Effect of monoclonal anti-ANP antibodies on the acute functional adaptation to unilateral nephrectomy

Kidney glomerular filtration rate plasticity after transplantation

Since the first living donor kidney transplantation about six decades ago, significant progress has been made in terms of extending allograft survival. However, to date, only a small number of studies have compared the functional changes of the donated kidney to that of the remaining kidney. Although relatively small, the study by Gonzalez Rinne et al. demonstrated the adaptive capacity of the transplanted kidney in 30 donor-recipient pairs. The glomerular filtration rate (GFR) in both donors and recipients was obtained 12 months after transplantation and the authors identified three scenarios: (i) where donors had a higher GFR than recipients; (ii) where donors had a lower GFR than recipients; and (iii) where donors had a similar GFR to recipients. The mechanisms mediating GFR adaptability after kidney transplantation seem to be associated with body surface area (including sex differences in body surface area). Microstructural analysis of human and animal models of renal physiology provides some clues to the physiological adaptation of the transplanted organ. The nephron number from endowment and age-related loss and the adaptive ability for compensatory glomerular hyperfiltration likely play a major role.

Clinical value of natriuretic peptides in chronic kidney disease

According to several lines of evidence, natriuretic peptides (NP) are the main components of a cardiac-renal axis that operate in clinical conditions of decreased cardiac hemodynamic tolerance to regulate sodium homeostasis, blood pressure and vascular function. Even though it is reasonable to assume that NP may exert a relevant role in the adaptive response to renal mass ablation, evidence gathered so far suggest that this contribution is probably complex and dependent on the type and degree of the functional mass loss. In the last years NP have been increasingly used to diagnose, monitor treatment and define the prognosis of several cardiovascular (CV) diseases. However, in many clinical settings, like chronic kidney disease (CKD), the predictive value of these biomarkers has been questioned. In fact, it is now well established that renal function significantly affects the plasmatic levels of NP and that renal failure is the clinical condition associated with the highest plasmatic levels of these peptides. The complexity of the relation between NP plasmatic levels and CV and renal functions has obvious consequences, as it may limit the predictive value of NP in CV assessment of CKD patients and be a demanding exercise for clinicians involved in the daily management of these patients. This review describes the role of NP in the regulatory response to renal function loss and addresses the main factors involved in the clinical valorization of the peptides in the context of significant renal failure.

Sodium balance and blood pressure response to salt ingestion in uninephrectomized rats

The possible role of extracellular volume (ECV) expansion in prandial/postprandial natriuresis was evaluated in control, sham-operated (SO), and uninephrectomized (UNX) male Wistar rats fed a 0.64 (normal salt, NS) or 8 (high salt, HS) g% NaCl diet for seven days after UNX. We thus determined daily NaCl, diet, and water intake and Evans blue and inulin spaces on day 7. Finally, we determined Na and water clearance after a single i.g. Na load (581 micromol/100 g body weight) under chloralose/ketamine anesthesia in UNX and control HS rats. NaCl, diet, and water intakes were comparable beyond day 5. Plasma volume and ECV were similar in all groups. With NS diet, glomerular filtration rate (GFR) in UNX was compensated but lower than that of SO rats (0.55 vs. 0.74 ml/min per 100 g body weight). Blood pressure (BP) was 111 mm Hg in SO controls and 112 mm Hg in the UNX group. After oral Na loading, BP rose in both groups and remained higher in UNX (134 vs. 126 mm Hg at 15 minutes, 130 vs. 118 mm Hg at 225 minutes). Cumulative Na and water excretions were similar (513 and 610 micromol/100 g body weight, 1.97 and 2.35 ml/100 g body weight in SO and UNX, respectively). Chronically salt-loaded UNX rats seem to maintain dietary Na balance by mechanism(s) other than volume expansion.

