Na-K-ATPase-inhibiting and glucose-6-phosphate dehydrogenase-stimulating activity of plasma and hypothalamus of the Okamoto spontaneously hypertensive rat

Abstract

The plasma of normal man and the rat, and an acetone extract of hypothalamus from the rat, have an ability to inhibit Na-K-ATPase which is related directly to salt intake. The ability of the plasma to inhibit Na-K-ATPase is raised in essential hypertension. The ability of plasma and of an acetone extract of hypothalamus from six spontaneously hypertensive (SHR) rats and six normotensive control (WKY) rats to inhibit Na-K-ATPase of fresh guinea-pig kidney was studied using cytochemical bioassay techniques. With a validated assay, which measures the capacity of biological samples to stimulate glucose-6-phosphate dehydrogenase (G6PD) as an index of their capacity to inhibit Na-K-ATPase, the mean G6PD-stimulating ability of the plasma from the SHR and the WKY rat was 772.3 +/- 48.1 units/ml and 12.5 +/- 2.6 units/ml respectively (P less than 0.01) and of the hypothalamic extracts it was 2.2 +/- 1.7 X 10(8) and 4.5 +/- 1.8 X 10(4) units/hypothalamus (P less than 0.01). With a semi-quantitative cytochemical assay, which measures Na-K-ATPase activity directly, plasma and an acetone extract of hypothalamus from the spontaneously hypertensive rat had much greater capacities to inhibit Na-K-ATPase than plasma and extract from the WKY rat. These raised levels of Na-K-ATPase inhibitory activity in the plasma of the SHR rat are similar to the highest values found in the plasma of patients with essential hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous digitalislike circulating substances in spontaneously hypertensive rats.

“…It is difficult to reconcile these ambiguous results concerning the Na + ,K + -ATPase inhibition with those of Millet et al, 21 who reported that, compared with that of WKY, plasma from SHR exerts a very marked stimulation of the activity of the renal glucose 6-phosphate dehydrogenase in fresh guinea pig kidney proximal tubule; this stimulation was usually associated with reciprocal changes in Na + ,K + -ATPase activity. They have also confirmed that SHR plasma does induce a transient inhibition of Na + ,K + -ATPase activity in the same cells.…”

“…The difference between these and our results cannot be explained by different Na + intakes, as with the diets of both their and our animals the urinary Na + excretion averaged 1 mmol/24 hr. Methodological differences are more likely to be involved, including the origin of the Na + ,K + -ATPase (rat or guinea pig semipurified enzyme or tissue slices), the amount of plasma studied (1.8 or down to 10~5), the time course of inhibition (stable or transient), and our use of deproteinized plasma, not whole plasma such as Millet et al 21 used, because of the high nonspecific inhibition observed with whole plasma under our experimental conditions. The results of these authors are, however, in agreement with the increased inhibition of Na + fluxes from erythrocytes and the high digoxinlike immunoreactivity of SHR plasma that we described.…”

“…The presence of high amounts of compound(s) able to inhibit the active Na + transport in plasma and hypothalamus of SHR has been recently reported on the basis of indirect or semiquantitative cytochemical assays. 21 In contrast, in vitro experiments on cell Na + transport did not confirm that active Na + transport inhibitors are present in SHR plasma. Studies of plasma-induced changes in Na + fluxes from erythrocytes, 22 -2 * white blood cells, or rat thymocytes 25 favor the participation of an inherited membrane defect in SHR, rather than the participation of a plasma substance.…”

Cytochemical bioassays: every dog has its day

“…Absolute plasma vasopressin values obtained by the cytochemical bioassay were comparable to those measured by radioimmunoassay (r ¼ þ0.97, p < 0.001). This assay was later used to study hypertensive rats 41,42 and to determine the vasopressin levels in neonates. 43 One of the major drawbacks to these bioassays was the low throughput of the assay system.…”

Cytochemically assayable Na+,K+-ATPase inhibition by Milan hypertensive rat plasma.

“…W ITH the use of cytochemical techniques 12 we have previously demonstrated that plasma from normal humans 3 and rats 4 on a high sodium intake, from patients with essential hypertension, 3 and from adult spontaneously hypertensive rats (SHR) 6 have a heightened ability to inhibit Na + ,K + -adenosine triphosphatase (ATPase). It therefore appears that these two forms of hereditary hypertension are associated with a rise in the concentration of a cytochemically bioassayable circulating Na + ,K + -ATPase inhibitor that is controlled by salt intake in normal humans and animals.…”