Primary hyperaldosteronism (PHA) is suggested to be more common in cats than previously thought. Because of its profibrotic and proinflammatory effects, aldosterone may contribute to the progression of hypertension and kidney damage.

The aim of the present study was to perform a pilot study on the plasma aldosterone concentration (PAC), plasma renin activity (PRA), and hypertension in cats with chronic azotemia in Sweden.

Twenty-one cats with chronic azotemia were included in the study. Blood samples were collected into pre-chilled EDTA tubes and centrifuged at +4°C. The separated plasma was stored at -80°C until transport at -70°C to the commercial laboratory for analysis. PAC was measured with an ELISA, PRA with a radioimmunoassay, and blood pressure (BP) with high-definition oscillometry. Statistical analysis was performed with non-parametric tests with the free software R version 3.3.2.

In the 21 cats, median PAC was 21 pmol/L (range, <20 to 127 pmol/L; reference range, 87 to 224 pmol/L). In seventeen cats the PAC was below reference range; in 10 of these the PAC was below detection limit (20 pmol/L). Median PRA was 0.30 ng/ml/hr (range, 0.0 to 4.5 ng/ml/hr; reference range, 0.14 to 3.85 ng/ml/hr). Five of the 21 cats had a PRA below the reference range. Median aldosterone-to-renin activity ratio (ARR) was 86 (range, 14 to 4300). Eleven of the 21 cats were hypertensive (BP≥160 mm Hg). Median PAC in hypertensive cats was 43 pmol/L (range, <20 to 127). Median PAC in normotensive cats was <20 pmol/L (range, <20 to 77). There was no statistical difference in PAC or PRA between hypertensive and normotensive cats (Mann-Whitney-Wilcoxon test, p=0.09 and p=0.10, respectively).

Five of the 6 cats with a PAC >70 pmol/L were hypertensive. Four of the 5 hypertensive cats had a PRA below or in the lower reference range. The ARR in these 4 cats was 513, 673, 720, and 1200. One cat (ARR 1200) was euthanized. Histopathological examination revealed a mixed diffuse and nodular hyperplasia of the z. glomerulosa of the right adrenal gland, and bilaterally chronic to active interstitial nephritis. The remaining two cats had an ARR of 23 and 122.

The results of the present study indicate presence of renin-independent aldosterone secretion in 19% of the cats with chronic azotemia. A surprisingly high proportion of the cats had a subnormal PAC. This is an observation that needs further investigation, before conclusions are drawn.

Disclosures

Disclosures to report:

A scholarship from the Foundation of Elsa Paulssons memorial fund was granted to finance a part of the costs of this study. Dr Hanson has received European Society Endocrinology/Dechra Veterinary Products travel grant for researchers in veterinary endocrinology, and financial support from the Foundation for Research, Agria Insurance Company, the Swedish Research Council, and Thure F and Karin Forsbergs Stiftelse.