Phasic changes in bone CO2 fractions, calcium, and phosphorus during chronic hypercapnia

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Abstract
Bone CO2 buffering system and bone Ca and P were studied in guinea pigs exposed to 1% CO2 for up to 8 wk and killed at weekly intervals together with control animals of the same age. Measurements were made of arterial CO2 tension, pH, standard bicarbonate and bone Ca and P. Heat-stabile bone CO2 (carbonate) was determined as dry bone CO2 and heat-labile bone CO2 (bicarbonate) as .DELTA. [difference] wet-dry bone CO2. During the first 3-4 wk of exposure to 1% CO2, a systemic acidosis was found as indicated in a lowered pH, increased arterial CO2 tension and decreased standard bicarbonate. The acidosis subsided during the last 4 wk of exposure. Phasic changes in bone bicarbonate were observed as shown in immediate rise lasting for 2 wk followed by a 2 wk decline and 2nd rise after 6 and 8 wk. Bone carbonate exhibited the opposite change during the first 4 wk and thereafter remained stable at an elevated level. Bone Ca and P fell in association with increasing bone bicarbonate and rose with increasing bone carbonate.