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 < 0·01) and of the hypothalamic extracts it was 2·2 ± 1·7 × 10⁸ and 4·5 ± 1·8 × 10⁴ units/hypothalamus (P < 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. The results suggest that the substance responsible for the increased capacity of the plasma to inhibit Na-K-ATPase may originate from the hypothalamus and that it may, in part, be involved in the mechanisms which induce the rise of arterial pressure in inherited forms of hypertension. J. Endocr. (1986) 108, 69–73