Changes in plasma concentrations of luteinizing hormone, progesterone, and testosterone in turkey hens during the ovulatory cycle.

Changes in luteinizing hormone (LH), progesterone, and testosterone concentrations were determined in blood samples taken every 10 min for 26 hr during an ovulatory cycle in laying turkey hens. During the 26-hr sampling period, one peak of both LH and progesterone and numerous peaks of testosterone were detected. The concentration of LH in plasma increased from basal level (2.44-4.0 ng/ml) to maximum level (8.57-24.3 ng/ml) over 1 to 2 hr and then declined over 3 to 5 hr to a basal level. The duration of the descending portion of the peak was about double that of the ascending portion. The concentration of progesterone increased rapidly from a basal level of 1.18-1.65 ng/ml to a peak of 6.18-11.87 ng/ml and then maintained a plateau before rapidly declining to basal level. The concentration of testosterone increased from a basal level of 0.06-0.09 ng/ml to a peak level of 0.13-0.30 ng/ml. All maximum levels of testosterone preceded those of LH, and all maximum levels of LH preceded those of progesterone. The durations of the progesterone peaks were longer than those of the LH peaks. Progesterone concentrations returned to basal level after LH had returned to basal level, although the initial increase in progesterone concentration was earlier, later, or at the same time as LH. Peak durations of testosterone were variable. The preovulatory surges of LH and progesterone of five of nine sets of samples started at the end of the scotophase and ended during the beginning portion of the photophase. In three of nine sets both the start and the end occurred druing the scotophase and in one of nine sets during the photophase. It was concluded from this study that the patterns of secretion of LH, progesterone, and testosterone were similar in that the preovulatory surge was superimposed on a relatively stable basal level, while the temporal relationships of the ovulatory surges of these hormones were variable. The preovulatory surges were more tightly associated with ovulation rather than with photoperiod. Neither progesterone nor testosterone might be an initiator of the LH surge prior to ovulation.