An interpretation of acute changes in plasma45Ca following parathyroid hormone administration to thyroparathyroidectomized rats |
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Authors: | R V Talmage S H Doppelt F B Fondren |
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Institution: | (1) Department of Surgery, Division of Orthopaedic Surgery, University of North Carolina, School of Medicine, Chapel Hill, North Carolina;(2) Orthopaedic Research Laboratories, University of North Carolina, School of Medicine, Rm. 241 Clinical Sciences Bldg. #229 H, 27514 Chapel Hill, NC, USA |
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Abstract: | Acute changes in plasma calcium and45Ca were studied in young adult male thyroparathyroidectomized (TPTX) rats injected with moderate doses of parathyroid hormone (PTH). For plasma calcium changes, comparison was made between rats fasted or fed prior to PTH injection. For plasma45Ca changes, the effect of the time of administration of the radionuclide was also studied; this included rats injected with PTH 1 h after radionuclide ( 1 h45Ca ), 18 h later ( 18 h45Ca ) and more than 6 days later ( 6 day45Ca ). The results can be summarized as follows: (1) Plasma calcium changes were greater when PTH was injected into fed rather than into fasted rats. (2) PTH always produced a relative increase (compared to controls tested concurrently) in plasma45Ca concentrations. This increase was the same in the 1 h45Ca and the 18 h45Ca groups. (3) Plasma45Ca rose at least temporarily following PTH injection in the 18 h45Ca group. (4) The45Ca rise following PTH was always greater in fed than in fasted groups. (5) Plasma45Ca specific activities (S.A.) tended to rise in the 6 day45Ca group and to fall in the 18 h45Ca group, following PTH injection. However, the45Ca S.A. was always higher in fed than fasted groups. (6) In a few experiments in which32P was injected with45Ca, specific activity changes in plasma45Ca following PTH injection werenot accompanied by similar changes in32P specific activity.These results could not be adequately explained by PTH effects on bone resorption, but the data supported the postulate that PTH controls plasma calcium concentrations by increasing transport of calcium through the osteocyte-lining cell (osteoblast) bone cell complex from the bone fluid compartment to the ECF. |
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Keywords: | Parathyroid hormone Plasma calcium Radiocalcium Bone |
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