Aldosteronoma in a dog with polyuria as the leading symptom

In a 10-year-old castrated male shorthaired German pointer polyuria was ass ociated with slight hypokalemia, hypophosphatemia and alkalosis, as well as elevated plasma concentrations of a glucocorticoid-inducible iso-enzyme of alkaline phosphatase. Repeated measurements of urinary corticoids and norm al suppressibility of the hypothalamus-pituitary-adrenocorticial axis exclu ded glucocorticoid excess, Urine osmolality (Uosm) did not increase during administration of the vasop ressin analogue desmopressin. At the time water deprivation had caused Uosm to rise from 300 to 788 mOsm/kg, there was also plasma hypertonicity. Duri ng hypertonic saline infusion the osmotic threshold for vasopressin release was increased. The combination of elevated plasma aldosterone concentrations and unmeasura bly low plasma renin activity pointed to primary hyperaldosteronism. As ini tially computed tomography (CT) did not reveal an adrenocortical lesion, th e dog was treated with the aldosterone antagonist spironolactone. This caus ed Uosm to rise in a dose-dependent manner. However, well-concentrated urin e was only achieved with doses that gave rise to adverse effects. Once repeated CT, using 2-mm-thick slices, had revealed a small nodule in t he cranial pole of the left adrenal, unilateral adrenalectomy was performed which resolved the polyuria completely. Also the plasma concentrations of kalium, aldosterone and renin activity returned to within their respective reference ranges. The adrenocortical nodule had the histological characteri stics of an aldosteronoma, with the non-affected zona glomerulosa being atr ophic. In this dog with primary hyperaldosteronism the polyuria was characterized by vasopressin resistance and increased osmotic threshold of vasopressin re lease, similar to the polyuria of glucocorticoid excess. The possibility is discussed that the polyuria of glucocorticoid excess is actually a mineral ocorticoid effect. (C) 2001 Elsevier Science Inc. All rights reserved.