Calcitonin stimulation of urine flow and sodium excretion in the starling

Renal effects of synthetic salmon calcitonin (CT) were examined in normal and parathyroidectomized (PTX) starlings, Sturnus vulgaris. Standard clearance studies were performed. Anesthetized birds were infused with [14C]-inulin in 2.5% mannitol containing either 0.25% gelatin alone as a control, or gelatin plus CT (2 IU CT/h; Armour). In intact starlings, CT significantly increased urine flow and relative clearance of sodium (CNa/CIn). CCa/CIn was significantly elevated only 40 min after start of hormone infusion. No significant change occurred in CK/CIn, CPO4/CIn or in serum levels of Na, K, Ca, or PO4. In PTX starlings, CT induced significantly higher CNa/CIn. Urine flow was significantly higher at 40 and 60 min, whereas CK/CIn increased significantly only 20 min following start of CT infusion. Serum calcium decreased significantly 1 h after hormone administration and was accompanied by increased incidence of tetany. Serum phosphate levels were significantly lower than those of corresponding PTX controls 1 h post-CT, indicating that CT prevented the expected hyperphosphatemia. Higher CT dose (20 IU/h) in PTX birds substantially enhanced urine flow, CNa/CIn, CK/CIn, and occurrence of tetany.