Urinary cortisol/cortisone ratios in hypertensive and normotensive cats

Aldosterone and the mineralocorticoid receptor in renal injury: A potential therapeutic target in feline chronic kidney disease

There is a growing body of experimental and clinical evidence supporting mineralocorticoid receptor (MR) activation as a powerful mediator of renal damage in laboratory animals and humans. Multiple pathophysiological mechanisms are proposed, with the strongest evidence supporting aldosterone-induced vasculopathy, exacerbation of oxidative stress and inflammation, and increased growth factor signalling promoting fibroblast proliferation and deranged extracellular matrix homeostasis. Further involvement of the MR is supported by extensive animal model experiments where MR antagonists (such as spironolactone and eplerenone) abrogate renal injury, including ischaemia-induced damage. Additionally, clinical trials have shown MR antagonists to be beneficial in human chronic kidney disease (CKD) in terms of reducing proteinuria and cardiovascular events, though current studies have not evaluated primary end points which allow conclusions to made about whether MR antagonists reduce mortality or slow CKD progression. Although differences between human and feline CKD exist, feline CKD shares many characteristics with human disease including tubulointerstitial fibrosis. This review evaluates the evidence for the role of the MR in renal injury and summarizes the literature concerning aldosterone in feline CKD. MR antagonists may represent a promising therapeutic strategy in feline CKD.

Hypokalaemia in a hyperthyroid domestic shorthair cat with adrenal hyperplasia

A 13-year-old female domestic shorthair cat presented with polyphagia and weight loss. Marked systolic hypertension was found on examination. Elevated total thyroxine levels confirmed hyperthyroidism, and hypokalaemia was also documented. A euthyroid state and normotension were achieved following 4 weeks of treatment with carbimazole and amlodipine. Despite potassium supplementation, the hypokalaemia worsened. Abdominal ultrasonography revealed left adrenomegaly. Plasma aldosterone concentrations were initially in the lower half of the reference interval and, when repeated 2 months later, were undetectable. Urea and creatinine remained in the lower half of the reference interval throughout treatment, and urine specific gravity suggested good urine concentrating ability. The fractional excretion of potassium confirmed a renal source of potassium loss. Blood gas analysis was unremarkable. It was theorised that an aldosterone precursor was causing signs of mineralocorticoid excess and undetectable plasma aldosterone levels. Treatment with an aldosterone receptor antagonist successfully increased the serum potassium concentration. Owing to difficulties administering medication and associated effects on life quality the cat was euthanased. Adrenal hyperplasia was apparent on post-mortem histopathology.

Hypertension in small animal kidney disease

Kidney disease is commonly associated with hypertension in dogs, cats and other species. There are multiple mechanisms underlying the development of renal hypertension including sodium retention, activation of the renin-angiotensin system and sympathetic nerve stimulation. The relative importance of these and other mechanisms may vary both between species and according to the type of kidney disease that is present. Consideration of underlying disease mechanisms may aid in the rational choice of therapy in hypertensive patients.