Wei, C

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) is a newly described 52-amino acid peptide originally isolated from extracts of human pheochromocytoma and, more recently, detected in human plasma. Based on the report that ADM mRNA and immunoreactivity are present in the kidney, the current study was designed to determine the renal distribution of ADM by immunohistochemistry and the renal biological actions of ADM. In the immunohistochemical studies, the present investigation demonstrated the localization of ADM in glomeruli, cortical distal tubules, and medullary collecting duct cells of the normal canine kidney. In the in vivo studies, ADM was administered (0.25 ng.kg-1.min-1 in group I and 1, 5, and 25 ng.kg-1.min-1 in group II) intrarenally in normal mongrel dogs with the contralateral kidney receiving only saline vehicle. Intrarenal infusion of ADM resulted in a marked diuretic and natriuretic response, whereas the contralateral kidney showed no renal effects. These significant natriuresis and diuresis in the ADM kidney were associated with increases in glomerular filtration rate and fractional sodium excretion and with a decrease in distal tubular sodium reabsorption. Intrarenal infusion of ADM also caused an increase in mean arterial blood pressure and a decrease in heart rate. Plasma concentrations of atrial natriuretic peptide, renin activity, aldosterone, and guanosine 3',5'-cyclic monophosphate were not changed during the infusion of ADM. The current study demonstrates that ADM is present in renal glomerular and tubular cells and is a potent natriuretic peptide that may play an important role in the regulation of sodium excretion.

C-type natriuretic peptide (CNP) is an endothelium-derived peptide that shares structural homology with atrial natriuretic peptide (ANP). CNP causes greater endothelium-independent relaxations in veins compared with arteries. Relaxations to CNP in porcine coronary arteries are mediated by hyperpolarization of the smooth muscle membrane. Experiments were designed to investigate the mechanism(s) by which CNP causes relaxation in canine femoral veins. Rings of canine femoral veins without endothelium were suspended for measurement of isometric force in organ chambers. Concentration-response curves to CNP were obtained in veins contracted with either endothelin-1 (10(-8) M), KCl (40 mM), phenylephrine (10(-6) M) or prostaglandin F2 alpha (2 x 10(-6) M) in the absence and presence of BQ-123 (10(-6) M), NG-monomenthyl-L-arginine (L-NMMA; 10(-4) M), HS-142-1 (10(-5) M), methylene blue (10(-5) M), or potassium channel blockers, tetraethylammonium chloride (TEA; 10(-3) M), charybdotoxin (10(-7) M), glibenclamide (10(-7) M), or apamin (10(-7) M). Relaxations to CNP were significantly attenuated when the tissue was contracted with KCl and endothelin-1. During contraction to either phenylephrine or prostaglandin F2 alpha, relaxations to CNP were inhibited by HS-142-1, methylene blue, TEA, and charybdotoxin, but not by L-NMMA, glibenclamide, or apamin. In separate experiments, guanosine 3',5'-cyclic monophosphate increased twofold within 10-60 s after the addition of CNP (10(-8) M). These data suggest that CNP mediates relaxation of canine femoral veins through activation of large-conduction, calcium-activated potassium channels and activation of particulate and soluble guanylate cyclase.

The present study was undertaken to investigate the presence of C-type natriuretic peptide (CNP) immunoreactivity in cultured human vascular endothelial cells and in human plasma. CNP immunoreactivity was present in cultured human aortic endothelial cells by both immunohistochemical staining and by radioimmunoassay. With the utilization of gel permeation chromatography, this immunoreactivity proved to be consistent with the higher molecular weight CNP-53. CNP immunoreactivity was also present in human plasma (n = 22) at low picogram concentrations (6.5 +/- 0.2 pg/ml) by specific radioimmunoassay. This immunoreactivity was consistent with the lower molecular weight CNP-22 by gel permeation chromatography. These findings suggest that the vascular endothelium may be the site of CNP production. The isolation of different molecular forms of CNP in tissue and plasma may be consistent with a storage form of the peptide in endothelial cells CNP-53, while CNP-22 circulates in plasma. In summary, the present study is consistent with CNP being a peptide of endothelial cell origin.

Congestive heart failure (CHF) is a pathophysiological condition associated with increased plasma levels of atrial natriuretic factor (ANF), a peptide hormone of cardiac origin that participates in the homeostatic control of intravascular volume and vascular tone. Atrial myocytes serve as the principal source of ANF under physiological conditions, although recent studies have demonstrated that ventricular myocardium may also synthesize ANF in models of CHF associated with ventricular hypertrophy. The current study was designed to investigate the roles of atrial and ventricular myocardium to synthesize, store, and release ANF during the evolution of tachycardia-induced CHF in the dog. The present study demonstrates a persistent elevation of plasma ANF during the evolution of CHF. In acute CHF (3 h), plasma ANF increased independent of cardiac ANF synthesis. In chronic CHF (15 and 30 days), plasma ANF is maintained by an increase in atrial synthesis and release of the peptide, without recruitment of ventricular ANF synthesis. The present study demonstrates that in acute CHF the increase in plasma ANF is regulated by release of stored peptide, and in chronic CHF the persistent elevation of plasma ANF is maintained by an increase in atrial synthesis of ANF.