Estimation of 24-h aldosterone secretion in the dog using the urine aldosterone:creatinine ratio

Aldosterone-progesterone relationship in sexually intact Chihuahua bitches

BACKGROUND

Aldosterone represents an important target of heart failure therapy and may be a valuable indicator of the renin-angiotensin-aldosterone system activity. However, its assessment might be challenging because of the effect of individual factors. In a recent study, intact female dogs showed the highest value of urinary aldosterone-to-creatinine ratio (UAldo:C) compared to other sex categories. In humans and rodents, an influence of progesterone has been reported by several studies. To our knowledge, the relationship between aldosterone and progesterone has not yet been investigated in dogs. The aim of this prospective study was to investigate this relationship in sexually intact Chihuahua females, measuring both hormones twice in the same bitch, that is in anoestrus when progesterone concentrations are baseline and in dioestrus when they are high.

RESULTS

The study population consisted of 14 sexually intact Chihuahua bitches. Serum progesterone (34.06 (21.17-44.90) vs. 0.19 [0.13-0.38] ng/ml; P < 0.001) and urinary aldosterone (9886.98 ± 5735.22 vs. 5005.72 ± 2127.73 pg/ml; P = 0.01) were significantly higher in dioestrus compared to anoestrous. Urinary aldosterone-to-creatinine ratio was higher in dioestrus compared to anoestrus (4.16 [3.17-6.80] vs. 3.39 ± 1.64 µg/g), but it did not reach the statistical significance (P = 0.056). Serum progesterone showed a moderate positive correlation with urinary aldosterone (ρ = 0.638, P < 0.001) and UAldo:C (ρ = 0.516, P = 0.005).

CONCLUSIONS

The results of the present study suggest the existence of a progesterone-aldosterone relationship in canine species, indicating that sex and phase of reproductive cycle should be taken into account when interpreting aldosterone concentrations. Further studies are needed to confirm these results on a larger canine population and to identify the underlying mechanisms in this species.

Factors affecting the urinary aldosterone-to-creatinine ratio in healthy dogs and dogs with naturally occurring myxomatous mitral valve disease

BACKGROUND

Chronic renin-angiotensin-aldosterone system (RAAS) activation in course of heart diseases contributes to cardiac remodeling and heart failure. Myxomatous mitral valve disease (MMVD) is characterized by different stages of severity and trend of RAAS activity during the course of the disease is still uncertain. The urinary aldosterone-to-creatinine ratio (UAldo:C) has been proven to reflect RAAS activation in dogs and might be a useful marker in monitoring therapy and disease progression, but data about this parameter need to be expanded. The objective of this study was to evaluate the UAldo:C in healthy dogs and dogs with naturally occurring MMVD, and to investigate the relationships between this parameter and clinical, echocardiographic and laboratory variables.

RESULTS

The study population consisted of 149 dogs: 49 healthy and 100 MMVD dogs (45 stage B1, 13 stage B2 and 42 stage C). Urinary aldosterone-to-creatinine ratio was not significantly different among healthy and MMVD dogs of any stages. Breed, sex and age showed a significant impact on UAldo:C. In particular, Chihuahua and Cavalier King Charles spaniel showed significantly higher UAldo:C than other breeds, as well as intact females than other genders. In stage C dogs, UAldo:C appeared to be increased by spironolactone and was positively associated with furosemide dose (P = 0.024). Aldosterone breakthrough (ABT) appeared to occur in 36% (8/22) of stage C dogs not receiving spironolactone. A significant positive association between UAldo:C and left atrium-to-aortic root ratio (LA/Ao) was found.

CONCLUSIONS

Individual factors such as breed, sex and age appeared to influence UAldo:C, and therapy seemed to add further variability. In the light of these results, comparing the UAldo:C of a single patient with a population-based reference value might lead to wrong interpretations and an individual monitoring should be considered. The prevalence of ABT in the present study (36%) was in line with those previously reported. However, due to the high individual variability of UAldo:C found in the study, even this result should be re-evaluated in the setting of an individual longitudinal approach. The positive association between UAldo:C and LA/Ao supports the mutual relationship between RAAS and cardiac remodeling.

Comparison between the effects of torsemide and furosemide on the renin-angiotensin-aldosterone system of normal dogs

INTRODUCTION/OBJECTIVES

We hypothesized that torsemide and furosemide, at approximately equipotent dosages (similar diuresis), would have comparable effects on the circulating renin-angiotensin-aldosterone system.

