An adequate concentration of carbon dioxide was found necessary for optimal effects of parathyroid hormone (PTH) on fetal rat bones cultured for 72 hr in vitro. A submaximal dose of PTH effective in a medium gassed with 5% CO2 in air was found to have little or no effect in a medium gassed with 0.6% CO2 in air and maintained at the same pH (7.4). The effect of PTH in 0.6% CO2 could be significantly increased by addition of sodium oxaloacetate (OAA), 10-3M. PTH effect in an air gassed medium buffered with amine buffers was also increased by the addition of oxaloacetate. These data suggest that oxaloacetate production may have been inadequate in CO2 deficient media. The requirement for CO2 was further investigated by the use of a carbonic anhydrase inhibitor, acetazolamide. At 4 x 10-4M, acetazolamide completely inhibited the effect of a maximal concentration of PTH in 5% CO2 gassed medium. At 10-5M, it had no effect in the 5% CO2, but completely inhibited the effect of this dose of PTH in 0.6% CO2 or air. These latter results confirm the importance of the CO2 bicarbonate system in bone resorption.
|Original language||English (US)|
|Number of pages||1|
|Issue number||3 (I)|
|State||Published - Jan 1 1973|
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