Reprint of "The origin and metabolism of vitamin D in rainbow trout".

An explanation for the origin and the high concentration of vitamin D (cholecalciferol) in some species of fish is still not apparent. Because fish may live in deep water and may, thus, not be exposed to solar ultraviolet (UV) light, it is commonly assumed that vitamin D found in their livers and adipose tissue has been derived from a food chain, originating in zooplankton exposed to UV light at the water surface. To investigate the metabolism and possible origin of vitamin D in fish, rainbow trout were reared from eggs, in the absence of light, and were fed a vitamin D-free diet. When small quantities of radioactively-labelled vitamin D were injected or fed to these trout, much of the radioactivity was found as excreted metabolites in bile. Hence, even when they are vitamin D deficient, trout vigorously catabolise and excrete exogenous vitamin D. The main vitamin D metabolite found in plasma of non-deficient trout was 1,25-dihydroxycholecalciferol [1,25(OH)2D3]. This was produced in the liver by an enzyme process that was strongly stimulated in vitamin D deficiency. When vitamin D was fed for several weeks to vitamin D-deficient trout, plasma 1,25(OH)2D3 levels rose to 180pg/ml and the fish became hypercalcemic. When vitamin D-deficient fish were inadvertently exposed to 60W incandescent light for 24h, they became moribund and died. It was subsequently found that vitamin D-deficient trout can produce vitamin D in skin when exposed to blue light at wavelengths between 380 and 480nm. It is concluded that trout, like terrestrial vertebrates, produce 1,25(OH)2D3 as the functional form of vitamin D and that this has an effect on calcium homeostasis. Furthermore, vitamin D is formed in the skin of these fish by the photochemical action of visible light on 7-dehydrocholesterol. Elucidation of the physicochemical mechanism of this process requires further research.

The origin and metabolism of vitamin D in rainbow trout.

An explanation for the origin and the high concentration of vitamin D (cholecalciferol) in some species of fish is still not apparent. Because fish may live in deep water and may, thus, not be exposed to solar ultraviolet (UV) light, it is commonly assumed that vitamin D found in their livers and adipose tissue has been derived from a food chain, originating in zooplankton exposed to UV light at the water surface. To investigate the metabolism and possible origin of vitamin D in fish, rainbow trout were reared from eggs, in the absence of light, and were fed a vitamin D-free diet. When small quantities of radioactively-labelled vitamin D were injected or fed to these trout, much of the radioactivity was found as excreted metabolites in bile. Hence, even when they are vitamin D deficient, trout vigorously catabolise and excrete exogenous vitamin D. The main vitamin D metabolite found in plasma of non-deficient trout was 1,25-dihydroxycholecalciferol [1,25(OH)2D3]. This was produced in the liver by an enzyme process that was strongly stimulated in vitamin D deficiency. When vitamin D was fed for several weeks to vitamin D-deficient trout, plasma 1,25(OH)2D3 levels rose to 180 pg/ml and the fish became hypercacemic. When vitamin D-deficient fish were inadvertently exposed to 60 W incandescent light for 24h, they became moribund and died. It was subsequently found that vitamin D-deficient trout can produce vitamin D in skin when exposed to blue light at wavelengths between 380 and 480 nm. It is concluded that trout, like terrestrial vertebrates, produce 1,25(OH)2D3 as the functional form of vitamin D and that this has an effect on calcium homeostasis. Furthermore, vitamin D is formed in the skin of these fish by the photochemical action of visible light on 7-dehydrocholesterol. Elucidation of the physicochemical mechanism of this process requires further research.

Bioconcentration of nonylphenol in fathead minnows (Pimephales promelas).

Bioconcentration of p-nonylphenol (NP) by fathead minnows was determined under laboratory conditions. Fish were exposed continuously for 42 days to 0.33, 0.93 and 2.36 microg NP/l in a flow-through system. NP was Soxhlet extracted from whole fish homogenates with dichloromethane (DCM). The resulting extract was concentrated and bulk lipids removed by gel permeation and silica-gel chromatography. Compounds were identified and quantified by reverse-phase high-pressure liquid chromatography (RP-HPLC) with fluorescence detection. Mass spectrometry was used for verification of peak assignments. Bioconcentration factors (BCFs) ranged from 245 to 380.

Effects of nonylphenol ethoxylate exposure on reproductive output and bioindicators of environmental estrogen exposure in fathead minnows Pimephales promelas.

Nonylphenol ethoxylates (NPEOs) were evaluated in the laboratory for potential effects on the reproductive physiology and fecundity of fathead minnows (Pimephales promelas). Groups of three adult male and three female fathead minnows were exposed in a continuous flow-through system to 0, 0.21, 0.65, 2.1, or 7.9 microg NPEO/L for 42 d. Rabbit anti-goldfish vitellogenin (VTG) antiserum was prepared and a competitive enzyme-linked immunosorbent assay (ELISA) was adapted for measurement of plasma VTG in fish following exposure. Plasma 17beta-estradiol (E2) and testosterone (T) were also quantified by ELISA at the end of the exposure. Neither survival nor fecundity of fathead minnows exhibited a concentration-dependent response to NPEOs. No significant differences were observed in plasma VTG concentrations among treatments for males or females. Mean plasma VTG concentrations in females ranged from 291.7 to 895.1 microg VTG/ml among treatments and did not overlap with mean concentrations measured in the plasma of males, which ranged from less than the method detection limit (0.27 microg VTG/ml) to 3.2 microg VTG/ml. Plasma E2 concentrations exhibited a significant difference between males and females within all NPEO treatments, but no differences were observed among treatments. Similarly, plasma T concentrations did not exhibit a concentration-dependent response to NPEOs.

Effects of waterborne exposure to 4-nonylphenol and nonylphenol ethoxylate on secondary sex characteristics and gonads of fathead minnows (Pimephales promelas).

Fathead minnows were exposed to 4-nonylphenol (NP) or nonylphenol ethoxylate (NPEO) to determine the effects of these weak estrogen agonists on secondary sex characteristics and gonads of sexually mature males and females during 42-day continuous-flow exposures. Neither NP nor NPEO caused statistically significant effects on tubercles or fatpad size at the concentrations tested. Exposure to 1. 1 or 3.4 micrograms NP/L caused changes in the number and size of Sertoli cells and germ cell syncytia. Necrotic aggregates of various stages of germ cells in the spermatogenic sequence were observed in the testes of males exposed to NP. Electron microscopy of the testes of NP-exposed males revealed the presence of phagocytic cells in the lumina of seminiferous tubules. The cytoplasm of some Sertoli cells was distended with myelin figures and necrotic spermatozoa. No significant effects on the stages of follicular development were observed in females exposed to NP. There were no differences in the gonads or secondary sex characteristics of males or females exposed to 5.5 micrograms NPEO/L, the greatest concentration studied. The histologic responses observed are sensitive indicators of waterborne exposure to NP at environmentally relevant concentrations, but not as sensitive as induction of plasma vitellogenin. The secondary sex characteristics were not affected by concentrations of NP or NPEO as great as 3.4 or 5.5 micrograms/L, respectively. Histologic responses occurred at concentrations that were less than the final chronic value based on survival and approximately the same as those required to cause effects on egg production. The histologic effects caused by NP were similar to, but not exactly the same as those caused by exposure of fathead minnows to 17 beta-estradiol.