ANIMALS, MATERIALS AND METHODS

Six, healthy, middle-aged, male Beagles were randomized to receive torsemide (0.1 mg/kg PO q 12 h), furosemide (2.0 mg/kg PO q 12 h), or placebo for 10 days during three separate periods, separated by a 10-day washout period, in a crossover design. Blood was collected on days 1, 5, and 9 and 24-h urine collection ended on days 2, 6, and 10. After repeated measures analysis and Bonferonni correction, variables with an adjusted p<0.05 were investigated further, using Tukey's method.

RESULTS

Twenty-four-hour urine production differed significantly between the diuretics only on day 10, with torsemide causing a 38% greater diuresis than furosemide. There was, however, no significant difference in average 3-day diuresis. There were no significant differences between diuretics in the 24-h urinary excretion of sodium, chloride, or potassium, though furosemide caused less kaliuresis than torsemide. Serum renin, angiotensin II, and aldosterone and the urine aldosterone-to-creatinine ratio were significantly increased in the diuretic groups, as compared to placebo on days 5/6 and 9/10. There were no significant differences in these values between diuretics. Creatinine and blood urea nitrogen concentrations rose comparably in the diuretic groups, remaining within reference intervals in all dogs.

CONCLUSIONS

At approximately equipotent dosages (20:1), torsemide and furosemide produced comparable renin-angiotensin-aldosterone system activation. Torsemide's similar potassium excretion profile to furosemide decreases support for a hypothesized mineralocorticoid-receptor blocking capability.

A prospective, randomized, double-blind, placebo-controlled pilot study of sacubitril/valsartan (Entresto) in dogs with cardiomegaly secondary to myxomatous mitral valve disease

Background

The effects of sacubitril/valsartan (S/V) on the renin‐angiotensin‐aldosterone system (RAAS) in dogs with cardiomegaly secondary to myxomatous mitral valve disease (MMVD) are currently unknown.

Objectives

To determine the pharmacodynamic effects of S/V on the RAAS, natriuretic peptide concentrations, systolic arterial pressure (SAP), tests of renal function, and serum electrolyte concentrations in dogs with cardiomegaly secondary to MMVD.

Animals

Thirteen client‐owned dogs weighing 4‐15 kg with American College of Veterinary Internal Medicine (ACVIM) Stage B2 MMVD.

Methods

Prospective, randomized, double‐blind, placebo‐controlled pilot study of S/V in dogs with ACVIM Stage B2 MMVD.

Results

Thirteen dogs were recruited: S/V (n = 7) and placebo (n = 6). The median percentage increase in urinary aldosterone to creatinine ratio (UAldo : C) between day 0 and day 30 was significantly lower in the S/V group (12%; P = .032) as compared with the placebo group (195%). The median percentage decrease of NT‐proBNP concentration from day 0 to day 30 was not statistically different between groups (P = .68). No statistical differences were seen in echocardiographic, thoracic radiographic, SAP, or serum biochemical test results measured at any time point between groups. No adverse events were observed for dogs in either group.

Conclusion and Clinical Importance

Sacubitril/valsartan may provide a new pharmaceutical method to effectively inhibit the RAAS in dogs with ACVIM Stage B2 MMVD.

Pharmacodynamic assessment of diuretic efficacy and braking in a furosemide continuous infusion model

INTRODUCTION

Diuretic failure is a potential life-ending event but is unpredictable and poorly understood. The objectives of this study were to evaluate pharmacodynamic markers of furosemide-induced diuresis and to investigate mechanisms of diuretic braking in dogs receiving constant rate infusion (CRI) of furosemide.

ANIMALS

Six healthy male dogs.

METHODS

Raw data and stored samples from one arm of a previously published study were further analyzed to mechanistically investigate causes of diuretic braking in these dogs. Urine volume was recorded hourly during a 5-h furosemide CRI. Urine and blood samples were collected hourly to measure serum and urine electrolytes, urine aldosterone, and plasma and urine furosemide. Serum electrolyte fractional excretion was calculated. Urine sodium concentration was indexed to urine potassium (uNa:uK) and urine furosemide (uNa:uFur) concentrations, plasma furosemide concentration was indexed to urine furosemide concentration (pFur:uFur), and urine aldosterone was indexed to urine creatinine (UAldo:C). Temporal change and the relationship to urine volume were evaluated for these measured and calculated variables.

