Effect of increased level of CO2 exposure in a closed environment on calcium and phosphorus balance in rats.

ABSTRACT

In rats, exposed to increased ambient CO2 level (1.5%) for 30 days a 40% reduction in food intake during first 10 days was observed which subsequently improved. Similarly the body weight also declined initially, which showed progressive gain thereafter, almost reaching that of ad libitum fed control by 30th day. The lowered Ca intake consequent to reduced food consumption was followed by diminution in renal and faecal excretion of Ca. The lowered renal Ca excretion was probably unrelated to reduced Ca intake, since the pair-fed-control, not exposed to raised CO2 level, did not show any such alteration. The net result was a drastic reduction in Ca balance despite the diminution in its excretion. Though the intake and renal excretion of P were reduced in the CO2 exposed group due to a reduction in food intake, the P balance showed a cyclic pattern as in the pair-fed controls. The serum Ca after 30 days' exposure remained unchanged while the serum inorganic P showed a variation. The data indicated that hypercapnia produced hypophagia which affected growth of rats. The reduced renal excretion of Ca may not pose a risk on calcification of soft tissues, since its retention was also reduced on exposure to raised concentration of CO2.