LOW-TEMPERATURE AND SHORT DAYS TOGETHER INDUCE THYROID ACTIVATION AND SUPPRESSION OF LH-RELEASE IN JAPANESE-QUAIL

We have found in Japanese quail that low ambient temperature is required to terminate breeding activity in the presence of short days (Wada et al., 1990, Gen. Comp. Endocrinol. 80, 465-472; Tsuyoshi and Wada, 1992, Gen. Comp. Endocrinol. 85, 424-429). To elucidate the mechanism for photoperiodic and temperature regulation of the release of luteinizing hormone (LH), several serum variables were measured in three groups of mature male birds: (a) birds kept on long days of 16L:8D, 24 hr at 19° as an initial control group (Group IC), (b) birds transferred from long days to short days of 8L:16D, 24 hr at 19° (Group S) for 14 days, and (c) birds transferred to short days of 8L:16D and low temperature cycles of 12 hr. 19°:12 hr, 9° (Group SL) for 14 days. Testicular mass and plasma concentrations of LH significantly decreased to nonbreeding levels in Group SL, but not in Group S, confirming our previous results. Hematocrit, serum osmolarity, and concentrations of Na+, K+, Ca2+, Mg2+, and Cl ions were not different among the three groups. Serum concentrations of free fatty acids were increased in Group SL, but the increase was not statistically significant. On the other hand, plasma concentrations of thyroid hormones changed significantly; thyroxine (T4), but not triiodothyronine (T3), increased in Group S, and T3, but not T4, increased in Group SL. To follow the changes in plasma levels of LH, T4, and T3 during the treatments, blood samples were collected every other day for 2 weeks from birds in the three groups of mature male birds described above. In Group C, plasma concentrations of LH, T4, and T3 did not change during the experimental period. In Group S, plasma concentrations of LH remained at relatively high levels and T4 increased after an initial decrease; T4 showed a slight increase. In Group SL, plasma concentrations of LH decreased rapidly to the nonbreeding level and T3 showed a great increase, while changes in T4 were basically similar to those in Group S. These results indicate that thyroid hormones are involved when a breeding season terminated by short days and low temperature, and they suggest that T3 and 5'- monodeiodination of T4 are at least a part of the mechanism. © 1993 Academic Press, Inc.