Calcium homeostasis in the foetal guinea pig.

Abstract

Plasma total calcium levels have been studied in pregnant guinea pigs and their foetuses from 26 days of gestation to term. Between 28 days and 33–39 days the foetal plasma calcium falls from nearly the maternal level (9·6 mg/100 ml.) to 5·5 mg/ 100 ml. Thereafter the foetal plasma calcium rises, reaching the maternal level at term. No trend is found in the maternal levels. Foetal skeletal ossification was studied using an alizarin stain technique. Ossification centres appeared first in the clavicle, face and skull at 26 days of gestation. After 27 days gestation (foetal plasma protein = 1 g/100 ml.) there is a steady rise in foetal plasma protein level and at term foetal and maternal levels are approximately equal. Between 41 days gestation and term foetal blood is consistently more acid than maternal blood and has a higher pCO2 and lower pO2. There is no evidence of a progressive change during gestation in pH, pO2 or pCO2 in either foetal or maternal blood. It is concluded that the fall in foetal plasma calcium between 28 days and 33–39 days gestation may be due to calcification of the foetal skeleton before the full establishment of calcium homeostasis in the foetus. Increasing foetal plasma protein concentration or foetal parathyroid activity may account for the rise in foetal plasma calcium after 33–39 days.