Osteopetrosis in the toothless (t1) rat: presence of osteoclasts but failure to respond to parathyroid extract or to be cured by infusion of spleen or bone marrow cells from normal littermates.

Osteoclast have been observe for the first time in toothless (t1) rats, a mutation with inherits osteopetrosis as an autosomal recessive. The ability of t1 rats to raise the serum calcium concentration after injection of parathyroid extract was severely limited when compared with normal littermates. In addition, osteopetrosis in t1 rats is not cured by radiation and infusion of normal spleen or bone marrow cells from normal littermates, a method know to cure osteopetrosis in mutants of this and other species. This indirect evidence for a reduction in bone resorption as a cause of osteopetrosis in this mutation and the failure of transplanted cells to cure the disease are discussed in relation to the development and function of osteoclasts.