Specific binding of atrial natriuretic polypeptide to renal basolateral membranes in spontaneously hypertensive rats (SHR) and stroke-prone SHR

TA repeat variation, Npr1 expression, and blood pressure: impact of the Ace locus

The activity of the atrial natriuretic peptide receptor (Npr1) is altered in spontaneously hypertensive rats (SHR) in relation to its mRNA levels, suggesting abnormal transcriptional control in hypertension. A single-stranded conformational polymorphism caused by a repetitive dinucleotide segment of 10 TA in BN-Lx and of 40 TA in SHR was localized at position -943 relative to the transcription start site of the Npr1 gene, downstream of a putative cGMP-regulatory region, and was the only sequence difference noted between the two strains. Transient transfections of -1520 to -920 Npr1 promoter-SV40-luciferase fusion vector showed that the construct from BN-Lx stimulated the SV40 promoter, whereas that from SHR slightly inhibited it. In contrast to the BN-Lx construct, the activity of the SHR fragment was refractory to downregulation by atrial natriuretic peptide. Genotype-phenotype correlation studies in recombinant inbred strains (RIS) derived from BN-Lx and SHR crosses revealed significant correlations of the TA repeat with basal guanylyl cyclase activity and Npr1 mRNA levels. The correlations were heightened by a locus on chromosome 10 containing the Ace gene. The highest basal guanylyl cyclase activity and Npr1 mRNA values were found in RIS with both genes (Npr1/Ace) of BN genotypes, whereas the lowest were recorded in RIS, with the SHR genotypes at both loci. This was inversely correlated with diastolic blood pressure in these strains. In conclusion, the longer TA repeat unit in the promoter of Npr1 of SHR, in tandem with a putative cGMP responsive element, regulates the transcription of the Npr1 gene with consequences on diastolic blood pressure.

Impaired vasorelaxant responses to natriuretic peptides in the stroke-prone phenotype of spontaneously hypertensive rats

BACKGROUND

We have previously shown that a locus on rat chromosome 5, termed STR 2, co-localizes with the genes encoding atrial natriuretic and brain natriuretic peptides, and is closely linked to the development of strokes in rats of a F2 hybrid cohort obtained by crossing stroke-prone spontaneously hypertensive rats and spontaneously hypertensive rats. We also demonstrated that there are significant differences in vascular functioning that are co-segregated with stroke latency of stroke-prone spontaneously hypertensive rats.

OBJECTIVE

To investigate the vascular responses to natriuretic peptides in the stroke-prone phenotype of spontaneously hypertensive rats.

DESIGN AND METHODS

In view of the important vasoactive properties of natriuretic peptides, we tested the vascular responses to 10(-11)-10(-9) mol/l atrial natriuretic peptide and to 10(-11)-10(-7) mol/l brain natriuretic peptide in isolated rings of aortas and internal carotid arteries obtained from stroke-prone and stroke-resistant spontaneously hypertensive rats. The 6-week-old rats were exposed for 4 weeks either to their regular diet (n = 15 of both strains) or to the stroke-permissive Japanese-style diet (n = 14 of both strains). A group of 14 normotensive, age-matched and sex-matched Wistar-Kyoto rats was also studied.

RESULTS

Systolic blood pressures in stroke-prone and stroke-resistant spontaneously hypertensive rats were similar, and were significantly higher than those in Wistar-Kyoto rats. Vascular responses to nitroglycerin, atrial natriuretic peptide, and brain natriuretic peptide in rats of the two hypertensive strains and in Wistar-Kyoto rats fed their regular diet were comparable. In contrast, the vasorelaxant responses to atrial natriuretic peptide in stroke-prone spontaneously hypertensive rats fed Japanese diet were lower both in aortas and in internal carotid arteries than were those in spontaneously hypertensive rats (both P < 0.05 by analysis of variance) and in Wistar-Kyoto rats (both P < 0.05). Similarly, vasorelaxant responses to brain natriuretic peptide were lower both in aortas and in internal carotid arteries of stroke-prone spontaneously hypertensive rats than they were in spontaneously hypertensive rats (both P < 0.05) and in Wistar-Kyoto rats (P < 0.05). The responses to nitroglycerin in the stroke-prone spontaneously hypertensive rats and spontaneously hypertensive rats fed Japanese-style diet were also similar.

