Further characterization of the natriuretic factor derived from kidney tissue of volume-expanded rats. Effects on short-circuit current and sodium-potassium-adenosine triphosphatase activity.

Abstract

SUMMARY Boiled homogenates of kidneys from volume-expanded and hydropenic rats were subjected Co column chroniatography. The fraction eluting within the range of partition coefficients (K av ) 0.76-0.89 (fraction III) was lyophilized and the effects of this semipurified preparation were assessed on short-circuit current (SCC) across isolated frog skin, on rat kidney cortex Na-K-ATPase activity, and on sodium excretion by the rat in vivo. At a dose of 500 ftg/ml, fraction III from expanded rat kidney inhibited SCC by 21 ± 5% (P < 0.01), whereas the same fraction from hydropenic rat kidney produced an insignificant change in SCC of 2 ± 8%. In a dose-response study, 50, 150, 500, and 1,500 pg/ml of fraction III from expanded rat kidney inhibited SCC by 4, 8, 19, and 28%, respectively; 500, i.OOOVand 1,500 M g/ml inhibited Na-K-ATPase activity by 11, 22, arid 49%, respectively. An identical study with fraction III from hydropenic animals showed no significant effect in either assay. Also, fractions from expanded and hydropenic rats, eluted after fraction III (fractions IV and V), had no effect on SCC or Na-K-ATPase activity. Fraction HI also produced significant natriuresis in vivo at a dose of 500 ^g/ml, confirming our observations that a natriuretic principle may be recovered from the kidneys of volumeexpanded rats. We suggest that this natriuretic principle may act by reducing active sodium transport via inhibition of Na-K-ATPase.SEVERAL STUDIES now have shown that natriuretic factors can be found in both the serum and the urine of volume-expanded or uremic animals and humans.1 " 9 These factors not only produce a natriuresis when injected into test animals but also inhibit transepithelial sodium transport in anuran membrane preparations such as the isolated frog skin or toad bladder.1 ' 10 ' 13 The term "antinatriferic" has been used to describe this latter effect.11 In a recent study, kaplan et a!.13 have shown that the natriuretic factor obtained from uremic urine increases intracellular sodium content of and decreases pyruvate oxidation by isolated toad bladder cells. These findings suggest that this natriuretic factor inhibits active sodium transport either through interference with ATP generation via the tricarboxylic acid cycle or with some step in the active transport sequence, possibly the transport enzyme, Na-K-ATPase.Previous work from this laboratory 14 has demonstrated that a natriuretic factor also can be isolated from kidneys of volume-expanded rats but is not found in kidneys of hydropenic rats. In the present study we have shown in addition that this factor inhibits transepithelial sodium transport by isolated frog skin in a dose-dependent manner. Furthermore, the factor inhibits Na-K-ATPase activity of Received November 21, 1974; accepted for publication December 22, 1975. pooled rat kidney cortex homogenates with a similar dose-response relationship. Methods PREPARATION OF MATERIALFemale Sprague-Dawley rats (250-300 g) were infused with 0.9% saline through a jugular venous cannula. An amoun...

Endogenous Cardiotonic Steroids: Physiology, Pharmacology, and Novel Therapeutic Targets

“…In distinction from digoxin or ouabain, the endogenous CTS described by Hillyard et al (1976) did have an appreciable effect on renal Na + /K + -ATPase activity. Work from our laboratories has demonstrated that MBG has potent effects on rat renal Na + /K + -ATPase activity, which can be reversed in vivo by administration of anti-MBG antibodies.…”

Endogenous cardiotonic steroids and salt-sensitive hypertension

“…Before identification of individual CTS in the mammalian tissues, it had been demonstrated that the endogenous CTS are capable of substantially inhibiting renal Na/K-ATPase activity [47]. Three potential mechanisms may be offered to describe how low nanomolar or subnanomolar concentrations of CTS present in mammalian plasma promote natriuresis via interaction with renotubular Na/K-ATPase.…”

Basal Activity of the Natriuretic Factor Extracted from the Rat Kidney as a Function of the Diet and its Role in the Regulation of the Acute Sodium Balance

“…The present study was designed to investigate in the rat the effect of acute extracellular volume expansion and sodium intake on 385 0143-522 1/80/0503859731.50/1 the amount of this inhibitor which could be extracted from kidney tissue. The work was done (a) to confirm the previous observation by Gonick & Saldanha (1975) and by Hillgard, Lu & Gonick (1976) that natriuretic material can be extracted from the kidney tissue after such a stimulus, and (b) to estimate the influence of the sodium content of the diet on the degree of activity of the natriuretic factor in non-expanded and acutely volume-expanded animals.…”