Heublein, D. M.

C-type natriuretic peptide (CNP) is a vasoactive and antimitogenic peptide that is structurally similar but genetically distinct from atrial natriuretic peptide. While first discovered in the brain, CNP has been shown to be produced by endothelial cells and may function in a paracrine and autocrine fashion in the control of vascular tone. Recently, CNP immunoreactivity and B-type natriuretic peptide receptors (NPR-B), for which CNP is a specific ligand, have been identified in the kidney. The present study was designed to determine whether renal epithelial cells produce and secrete CNP and whether CNP immunoreactivity is present in canine kidney. Opossum kidney (OK) cells that express proximal tubular cell characteristics were incubated for 6 h in fetal calf serum-free Dulbecco's modified Eagle's medium (DMEM). CNP immunoreactivity was measured in the preincubation and 6-h conditioned media by radioimmunoassay (RIA) using a specific antibody to CNP-22. Furthermore the molecular form of this CNP-like protein was determined by reverse-phase high-performance liquid chromatography (HPLC), and intracellular localization of the CNP immunoreactivity was determined by immunohistochemical staining. CNP immunoreactivity was also determined in renal tissue from dogs subjected to saline or endothelin infusion. Six-hour incubation in DMEM resulted in accumulation of CNP immunoreactivity (baseline below detection level vs. 6 h = 117.3 +/- 8.3 pg/ml, P < 0.001). Intracellular CNP concentration determined after sonication was 1.9 +/- 0.2 micrograms/g protein, and immunohistochemical staining for CNP was markedly positive in the cytoplasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenomedullin (ADM), originally discovered in human pheochromocytoma, is also of renal cell origin and has natriuretic and diuretic actions. The present study was designed to investigate the role of prostaglandins and renal nerves in the renal hemodynamic and natriuretic actions ofADM. ADM was administered intrarenally (1, 5 and 25 ng x kg(-1) x min(-1)) with and without prostaglandin inhibition (meclofenamate, 5 mg/kg intravenous bolus) in anesthetized normal mongrel dogs (n = 5, each). To elucidate the role of renal nerves, ADM was administered intrarenally to the denervated kidney in five dogs. ADM mediated a natriuretic action via increases in glomerular filtration rate and decreases in distal tubular sodium reabsorption, which was attenuated by renal denervation and completely abolished by prostaglandin inhibition. The renal vasodilatation induced by ADM was attenuated by meclofenamate, as well as by renal denervation, although not significantly. Additionally, renal nerves mediated hemodynamic effects of hypertension that were produced by intrarenal infusion of ADM. This study establishes an important mechanistic role for renal prostaglandins as a mediator of ADM-mediated natriuresis at the level of the glomerulus and terminal nephron.

Previous studies have demonstrated that the biological actions of atrial natriuretic factor (ANF) are mediated via increases in its intracellular second messenger guanosine 3',5'-cyclic monophosphate (cGMP). Because cGMP egresses rapidly from target cells after ANF binding to particulate guanylate cyclase-linked receptors, extracellular cGMP may be a useful biological marker for the action of ANF in vivo under pathophysiological conditions. The present studies tested the hypothesis that the avid sodium retention and renal ANF resistance characteristic of chronic congestive heart failure (CHF) are associated with attenuated renal cGMP responses to ANF. We assessed the natriuretic and cGMP responses to endogenous and exogenous ANF during the evolution of CHF produced by 6 days of rapid ventricular pacing in conscious dogs (n = 6). Simultaneous measurement of plasma and urinary cGMP concentrations allowed determination of the net renal generation of cGMP, an indicator of the renal contribution to total urinary cGMP excretion. In early CHF, increased sodium excretion and renal cGMP production were observed in association with increases in plasma ANF. Exogenous ANF administration (10 micrograms/kg iv) before CHF also produced parallel increases in sodium excretion and renal cGMP production. In more advanced CHF produced by 6 days of pacing, we observed avid sodium retention in association with reversal of earlier increases in renal cGMP production despite progressive increases in circulating ANF. Natriuretic and renal cGMP responses to exogenous ANF were similarly attenuated in chronic CHF. These studies suggest that 1) renal cGMP production is a useful biological marker for the renal natriuretic action of ANF; 2) endogenous ANF contributes to the maintenance of sodium excretion in early CHF via increases in renal cGMP production; and 3) the avid sodium retention and renal ANF resistance in advanced CHF are, in part, linked to attenuated renal cGMP responses to endogenous and exogenous ANF.