CONCLUSION

The vasorelaxant effects of natriuretic peptides are impaired in stroke-prone spontaneously hypertensive rats. This abnormality could play a role in the pathogenesis of stroke incidence in this hypertensive model.

Tissue distribution and localization of natriuretic peptide receptor subtypes in stroke-prone spontaneously hypertensive rats

OBJECTIVE

To investigate tissue distribution and localization of the natriuretic peptide receptor (NPR) subtypes' messenger RNA (mRNA) and to compare their expression between stroke-prone spontaneously hypertensive rats (SHR-SP) and Wistar-Kyoto (WKY) rats.

METHODS

Total RNA was extracted from organs of SHR-SP and WKY rats aged 13 weeks. The mRNA level was examined by RNase protection assay. The localization of the transcripts was determined by in-situ hybridization.

RESULTS

In SHR-SP aged 13 weeks, NPR-A was expressed most abundantly in the adrenal gland, lung and aorta, in that order. NPR-B was expressed highly in the uterus and ovary, and also in the lung, adrenal, and brain. NPR-C was expressed predominantly in the atrium and mesentery, less so in the lung, vein, and kidney. In the adrenal gland, NPR-A was expressed mainly in zona glomerulosa cells. In the atrium, NPR-C was expressed throughout the wall. In the mesentery, NPR-C mRNA was detected mainly in adipocytes. In the kidney, NPR-C was found predominantly in podocytes. Whereas the levels of expression of NPR subtypes in most tissues examined did not differ between SHR-SP and WKY rats, the NPR-C mRNA level was significantly greater in the kidneys of SHR-SP than it was in those of WKY rats.

CONCLUSIONS

These results indicated that each NPR subtype had a distinct tissue distribution pattern and that the expression of NPR-C in the kidneys of SHR-SP was greater than that in the kidneys of WKY rats.

Atrial natriuretic peptide-C receptor and membrane signalling in hypertension

Atrial natriuretic peptide (ANP) regulates a variety of physiological parameters, including the blood pressure and intravascular volume, by interacting with its receptors present on the plasma membrane. ANP receptors are of three subtypes: ANP-A, -B and -C receptors. ANP-A and ANP-B receptors are guanylyl cyclase receptors, whereas ANP-C receptors are coupled to adenylyl cyclase inhibition or phospholipase C activation through inhibitory guanine nucleotide-regulating protein. Unlike other G protein-coupled receptors, ANP-C receptors have a single transmembrane domain and a short cytoplasmic domain of 37 amino acids, the cytoplasmic domain has a structural specificity like those of other single-transmembrane-domain receptors and 37 amino-acid cytoplasmic domain peptide is able to exert is inhibitory effect on adenylyl cyclase. The activation of ANP-C receptor by C-ANP(4-23) (a ring-deleted peptide of ANP) and C-type natriuretic peptide inhibits the mitogen-activated protein kinase activity stimulated by endothelin-3, platelet-derived growth factor and phorbol-12 myristate 13-acetate. C-ANP also inhibits mitogen-induced stimulation of DNA synthesis, indicating that the ANP-C receptor plays a role in cell proliferation through an inhibition of mitogen-activated protein kinase and suggesting that the ANP-C receptor might also be coupled to other signal transduction mechanism(s) or that there might be an interaction of the ANP-C receptor with some other signalling pathways. ANP receptor binding is decreased in most organs in hypertensive subjects and hypertensive animals. This decrease is consistent with there being fewer guanylyl cyclase-coupled receptors in the kidney and vasculature and selective inhibition of the ANP-C receptor in the thymus and spleen. Platelet ANP-C receptors are decreased in number in hypertensive patients and spontaneously hypertensive rats. ANP-A, -B and -C receptors are decreased in number in deoxycorticosterone acetate-salt-treated kidneys and vasculature; however, the responsiveness of adenylyl cyclase to ANP is augmented in the vasculature and heart and is attenuated completely in platelets. These alterations in ANP receptor subtypes may be related to the pathophysiology of hypertension. Several hormones such as angiotensin II, ANP and catecholamines, the levels of which are increased in hypertension, downregulate or upregulate ANP-C receptors and ANP-C receptor-mediated inhibition of adenylyl cyclase. It can be suggested that the antihypertensive action of several types of drugs such as angiotensin converting enzyme inhibitors, angiotensin type 1 receptor antagonists and beta2-adrenergic antagonists may partly be attributed to their ability to modulate the expression and function of the ANP-C receptor.

