The heartmate left ventricular assist system: first successful implantation in Missouri

We report a case of the first successful implantation of the HeartMate left ventricular assist system as a bridge to heart transplant in the state of Missouri. Indications, technique of insertion, patient selection, outcomes and future applications are discussed.

Renal effects of leptin in normotensive, hypertensive, and obese rats

The hemodynamic, hormonal, and renal excretory effects of intravenous bolus administration of synthetic murine leptin were examined in groups of anesthetized normotensive (Sprague-Dawley), hypertensive (spontaneously hypertensive), and both lean and obese Zucker rats. In the normotensive animals (n = 8) an intravenous bolus of 400 microgram/kg of leptin produced a significant six- to sevenfold elevation in sodium excretion compared with controls (n = 8). The onset of natriuresis was delayed for approximately 30-45 min. Mean arterial pressure (MAP), creatinine clearance, plasma renin activity (PRA), and plasma aldosterone concentration (PAC) remained unchanged. In contrast, the hypertensive rats were refractory to the natriuretic effects of leptin when infused either with 400 (n = 8) or 1,600 (n = 8) microgram/kg. Also in these animals MAP, creatinine clearance, PRA, and PAC were unmodified. Finally, whereas lean Zucker rats (n = 8) responded very similarly to the Sprague-Dawley animals, the natriuretic effect of the hormone was attenuated in the obese Zucker groups. At 400 microgram/kg (n = 8) no natriuresis was elicited, but at 1,600 microgram/kg (n = 8) a modest but significant two- to threefold increment in sodium excretion was observed in the obese rats. In both Zucker groups, MAP, creatinine clearance, PRA, and PAC were unchanged. Collectively, these results demonstrate a significant natriuretic effect of exogenous leptin in the normal rat and a blunted saluretic response in hypertension and obesity. It is suggested that leptin may be a potential salt-excretory factor in normal rats and may function pathophysiologically in obesity and hypertension.

Indomethacin attenuates the renal actions of atrial natriuretic factor in dogs with chronic heart failure

The interaction between renal prostaglandins and atrial natriuretic factor (ANF) for the regulation of renal hemodynamic and excretory function was examined in conscious dogs with arteriovenous fistula and chronic compensated high-output heart failure (n = 6). After two control clearance periods, 100 ng/kg/min ANF was administered for the duration of the study. After two clearance periods with ANF infusions, 10 mg/kg indomethacin intravenous bolus was given, and three additional clearance periods were obtained. Atrial natriuretic factor alone increased sodium excretion from a baseline of 25 +/- 7 microEq/min to 158 +/- 24 microEq/min (P < 0.05), whereas creatinine clearance was elevated by 9 mL/min (P < 0.05). Indomethacin reduced ANF-induced sodium excretion and creatinine clearance by 75% (P < 0.05) and 35% (P < 0.05), respectively. In a time control series in dogs with arteriovenous fistula (n = 4), indomethacin vehicle did not alter ANF-induced natriuresis or renal hemodynamic function. These results suggest a modulatory role of the prostaglandins on the renal response to ANF infusions in this canine model of compensated heart failure.

Pressure-dependent renin release during chronic blockade of nitric oxide synthase

We evaluated pressure-dependent stimulation of renin release in rats with sustained hypertension induced by chronic blockade of nitric oxide synthase with N omega-nitro-L-arginine methyl ester (L-NAME) for 5 to 7 days. Rats were anesthetized and catheters were inserted into the carotid artery and abdominal aorta for measurement of arterial pressures. An adjustable snare was placed around the suprarenal aorta, and this snare was tightened to reduce renal perfusion pressure. Pressure-dependent renin release was evaluated in hypertensive rats by reducing renal perfusion pressure to 125, 85, and 65 mm Hg. Renin release was also evaluated in normotensive control rats at these same pressures. Basal systemic arterial pressures averaged 159 +/- 3 and 124 +/- 4 mm Hg (P < .001), respectively, in the L-NAME-treated (n = 22) and normotensive control (n = 18) rats. Basal plasma renin activity was lower in L-NAME than control rats (5.0 +/- 0.3 versus 9.5 +/- 1.3 U, P < .01), and plasma renin activity was markedly attenuated at all comparable levels of renal perfusion pressure. Maximal plasma renin activity levels were achieved at perfusion pressures reduced to 65 mm Hg, and plasma renin activity averaged 14 +/- 2 and 34 +/- 7 U (P < .01) in L-NAME hypertensive and control rats, respectively. However, infusion of the nitric oxide donor sodium nitroprusside similarly stimulated plasma renin activity levels to 39 +/- 3 and 45 +/- 3 U (P > .05), in the hypertensive and normal control groups, respectively. Overall, these findings are consistent with the hypothesis that prolonged L-NAME administration attenuates pressure-dependent renin release by inhibiting nitric oxide formation, which may function as a paracrine mechanism inversely linking renal perfusion pressure with the stimulation of renin release.