RESULTS

Urine volume was significantly correlated with urine electrolyte amounts and with uNa:uK. The ratio of pFur:uFur decreased during the infusion, whereas furosemide excretion was unchanged.

CONCLUSIONS

There was a strong relationship between urine volume and absolute urine electrolyte excretion. Urine volume was strongly correlated to uNa:uK, giving it potential as a spot indicator of urine production during diuresis. The decrease in uNa:uK over time during the infusion is consistent with mineralocorticoid modification of urinary electrolyte excretion, supporting renin-angiotensin-aldosterone activation as a cause of diuretic braking in this model.

Furosemide continuous rate infusion diluted with 5% dextrose in water or hypertonic saline in normal adult dogs: a pilot study

OBJECTIVE

The goal of this study was to investigate the short-term safety and diuretic efficacy of furosemide constant rate infusion (CRI) diluted with 5% dextrose in water (D5W) compared to dilution with 2.4% hypertonic saline in healthy dogs.

ANIMALS

Six healthy dogs.

METHODS

Dogs were studied in a randomized, blinded, crossover manner. Furosemide 3.3mg/kg was diluted to 2.2mg/mL with either 1.5mL/kg D5W for the DEX method or with 1.0mL/kg D5W and 0.5mL/kg of 7.2% hypertonic saline for the H-SAL method. After a 0.66mg/kg furosemide IV bolus, the infusion rate was 0.3 mL/kg/hr for 5 h such that both methods delivered 0.66 mg/kg/hr (total 3.3mg/kg) furosemide in equal volume for the study duration. Urine output, water intake, central venous pressure (CVP), physical parameters, furosemide concentrations, blood and urine electrolytes, and urine aldosterone to creatinine ratio (UAldo:C) were evaluated.

RESULTS

Measured variables were not different between methods but showed changes over time consistent with diuresis. Mean CVP decreased over time similarly for both methods. Plasma furosemide and urine concentrations were stable and not different between methods. Both furosemide CRI methods showed an increase in the UAldo:C, however, the rise was greater for DEX than for H-SAL.

CONCLUSIONS

Diuresis was similar for both furosemide CRI methods; however, the H-SAL method induced less renin-angiotensin-aldosterone system activation than the DEX method. The absence of intravascular volume expansion based on CVP suggests that dilution of a furosemide CRI with 2.4% hypertonic saline may be well tolerated in heart failure.

Effects of high doses of enalapril and benazepril on the pharmacologically activated renin-angiotensin-aldosterone system in clinically normal dogs

OBJECTIVE

To determine whether high doses of enalapril and benazepril would be more effective than standard doses of these drugs in suppressing the furosemide-activated renin-angiotensin-aldosterone system (RAAS).

ANIMALS

6 healthy Beagles.

PROCEDURES

2 experiments were conducted; each lasted 10 days, separated by a 2-week washout period. In experiment 1, all dogs received furosemide (2 mg/kg, PO, q 12 h) and enalapril (1 mg/kg, PO, q 12 h) for 8 days (days 0 through 7). In experiment 2, dogs received furosemide (2 mg/kg, PO, q 12 h) and benazepril (1 mg/kg, PO, q 12 h) for 8 days. Effects on the RAAS were determined by assessing serum angiotensin-converting enzyme (ACE) activity on days -1, 3, and 7; serum aldosterone concentration on days -2, -1, 1, 3, and 7; and the urinary aldosterone-creatinine ratio (UAldo:C) in urine collected in the morning and evening of days -2, -1, 1, 3, and 7.

RESULTS

High doses of enalapril and benazepril caused significant reductions in serum ACE activity on all days but were not more effective than standard doses used in other studies. Mean UAldo:C remained significantly higher on days 2 through 7, compared with baseline values. Serum aldosterone concentration also increased after drug administration, which mirrored changes in the UAldo:C.

CONCLUSIONS AND CLINICAL RELEVANCE

In this study, administration of high doses of enalapril and benazepril significantly inhibited ACE activity, yet did not prevent increases in mean urine and serum aldosterone concentrations resulting from furosemide activation of RAAS. This suggested that aldosterone breakthrough from ACE inhibition was a dose-independent effect of ACE inhibitors.

Evaluation of subacute change in RAAS activity (as indicated by urinary aldosterone:creatinine, after pharmacologic provocation) and the response to ACE inhibition

Objective:

The objective of this study was to evaluate subacute changes in renin–angiotensin–aldosterone system (RAAS) activity during angiotensin-converting enzyme inhibitor (ACEI) therapy in dogs with experimental RAAS activation.

