Effects of the parathyroid hormone antagonist [Tyr34]bPTH-(7-34)amide on avian renal phosphate transport

Add time:07/22/2019    Source:sciencedirect.com

The in vivo parathyroid hormone antagonist, [Tyr34]bPTH-(7-34)amide, was tested for its ability to block endogenous parathyroid hormone (PTH) activity in parathyroid-intact European starlings. The inhibitor was infused at two dose levels, 0.005 and 0.05 mg/hr. A third group received a vehicle/control infusion. High-dose infusion led to rapid and significant decreases in plasma calcium and in both absolute and relative phosphate (Pi) excretion. Low-dose infusion significantly reduced plasma calcium, but had no effect on Pi excretion. Plasma Pi tended to increase with time in all three groups. Removal of the antagonist after 140 min of high-dose infusion led to a rapid recovery of relative Pi excretion, and a subsequent overshoot to more than twice the original control level. To further test the ability of the antagonist to block endogenous PTH activity, an EGTA challenge was used to induce hypocalcemia and subsequent elevation of circulating PTH levels. In vehicle-infused birds, EGTA challenge led to a doubling of relative Pi excretion, but in birds receiving the high-dose infusion, no effect of EGTA was observed. These results demonstrate that [Tyr34]bPTH-(7-34)amide can completely block endogenous PTH activity in birds at the receptor level, including the hormone response of the renal Pi secretory transport mechanism.

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