Influence of thyro-parathyroidectomy and of parathyroid hormone upon state of calcium in serum of the cat.

Trendelenburg and Goebel1 demonstrated that serum from thyro-parathyroidectomized cats, when used as a nutrient fluid for the isolated heart of the frog, diminished the amplitude of contraction of the heart, as compared with serum from normal cats. They attributed this effect to a reduction in the total calcium of the serum, with a corresponding decrease in ionized calcium, but were unable to rule out the possibility of the formation of an un-ionized compound of calcium, presumably by combination with an organic acid.Two of the authors have shown that the sensitivity of the frog's heart to changes in the concentration of calcium is specific for ionized calcium, bound calcium being inert with respect to the preparation, and have utilized this property of the heart for direct quantitative estimations of Ca++ concentrations in biological fluids.2 They have also shown3 that the ionization of calcium in the protein-containing fluids of the human body follows, as a first approximation, a simple mass-law relatio...