Defective ANF-R2/ANP-C receptor-mediated signalling in hypertension

In the present studies we have shown that atrial natriuretic factor (peptide) receptor of ANF-R2/ANP-C type is coupled to adenylyl cyclase/cAMP signal transduction system through Gi-regulatory protein and is implicated in mediating some of the physiological responses of atrial natriuretic factor or peptide (ANP). ANF-R2/ANP-C receptor-mediated adenylyl cyclase inhibition was altered in hypertension. This alteration was tissue specific. In heart, aorta, brain and adrenal, the extent of inhibition of adenylyl cyclase by ANP was enhanced in SHR as compared to age-matched WKY, whereas in platelets, the ANP-mediated inhibition was completely attenuated. The enhanced inhibition of adenylyl cyclase by ANP was also observed in heart and aorta from DOCA-salt hypertensive rats. In addition, the augmented inhibition of adenylyl cyclase by ANP was observed in 2 weeks and older SHR but not in 3-5 days old SHR. Similarly, in DOCA-salt hypertensive rats, the enhanced inhibition of adenylyl cyclase by ANP was observed after 2 weeks of DOCA-salt treatment when the blood pressure was also enhanced, however one week older SHR but not in 3-5 days old SHR. Similarly, in DOCA-salt hypertensive rats, the enhanced inhibition of adenylyl cyclase by ANP was observed after 2 weeks of DOCA-salt treatment when the blood pressure and augmented ANP-mediated inhibition of adenylyl of DOCA-salt treatment did not result in an augmented blood pressure and augmented ANP-mediated inhibition of adenylyl cyclase, suggesting that blood pressure increase may be responsible for the enhanced responsiveness of ANP to adenylyl cyclase inhibition. However, in genetic model of hypertension, the increased inhibition of adenylyl cyclase by ANP at 2 weeks of age (when the blood pressure is normal) may be implicated in the pathogenesis of hypertension. The augmented inhibition of adenylyl cyclase in cardiovascular tissues from SHR and DOCA-salt hypertensive rats may be due to the upregulation of ANF-R2/ANP-C receptors or due to the amplification of post-receptor signalling mechanisms.

Increased cyclic guanosine monophosphate production and overexpression of atrial natriuretic peptide A-receptor mRNA in spontaneously hypertensive rats

Atrial natriuretic peptide (ANP) specifically stimulates particulate guanylate cyclase, and cyclic guanosine monophosphate (cGMP) has been recognized as its second messenger. Spontaneously hypertensive rats (SHR) have elevated plasma ANP levels, but manifest an exaggerated natriuretic and diuretic response to exogenous ANP when compared to normotensive strains. In isolated glomeruli, the maximal cGMP response to ANP corresponds to a 12- to 14-fold increase over basal levels in normotensive strains (Wistar 13 +/- 2; Wistar-Kyoto 12 +/- 2; Sprague-Dawley 14 +/- 2) while a maximal 33 +/- 3-fold elevation occurs in SHR (P < 0.001). This hyperresponsiveness of cGMP is reproducible in intact glomeruli from SHR from various commercial sources. Furthermore, this abnormality develops early in life, even before hypertension is clearly established, and persists despite pharmacological modulation of blood pressure, indicating that it is a primary event in hypertension. In vitro studies have revealed a higher particulate guanylate cyclase activity in membranes from glomeruli and other tissues from SHR. This increase is not accounted for by different patterns of ANP binding to its receptor subtypes between normotensive and hypertensive strains, as assessed by competitive displacement with C-ANP102-121, an analog which selectively binds to one ANP receptor subtype. The hyperactivity of particulate guanylate cyclase in SHR and its behavior under basal, ligand (ANP), and detergent-enhanced conditions could be attributed either to increased expression or augmented sensitivity of the enzyme. Radiation-inactivation analysis does not evoke a disturbance in the size of regulatory elements normally repressing enzymatic activity, while the expression of particulate guanylate cyclase gene using mutated standard of A- and B-receptors partial cDNAs, quantified by polymerase chain reaction (PCR) transcript titration assay, manifests a selective increase of one guanylate cyclase subtype. Our data suggest that in hypertension, genetic overexpression of the ANP A-receptor subtype is related to the exaggerated biological response to ANP in this disease.

