Developmental change of kidney receptor for atrial natriuretic factor in spontaneously hypertensive rat

Renal atrial natriuretic peptide receptors binding properties and function are resistant to DOCA-salt-induced hypertension in rats

Atrial natriuretic peptide receptor types A (NPR-A) and C (NPR-C) binding properties and functional characteristics in renal glomeruli have been investigated in deoxycorticosterone acetate (DOCA)-treated hypertensive Wistar-Kyoto (WKY) rats and their respective controls. We found that DOCA administration had no significant effect on the maximum binding capacity or the affinity of renal NPR-A and NPR-C. NPR-C is involved in the regulation of cAMP production. Our results indicate that the cAMP production by NPR-C is not altered in DOCA-induced hypertension, since ANP(1-28), CNP(1-22) and C-ANP, which specifically bind to NPR-C, show a similar inhibitory effect on cAMP production stimulated by the physiological agonist histamine in glomeruli from DOCA-treated rats and controls. Finally, we have found that DOCA-induced hypertension does not modify NPR-A or NPR-C expression in rat glomerular membranes. These findings indicate that NPR-A and NPR-C binding properties and NPR-C-mediated inhibition of cAMP generation remain unaltered in DOCA-treated rats.

Computerized approach using autoradiography to quantify atrial natriuretic peptide receptors in the DOCA-salt hypertensive rat kidney

The alteration of atrial natriuretic peptide (ANP) receptors was investigated in the kidney of deoxycorticosterone acetate (DOCA)-salt treated hypertensive rats. The absolute amount of renal ANP receptors was determined in a membrane homogenate binding study of rat whole kidneys. Administration of DOCA-salt led to a decrease in renal ANP receptors after 3 weeks (prehypertensive state) and 6 weeks (established hypertensive state) of treatment. In vitro macro-autoradiography (ARG) was then performed with [125I]ANP to localize and to quantitate specific renal ANP receptors. ARG revealed that specific ANP binding was distributed mainly over the renal cortex with the inner medulla next in frequency. Renal ANP receptors were therefore quantified over the cortex and the inner medulla using the computerized microdensitometry of ARG. A significant reduction in renal ANP receptors was observed in the DOCA-salt treated rats after 3 and 6 weeks of treatment with decrements observed in both the cortex and inner medulla. These alterations may be related to the pathophysiology of hypertension.

Pathogenesis of the essential hypertensions

The pathogenesis of essential hypertension (EH) is reviewed with a special focus on the development phase or the pre-hypertensive period. Three animal models are presented: the spontaneously hypertensive rat, the Dahl's salt-sensitive rat, and the Milan hypertensive rat. Some of the findings in animal models have inspired new fields and technical approaches for studying EH in man. From the original idea of Page, a new mosaic of various etiological parameters serves as a basis for reviewing the multiple facets of EH in man. One must conclude that EH is heterogeneous disease and most likely every single hypertensive patient belongs to a subgroup of the whole population of hypertensives.

Amiloride differentially modulates ANP binding in human thyroid cells and bovine endothelial cells

The diuretic and sodium channel inhibitor, amiloride, has been shown to increase atrial natriuretic peptide (ANP) binding several fold in certain cell types, but in other tissues it causes only marginal increases in specific ANP binding. In the present report we compare the effects of amiloride on ANP binding in bovine endothelial cells and human thyroid-derived cells, two cell types which differ in their predominant ANP receptor subtype. We found that amiloride (10(-3) M) increased specific [125I]ANP binding to 750% above control in endothelial cells, but among several thyroid cultures tested the maximal increase in ANP binding with amiloride was only 23% above control. Moreover, most of the thyroid cultures showed decreased ANP binding in the presence of amiloride. The increased ANP binding in endothelial cells exposed to amiloride is best explained by an increased affinity of the receptor for its ligand since the drug lowered the Kd of ANP binding from 0.73 nM to 0.16 nM without affecting the receptor binding capacity. The degree of amiloride enhancement of ANP binding in endothelial cells is increased with time in culture (200% above control at 5 days, 750% above at 30 days) suggesting the increase of an amiloride-sensitive receptor relative to an amiloride-insensitive receptor. The fact that the amiloride-induced decrease in ANP binding in thyroid cells was not exacerbated by pre-incubation with amiloride suggested that the observed amiloride effect was not due to increased receptor internalization with the drug. These results support a hypothesis that ANP receptor subtypes associated with separate signal transduction mechanisms might be modulated in an opposite manner by the binding of amiloride.

Role of the kidney in the pathogenesis of primary hypertension

Primary hypertension in animals and humans probably represents several different pathophysiological states rather than being a uniform nosological entity. Among other factors, renal mechanisms may be primarily and secondarily involved. The availability of genetically homologous animal models for hypertension has greatly promoted studies on the etiology and pathogenesis of high blood pressure disease. In particular, renal transplantation studies between genetically hypertensive and normotensive rats from three different models have provided strong evidence for a primary role of the kidney in genetic hypertension. Other factors, such as vascular, neural, and humoral mechanisms have also been shown to be involved and may be particularly effective in increasing blood pressure, when they act through the kidney. Several functional and biochemical differences have been identified between kidneys from genetically hypertensive and normotensive animals. However, the relative contribution of each of these factors to the development of primary hypertension remains to be determined. Evidence from studies on human renal graft recipients also indicates that, among other factors, the kidney plays an important role in the development of primary hypertension in humans.