Effect of Vitamin D Repletion by Medication Versus Sunlight-Exposure on the Testicular Functions of Vitamin D Deficient Rats

Abstract
Background: The causal relationship between Vitamin D (VD) and gonadal function is still under-investigated especially the impact of VD repletion on the testicular structure and function. The sunlight exposure as a natural source of VD and VD supplementation are the fundamental remedies for VD repletion during deficiency conditions.
Aim of Study: To compare the efficacy of VD medications versus sunlight exposure on the testicular functions and histology in adult rats.
Material and Methods: Sixty weaned male albino rats (103.12±11.67g) were fed either a synthetic balanced formula with normal VD level (group A, n=30), or fed a customized synthetic diet with traces of VD (group B, n=30) for 6 weeks. Rats in both groups were further subdivided into three sub-groups (n=10 each): Oil-treated control (subgroup A-I and B-I), VD3 treated (subgroup A-II and B-II) which were given a dose of 75mg of VD3/rat every other day via a feeding tube, and the sun-exposed (subgroup A-III and B-III) which were exposed daily to the direct sunlight from 9am to 1pm. Plasma 25-hydroxyvitamin D (25OHVD) and testosterone (T) were measured by ELISA kits. After euthanasia, the testes were isolated, and the number of spermatids per each gram of testicular tissue and Daily Sperm Production (DSP) were calculated. Furthermore, testicular sections were stained and examined under a light microscope.
Results: VD deficient rats showed a marked reduction of T when compared with normal control (p<0.001), positive correlation with plasma 25OHVD (r=0.739, p<0.05) and histologically, there were a reduction in the Leydig cell mass and degenerative changes in all levels of the spermatogenesis. Repletion of VD by the supplement (subgroup B-II) showed a better increment of the plasma T than in sun-exposed rats. Sunlight produced a T-stimulatory effect without a concomitant rise of the 25OHVD but the Ca level was normalized in subgroup B-III (vs. A-I, p>0.05). The spermatid count per g of testis and DSP were significantly improved in both sub-groups (B-II and B-III) when compared with deficient controls (p<0.05), with no difference between both modalities of VD repletion. Microscopically, a marked improvement of germinal epithelium and all stages of spermatogenesis, together with an increase in Leydig cell counts were detected in subgroup B-II rather than in subgroup B-III.
Conclusions: VD supplementation could improve plasma T levels and structure of the testes better than sunlight exposure. Sunlight exposure improved T level by a non-VD-dependant mechanism, most probably by normalization of the Ca level. Future research should investigate the underlying mechanisms.