Experimental glaucoma significantly decreases atrial natriuretic factor (ANF) receptors in the ciliary processes of the rabbit eye

ANF binding sites were analysed in the ciliary processes of rabbits with unilateral experimental glaucoma which had been induced by injecting alpha-chymotrypsin into the posterior chamber of the right eyes. The intraocular pressure (IOP) of glaucomatous eyes was significantly greater (28.4 +/- 4 mmHg) than that of normotensive control eyes (13.1 +/- 1.4 mmHg, mean +/- S.E.M., n = 23, P less than 0.05). ANF concentrations in aqueous humour and the ciliary processes were significantly higher in glaucomatous eyes (91 +/- 2 pg ml-1 and 30.4 +/- 4.2 pg g-1 wet weight) than in normal eyes (3.1 +/- 2.2 pg ml-1 and 10.2 +/- 2.7 pg g-1 wet weight, respectively, n = 6, P less than 0.01). The number of ANF-binding sites (Bmax) in the ciliary processes of glaucomatous rabbit eyes was significantly decreased in comparison to the controls (24 +/- 4 vs. 13 +/- 3 fmol mg-1 protein, n = 10, P less than 0.05). These data suggest that ANF receptors in the ciliary processes are down-regulated and that ANF may play an important role in the pathophysiology of experimental glaucoma.

Role of endogenous atrial natriuretic peptide in regulating sodium excretion in spontaneously hypertensive rats. Effects of neutral endopeptidase inhibition

To explore whether pathophysiological plasma levels of atrial natriuretic peptide (ANP) actually involve sodium excretion in spontaneously hypertensive rats (SHR), we examined the in vivo and ex vivo effects of ANP and an endopeptidase inhibitor, thiorphan, on urinary sodium excretion and the elimination rate of ANP. We found the following: 1) The basal plasma ANP level was higher in 16-week-old SHR than in Wistar-Kyoto (WKY) rats (109 +/- 10 [SEM] versus 63 +/- 4 pg/ml, p less than 0.001). Thiorphan (30 mg/kg i.v.) significantly increased plasma ANP by 60% in both SHR and WKY rats. However, increases in urinary sodium excretion (+290% versus +130%, p less than 0.05) and cyclic GMP (+160% versus +60%, p less than 0.05) were greater in SHR than in WKY rats. Urinary excretion of ANP was markedly increased by thiorphan, and its increase was greater in SHR than in WKY rats. 2) The thiorphan-induced natriuresis was substantially attenuated by antiserum for ANP but not by a bradykinin receptor antagonist. 3) Isolated SHR kidneys excreted 50% less sodium than WKY rat kidneys at perfusion pressures of 100 and 160 mm Hg (p less than 0.05). Urinary sodium excretion was increased at the perfusate ANP level of 100 pg/ml, a concentration similar to the SHR plasma ANP (+70% at 160 mm Hg). 4) After bolus administration of ANP to the isolated kidney, the ANP concentration of the recirculating perfusate decreased rapidly in a log-linear fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic factor and volume expansion-induced natriuresis in the spontaneously hypertensive rat

