Changes in renal function of the chicken associated with calcitonin and parathyroid hormone

We have studied the effects of bovine parathyroid hormone (PTH) and salmon calcitonin (CT) on plasma calcium (Ca) and phosphate levels and on renal function in intact and parathyroidectomized (PTX) chickens, using a simple technique that separates urine from feces. In immature males and egg-laying females, the intravenous injection of PTH (10-20 IU/kg body wt) caused a transient fall in plasma Ca and phosphate levels, which was followed by an increase to a maximal level 20-30 min after the injection. By contrast, adult cockerels seldom showed any variation in plasma Ca or phosphate levels. In all birds, treatment with PTH increased glomerular filtration rate, urine flow rate, phosphate clearance, and Ca clearance, although this peaked later and remained elevated longer than did the phosphate clearance. The infusion of CT (1-20 U/kg over 30 min) caused a significant decrease in plasma Ca only in PTX or partially PTX chickens. All birds showed an increased GFR, urine volume, and urinary Ca excretion. In parathyroid-intact birds, the renal clearance of phosphate also increased, but peaked later and remained high longer than did Ca clearance, suggesting an increased endogenous PTH secretion. We conclude that plasma Ca and phosphate homeostasis in the chicken, as in the mammal, depends on a balanced release of PTH and CT. However, in the chicken, the response time is faster, thus minimizing the fluctuations in plasma Ca and phosphate levels resulting from exogenous hormone administration. This rapid homeostatic response is less effective when Ca demands by the body are high as in the growing or laying bird.