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Keywords:

  • Aldosterone:renin ratio;
  • Blood pressure;
  • Feline;
  • Hyperthyroidism;
  • Plasma renin activity

Background

Hypertension is present in some hyperthyroid cats at diagnosis or can develop after treatment for hyperthyroidism. Activation of the renin-angiotensin-aldosterone system (RAAS) could be involved in the pathogenesis of hypertension.

Hypothesis

Hyperthyroid cats that develop hypertension before or after treatment for hyperthyroidism will have greater RAAS activation than normotensive cats.

Animals

Ninety-nine hyperthyroid cats.

Methods

Retrospective case–control study. Plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were measured in untreated hyperthyroid hypertensive cats (HT-Pre group), initially normotensive hyperthyroid cats that develop hypertension after treatment (HT-Post group), and hyperthyroid cats that are normotensive (NT group). Data are presented as median [25th, 75th percentile].

Results

Baseline PRA was not significantly different among the 3 groups (HT-Pre group 1.50 [0.05, 2.37] ng/mL/h, HT-Post group 0.66 [0.17, 2.31] ng/mL/h, NT group 1.11 [0.57, 2.18] ng/mL/h; P = .44). PRA decreased significantly after treatment in the NT group (1.09 [0.53, 2.47] versus 0.22 [0.05, 0.76] ng/mL/h; P < .001) and the HT-Post group (0.71 [0.17, 2.33] versus 0.28 [0.07, 0.57] ng/mL/h; P = .006). Baseline PAC was not significantly different among the 3 groups (HT-Pre group 72.2 [40.0, 145.6] pg/mL, HT-Post group 69.7 [43.3, 142.6] pg/mL, NT group 109.0 [68.2, 184.6] pg/mL; P = .10). PAC decreased significantly after treatment in the NT group (114.4 [56.6, 204.1] versus 59.5 [32.4, 98.2] pg/mL; P < .001) but did not change significantly in the HT-Post group (61.2 [44.9, 124.0] versus 58.4 [42.0, 97.7] pg/mL; P = .59).

Conclusions and Clinical Importance

RAAS activation occurs in hyperthyroid cats, but is not associated with the development of hypertension. PAC is not influenced by changes in PRA in hyperthyroid cats that develop hypertension after treatment, perhaps indicating RAAS dysfunction in these cats.