Studies on the volume and the activity of the parathyroid glands in osteoporosis of disuse in the adult rat.

Inactivity of the right hind leg was brought about in adult male Sprague-Dawley rats by a) immobilisation in a plaster cast and b) by resection of the sciatic nerve. Determinations of the volume and the activity of the parathyroid glands by morphological methods showed that the parathyroids were, on the whole, not affected by the treatment. Some significant differences observed in some examined parameters should, however, suggest hypofunction of the glands. The serum-calcium level was significantly higher in the treated than in the control rats in the first experiment. No significant differences in serum calcium between treated and control animals were observed in the second experiment. These observations were considered to indicate that the development of localised osteoporosis in these two forms of inactivity did not depend on hyperactivity of the parathyroids. The observed differences in serum-calcium content between the two experiments may suggest that localised osteoporosis in the two cases developed through different pathomechanisms.