ROLE OF CALCITONIN IN CALCIUM HOMOEOSTASIS IN THE CHICK EMBRYO

Abstract

SUMMARY A radioimmunoassay for chicken calcitonin (CT) was used to study changes in the normal levels of CT in the circulation of chick embryos during incubation and in hatched chicks. The hormone was detectable in embryos whenever the plasma concentration of calcium was greater than 2·5 mmol/l. The level of CT at the time of 'pipping' was exceptionally high but when pipping was artificially advanced or retarded the peak of CT was dissociated from the physiological event of pipping. When embryos were injected with calcium, CT secretion was stimulated but the maximum level induced was substantially less than the normal peak level observed at pipping although an extreme degree of hypercalcaemia developed. When CT was removed from the embryonic circulation by injecting anti-CT plasma, a mild but statistically significant hypercalcaemia developed and in another experiment exogenous CT significantly decreased an artificially induced hypercalcaemia. The β-antagonist, propranolol, decreased and the β-agonist, isoprenaline, increased concentrations of CT in the circulation. We suggest that the role of CT in the chick embryo may be to restrict the hypercalcaemia resulting from the large movement of calcium from the eggshell to the developing embryo and its yolk-sac and that one of the natural stimuli for the release of CT in the late stages of incubation could be β-adrenergic.