Short photoperiods reduce vascular endothelial growth factor in the testesof Peromyscus leucopus

Testicular regression in rodents occurs after short-day exposure. Vascular support is withdrawn during regression, and, presumably, new angiogenesis i s inhibited. Blood vessel growth and maintenance are regulated by paracrine factors, including vascular endothelial growth factor (VEGF). Reduced angi ogenesis may contribute to the onset of photoperiod-induced regression; i.e ., reduction of VEGF protein would be detected early during gonadal atrophy . Alternatively, loss of blood vessel maintenance may reflect reduced testi cular volume. If true, VEGF would not be expected to decline until signific ant regression occurred. To discriminate between these hypotheses, white-fo oted mice (Peromyscus leucopus) were maintained in either long (LD 16:8) or short (LD 8: 16) photoperiod. Immunohistochemical and Western analyses rev ealed high VEGF expression in Leydig and Sertoli cells in long-day housed m ales and reduced VEGF expression in short-day housed males. Reductions in V EGF preceded decreases in both seminiferous tubule diameter and spermatogen ic activity by 6 wk and reduced testis mass by 8 wk, suggesting that change s in VEGF are not a consequence of gonadal regression and that VEGF may pla y a critical role in photoperiodic regulation of testicular function.