Interrelationship between thyroid and gonadal function in female Japanese quail kept under short and long photoperiods.

The concentrations of progesterone, testosterone, oestrone, oestradiol, thyroxine (T4) and tri-iodothyronine (T3) in the plasma of 8-week-old female Japanese quail exposed to short (6 h light: 18 h darkness; 6L:18D) and long (18L:6D) photoperiods were determined by radioimmunoassay after ovariectomy, thyroidectomy and treatment with T4. In birds exposed to short days treatment with T4 slightly increased both the concentrations of progesterone, oestrone and oestradiol in plasma and the weight of the ovaries, while ovariectomy increased the testosterone and oestradiol concentrations in plasma. In birds exposed to a long photoperiod, treatment with T4 reduced the level of all the sex steroids measured, ovarian weight and egg production. Thyroidectomy increased the concentration of progesterone in plasma and decreased that of oestradiol. Photostimulation decreased the concentration of T4 in plasma of intact birds while it was ineffective in ovariectomized birds. Ovariectomy did not influence the concentration of T4 in the plasma of birds exposed to either long or short days but the level of T3 was slightly increased in the plasma of birds exposed to short days and markedly increased in the photostimulated group. It would seem, therefore, that whilst there is a distinct relationship between thyroid function and that of the ovary the relationship between ovarian and thyroid function is less marked.