BIOASSAY OF CALCITONIN BY DETERMINATIONS OF BLOOD CALCIUM-45 LEVELS IN RATS AND MICE

Author:

Melander Arne

Abstract

ABSTRACT The possibility of measuring calcitonin by determinations of blood 45Ca in young rats and mice was investigated. Blood samples were taken by orbital puncture on conscious animals. In both species blood 45Ca levels fell rapidly during the first 24 h after one sc injection of 45CaCl2. Thereafter, the elimination rate was slow, indicating that an equilibrium state was reached. During this period, single iv injections of highly purified porcine calcitonin induced log-dose-dependent blood 45Ca reductions in both rats and mice. Maximal responses were recorded at 30 min after injection, and the log-dose-response regressions were linear between 0.1 and 5.0 mU in young rats, and between 2.0 and 80.0 mU in young mice. The mean indices of precision were 0.18 and 0.27, respectively. Blood 45Ca reductions were also recorded on injection of extracts from rat thyroids, cat thyroids and chicken ultimobranchial glands, as well as an injection of plasma from patients with thyroid medullary carcinoma. No reduction in blood 45Ca was obtained by injections of ACTH, TSH, cortisone, thyroxine, or insulin. The responses to calcitonin were augmented if the animals had had a low calcium intake before the experiment, and/or if the animals were injected with 0.075 m NaH2PO4 immediately before injection of the hormone. Rats were more sensitive than mice to porcine calcitonin and to rat and cat thyroid extracts, while the opposite was true with chicken ultimobranchial extracts. No inter-species difference was recorded with human calcitonin. The assay appears to be useful for both clinical and experimental purposes.

Publisher

Bioscientifica

Subject

Endocrinology,General Medicine,Endocrinology, Diabetes and Metabolism

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