Measurement of Calcium-Lowering Hormones

Detection and Measurement of Calcium-Lowering Hormones 5.1. Bioassay Pboceduees 

Several animal species have been used in the biological assay of calcium-lowering hormones. For reasons of size, the rat is most commonly used, although mice have been claimed to be more responsive to human thyrocalcitonin preparations (S2). For studies of the course of thyro-calcitonin action in which serial blood samples were required, both pigs (C5) and goats (F4) have been used. For assessment of the potency of hoimone preparations, bioassay in rats is in general satisfactory. 

The method described by Hirsch et al. (H4) uses intact male rats previously maintained on a low-calcium diet for 4 days. Standard and unknown preparations are injected subcutaneously into parallel groups of test animals, and after 1 hour blood samples are collected by cardiac puncture under ether anesthesia. The plasma calcium levels are measured, and the relative potencies of the preparations are calculated by standard statistical procedures. The mean index of precision of ten consecutive assays was reported as 0.23 0.025. 

As was mentioned earlier, there appears to be considerable species variation in the secretion of thyrocalcitonin, and likewise there are reports of species variations in sensitivity to exogenous thyrocalcitonin preparations. Care et al. (C8) found sheep to be considerably less responsive to exogenous sheep thyrocalcitonin than pigs to porcine thyrocalcitonin. Smith et al. (S2) were unable to demonstrate hypocalcemic activity in human thyroid extracts injected into monkeys or rats, but found the mouse to be responsive. On the other hand, Milhaud et al. (M12) demonstrated hypocalcemic activity in human thyroid extracts in the rat and monkey, although these responses were obtained only after injecting much larger doses than would have been required had porcine 

Although few details have been published on the effects of age and diet on sensitivity in bioassays of thyrocalcitonin, most workers appear 

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