Barlet J P, Gaumet N, Coxam V, Davicco M J
INRA Clermont-Theix, Saint-Genès-Champanelle.
Ann Endocrinol (Paris). 1998 Nov;59(4):281-90.
The hypocalcemic and hypophosphatemic peptide calcitonin (CT) is secreted by mammalain thyroid parafollicular cells and fish ultimobranchial body. Over a dozen species of CTs have been cloned and/or sequenced. They can be separated 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 renal tubular phosphate reabsorption, respectively. CT receptors (CTRs) are members of a subfamily of seven-transmembrane domain, G protein-coupled receptors that include those for several other peptide hormones. Basic amino acid substitutions within the CT molecule enhance potency, probably by conferring a helical structure to the peptide. This might explain the enhanced potency of fish CTs for mammalian CTRs. The presence and secretion of salmon CT-like immunoreactive material have been described in both the murine and human central nervous systems, which possess CTRs. These findings are consistent with a role for this peptide acting as a neurotransmitter in mammals. Stanniocalcin (STC) is another hypocalcemic hormone originally identified in fish. In fish STC exerts its anti-hypercalcemic effect by regulating calcium and phosphate transports by the gills, intestine and kidney. Although fish ultimobranchial cells are much less responsive to the secretagogic effects of Ca2+ than mammalian parafollicular cells, the secretion of both CT and STC are positively regulated by extracellular calcium. STC has also been recently identified in humans and rats. It is released by some renal tubular cells and might play a role in the regulation of phosphate metabolism. Nevertheless, the true physiologic roles for CT in fish and STC in mammals, respectively, remain unknown.
降钙素（CT）是一种具有低钙血症和低磷血症作用的肽，由哺乳动物的甲状腺滤泡旁细胞和鱼类的后鳃体分泌。已有十几种CT被克隆和/或测序。根据结构和生物学相似性，它们可分为三类：硬骨鱼/鸟类、偶蹄目动物以及人类/大鼠。在哺乳动物中，CT分别通过抑制破骨细胞的骨吸收和肾小管对磷酸盐的重吸收来发挥其抗高钙血症和低磷血症的作用。CT受体（CTR）是七跨膜结构域G蛋白偶联受体亚家族的成员，该亚家族还包括其他几种肽类激素的受体。CT分子内的碱性氨基酸取代增强了其效力，可能是通过赋予该肽螺旋结构实现的。这或许可以解释鱼类CT对哺乳动物CTR的效力增强现象。在具有CTR的小鼠和人类中枢神经系统中，均已发现类似鲑鱼CT的免疫反应性物质的存在和分泌。这些发现与该肽在哺乳动物中作为神经递质的作用相一致。鲽鱼降钙素（STC）是另一种最初在鱼类中发现的降钙激素。在鱼类中，STC通过调节鳃、肠道和肾脏对钙和磷酸盐的转运来发挥其抗高钙血症作用。尽管鱼类后鳃细胞对Ca2+分泌作用的反应性远低于哺乳动物的滤泡旁细胞，但CT和STC的分泌均受到细胞外钙的正向调节。最近在人类和大鼠中也发现了STC。它由一些肾小管细胞释放，可能在磷酸盐代谢调节中发挥作用。然而，CT在鱼类和STC在哺乳动物中真正的生理作用仍不清楚。
