Tissue distribution of 7-dehydrocholesterol, vitamin D3 and 25-hydroxyvitamin D3 in several species of fishes.

A high-performance liquid chromatographic (HPLC) method for simultaneous determination of 7-dehydrocholesterol (7-DHC), vitamin D3 and 25-hydroxyvitamin D3 (25-OH-D3) in tissues of fishes was established, and using this method the tissue distribution of the sterols in lamprey (Entosphenus japonicus), great blue shark (Prionace glauca), skipjack (Katsuwonus pelamis) and albacore (Thunnus alalunga) was investigated. The results are summarized in the following: Although the alimentary canal, gall bladder and roe of lamprey and the alimentary canal of great blue shark contained comparatively high levels of 7-DHC (higher than 2,000 ng/wet tissue g), the other tissues of lamprey and great blue shark and all tissues of skipjack and albacore contained only low levels of 7-DHC (lower than 1,000 ng/g). There was no significant correlation between the levels of 7-DHC and vitamin D3. The contents of 7-DHC in the skin of skipjack and albacore were only 1/1,000 of those in the skin of rats. Although the contents of vitamin D3 in the liver of skipjack and albacore were extremely high (41,240 and 21,000 ng/g, respectively), those in the skin were very low (454 and 257 ng/g, respectively). 25-OH-D3 was detected in the viscera of skipjack, but the levels were not very high (lower than 150 ng/g). These levels were not significantly correlated with those of vitamin D3. The results suggest that large quantities of vitamin D3 in the liver of skipjack and albacore are supplied by other biosynthetic routes or by intake of vitamin D3 rather than by photochemical biosynthesis.