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American Zoologist 1983 23(3):719-727; doi:10.1093/icb/23.3.719
© 1983 by The Society for Integrative and Comparative Biology
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Evolution of Calcium Regulation in Lower Vertebrates1

NANCY B. CLARK
Biological Sciences Group, University of Connecticut Storrs, Connecticut 06268

Calcium regulation in lower vertebrates appears to be a continuum. The predominant hypercalcemic hormone in reptiles, birds and mammals is parathyroid hormone, while the major hypercalcemic control in fishes is a pituitary factor, probably prolactin. In the amphibians dual controlling mechanisms are at work, so that both the pituitary and parathyroids exert their influence. Prolactin may still retain some hypercalcemic potency in the higher vertebrate groups, either directly or indirectly by influencing the secretion of other hypercalcemic hormones. On the other hand, parathyroid hormone does not occur in, nor does it elevate blood calcium in fishes. It thus seems to be a new invention of tetrapods, or possibly to have evolved from a pituitary factor of fishes. The ability to lower blood calcium seems to be very important in seawater fishes, in which the corpuscles of Stannius exert major control. In terrestrial forms, the corpuscles of Stannius are not present, and hypocalcemic factors assume a minor role in overall calcium regulation


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