Effects of calcitonin on plasma calcium and phosphate in the mudskipper, Periophthalmodon schlosseri (Teleostei), in water and during exposure to air

Stimulatory effects of short-term calcitonin administration on plasma calcium, magnesium, phosphate, and glucose in juvenile Siberian sturgeon Acipenser baerii

Calcitonin (CT) has a potential function in calcium (Ca) regulation, but there are conflicting observations in fishes. Because of the lack of calcified endoskeleton, sturgeons have low Ca circulating compared with teleost fish and the function of CT on Ca in sturgeon is very less understood. The purpose of this study was to investigate the impact of injection of salmon CT on plasma Ca, magnesium (Mg), phosphate (PHO), and glucose levels of juvenile Siberian sturgeon Acipenser baerii. Sixteen-month-old fish (429.6 ± 12.1 g) were intraperitoneally injected with a single dose of CT (5 μg kg^-1 BW) and saline solution as a control group. Thereafter, blood sampling was performed at 0, 1, 2, 4, 6, 12, 24, and 48 h after injection. CT produced marked increases in all variables measured. The highest levels of Ca (6.77 ± 0.53 mg dL^-1), Mg (9.79 ± 0.16 mg dL^-1) and PHO (1.74 ± 0.05 mg dL^-1) were recorded at 2 h after CT injection and showed significant difference compared with control treatment (Ca 4.75 ± 0.12 mg dL^-1; Mg 5.47 ± 0.16 mg dL^-1 and PHO 1.23 ± 0.06 mg dL^-1). It also likely produced hyperglycemia. However, the differences with the controls were not statistically significant, possibly due to interference with the hyperglycemia induced by the stress of injection. Our results showed that the injection of 5 μg kg^-1 BW CT to Siberian sturgeon has an incremental effect on plasma Ca, Mg, and PHO. The increase in plasma Ca level indicated that CT has a potent hypercalcemic effect in sturgeon under laboratory condition, in contrast to the hypocalcemic effects reported for teleosts.

Type II Na+-phosphate Cotransporters and Phosphate Balance in Teleost Fish

Teleost fish are excellent models to study the phylogeny of the slc34 gene family, Slc34-mediated phosphate (P_i) transport and how Slc34 transporters contribute P_i homeostasis. Fish need to accumulate P_i from the diet to sustain growth. Much alike in mammals, intestinal uptake in fish is partly a paracellular and partly a Slc34-mediated transcellular process. Acute regulation of P_i balance is achieved in the kidney via a combination of Slc34-mediated secretion and/or reabsorption. A great plasticity is observed in how various species perform and combine the different processes of secretion and reabsorption. A reason for this diversity is found in one or two whole genome duplication events followed by potential gene loss; consequently, teleosts exhibit distinctly different repertoires of Slc34 transporters. Moreover, due to habitats with vastly different salinity, teleosts face the challenge of either preserving water in a hyperosmotic environment (seawater) or excreting water in hypoosmotic freshwater. An additional challenge in understanding teleost P_i homeostasis are the genome duplication and retention events that diversified peptide hormones such as parathyroid hormone and stanniocalcin. Dietary P_i and non-coding RNAs also regulate the expression of piscine Slc34 transporters. The adaptive responses of teleost Slc34 transporters to e.g. P_i diets and vitamin D are informative in the context of comparative physiology, but also relevant in applied physiology and aquaculture. In fact, P_i is essential for teleost fish growth but it also exerts significant adverse consequences if over-supplied. Thus, investigating Slc34 transporters helps tuning the physiology of commercially valuable teleost fish in a confined environment.

Influence of calcitonin on serum calcium levels of intact or hypophysectomized freshwater catfish Heteropneustes fossilis

Serum calcium levels were markedly reduced in male freshwater catfish Heteropneustes fossilis following hypophysectomy. The administration of salmon calcitonin to intact fish had no effect on serum calcium level, whereas the same treatment to hypophysectomized fish induced hypocalcemia.

Salmon calcitonin induced hypocalcemia and hyperphosphatemia in an elasmobranch, Dasyatis akajei

Salmon calcitonin (5 micrograms/kg body wt) was administered in an elasmobranch, Dasyatis akajei, to investigate the effects upon plasma calcium and inorganic phosphate. The hormone produced hypocalcemia and hyperphosphatemia in the stingray. It is concluded that calcitonin may have a role in calcium homeostasis by a mechanism different from that on bones.

Changes in plasma vitellogenin, sex steroids, calcitonin, and thyroid hormones related to sexual maturation in female brown trout (Salmo trutta)

Female brown trout (Salmo trutta) from a wild strain (Baltic sea trout) and a cultured strain were sampled individually for blood plasma at regular intervals during the period around final sexual maturation. The plasma samples were analyzed for vitellogenin (VTG), estradiol-17 beta, testosterone, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P), calcitonin, tri-iodothyronine (T3), thyroxine (T4), and total and free plasma calcium. In the wild fish, VTG, estradiol-17 beta, and testosterone peaked 30 days before ovulation, while 17,20 beta-P had a sharp peak at ovulation. Both T3 and T4 declined at the beginning of the sampling period, reached minimal levels 30 days before ovulation, and rose sharply at the time of ovulation. Calcitonin levels were elevated during final maturation. Total plasma calcium correlated with plasma VTG levels. In the cultured strain, sampling was started 2 weeks before ovulation. The levels of VTG, estradiol-17 beta, and testosterone decreased throughout the sampling period. 17,20 beta-P and calcitonin concentrations were high during the period close to ovulation. Plasma thyroxine remained at basal levels in cultured trout. The discrepancies observed between wild and cultured females may be due to differences in stress susceptibility, environmental conditions, life cycles, or to genetic divergence between the strains.