title: Diurnal rhythms in Ca transfer into bone, Ca release from bone, and bone resorbing activity in serum of rats.
abstract: To characterize diurnal rhythms in calcium transfer in and out of bone, rats were adapted to a 12:12 h light-dark illumination program (with light from 0600 to 1800 h). For studies of deposition, rats were injected with 45CaCl2 at 0300, 0700, 1100, 1500, 1900 or 2300 h and killed with chloroform inhalation 60 min later, and radioactivity was determined in tibia and mandibular incisor. Peak deposition occurred at 2400 h, with a nadir at 1200 h. For studies of radionuclide release, rats were prelabeled with 45CaCl2 for 6 days and serum obtained from the tail at 4-h intervals. 45Ca and specific activity were maximal around 1200-1600 h and lowest late in the dark period. To determine the role of humoral factor(s), fetal rat limb bones were cultured in media prepared with sera from light-dark-adapted rats. Activity was maximal in serum collected at 0800 h and minimal at 1600 h. Heat inactivation at 100 degrees C for 5 min eliminated the difference between the peak and nadir. The results suggest that a heat-sensitive humoral factor(s) regulates diurnal rhythms in calcium metabolism.
authors.affiliation: Department of Pharmacology, Tohoku University School of Dentistry, Sendai, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Shinoda
authors.forename: P H
authors.initials: PH
authors.lastname: Stern
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000493:pharmacokinetics*; D002132:Calcium Radioisotopes; D002940:Circadian Rhythm; D016207:Cytokines / Q000097:blood*; D007180:Incisor / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013977:Tibia / Q000378:metabolism; D013997:Time Factors
chemical_list: D002132:Calcium Radioisotopes; D016207:Cytokines; C025940:bone resorption factor; D002118:Calcium