Brain interstitial fluid calcium concentration during development in the rat: control levels and changes in acute plasma hypercalcaemia

Age-related changes in brain interstitial fluid (ISF) ionic calcium, in ionic and total calcium in plasma and the effect of plasma hypercalcaemia on ISF calcium have been studied in rats aged between late gestation and adult. ISF ionic Ca2+] decreased significantly with development from 1.6 mM to 1.2 mM. Plasma ionic Ca2+] was not significantly different from ISF Ca2+] apart from a transient hypocalcaemia at birth which was not reflected in the ISF. Plasma total calcium was around 2X ionic Ca2+] and showed the same age-related decrease. In acute plasma hypercalcaemia induced by calcium gluconate injections, there was only weak regulation of ISF Ca2+ at 21 days gestation but a rapid improvement after birth resulted in excellent control by 5 days.