Publisher Summary This chapter discusses the control of calcium regulating hormones in the vertebrates. Control of ionic calcium levels of the extracellular fluids is mandatory for all vertebrates because only minor changes of calcium, in particular the ionized calcium fraction, have pronounced effects on the permeability of cell membranes to ions and, consequently, on important physiological processes, such as muscle contraction, nerve signal transduction, and control of cellular metabolism. Calcium uptake is balanced by renal calcium excretion, with exception of periods of body growth or, in females, periods of reproduction and parental care. Parathyroid hormone (PTH) dominates the control of the Ca2+ concentration of the extracellular fluid by its calcium-mobilizing action on bone and, indirectly, via its control of the synthesis of 1,25(OH)2D3, intestinal calcium absorption. Calcitonin (CT) reduces the extracellular calcium concentration by inhibiting osteoclastic bone resorption and by promoting calcium deposition in the skeleton. In the terrestrial vertebrates, the evidence for the involvement of prolactin (PRL) in calcium metabolism is limited to calcium handling during gestation and lactation in mammals.

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Control of calcium regulating hormones in the vertebrates: parathyroid hormone, calcitonin, prolactin, and stanniocalcin.

Effects of dietary phytase and cholecalciferol on phosphorus bioavailability in rainbow trout (Oncorhynchus mykiss).

Stanniocalcin (STC) is a glycoprotein hormone that is secreted by the corpuscle of Stannius, an endocrine gland of bony fish, and is involved in calcium and phosphate homeostasis. The related mammalian proteins, STC1 and STC2, are expressed in a wide variety of tissues. The ovaries have the highest level of STC1, and this increases during pregnancy and lactation. STC1 is present in breast ductal epithelium, and its expression is induced by BRCA1, a tumor suppressor gene that has an important role in breast and ovarian cancer. The expression of STC2 is induced by estrogen, and there is a positive correlation between the level of expression of estrogen receptor and expression of both STC1 and STC2 in breast cancer. This article reviews the data currently available regarding the mammalian STCs, and discusses the roles they may play in normal physiology and in breast and other cancers.

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Mammalian stanniocalcins and cancer.

The interaction of vitamins, minerals and diet composition in the diet of fish

Fish store large quantities of vitamin D in their liver and fat tissues, including the fat associated with muscle, and this makes fish an important dietary source of vitamin D. Fish do not synthesize vitamin D and are fully dependent on dietary sources to meet their requirement. Under natural circumstances planktonic vitamin D accumulates in the aquatic food chain. In aquaculture, formulated diets are used and vitamin D intake can be manipulated. The minimum dietary requirement for vitamin D has been established in several fish species. The role of vitamin D in fish physiology is still enigmatic. Till the 1970s there was consensus that fish accumulate but not metabolize vitamin D. There is substantial evidence now, four decades later, that fish have a vitamin D endocrine system with similar functions as in mammals. We here summarize the major characteristics of the fish vitamin D endocrine system. The hydroxylation of vitamin D to more polar metabolites, their plasma levels and protein-bound transport in blood plasma will be discussed. The vitamin D receptor profile, receptor distribution and responses to vitamin D are reviewed for the key target tissues (gill, intestine, kidney and bone). We will address the classical slower actions through transcription factors as well as the faster G-protein coupled (membrane) receptor mediated effects. We then review the dietary requirement of vitamin D in aquaculture and address some lesser known functions of the vitamin D endocrine system.

The significance of vitamin D for fish: a review.

1. 1. Vitamin D 3 (5000 i.u. and 100 i.u./100 g body wt) and 1,25-dihydroxycholecalciferol (0.5 unit, 5 units and 500 units/100 g body wt) were administered daily to the male catfish, Clarias batrachus for 17 days. The serum calcium and inorganic phosphate levels were measured colorimetrically. 2. 2. The serum calcium level increased significantly in all the treated groups and is dose-dependent. 3. 3. The serum inorganic phosphate was elevated in the treated groups (except in the group where only 100 units vitamin D 3 /100 g body wt was administered). 4. 4. This is the first report of the 1,25-dihydroxyvitamin D 3 -induced hypercalcemia in fish.

Dose-dependent vitamin D3 and 1,25-dihydroxyvitamin D3-induced hypercalcemia and hyperphosphatemia in male catfish Clarias batrachus

Vitamin D3-induced hypercalcaemia in male catfish, Clarias batrachus.

Administration of 1, 25 dihydroxyvitamin D3 (1, 10 or 50 U/100g bw) to the catfish, Clarias batrachus for 10 days activated the corpuscles of Stannius.

Corpuscles of Stannius of Clarias batrachus in Response to 1, 25 Dihydroxyvita min D3 Administration

Ultimobranchial Gland of Freshwater Catfish, Heteropneustes fossilis in Response to Deltamethrin Treatment

Seasonal changes in the structure and behaviour of stannius corpuscles and serum calcium level of Clarias batrachus in relation to the reproductive cycle

Shyam Prakash Srivastav

Papers

Dose-dependent vitamin D3 and 1,25-dihydroxyvitamin D3-induced hypercalcemia and hyperphosphatemia in male catfish Clarias batrachus

Vitamin D3-induced hypercalcaemia in male catfish, Clarias batrachus.

Corpuscles of Stannius of Clarias batrachus in Response to 1, 25 Dihydroxyvita min D3 Administration

Ultimobranchial Gland of Freshwater Catfish, Heteropneustes fossilis in Response to Deltamethrin Treatment

Seasonal changes in the structure and behaviour of stannius corpuscles and serum calcium level of Clarias batrachus in relation to the reproductive cycle