Effects of porcine calcitonin (five MRC units per kilogram per day) on development of osteoporosis induced by cortisone (fifteen milligrams per kilogram per day) have been investigated in adult rabbits. Measurements of surface undergoing resorption and formation were determined from cross sections of femoral mid-diaphyses, femoral metaphyses, ribs, and vertebral bodies using the quantitative microradiographic method of Jowsey. Intact femora and vertebral bodies were evaluated for gross rarefaction by high resolution macnoradiography. Bone mass per unit area was determined and mineral content of femora, ribs, and vertebrae was esimated by ashing.

Cortisone treatment alone: (1) decreased bone formation and increased bone resorption at all skeletal sites evaluated, (2) decreased the amount of bone mass per unit area in both cortical and cancellous specimens, (3) caused gross macroradiographic rarefaction of femora and vertebral bodies, and (4) reduced the ash weight of ribs and vertebrae.

Calcitonin treatment alone: (1) increased bone formation in cortical specimens and reduced bone resorption in vertebral bodies, (2) caused increased density of metaphyseal zones of vertebral bodies as shown by macroradiognaphy, and (3) increased the ash content of femora, ribs, and vertebrae.

When compared with specimens removed from animals receiving only cortisone, specimens removed from animals receiving both hormones exhibited: (1) reduction in bone resorption rates in the cancellous specimens, (2) increased rates of bone formation in femoral diaphyses, (3) increased mass per unit area in both cortical and cancellous bone, (4) less macroradiographic rarefaction of femora and ventebral bodies, and (5) increased ash content of vertebral bodies.

These results support the possibility that exogenous calcitonin may be capable of retarding some of the detrimental effects of the adrenal cortical steroids on osseous tissue, especially cancellous bone.