Plasma renin activity and aldosterone concentrations in hypertensive cats with and without azotemia and in response to treatment with amlodipine besylate

Abstract

Background: Role of renin-angiotensin aldosterone system (RAAS) in feline systemic hypertension is poorly understood.

Objectives: Examine plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) in normotensive and hypertensive cats with variable renal function and in response to antihypertensive therapy.

Animals: One hundred and ninety-six cats >9 years from first opinion practice.

Methods: PRA, PAC, and aldosterone-to-renin ratio (ARR) were evaluated in cats recruited prospectively and grouped according to systolic blood pressure (SBP) and renal function (nonazotemic normotensive [Non-Azo-NT], nonazotemic hypertensive [Non-Azo-HT], azotemic normotensive [Azo-NT], azotemic hypertensive [Azo-HT]). Changes in PRA and PAC were evaluated with antihypertensive therapy (amlodipine besylate).

Results: Plasma renin activity (ng/mL/h; P = .0013), PAC (pg/mL; P < .001), and ARR (P = 0.0062) differed significantly among groups. PRA (ng/mL/h) was significantly lower in hypertensive (Non-Azo-HT; n = 25, median 0.22 [25th percentile 0.09, 75th percentile 0.39], Azo-HT; n = 44, 0.33 [0.15, 0.48]) compared with Non-Azo-NT cats (n = 57, 0.52 [0.28, 1.02]). Azo-HT cats had significantly higher PAC (n = 22, 149.8 [103.1, 228.7]) than normotensive cats (Non-Azo-NT; n = 26, 45.4 [19.6, 65.0], Azo-NT; n = 18, 84.1 [38.6, 137.8]). ARR was significantly higher in Azo-HT (n = 20, 503.8 [298.8, 1511]) than Azo-NT cats (n = 16, 97.8 [77.0, 496.4]). Significant increase in PRA was documented with antihypertensive therapy (pretreatment [n = 20] 0.32 [0.15-0.46], posttreatment 0.54 [0.28, 1.51]), but PAC did not change.

Conclusions and clinical importance: Hypertensive cats demonstrate significantly increased PAC with decreased PRA. PRA significantly increases with antihypertensive therapy. Additional work is required to determine the role of plasma aldosterone concentration in the pathogenesis of hypertension and whether this relates to autonomous production or activation of RAAS without demonstrable increase in PRA.

Keywords: Blood pressure; Cats; Chronic kidney disease.

Figure 1

Comparison of extracted aldosterone concentration, plasma renin activity, and aldosterone‐to‐renin ratios in cats grouped according to renal and blood pressure status. Comparison of (A) extracted aldosterone concentration (PAC), (B) plasma renin activity (PRA), (C) aldosterone‐to‐renin ratio (ARR). Horizontal bars represent the median PAC, PRA, or ARR for each group. The dashed line represents the upper limit of the reference interval generated from the group of normal geriatric cats for each parameter. Non‐Azo‐NT; nonazotemic normotensive, Non‐Azo‐HT; nonazotemic cats with systemic hypertension, Azo‐NT; azotemic cats normotensive, Azo‐HT; azotemic cats with systemic hypertension. *indicates statistical significance (P < .05) was attained on posthoc analysis.

Figure 2

Comparison of extracted aldosterone concentration, plasma renin activity, and aldosterone‐to‐renin ratios in cats grouped according to renal status. Comparison of (A) extracted aldosterone (PAC; P = .917; Group 1 n = 39, Group 2 n = 28, Group 3 n = 20), (B) plasma renin activity (PRA; P = .903; Group 1 n = 82, Group 2 n = 60, Group 3 n = 33), or (C) aldosterone‐to‐renin ratio (ARR; P = .772; Group 1 n = 32, Group 2 n = 25, Group 3 n = 16) between groups. Horizontal bars represent the median PAC, PRA, or ARR. The dashed line represents the upper limit of the reference interval generated from the group of nonazotemic geriatric cats for each parameter. Open symbols represent hypertensive cats within each group.

Figure 3

(A) Line chart demonstrating change in plasma aldosterone concentration before and after treatment with amlodipine besylate. No significant change in plasma aldosterone concentration was demonstrated with amlodipine besylate therapy (P = .584; n = 24). Median time between measurements 35 days (25th percentile 14, 75th percentile 56). (B) Line chart demonstrating change in plasma renin activity before and after treatment with amlodipine besylate. A significant increase (P < .001; n = 20) in plasma renin activity was demonstrated with amlodipine besylate therapy. Median time between measurements 28 days (25th percentile 14, 75th percentile 56).