Effect of 6-dehydro-DOCA and 6-dehydro-9 alpha-fluorocortisol acetate on the excretion of sodium and potassium in the rat

The selective mineralocorticoid receptor modulator AZD9977 reveals differences in mineralocorticoid effects of aldosterone and fludrocortisone

Introduction:

AZD9977 is a novel mineralocorticoid receptor (MR) modulator, which in preclinical studies demonstrated organ protection without affecting aldosterone-regulated urinary electrolyte excretion. However, when tested in humans, using fludrocortisone as an MR agonist, AZD9977 exhibited similar effects on urinary Na⁺/K⁺ ratio as eplerenone. The aim of this study is to understand whether the contradictory results seen in rats and humans are due to the mineralocorticoid used.

Materials and methods:

Rats were treated with single doses of AZD9977 or eplerenone in combination with either aldosterone or fludrocortisone. Urine was collected for five to six hours and total amounts excreted Na⁺ and K⁺ were assessed.

Results:

AZD9977 dose-dependently increased urinary Na⁺/K⁺ ratio in rats when tested against fludrocortisone, but not when tested against aldosterone. Eplerenone dose-dependently increased urinary Na⁺/K⁺ ratio when tested against fludrocortisone as well as aldosterone.

Conclusions:

The data suggest that the contrasting effects of AZD9977 on urinary electrolyte excretion observed in rats and humans are due to the use of the synthetic mineralocorticoid fludrocortisone. Future clinical studies are required to confirm the reduced electrolyte effects of AZD9977 and the subsequent lower predicted hyperkalemia risk.

Experimental cardiac hypertrophy induced by oral administration of mineralocorticoid and saline in rats

We suggest a new, easily applicable way of myocardial hypertrophy induction in rats. Forty randomized age-matched male Wistar rats were divided into 2 groups of 20 each: a control group and an orally administered fludrocortisone/salt group. Myocardial hypertrophy was estimated by measuring body weight, heart-weight-to-body-weight ratio and ventricular free wall thickness. Moderate myocardial hypertrophy without heart failure was established in fludrocortisone/salt group in 4 weeks. Our method is effective and low cost, and it provides a model of hypertrophic heart.

Effect of various 6-dehydro-corticosteroids, 9, 11-dehydro-DOCA and 9 alpha-fluoro-DOCA on the fluxes of sodium and potassium

The introduction of a double bond at carbons 6 and 7 (6-dehydro-derivatives) of deoxycorticosterone acetate (DOCA), cortisol-21-acetate, 9 alpha-fluorocortisol-21-acetate (9 alpha-F-C-ac) and aldosterone-21-acetate substantially reduces affinity for Type II receptors but not for Type I receptors. Such a modification changes the effect of these steroids on urinary excretion of Na+ and K+. 6-Dehydro-derivatives will thus bind preferentially to receptor Type I inducing the retention of sodium and compete with mineralocorticoids for such receptors. The increase in both natriuresis and kaliuresis when corticosteroids and their 6-dehydro-derivatives are administered together may be interpreted as evidence for a Type II receptor mediation of those ion fluxes. The ionic changes are not mediated by the (Na+ + K+)-ATPase system. The fluoration at 9 and the dehydrogenation at C9C11 of DOCA result in a strong increase of binding to Type I receptor and of sodium retention.