The implication of atrial natriuretic factor (ANF) during acute volume expansion in the spontaneously hypertensive rat (SHR) was evaluated. The effect of short-term afterload relief was also investigated. Fourteen- to 15-week-old SHR and Wistar-Kyoto (WKY) rats were treated with hydralazine for 5 days. The systolic blood pressure (BP) of SHR decreased to normotensive levels but cardiac hypertrophy was not reduced. Isotonic, iso-oncotic volume expansion (equivalent to 10% of total blood volume) was performed 3 times at 15-min intervals on conscious animals. The effect of volume expansion on central venous pressure was identical among the groups. Changes in left ventricular end-diastolic pressure (LVEDP) induced by volume expansion were greater in SHR than in WKY rats and were not affected by treatment. The increases in plasma N-terminal ANF (ANF-(1-98)) concentrations were larger in both treated and untreated SHR verses WKY rats. Despite enhanced ANF release in SHR, the overall magnitude of the diuretic and natriuretic responses to volume expansion was similar in all groups. The natriuretic response was strongly correlated with plasma ANF in WKY rats, this relationship was weak in control SHR, and restored by treatment. It is suggested that ANF release is not impaired in SHR at a 10% volume load; however, there seems to be a lower renal responsiveness to ANF in SHR.

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.

Glomerular atrial natriuretic factor receptors in spontaneously hypertensive rats

There are differences in the renal handling of sodium between spontaneously hypertensive rats (SHR) and their normotensive controls. We investigated whether this difference may be associated with changes in plasma and tissue atrial natriuretic factor (ANF) levels and with alterations in glomerular ANF receptors at 4, 8, 12, and 16 weeks of age. Age-matched Wistar-Kyoto (WKY) and Wistar rats were used as normotensive controls. Systolic blood pressure was higher in SHR at 8, 12, and 16 weeks, and cardiac hypertrophy was also present in these animals at 4 weeks. Plasma ANF C- and N-terminal concentrations were greater than in both normotensive groups at 8 and 16 weeks. ANF in the right atrium was higher in SHR than in WKY rats and identical to that in the Wistar group at 4 and 8 weeks. ANF in the left atrium was lower in SHR than in both control groups at week 12. No differences were found in ventricular ANF content. The density of glomerular ANF binding sites increased with age in WKY and Wistar rats but not in SHR. At weeks 8, 12, and 16, both normotensive groups had a higher density of binding sites than SHR, but binding site affinity was greater in SHR at weeks 8 and 12. After incubation with increasing concentrations of ANF, the production of cyclic guanosine monophosphate (cGMP) by isolated glomeruli from 16-week-old rats was lower in SHR than in both normotensive groups. We conclude that the development of hypertension in SHR is associated with higher plasma ANF levels and decreased glomerular ANF receptor density and glomerular cGMP production.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide and angiotensin II binding sites in cerebral capillaries of spontaneously hypertensive rats

1. We carried out investigations on specific atrial natriuretic peptide (ANP) and angiotensin II (ANG) binding sites in capillaries isolated from the cerebral cortex of spontaneously hypertensive rats (SHR), an animal model of human essential hypertension, and also from Wistar Kyoto rats (WKY). 2. In an equilibrium binding study done in the presence of increasing concentrations of the radiolabeled ligands, the binding of 125I-rat alpha-ANP (1-28) [ANF-(99-126)] (125I-rANP) and 125I-ANG (5-L-isoleucine) (125I-ANG) to the cerebral capillaries was single and of a high affinity. 3. The maximum binding capacity (Bmax) and dissociation constant (Kd) in the 125I-rANP binding of 20-week-old, hypertensive SHR was significantly lower than in age-matched, normotensive WKY. Conversely, a significant increase in the Bmax of 125I-ANG binding of adult SHR was observed, with a significant decrease in the Kd. 4. There was no differences in the Bmax of 125I-rANP and 125I-ANG binding between 4-week-old, prehypertensive SHR and age-matched WKY. However, there was a significant decrease in the Kd of 125I-rANP binding of SHR. 5. As a dramatic change in the binding kinetics of 125I-rANP and 125I-ANG was noted in the cerebral capillaries of adult sustained-hypertensive SHR, the possibility that ANP and ANG play a role in the etiology of dysfunction of the blood-brain barrier complicated with hypertension, by interacting with specific receptors, would have to be considered.