Methods:

Analysis of data (urine aldosterone:creatinine ratio (UAldo:C) and serum angiotensin-converting enzyme activity), in 31 healthy dogs with furosemide or amlodipine-activated RAAS that received an ACEI. When furosemide or amlodipine activation of RAAS preceded ACEI administration, incomplete RAAS blockade (IRB) was defined as a UAldo:C greater than (a) the dog’s ‘activated’ baseline value or (b) a population-derived cut-off value (mean + 2 SD (>1.0 μg/g) of pretreatment UAldo:C from our population of research dogs). In studies where RAAS activation occurred concurrently with ACEIs, IRB was defined as (a) a UAldo:C greater than either twofold the dog’s prestimulation baseline value or (b) 1.0 µg/g. Dogs were followed for 7–17 days.

Results:

Serum angiotensin-converting enzyme activity was measured in 19 dogs and was significantly reduced (P<0.0001) after ACEI administration. The overall incidence of IRB, when RAAS activation preceded ACEI administration, was 33% and 8% for definitions (a) and (b), respectively. The overall incidence of IRB, when ACEIs were concurrent with RAAS activation, was 65% and 61% for definitions (a) and (b), respectively.

Conclusion:

Increases in UAldo:C, despite ACEI administration, is evidence of IRB in this subacute model of experimental RAAS activation and suppression.

Aldosterone breakthrough with benazepril in furosemide-activated renin-angiotensin-aldosterone system in normal dogs

Pilot studies in our laboratory revealed that furosemide-induced renin-angiotensin-aldosterone system (RAAS) activation was not attenuated by the subsequent co-administration of benazepril. This study was designed to evaluate the effect of benazepril on angiotensin-converting enzyme (ACE) activity and furosemide-induced circulating RAAS activation. Our hypothesis was that benazepril suppression of ACE activity would not suppress furosemide-induced circulating RAAS activation, indicated by urinary aldosterone concentration. Ten healthy hound dogs were used in this study. The effect of furosemide (2 mg/kg p.o., q12h; Group F; n = 5) and furosemide plus benazepril (1 mg/kg p.o., q24h; Group FB; n = 5) on circulating RAAS was determined by plasma ACE activity, 4-6 h posttreatment, and urinary aldosterone to creatinine ratio (UAldo:C) on days -1, -2, 1, 3, and 7. There was a significant increase in the average UAldo:C (μg/g) after the administration of furosemide (Group F baseline [average of days -1 and -2] UAldo:C = 0.41, SD 0.15; day 1 UAldo:C = 1.1, SD 0.56; day 3 UAldo:C = 0.85, SD 0.50; day 7 UAldo:C = 1.1, SD 0.80, P < 0.05). Benazepril suppressed ACE activity (U/L) in Group FB (Group FB baseline ACE = 16.4, SD 4.2; day 1 ACE = 3.5, SD 1.4; day 3 ACE = 1.6, SD 1.3; day 7 ACE = 1.4, SD 1.4, P < 0.05) but did not significantly reduce aldosterone excretion (Group FB baseline UAldo:C = 0.35, SD 0.16; day 1 UAldo:C = 0.79, SD 0.39; day 3 UAldo:C 0.92, SD 0.48, day 7 UAldo:C = 0.99, SD 0.48, P < 0.05). Benazepril decreased plasma ACE activity but did not prevent furosemide-induced RAAS activation, indicating aldosterone breakthrough (escape). This is particularly noteworthy in that breakthrough is observed at the time of initiation of RAAS suppression, as opposed to developing after months of therapy.

Effect of furosemide and high-dosage pimobendan administration on the renin-angiotensin-aldosterone system in dogs

OBJECTIVE

To determine whether a high dosage of pimobendan, when administered concurrently with moderate-dosage furosemide to healthy dogs, would activate the renin-angiotensin-aldosterone system (RAAS) more than furosemide alone.

ANIMALS

12 healthy dogs.

PROCEDURES

6 dogs received furosemide (2.0 mg/kg, PO, q 12 h) only, as an RAAS activator, for 10 days. The other 6 dogs received furosemide (2.0 mg/kg, PO, q 12 h) and pimobendan (0.6 mg/kg, PO, q 12 h) for 10 days. The effect of these drugs on the RAAS was determined by measurement of the aldosterone-to-creatinine ratio (A:C) in urine collected in the morning and evening of study days -2, -1, 1, 5, and 10.

