Avian renal responses to oxidized and nonoxidized bPTH(1-34)

The hypotensive, hypercalcemic, and hyperphosphaturic responses to bovine synthetic 1-34 amino acid parathyroid hormone [bPTH(1-34)] were simultaneously evaluated in anesthetized laying hens, and compared to the same responses to oxidized (0.3% hydrogen peroxide) bPTH(1-34) prepared from the same commercial batch of hormone. The oxidized and nonoxidized hormones were administered intravenously into separate groups of animals, which were also receiving a constant intravenous infusion of inulin and p-aminohippuric acid (PAH) to serve as renal clearance test markers. bPTH(1-34) caused a 33.25 +/- 7.05 mm Hg decrease in mean arterial blood pressure. The corresponding change in response to the oxidized hormone preparation was a 10.75 +/- 1.49 mm Hg decrease, a significant reduction in hypotensive activity compared to the intact hormone. In contrast, oxidation had no influence on the hypercalcemic or hyperphosphaturic (relative clearance of phosphate, CPO4/CIn) responses to bPTH(1-34), both preparations causing significant and parallel increases in these variables. Both hormone preparations also caused increases in urine flow rate, GFR, CPAH, CCa/CIn, CK/CIn, CNa/CIn, and urine pH. However, on the basis of percentage change from the respective control periods, only CNa/CIn and urine pH showed significant differences between the two hormone preparations, with the intact hormone causing greater natriuresis and urine alkalinization than the oxidized hormone. The failure of peroxide oxidation to significantly affect the renal hyperphosphaturic response to bPTH(1-34) in chickens contrasts with results reported on mammalian species, and may be related to differences in the mechanism of renal phosphate transport between these groups.