Diurnal variations in plasma calcium, parathormone and calcitonin levels and crop gland activity in pigeon.

Circulating levels of plasma calcitonin and parathormone were measured in the pigeon by radio immunoassay in relation to plasma concentrations of calcium. Adult birds undergoing 3 particular phases of crop gland activity (Group 1.--4 days prior to hatching, Group 2.--2 days following hatching, Group 3.--12 days following hatching), were used as experimental animals. Calcium showed a marked circadian rhythm and the levels of plasma calcitonin and parathormone fluctuate similarly with calcium changes. Significant differences between treatment groups were noted for calcium, calcitonin and parathormone, indicating the interacting control of calcium mobilization and utilization by these two hormones during crop gland activity.