Modification of testicular and thyroid function by chronic exposure to short photoperiod: A comparison in four rodent species

1. 1. Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10hr light:14hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T₄) levels and free T₄ index (FT₄I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). 2. 2. C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T₃ uptake (T₃U) values. 3. 3. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T,U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T₄ and triiodothyronine (T₃,) values nor the FT₄I and free T₃ index (FT₃,I). 4. 4. White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T₄ and T₃ levels were unaffected. 5. 5. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T₃ and in the FT₃I in the SP animals.