Whole-body irradiation inhibits the escape phenomenon of osteoclasts in bones of calcitonin-treated rats.
The escape phenomenon is characteristic of osteoclastic bone resorption in organ cultures, and calcitonin only transiently inhibits parathyroid hormone (PTH)-stimulated resorption. The present study demonstrated that the transient inhibition of osteoclastic bone resorption, a phenomenon reminiscent of escape, occurs in the bones of calcitonin (ECT)-treated rats and that whole-body irradiation inhibits this escape. Rats were treated with daily subcutaneous injections of ECT for 72 h. At 24 h ECT decreased the incidence of osteoclast profiles with ruffled borders both in the growth plate-metaphysis junction (GPMJ) and the metaphyseal trabecular bone region (MT). However, by 72 h the incidence in the MT had been restored to the level of the control. The trabecular bone volume in the ECT-treated bone did not differ significantly from the control value. Whole-body irradiation (600 rad) before the first injections of ECT prevented the re-activation of the ruffled border formation and increased the trabecular bone volume at 72 h. Irradiation diminished the number of osteoclasts in the ECT-treated bones to the level of the control. ECT-treated bones contained a greatly increased number of macrophage-like cells (MO). Irradiation prevented this ECT-induced increase in the number of MO. These results strongly suggest that the escape phenomenon in vivo involves the calcitonin-induced proliferation of cells in the mononuclear phagocyte system, with resultant increases in the number of osteoclasts and in the bone resorption activity of osteoclasts.
D000818:Animals; D001862:Bone Resorption / Q000187:drug effects / Q000528:radiation effects*; D002116:Calcitonin / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects / Q000528:radiation effects; D006132:Growth Plate / Q000166:cytology; D006996:Hypocalcemia / Q000503:physiopathology; D008264:Macrophages / Q000648:ultrastructure; D008297:Male; D010010:Osteoclasts / Q000187:drug effects / Q000528:radiation effects* / Q000648:ultrastructure; D010281:Parathyroid Hormone / Q000502:physiology; D051381:Rats; D011917:Rats, Inbred Lew; D014916:Whole-Body Irradiation
D010281:Parathyroid Hormone; D002116:Calcitonin