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The Rate of Rhodopsin Regeneration in the Bleached Eyes of Zinc-Deficient Rats in the Dark^1,2,

Department of Biochemistry and Biophysics, Iowa State University, Ames, IA 50011

Rats fed a zinc-deficient, phytate-containing diet (ZD rats) for 4 wk showed typical signs of zinc deficiency: reduced food intake, slow weight gain, a poor food efficiency ratio and subnormal zinc concentrations in the serum, femur and eye. Pair-fed, weight-matched rats fed a zinc-sufficient diet (PF rats) showed normal serum zinc values, intermediate femur zinc levels and eye zinc concentrations similar to those in ZD rats. The vitamin A status of all three groups, expressed as the concentration of vitamin A in the liver, was comparable. After extensive bleaching, the initial rate of rhodopsin regeneration in ad libitum-fed, zinc-sufficient rats (AL rats), ZD rats and PF rats was the same, whereas the extent of rhodopsin regeneration in AL rats kept in the dark for 120 min was almost twice that found in ZD and PF rats. These results are not consistent with the hypothesis that zinc deficiency primarily affects dark adaptation by reducing the activity of alcohol dehydrogenase in the eye. Rather, zinc deficiency and the generalized malnutrition that results from markedly reduced food intake seem to depress the synthesis of opsin, and probably other proteins as well, in the rod cells of the eye.

KEY WORDS: • zinc-deficiency • pair-fed, weight-matched controls • rats • rate and extent of rhodopsin regeneration • forms of vitamin A in the eye • zinc concentrations in serum, femur and the eye

¹ Journal Paper No. J-11470 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa; Project No. 2534.

² Supported by a grant-in-aid from the Competitive Research Grants Program of the Science and Education Administration, U.S. Department of Agriculture (59-2191-1-1-666-0), by the Iowa Agriculture and Home Economics Experiment Station and by the World Food Institute, Iowa State University.

³ International Research Fellow, World Food Institute, Iowa State University; CAPES, Fulbright Scholar, Brazilian Government Scholar.

⁴ Present address: Department of Complementary Medicine, University of Brasília, Brasília, Brazil.

⁵ To whom reprint requests should be addressed.

Manuscript received 13 June 1984. Revision accepted 9 September 1985.