Burnett, John C.

The particulate guanylyl cyclase A (pGC-A)/cGMP pathway plays important roles in regulating renal physiological function and as well as in counteracting pathophysiological conditions. Naturally occurring peptide pGC-A activators consist of atrial natriuretic peptide (ANP), b-type NP (BNP), and urodilatin (URO). These activators bind and activate pGC-A, generating the second messenger cyclic 3′,5′ guanosine monophosphate (cGMP). Cyclic GMP binds to downstream pathway effector molecules including protein kinase G (PKG), cGMP-gated ion channels, and phosphodiesterases (PDEs). These mediators result in a variety of physiological actions in the kidney, including diuresis, natriuresis, increased glomerular filtration rate (GFR) and organ protection, thus, opposing renal cellular injury and remodeling. Downstream proteins regulated by PKG include collagen 1 (Col-1), transforming growth factor beta (TGF-β) and apoptosis-related proteins. In addition to their physiological regulatory effects, pGC-A/cGMP signaling is critical for preserving renal homeostasis in different renal diseases such as acute kidney injury (AKI). Regarding therapeutic options, native pGC-A activators have short half-lives and their activity can be further enhanced by advances in innovative peptide engineering. Thus, novel designer peptide pGC-A activators with enhanced renal activity are under development.

Endothelin-1 (ET-1) is a peptide that has been implicated in congestive heart failure (CHF). Although increased concentrations of circulating ET-1 have been repeatedly demonstrated, the activation of local ET-1 in target tissues of CHF remains poorly defined. Our objective was to characterize ET-1 tissue concentrations and gene expression of prepro ET-1 in myocardial, renal, and pulmonary tissue in rapid ventricular pacing-induced canine CHF. Progressive rapid ventricular pacing (38 days) resulted in impaired cardiovascular hemodynamics, increased atrial and left ventricular mass, decreased renal sodium excretion, and increased ET-1 plasma concentrations (all P < 0.05). Tissue analysis revealed significant increases in local ET-1 during CHF in left ventricular, renal, and pulmonary tissue, whereas a moderate increase in left atrial ET-1 did not reach statistical significance. In contrast, prepro-ET-1 gene expression was increased more than threefold in pulmonary tissue and more than twofold in left atrial myocardium with no increase in left ventricular or renal gene expression. The present studies demonstrate a differential pattern of ET-1 activation in cardiorenal and pulmonary tissue with a strong accumulation of ET-1 in kidney and lung during CHF. Although the observed increase in left ventricular and renal ET-1 in association with unaltered gene expression is consistent with increased uptake, pulmonary and atrial tissue may contribute to increased circulating and local ET-1 in CHF.

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)

The endothelin (ET)-B receptor subtype is expressed on vascular endothelial and smooth muscle cells and participates in vasodilatation and vasoconstriction. Controversy exists regarding the role of the ET-B receptor as a mediator of systemic, pulmonary, and renal vasoconstriction in states of marked ET-1 activation. Moreover, the potential activation of endogenous ET-1 with secondary stimulation of the ET-A receptor in response to sarafotoxin S6c (S6c) remains unclear. This study was designed to assess the cardiovascular actions of ET-B activation with S6c in the presence and absence of selective ET-A antagonism with FR-139317 and dual ET-A/ET-B antagonism with SB-209670 in the anesthetized dog. Compared with time control ( n = 5), S6c increased from baseline systemic vascular resistance (SVR) [28 ± 7 vs. 14 ± 3 resistance units (RU), P < 0.05] and pulmonary vascular resistance (PVR) (3.2 ± 0.7 vs. 0.9 ± 0.3 RU, P < 0.05) and decreased cardiac output (CO) (−1.7 ± 0.3 vs. −0.5 ± 0.1 l/min, P < 0.05), with no differences in renal vascular resistance in association with increases in plasma ET-1. S6c also decreased mixed venous oxygen saturation ([Formula: see text]) (56 ± 6 vs. 76 ± 5%, P < 0.05). Selective ET-A receptor antagonism did not affect the actions of S6c, with the exception that ET-A receptor antagonism blocked the increase in SVR to high-dose S6c. Dual ET-A/ET-B receptor antagonism attenuated the increase from baseline in SVR (7 ± 1 vs. 28 ± 7 RU, P < 0.05) and PVR (0.7 ± 0.2 vs. 3.2 ± 0.7 RU, P < 0.05) and decrease from baseline in CO (−0.9 ± 0.1 vs. −1.7 ± 0.3 l/min, P < 0.05) and[Formula: see text] (−7 ± 3 vs. −20 ± 3%, P < 0.05) observed with S6c alone. In summary, this study demonstrates an important role of ET-B receptor activation in vivo, which results in increases in plasma ET-1 and systemic and pulmonary vasoconstriction and reductions in CO and [Formula: see text]. This study also supports a modest role for the ET-A receptor in mediating the systemic vasoconstrictor response to high-dose S6c.

Circulating atrial natriuretic factor (ANF) is regulated by clearance receptors (ANFR-C). C-ANF-(4-23) is a ring-deleted analogue of ANF, which binds specifically to ANFR-C. The present studies were undertaken to determine total metabolic (TMCR), pulmonary (PCR), and renal clearance rates (RCR) of ANF in a group of seven mongrel dogs in chronic congestive heart failure (CHF) in comparison with a control group (n = 6). TMCR was not altered in CHF [1,534 +/- 319 vs. control: 1,735 +/- 208 ml/min; P = not significant (NS)] in association with an elevation of circulating endogenous ANF (206 +/- 44 vs. control: 36 +/- 10 pg/ml; P < 0.01). Infusion of C-ANF-(4-23) reduced TMCR in both groups similarly (CHF: 753 +/- 134 vs. control: 972 +/- 156 ml/min; P = NS). PCR was lower in CHF (286 +/- 431 vs. 1,672 +/- 407 ml/min; P < 0.05), whereas RCR was not different (10 +/- 24 vs. control: 15 +/- 25 ml/min; P = NS). ANFR-C blockade did not facilitate urinary sodium excretion in CHF. These studies demonstrate that 1) TMCR does not contribute to elevated endogenous ANF in CHF; 2) total functional activity of the clearance receptor pathway is preserved in CHF; and 3) renal ANF metabolism and the clearance receptor pathway are not linked to the avid sodium retention and renal ANF resistance observed in chronic CHF.