Annual cycles of plasma gonadotropins and sex steroids in Japanese common pheasants, Phasianus colchicus versicolor.

Plasma levels of FSH, LH, and sex steroid hormones were monitored individually in 5 male and 15 female Japanese common pheasants once to thrice monthly for 13 months. The birds were reared in outdoor cages, each containing 1 male and 5 females, under natural conditions of temperature and photoperiod. Around the period of egg laying from April 19 to July 6, plasma levels of FSH, LH, estradiol-17 beta (E2), and progesterone (P) in females were high. The increases in circulating FSH and E2 occurred earlier (in March) than those in LH and P (from April to May); decreased levels were observed first for LH in mid-June, second for P and E2 in late June, and last for FSH in June to August. Regression analysis revealed that the temporal course in titer of E2 is better rationalized as being dependent on the level of FSH rather than LH, whereas that of P is more dependent on LH than on FSH. In males, FSH was elevated only in March to June, whereas the temporal course of plasma levels of LH was clearly bimodal with maxima in February and in September. The titer of testosterone (T) was high in March to June, coinciding approximately with the maximum level of FSH. FSH was positively correlated with T, whereas LH was not in a simple correlation analysis. However, multiple-correlation analysis revealed that the change in T was better explained by considering the influence of both FSH and LH.(ABSTRACT TRUNCATED AT 250 WORDS)