RELATIONSHIP OF A LOW BLOOD CALCIUM TO PARATHYROID SECRETION

Abstract

After alternate bleeding and transfusion of decalcified blood into both normal and acutely thyroparathyroidec-tomized dogs there was a fall in serum Ca to 5.5-7 mgs.%. Twenty to 30 mins. after the last transfusion the serum Ca rose 1-2 mgs. in both groups and no further change was observed during the next hr. This negative finding might be due to the short duration of the expts. After the intraven. inj. of Na oxalate (40 mgs. per kg.) into normal and acutely thyroparathyroidectomized dogs, there was a fall in serum Ca to 7 mgs.% or below, followed by a return to normal (within 1[image]-3[image] hrs.) only in intact animals. In the absence of a complete return to normal, the rise in serum Ca was at least twice that observed in the para-thyroidectomized animals. Decalcified blood perfused through the thyroid-parathyroid apparatus and the perfusate injected intraven. into normal dogs caused an increase in serum Ca of 1.3-4.9 mgs. within 1[image]-3 hrs., and in most instances an increase in serum inorganic P of almost the same magnitude. When normal blood was perfused through the thyroid-parathyroid gland, the collected perfusate upon intraven. inj. yielded no significant change in serum Ca. Histologic studies failed to demonstrate any significant difference between parathyroids perfused with normal or decalcified blood as compared with control unperfused gland. After perfusion the epithelial cells were normal in appearance. Apparently a low blood Ca is a direct stimulus for the parathyroid glands to produce more hormone, thus indicating a humoral control of parathyroid secretion.