Carotenoids, vitamin A and 7-dehydrosteroid in the frog (Rana temporaria)

Abstract

The occurrence of carotenoids and vit. A in frogs and tadpoles was studied and new metrical data were obtained on size and wt. Whole tadpoles were studied at different stages of development and the changes in total "xanthophyll" and carotene content recorded. The presence of chlorophyll is ascribed to green food undergoing digestion. The "xanthophyll"/carotene quotient declines from about 9 to about 3 as development proceeds. Vit. A was detectable in tadpole eyes. The wts. of frog organs expressed as percentage of body wt. are recorded. Much of the carotenoid actually ingested is contained in undigested food present in the alimentary tracts of insects or other prey. The frog does not ingest preformed vit. A but converts carotene to the vit. About 85% of the total vit. occurs in the liver (mainly as ester); the remainder is normally about equally divided between kidneys and eyes. Frog kidneys contain a higher proportion of vit. A than do mammalian kidneys. Most of the vit. A in the eye is ester, stored in the choroid. Carotenoids are dispersed over most organs but quite unevenly. The deposition of carotenoids in the ovaries is so large that a marked difference results between the sexes in carotenoid storage and utilization. Mature ovaries contain in relatively high concn. a substance showing the 4 absorption maxima characteristic of 7-dehydrocholesterol and ergosterol. Data were obtained on the seasonal variation in different organs of some or all of the following: carotene, "xanthophyll" (free, mono-ester, di-ester), vit. A (free and esterified) and total fat. The results on normal and fasting frogs reveal: (a) the retention of liver reserves in hibernation and inanition; (b) well-defined seasonal variations in the carotenoid storage of different organs; (c) some indication of the continuance of carotenoid metabolism during hibernation; (d) the overwhelming quantitative importance of the ovarian requirements; (e) a drain on vit. A reserves during reproduction; (f) the distinct patterns of storage and utilization of vit. A, carotenes, "xantho-phylls" and fat in the frog.