life. We proposed it could explain early neonatal hypocalcemia. Such renal resistance is well known in type 1 pseudohypoparathyroid patients and is explained by a defect of stimulatory GTP-dependent protein (Gs). To determine if functional immaturity in the Gs protein could be involved in PTH resistance, we studied 27 newborn babies: 7 full-term and 20 preterm babies. Biological activity of the Gs unit was determined on days 1, 3 and 10 after delivery by bioassay. No correlation was found between the Gs unit activity and either gestation or birth weight at these dates. Eight infants had hypocalcemia and their Gs unit activity did not differ from those with normocalcemia. Furthermore, we showed that the Gs unit is active from 29 weeks of gestation. We conclude that the Gs protein appears not to be involved in the pathophysiology of early renal resistance to PTH and therefore in early neonatal hypocalcemia.