590 DOWSE, NEUMAN, LANE, AND NEUMAN 



Calvaria have been extensively employed in a variety of studies 

 designed to show histological effects of parathyroid hormone ( Gail- 

 lard, 1959 ) , resorption in surviving culture ( Goldhaber, 1960 ) , and 

 the cellular role in maintaining calcium levels above those due to 

 passive solubility only (Raisz et ah, 1961). However, no comprehen- 

 sive biochemical studies of calvaria have to our knowledge yet ap- 

 peared. This is a ready-made tissue slice with a minimum of cut or 

 damaged cells. It has some mineralized matrix, but the cell popula- 

 tion, for bone, is high. There is but little contamination with marrow 

 cells. Morphologically, however, at least five general cell types pre- 

 dominate: osteoblasts, osteocvtes, osteoclasts, cartilage cells, and 

 preosseous mesenchymal cells. The principal advantages of this tissue 

 are convenience, reproducibilitv, and responsiveness to parathyroid 

 hormone in vitro (Gaillard, 1959). Nonetheless, the calvarium still 

 represents something of a compromise, and it is therefore emphasized 

 that the studies to be reported are on the metabolism of calvarium. 

 Though the data matj apply to bone cells in general, no such claim 

 is made. 



Experimental 



Procedure 



Randomized newborn rat pups were decapitated within 15 hours 

 of birth. The calvarium, a round section from the top of the skull, 

 including most of the parietal and parts of the frontal and occipital 

 bones, was quickly removed, freed of bits of connective tissue, and 

 halved at the midline. Left and right halves were placed alternately 

 in each of two weighed collecting bottles containing ice cold in- 

 cubation medium. Wet weight was used as the basis of reference, 

 since it was found at least as reliable as dry weight, noncollagen 

 nitrogen ( NGN ) , or deoxyribonucleic acid ( DN A ) . 



The medium emplo\ed was either Krebs-Ringer phosphate or 

 bicarbonate with the calcium reduced to a level of 1.2 mM or ab- 

 sent. Incubations were performed in a Warburg apparatus at 37 °G 

 after equilibration with the appropriate gas. Gontrol and experi- 

 mental measurements were made on paired flasks containing 6 to 

 10 alternating halves of the same calvaria. 



