DIURNAL RHYTHM IN SERUM TESTOSTERONE LEVELS AND THYMIDINE UPTAKE BY TESTES IN THE DOMESTIC FOWL

Serum testosterone levels were measured by radioimmunoassay at 3-hr. intervals in a total of 80 mature Dwarf Leghorn cocks, and incorporation of thymidine-3H in testes was measured by radioautography in an additional 24 birds. Serum testosterone was higher at night (P\u3c 0.02), averaging 7.14 ± 0.55 ng/ml during light hours (0900-1800 hr.), and 9.42 ± 0.73 ng/ml (P \u3c 0.02) during darkness (2100-0600 hr.). In a second experiment to determine the rate of incorporation of thymidine into testes, birds were inadvertently subject to continuous artificial light during the 24-hr. study period; uptake of thyrnidine-3H did not differ between day and nighttime periods, averaging 174 ± 5 and 177 ± 4 tritium-labeled cells per mm2, respectively. These data suggest that, during the Ohio spring season, testosterone production is favored at night. Spermatogenic DNA production may not vary diurnally, but the unusual lighting scheme involved may have altered the normal picture