RESULTS

Although there was an increase in the urine A:C during the study period in both groups, it was significant only for dogs that received both drugs. The urine A:C only differed significantly between groups on day 1, at which time A:C was greater in the group that received both drugs.

CONCLUSIONS AND CLINICAL RELEVANCE

High-dosage pimobendan administration neither substantially suppressed nor potentiated the RAAS when administered with furosemide in healthy dogs.

Short-term hemodynamic and neuroendocrine effects of pimobendan and benazapril in dogs with myxomatous mitral valve disease and congestive heart failure

BACKGROUND

Pimobendan and benazepril are frequently used with diuretics to treat dogs in congestive heart failure (CHF) caused by myxomatous mitral valve disease (MMVD).

AIM

To compare the short-term effects of pimobendan versus benazepril on pump function, heart size, and neuroendocrine profile in dogs with CHF caused by MMVD.

ANIMALS

Sixteen client-owned dogs.

MATERIAL AND METHODS

Seven-day prospective single-blinded study of dogs stabilized on furosemide monotherapy, randomized to pimobendan (0.4-0.6 mg/kg/day) or benazepril (0.25-1.0 mg/kg/day). Dogs had first-pass radionuclide angiocardiography, and heart size was measured by radiography and echocardiography. Circulating neuroendocrine hormones were measured.

RESULTS

Baseline variables did not differ between treatment groups. Greater decreases in the pimobendan than in the benazepril group were found for heart rate (P = .001), heart rate-normalized pulmonary transit time (P = .02), left atrial size (P = .03), and systolic and diastolic left ventricular diameters (P < .001 and P = .03, respectively) and volumes (P < .001 and P = .02, respectively), whereas ejection fraction increased more (P = .02) in the pimobendan group. Of the neuroendocrine hormones, only N-terminal proatrial natriuretic peptide (NT-ProANP) differed (P = .04) between groups. Within groups, plasma aldosterone increased (P = .01), and NT-proANP (P = .01) and NT-proB-type (P = .02) natriuretic peptide decreased in the pimobendan group, and NT-proANP (P = .02) and plasma vasopressin (P = .01) decreased in the benazepril group.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pimobendan improves short-term cardiac function more than benazepril in dogs with CHF caused by MMVD. Pimobendan treatment enables the heart to work at smaller end-systolic and diastolic dimensions while maintaining adequate forward stroke volume. Some of the treatment responses found in neuroendocrine profile might have therapeutic relevance.

Associations among serum N-terminal procollagen type III concentration, urinary aldosterone-to-creatinine ratio, and ventricular remodeling in dogs with myxomatous mitral valve disease

OBJECTIVE

To assess relationships among serum N-terminal procollagen type III concentration, urinary aldosterone-to-creatinine concentration ratio (UAC), and clinical variables in dogs with myxomatous mitral valve disease (MMVD) and healthy dogs.

ANIMALS

162 dogs with MMVD and 24 healthy control dogs of comparable age and body weight.

PROCEDURES

Blood and urine samples were collected from each dog. Dogs with MMVD underwent echocardiography and ECG. Ventricular diameter measurements were normalized for body weight. Serum N-terminal procollagen type III and urinary aldosterone concentrations were measured via radioimmunoassay. Each dog was examined on 1 to 3 occasions. Examinations were repeated at approximately 6-month intervals.

RESULTS

Serum N-terminal procollagen type III concentration decreased with increasing severity of MMVD and was negatively associated with age and left ventricular end-diastolic and end-systolic diameters. The UAC increased with prior percentage change in left ventricular end-diastolic diameter per month, subsequent percentage change in left ventricular end-systolic diameter per month, and treatment with diuretics and was negatively associated with age. Both UAC and serum N-terminal procollagen type III concentration were higher in Cavalier King Charles Spaniels than in other breeds when other measured variables were controlled for.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs with MMVD, echocardiographic indicators of left ventricular remodeling appeared to be associated with a decrease in serum concentration of a marker of collagen type III turnover and an increase in urinary aldosterone concentration.

Effects of furosemide and the combination of furosemide and the labeled dosage of pimobendan on the circulating renin-angiotensin-aldosterone system in clinically normal dogs

OBJECTIVE

To evaluate the effect of administration of the labeled dosage of pimobendan to dogs with furosemide-induced activation of the renin-angiotensin-aldosterone system (RAAS).

