Plasma Renin Activity and Plasma Concentrations of Aldosterone, Cortisol, Adrenocorticotropic Hormone, and α‐Melanocyte‐ Stimulating Hormone in Healthy Cats

Abstract

A pathogenetic role of the renin-angiotensin-aldosterone system has been implicated in cats in both systemic arterial hypertension and hypokalemic myopathy. Yet, measurement of plasma aldosterone concentrations (PACs) and plasma renin activity (PRA) has not unequivocally pointed to hyperaldosteronism as a cause of these conditions. To obtain appropriate reference ranges, this study included a large number (130) of healthy house cats of different breeds without a history of recent illness and plasma concentrations of urea and creatinine below the upper limit of the respective reference ranges. In addition, the pituitary-adrenocortical axis was studied by measuring plasma concentrations of adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), and cortisol. Reference ranges for PACs (110-540 pmol/L; 40-195 pg/mL), PRA (60-630 fmol/L/s; 0.3-3 ng/mL/h), and the aldosterone to renin ratio (ARR) (0.3-3.8) were very similar to those established in the same laboratory for humans in a supine position. No breed differences were found. The ARRs in neutered cats were significantly higher than in intact cats, primarily because of low PRA in neutered cats. The ARRs of cats > or = 5 years of age were significantly higher than those of cats < 5 years of age. The plasma concentrations of ACTH, alpha-MSH, and cortisol did not correlate significantly with PAC. Thus, although blood sampling was performed in cats in nonstandardized positions and was associated with a wide variation of stress responses, the references ranges of PAC, PRA, and ARR were similar to the relatively narrow limits established for humans under standardized conditions. The effects of neutering and aging on PRA and ARR warrant further investigation.

Urinary Aldosterone to Creatinine Ratio in Cats before and after Suppression with Salt or Fludrocortisone Acetate

“…Forty‐two cats from an animal shelter were enrolled in this study. The inclusion criteria were age ≥5 months, no remarkable findings on physical examination, systemic arterial blood pressure ≤160 mm Hg, plasma ARR below the upper reference limit (< 3.8 × 10 −9 ), 8 and laboratory results within the following reference ranges: plasma urea concentration 6.1–12.8 mmol/L, plasma creatinine concentration 76–164 μmol/L, plasma sodium concentration (Na) 146–158 mmol/L, plasma potassium concentration (K) 3.4–5.2 mmol/L, urine specific gravity (SG) >1.020, urinary total protein to creatinine ratio <10 × 10 −5 , and no remarkable abnormalities in the urine sediment.…”

“…PAC and PRA were measured at the Department of Nephrology of the University Medical Center, Utrecht, the Netherlands, as described previously 14 and validated for the cat 8 . Briefly, for measurement of PRA, 0.5 mL of plasma was incubated at 37 °C and pH 6.0 for 1 hour, in the presence of inhibitors of angiotensinases and angiotensin I converting enzyme.…”

“…The diagnosis of primary hyperaldosteronism in cats is at present mainly based upon the relation between the plasma aldosterone concentration (PAC) and plasma renin activity (PRA), ie, an increased plasma aldosterone to renin ratio (ARR) 6–8 . Practical disadvantages associated with determining the ARR include the large volume of blood (4 mL) that is required and the necessity to instantly freeze the plasma sample after collection.…”

Measurement of plasma renin concentration in cats by use of a fluorescence resonance energy transfer peptide substrate of renin

“…7,[19][20][21][22][23][24][25] Given that endog- Error bars are present but extremely small. The study reported here involved a novel assay with which changes in plasma renin concentration relative to the clinical stresses associated with renal autograft ischemia-reperfusion injury in cats were detected.…”

“…First, intra-and interlaboratory variation is substantial. 7 Strategies have been introduced to improve accuracy and efficiency of renin assays. 5 Third, because endogenous substrate (angiotensinogen) is used, the concen-tration of substrate may be a limiting factor 5 ; regardless of the total amount of substrate, the concentration of angiotensinogen affects the enzyme kinetics of renin and may cause variation in results.…”