Studies were performed in anesthetized dogs to determine plasma endothelin (ET) concentrations in the presence and absence of experimental congestive heart failure (CHF) produced by rapid ventricular pacing for 8 days. These studies were also designed to determine the effect of exogenous low-dose ET upon integrated cardiorenal and endocrine function in the presence and absence of CHF. In these studies, plasma ET was significantly elevated in CHF (3.25 +/- 0.39 pg/ml) compared with normal (1.03 +/- 0.21 pg/ml) or sham-operated (1.08 +/- 0.27 pg/ml) groups. Compared with the control group, which was characterized by a significant cardiorenal vasoconstrictor response to low-dose ET, a significant attenuation of the vasoconstrictor and antinatriuretic actions of ET was observed in the CHF group. Despite these differential responses, exogenous ET suppressed plasma renin activity (PRA) and activated aldosterone in both control and CHF groups. Thus these studies demonstrate for the first time that experimental CHF is characterized by elevated plasma ET in association with an attenuated cardiorenal response to exogenous ET. In contrast, low-dose ET inhibited PRC and activated aldosterone in the presence and absence of experimental CHF.

Atrial natriuretic factor (ANF) is a circulating 28-amino acid peptide that functions in the regulation of sodium homeostasis and vascular tone. ANF metabolism occurs via degradation by neutral endopeptidase 24.11 and binding to the ANF clearance receptor (ANFR-C). The present study was performed on anesthetized dogs, normal (control) and with experimental congestive heart failure (CHF), and was designed to investigate the ability of an ANF ligand specific for ANFR-C [C-ANF-(4-23)] to increase plasma ANF and also to evaluate the influence of ANFR-C on regional pulmonary and renal ANF clearances. C-ANF-(4-23) increased plasma ANF in controls (51 +/- 15 to 123 +/- 39 pg/ml; P < 0.05) and further increased plasma ANF in CHF dogs (242 +/- 30 to 327 +/- 34; P < 0.05), demonstrating that ANFR-C plays a significant role in the overall metabolism and clearance of ANF, even with chronically elevated ANF. Infusion of C-ANF-(4-23) produced a marked decrease in ANF pulmonary clearance (PCLANF) in controls (1,018 +/- 405 to -286 +/- 383 ml/min; P < 0.05); however, PCLANF was not altered by the ANF ligand in CHF dogs [-137 +/- 174 to -106 +/- 226 ml/min; not significant (NS)], suggesting an occupancy of ANFR-C or a downregulation of this receptor with chronically elevated plasma ANF. ANF renal clearance (RCLANF) was not altered in either group by C-ANF-(4-23) infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

The endothelium is the production site of several potent vasoactive substances that modulate vascular tone and growth. The present study was undertaken to investigate the presence and secretion of atrial natriuretic peptide (ANP) immunoreactivity from vascular endothelial cells. ANP immunoreactivity was present in cultured human aortic endothelial cells by both immunohistochemical staining and radioimmunoassay. ANP immunoreactivity was also detectable in culture medium from human aortic endothelial cells in low picogram concentrations. These findings suggest that vascular endothelium is a site of ANP production and secretion of ANP. There was a differential distribution of ANP and endothelin-1 (ET-1), with a higher ANP concentration in cell extracts and a higher ET-1 concentration in cell culture media. Although ANP has been conceived as a circulating endocrine hormone, these findings are consistent with ANP functioning also as an autocrine and paracrine modulator in the regulation of vascular tone and growth.

Atrial natriuretic peptide is an important peptide hormone of cardiac origin that functions to regulate cardiac preload via the regulation of sodium excretion. This natriuretic action occurs through activation of the particulate guanylyl cyclase-linked natriuretic peptide-A receptor. HS-142-1 is a newly discovered antagonist of the natriuretic peptide-A receptor that permits insight into the functional role of atrial natriuretic peptide in cardiorenal homeostasis. The first objective of this study was to define for the first time the intrarenal action of HS-142-1 on exogenous atrial natriuretic peptide-mediated natriuresis in anesthetized normal dogs. In group 1 (n = 6), which received intravenous atrial natriuretic peptide at 100 ng/kg per minute, intrarenal HS-142-1 (0.5 mg/kg bolus) attenuated atrial natriuretic peptide-induced increases in glomerular filtration rate, urine flow, sodium excretion, and renal cyclic GMP generation and decreases in distal tubular sodium reabsorption. The second objective was to determine whether endogenous atrial natriuretic peptide participates in the regulation of basal sodium excretion. In group 2 (n = 6), intrarenal HS-142-1 alone decreased both absolute and fractional sodium excretion and renal cyclic GMP generation and increased distal tubular sodium reabsorption. These studies demonstrate that HS-142-1 markedly attenuates exogenous atrial natriuretic peptide-mediated natriuresis via enhancement of distal tubular reabsorption and blunting of increases in glomerular filtration rate. Second, the current studies support a functional role for endogenous atrial natriuretic peptide in the regulation of basal sodium excretion.