Parathyroid hormone responses to calcium stress during eggshell calcification.

PTH bioactivity during the egg-laying cycle of the chicken has been measured by the cytochemical bioassay for PTH. During the period of eggshell calcification, PTH bioactivity is elevated. After completion of the shell the plasma PTH falls to a low level but is slightly raised again 2 h after ovulation. These results indicate that changes in bioactive PTH play an important role in the calcium metabolism of the chicken during this physiological calcium stress.