ABSTRACT

We studied the effects of ultraviolet B (UVB) exposure or administration of dietary vitamin D₃ on serum vitamin D₃, serum 25-hydroxyvitamin D₃ (25[OH]D), calcium, and phosphorus in juvenile black-throated monitor lizards (Varanus albigularis) deprived of all sources of vitamin D for 87 days. Deprivation resulted in significant decreases of circulating levels of 25(OH)D (25–35%), vitamin D₃ (73–76%), calcium (6%), and phosphorus (16%). The half-life of circulating 25(OH)D during deprivation was estimated to be from 128–139 days. After deprivation, eight monitors were given a single dose of UVB from exposure for 10–20 minutes to a Spectroline UVB lamp. The dose resulted in an average of 14.2% conversion of provitamin D₃ to previtamin D₃ and photoproducts within in vitro models. When administered once every week for 92 days, the dose failed to significantly modify the decline of serum 25(OH)D; however, the decline of vitamin D₃ seemed to level off. The overall effect of the UVB dosing was weak, and more frequent doses are probably needed to restore and maintain vitamin D status. Conversely, the oral administration of doses of vitamin D₃, averaging 10,000 IU/kg and administered orally once every week for 92 days to an additional eight vitamin D-deprived juvenile monitors, stopped the decline of 25(OH)D and caused a large increase (600%) in circulating levels of vitamin D₃ compared to predeprivation levels. Doses of dietary vitamin D₃ used in the post-deprivation phase of our study quickly restored a normal vitamin D status but were too high for maintenance and could possibly expose the animals to eventual intoxication. The predeprivation levels of vitamin D by (1) daily exposure to UVB gradients generated with a Westron 100-watt mercury-vapor lamp (averaging a daily maximum of 16% conversion of provitamin D to previtamin D₃ and photo-products within in vitro models), and (2) feeding monitors crickets gut-loaded with a commercial vitamin D-supplemented diet along with whole mice maintained the vitamin D status.