1,25-Dihydroxyvitamin D3 binding sites in the eye and associated tissues of the green lizard Anolis carolinensis.

Receptor autoradiography was used for the demonstration of specific binding of the tritiated steroid hormone 1,25-dihydroxyvitamin D3 in the eyes and associated tissues of Anolis carolinensis. A 100-fold excess of non-labelled 1,25-dihydroxyvitamin D3 abolished specific nuclear binding of tracer. Nuclear [3H]-1,25-dihydroxyvitamin D3 binding was present in all animals in the retina stratum ganglionare and stratum nuclear externum as well as in the cornea; however, binding was absent in the optic nerve, except in cells of the surrounding arachnoidea. Additional cranial tissues such as chondrocytes in the sclera, parasphenoid, skeletal muscle cells, and epithelial cells of the lacrimal and Harderian glands exhibited nuclear labelling. The results suggest that 1,25-dihydroxyvitamin D3 has genomic regulatory actions that involve cell proliferation, differentiation, and functions of certain cells of the eye and associated cranial tissues. The presence of vitamin D receptors in tissues of the eye and skeletal muscle in the reptile is in part different from that observed in mammals. In general, receptors for vitamin D and related target tissues appear to be even more extensive in lizards than has been observed in rodents, which may reflect a more extensive dependency of these tissues on solar environment and active seasonal and circadian regulation.