Calcium uptake in the duodenum, shell gland, and medullary bone of laying hen, and the effects of melatonin, serotonin, estradiol, and progesterone on this process were investigated at 0, 6, 12, and 18 hours after oviposition. Tissue was exposed to calcium for 2 minutes (time of active calcium uptake) or 5 minutes (time of calcium uptake saturation). Calcium uptake in the duodenum was greater at 12 and 18 hours than 0 or 6 hours after oviposition for 2 minute exposure, and was greater at 18 hours than 0, 6, or 12 hours after oviposition for 5 minute exposure. Calcium uptake in the shell gland was greater at 6 and 18 hours than at 12 hours after oviposition for both 2 and 5 minute exposures. Calcium uptake in medullary bone was highest at 12 hours and lowest at 6 hours after oviposition for 2 minute exposure, and was greater at 12 hours than 0, 6, or 18 hours after oviposition for 5 minute exposure. In vitro treatments of melatonin, serotonin, and estradiol resulted in increases in calcium uptake in medullary bone, but not in duodenum and shell gland. These results suggest that calcium uptake in duodenum, shell gland, and medullary bone in hen is under control of a biological clock. Furthermore, melatonin, serotonin, and estrogen may mediate medullary bone calcium uptake in part via fast-acting, membrane bound G-protein-coupled receptors.