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

Properties of human atrial natriuretic factor (ANF) binding to the crude membrane fraction of rat kidney were studied using the ANF-radiolabeled receptor assay; the developmental change of renal ANF receptors in three age groups of spontaneously hypertensive rats (SHR) was also investigated with the methods of radiolabeled receptor assay and the quantitative approach of in vitro macro-autoradiography. Temperature and incubation time greatly influenced ANF binding capacities because of the degradation of radiolabeled ligand. Addition of 5 mM MgCl2 to assay buffer was useful for the stabilization of ANF specific binding. Scatchard analysis suggested that the crude membrane fraction of rat's kidney had a single binding site with the apparent dissociation constant of 0.55 nM. In the study of the developmental change of renal ANF receptor in SHR, systolic blood pressure of the SHR at the age of 5 weeks and 12 weeks was significantly higher than that of age-matched Wistar-Kyoto (WKY) rats, but there was no significant difference in blood pressure between SHR and WKY rats at the age of 3 weeks. Concerning the radiolabeled receptor assay of ANF, the apparent dissociation constant and maximum binding capacity in SHR were low in all age groups when compared with those of WKY rats. In the in vitro macro-autoradiographic observation, the specific binding of ANF was localized mainly in the renal cortex, and these binding patterns of SHR and WKY rats were the same in all age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Blunted cGMP response to ANF in vascular smooth muscle cells of SHR

Abnormalities in the coupling of atrial natriuretic factor (ANF) receptors with the guanosine 5'-cyclic monophosphate (cGMP) system in vascular smooth muscle cells (VSMCs) may play a role in the pathophysiology of hypertension in the spontaneously hypertensive rat (SHR). This concept was examined in cultured, aortic VSMCs (passages 6-10) from SHR, Wistar-Kyoto (WKY), and American Wistar (Wis) rats. Quiescent VSMCs of the SHR (serum deprived for 24 h) had higher ANF receptor density (Bmax) and lower affinity [i.e., increased equilibrium dissociation constant (Kd)] than cells from normotensive controls. Maximal binding (Bmax) (specific binding sites/cell) values for these cells were SHR 112,855 +/- 6,951, WKY 48,650 +/- 3,607, and Wis 36,122 +/- 2,607 (means +/- SE; P less than 0.001 for SHR vs. both WKY and Wis). The Kd values were (in nM) SHR 1.20 +/- 0.098, WKY 0.657 +/- 0.065, and Wis 0.37 +/- 0.037 (P less than 0.001 for SHR vs. both WKY and Wis). Despite their higher Bmax, VSMCs of the SHR showed a substantially lower maximal stimulation of cGMP accumulation in response to ANF: 987 +/- 29.3, 1,992 +/- 574.2, and 2,019 +/- 273.8 fmol.4 min-1.10(6) cells-1 for SHR, WKY, and Wis, respectively (P less than 0.01 for SHR vs. Wis and P less than 0.02 for SHR vs. WKY). Further experiments demonstrated that the poor response of SHR VSMCs to the ANF was not due to a population of receptors that did not couple to the particulate guanylate cyclase. Such findings demonstrate a dissociation of the cGMP response to ANF from the binding of the hormone to its receptors in VSMCs of the SHR compared with controls. This appears to represent a primary and innate defect in these cells that may contribute to the hypertensive process in the SHR.

Specific binding of atrial natriuretic factor to renal glomeruli in Doca- and Doca-salt-treated rats correlation with atrial and plasma levels

Since volume expansion and high blood pressure (BP) are known stimuli of atrial natriuretic factor (ANF) release, and since this peptide may be involved in mineralocorticoid escape, we investigated the effects of chronic deoxycorticosterone (DOCA) and DOCA-NaC1 treatment on renal glomerular ANF receptor density and affinity in relation to atrial and plasma ANF levels. An increase in plasma immunoreactive ANF (IR-ANF) was observed both after two and four weeks of treatment. IR-ANF concentrations were elevated in the left atrium only in four-week DOCA treated rats. Administration of the mineralocorticoid alone resulted in a decreased density of glomerular ANF receptors in both time periods investigated. DOCA-NaC1-treated animals presented an increased receptor density during the pre-hypertensive stage (2 weeks) and a reduced density in the later hypertensive period (4 weeks). Receptor affinity in both groups was identical to that in the controls after 2 weeks and was augmented after 4 weeks of treatment. Our data suggest that the down-regulation of renal glomerular ANF receptors during chronic DOCA-NaC1 administration may play a role in the maintenance of high BP in this model of volume-expanded hypertension.