Prevention of reflex natriuresis after acute unilateral nephrectomy by melanocortin receptor antagonists

gamma-Melanocyte-stimulating hormone (gamma-MSH), atrial natriuretic peptide (ANP), and oxytocin have been identified as candidate hormonal mediators of the reflex natriuresis that follows acute unilateral nephrectomy (AUN). Pharmacological characterization of the third melanocortin receptor (MC3-R) indicates that it uniquely responds to physiological concentrations of gamma-MSH. We tested the roles of gamma-MSH, ANP, and oxytocin in the postnephrectomy natriuresis by carrying out AUN during continuous intrarenal infusion of specific antagonists for their cognate receptors. In anesthetized Sprague-Dawley rats, urinary sodium excretion (UNaV) increased from 0.34 +/- 0.04 to 1.12 +/- 0.11 mu eq/min 90 min after AUN (P < 0.001). No change in UNaV occurred in rats undergoing a sham AUN procedure. Plasma immunoreactive gamma-MSH concentration was 53 +/- 8 fmol/ml after sham AUN but 112 +/- 17 fmol/ml after AUN (P < 0.01). SHU-9119 and SHU-9005 are substituted derivatives of alpha-MSH with potent antagonism at the MC3-R in vitro. Infusion of these compounds at 5 pmol/min completely blocked the natriuretic response to AUN despite a similar elevation in plasma gamma-MSH (111 +/- 12 vs. 49 +/- 8 fmol/ml in sham rats, P < 0.01). Intrarenal infusion of the ANP receptor antagonist A-71915 (5 pmol/min) or the oxytocin receptor antagonist [d(CH2)(5)1, Tyr(Me)2,Orn8] vasotocin (10 pmol/min) effectively inhibited the natriuresis induced by intravenous infusion of ANP or oxytocin (each at 1 pmol/min), respectively, but did not block the natriuresis after AUN. Plasma immunoreactivity of these peptides was not increased after AUN. These results indicate that reflex natriuresis after AUN is accompanied by an increase in plasma gamma-MSH but not ANP or oxytocin concentration and is prevented by intrarenal infusion of receptor antagonists with selectivity for MC3-R. The data indicate that gamma-MSH or a closely related peptide mediates postnephrectomy natriuresis and provide further support for the possibility that gamma-MSH may play a wider role in sodium homeostasis.

Comparison of antiproliferative effects of atrial natriuretic peptide and transforming growth factor beta on rabbit kidney proximal tubule cells

The effects of atrial natriuretic peptide (ANP) and transforming growth factor beta (TGF beta) on cell proliferation were investigated in rabbit kidney proximal tubule cells. At 48 h, each agonist inhibited cell growth dose dependently. Moreover, the antiproliferative effect of both factors together was greater than that of each factor alone. However, coincubation of a high concentration (100 nM) of ANP and epidermal growth factor (EGF) was found to induce cell hypertrophy. This hypertrophic effect induced by ANP in the presence of EGF was mimicked by 8-BrcGMP but not by various cAMP analogues, at 100 microM, and was independent of the tyrosine kinase inhibitor genistein (10 microM). However, it was inhibited by 100 pM TGF beta. These in vitro results suggest that the antiproliferative effects of ANP and TGF beta may be part of a mechanism to modulate the hyperplastic effect of EGF in the renal proximal tubule during compensatory kidney growth.

Hypertrophy of rabbit proximal tubule cells is associated with overexpression of TGF beta

The expression of transforming growth factor beta (TGF beta) in proximal tubule cells from rabbit kidney cortex after uninephrectomy (UNX) was investigated. Cell protein and [3H]leucine incorporation in these cells were significantly increased, while cell number was decreased, at two weeks following UNX. At this time period after UNX, we found that proximal tubule cells showed a dramatic increase of cytoplasmic immunostaining with a pan-specific anti-TGF beta antibody. This was accompanied by a 3-fold increase in TGF beta 1 mRNA expression in these cells. Furthermore, proximal tubule cells from two-week uninephrectomized rabbits secrete about 2-fold higher TGF beta bioactivity to the cell conditioned medium compared to cells from sham-operated animals. Addition of anti-TGF beta 1, beta 2, beta 3 neutralizing antibody increased the growth of the former cells, and it abolished cell hypertrophy. These results indicate that hypertrophy of proximal tubule cells during compensatory renal growth is associated with overexpression of TGF beta.