Jp. Barlet et al., Calcitonin and stanniocalcin: particular aspects of the endocrine regulation of calcium metabolism in fish and mammals., ANN ENDOCR, 59(4), 1998, pp. 281-290
The hypocalcemic and hypophosphatemic peptide calcitonin (CT) is secreted b
y mammalian thyroid parafollicular cells and fish ultimobranchial body. Ove
r a dozen species of CTs have been cloned and/or sequenced. They can be sep
arated into three classes based on structural and biological similarities :
teleost/avian, artiodactyl, and human/rat. In mammals, CT exerts its anti-
hypercalcemic and hypophosphatemic effects by inhibiting osteoclastic bone
resorption and venal tubular phosphate reabsorption, respectively. CT recep
tors (CTRs) are members of a subfamily of seven-transmembrane domain, G pro
tein-coupled receptors that include those for several other peptide hormone
s. Basic amino acid substitutions within the CT molecule enhance potency, p
robably by conferring a helical structure to the peptide. This might explai
n the enhanced potency of fish CTs for mammalian CTRs. The presence and sec
retion of salmon CT-like immunoreactive material have been described in bot
h the murine and human central nervous systems, which possess CTRs. These f
indings are consistent with a role for this peptide acting as a neurotransm
itter in mammals.
Stanniocalcin (STC) is another hypocalcemic hormone originally identified i
n fish. In fish STC exerts its anti-hypercalcemic effect by regulating calc
ium and phosphate transports by the gills, intestine and kidney. Although f
ish ultimobranchial cells are much less responsive to the secretagogic effe
cts of Ca2+ than mammalian parafollicular cells, the secretion of both CT a
nd STC are positively regulated by extracellular calcium. STC has also been
recently identified in humans and mts. It is released by some renal tubula
r cells and might play a role in the regulation of phosphate metabolism. Ne
vertheless, the true physiologic roles for CT in fish and STC in mammals, r
espectively, remain unknown.