ANIMALS

12 healthy hound-type dogs.

PROCEDURES

Dogs were allocated into 2 groups (6 dogs/group). One group received furosemide (2 mg/kg, PO, q 12 h) for 10 days (days 1 to 10). The second group received a combination of furosemide (2 mg/kg, PO, q 12 h) and pimobendan (0.25 mg/kg, PO, q 12 h) for 10 days (days 1 to 10). To determine the effect of the medications on the RAAS, 2 urine samples/d were obtained for determination of the urinary aldosterone-to-creatinine ratio (A:C) on days 0 (baseline), 5, and 10.

RESULTS

Mean ± SD urinary A:C increased significantly after administration of furosemide (baseline, 0.37 ± 0.14 μg/g; day 5, 0.89 ± 0.23 μg/g) or the combination of furosemide and pimobendan (baseline, 0.36 ± 0.22 μg/g; day 5, 0.88 ± 0.55 μg/g). Mean urinary A:C on day 10 was 0.95 ± 0.63 μg/g for furosemide alone and 0.85 ± 0.21 μg/g for the combination of furosemide and pimobendan.

CONCLUSIONS AND CLINICAL RELEVANCE

Furosemide-induced RAAS activation appeared to plateau by day 5. Administration of pimobendan at a standard dosage did not enhance or suppress furosemide-induced RAAS activation. These results in clinically normal dogs suggested that furosemide, administered with or without pimobendan, should be accompanied by RAAS-suppressive treatment.

Aldosterone receptor antagonists--how cardiovascular actions may explain their beneficial effects in heart failure

Historically, aldosterone receptor antagonists (ARA) have been classified as 'potassium sparing diuretics'. However, the positive effect of spironolactone, the most extensively studied ARA, on morbidity and mortality observed in humans suffering cardiac insufficiency could not be explained by the renal effect of the drug alone, and a pivotal clinical study has led to extensive research. Many experimental studies have demonstrated that ARA have previously unexpected beneficial effects on the cardiovascular system including reduction in remodelling of the vascular smooth muscle cells and myocytes and improvement of endothelial cell dysfunction in heart failure. These effects improve vascular compliance and slow down the progression of left ventricular dysfunction and end-organ damage. Furthermore, aldosterone receptor blockade also restores the baroreceptor reflex, improving heart rate variability in heart failure in humans. Some of these effects have been demonstrated in dog models of cardiac disease and so justified further investigation of the potential benefit of ARA in dogs with congestive heart failure (CHF). Positive effects of spironolactone on morbidity and mortality appear to have been seen in studies conducted in dogs suffering from naturally occurring CHF. In addition, eplerenone has been shown to have benefits in canine models of heart failure. The precise mechanisms by which ARA produce these beneficial effects in dogs remain to be determined but this group of drugs clearly provide therapeutic actions out-with their diuretic effects.

Effect of spironolactone on diuresis and urine sodium and potassium excretion in healthy dogs

OBJECTIVES

To document the diuretic effect of different oral doses of spironolactone (SP) in healthy dogs.

BACKGROUND

SP is currently mentioned as a diuretic agent in the dog. However, the recommended doses were empirically defined and their corresponding diuretic effect has never been documented in dogs.

ANIMALS, MATERIALS AND METHODS

Eight adult Beagle dogs were used for two separate 2*2 cross-over designs. In the first cross-over, 4 dogs received SP orally for 8 days at 1 and 2mg/kg per day. In the second cross-over the 4 other dogs received SP similarly, but at 4 and 8 mg/kg per day. Dogs were weighed on the first and last day of each period. Plasma SP and canrenone (the main active metabolite of SP) were assayed by high performance liquid chromatography (HPLC). Daily water consumption, urine weight, urine specific gravity, and urine excretion of sodium and potassium were measured during the SP treatment.

RESULTS

Two hours after SP administration, SP was metabolized into canrenone. A significant 14 and 22% decrease in urine potassium excretion was observed at 1 and 2mg/kg, respectively, but not at the two other dose levels. Daily water consumption, urine weight, urine specific gravity, and urine excretion of sodium were not significantly altered by the SP treatment regardless of dose.

CONCLUSIONS

Repeated oral administration of SP at 1, 2, 4 or 8 mg/kg for 8 days had no effect on water and sodium diuresis in healthy dogs.