Renal excretion in gull chicks: effect of parathyroid hormone and calcium loading

Renal clearance experiments were performed on herring gull (Larus argentatus) and great black-backed gull chicks (L. marinus) to test the importance of parathyroid hormone (PTH), parathyroidectomy (PTX), and calcium loading on excretion patterns of sodium, potassium, calcium, and phosphate. PTX reduced the relative clearance of phosphate to near zero within 2 h. Conversely, PTH stimulated net secretion of phosphate within 40 min. Calcium loading caused a drop in phosphate excretion identical to that of PTX, presumably by inhibiting PTH secretion by the parathyroid glands. This also could be reversed by administration of PTH. Serum phosphate values were highest in PTX gulls and lowest in calcium-loaded gulls. The relative clearance of calcium (CCa/CIn) was elevated in calcium-loaded birds. However, CCa/CIn did not change significantly in response to either PTX or PTH in the sham-operated or PTX birds. Serum calcium values were highest in calcium-loaded gulls and lowest in PTX gulls, the reciprocal of the effects on serum phosphate.