Nitric oxide donors improve gut function after prolonged hypothermic ischemia

The objective of this study was to determine whether the nitric oxide (NO) donors, spermine NO and 3-morpholinosydonimine-N-ethyl-carbamide (SIN1), alter the mucosal and microvascular responses of the feline small intestine to 6 hr of hypothermic ischemia and 2 hr of normothermic reperfusion. Intestinal mucosal permeability was monitored using the blood-to-lumen clearance of 51Cr-EDTA. Lymph flow and lymphatic protein clearance estimates were used to assess intestinal microvascular fluid filtration and vascular protein leakage, respectively. Spermine NO (0.1 mmol/L) or SIN1 (0.5 mmol/L) was added to the luminal perfusate during the entire reperfusion period. Both NO donors were effective in attenuating the increased mucosal permeability to 51Cr-EDTA and the depressed net water absorption, relative to untreated intestinal preparations exposed to the same protocol. Intestinal lymph flow, lymphatic protein clearance, and capillary hydrostatic pressure were increased by a greater extent in preparations treated with spermine NO. These findings suggest that NO donors may improve mucosal function in intestinal allografts subjected to prolonged hypothermic ischemia. This protective effect on mucosal epithelium appears to be unrelated to an action of the NO donors on the microvasculature.

Atrial natriuretic peptide fragments in dogs with experimental heart failure

1. This study in the canine arteriovenous (AV) fistula model of high-output heart failure (HOHF) evaluated the chronic temporal changes in plasma ANF and pro ANF 31-67 and their relationship to body-fluid balance and the renin-aldosterone axis. In addition, the haemodynamic, hormonal and renal excretory effects of synthetic pro ANF 31-67 infusions were examined in normal and AV fistula dogs with compensated HOHF. 2. Following the construction of the AV fistula, the dogs exhibited chronic parallel elevations in right atrial pressure and the plasma concentrations of ANF and pro ANF 31-67. The gradual increases in the two peptides were associated with a gradual decrease in plasma renin activity and the re-establishment of sodium balance. 3. In normal and compensated AV fistula dogs, synthetic pro ANF 31-67 produced similar significant reductions in arterial blood pressure, right atrial pressure and elevations in urinary sodium excretion. These effects were not associated with increases in plasma or urinary cyclic GMP (cGMP). 4. These results suggest that the elevation in the endogenous circulating levels of pro ANF 31-67 in the AV fistula dogs may represent one chronic adaptive mechanism to achieve body fluid homeostasis. Furthermore, via potentially different mechanisms of action, ANF and pro ANF 31-67 may coordinate and contribute to the regulation of haemodynamic and renal function during physiological and pathophysiological situations.

Calcitonin gene-related peptide and the kidney

Calcitonin gene-related peptide (CGRP) is a recently discovered neurotransmitter that is extensively localized in fibers innervating vascular and endocrine systems. CGRP possesses potent vasorelaxant effects, and a role for this peptide in the regional regulation of blood flow has been suggested. Although pharmacologic evidence indicates that the renal vasculature is very sensitive to CGRP, the physiologic actions of this peptide on the kidney have not yet been fully elucidated. This short review focuses on relevant experimental and clinical information of the direct and indirect effects of CGRP on renal function with an emphasis on hemodynamics, sodium excretion, and the renin-angiotensin system.

Effects of renal denervation on postprandial sodium excretion in experimental heart failure

The hormonal, hemodynamic and renal excretory changes after an oral load of sodium were examined in renal-denervated dogs with an arteriovenous (AV) fistula and the syndrome of compensated high-output heart failure. After ingestion of a meal containing 125 meq of sodium, the total postprandial urinary sodium excretion and fractional sodium excretion were approximately twofold higher in the renal-denervated AV fistula dogs, compared with a control group with intact renal nerves (P < 0.05). The postprandial elevations in right atrial pressure, plasma atrial natriuretic factor, and filtered load of sodium were similar in the two groups (P > 0.05). Mean arterial pressure and plasma renin activity remained unchanged from baseline in the two subsets of animals (P > 0.05). In the renal-denervated AV fistula dogs, ingestion of a low-salt meal containing 2-3 meq of sodium produced elevations in creatinine clearance and filtered load of sodium of similar magnitude to the high-salt meal. However, the increases in sodium excretion and plasma atrial natriuretic factor were modest and inconsistent. These results demonstrate that the renal nerves play an important modulatory role for postprandial sodium metabolism after a high-salt meal in experimental compensated high-output heart failure. It is suggested that the renal nerves attenuate the expression of postprandial natriuretic mechanisms via a direct tubular mechanism of action.

Urinary angiotensin II: a marker of renal tissue activity?

The methodology for the collection, extraction, separation and measurement of urinary angiotensin II [the octapeptide, ANG(1-8)] is described. To determine the origin of urinary ANG(1-8), mean arterial pressure, renal hemodynamics and the arterial, renal venous and urinary concentrations of ANG(1-8) were examined prior to and following the constant intra-arterial infusion of tritiated angiotensin II [3H-ANG(1-8)] in graded doses of 0.5, 2.0 and 2.5 ng/kg/min in 5 uninephrectomized, anesthetized female dogs. The infusion of 3H-ANG-(1-8) had no significant effect on mean arterial pressure, glomerular filtration rate, renal blood flow or urine flow rate. The mean concentration of ANG(1-8) in the urine was 3.7 fmol/ml. None or only trace amounts of 3H-ANG(1-8) were detected in the urine in spite of marked increases in renal arterial 3H-ANG(1-8) concentrations. These observations suggest that urinary ANG(1-8) was derived de novo from the intrarenal generation of angiotensin II. In addition, plasma and urinary concentrations of ANG(1-8) were assessed in patients with essential hypertension undergoing treatment with either a diuretic (n = 14) or an angiotensin-converting enzyme inhibitor (n = 14). Although the concentrations of plasma ANG(1-8) responded appropriately to the respective therapies, the urinary excretion of ANG(1-8) was not different following either therapy. These data suggest that ANG(1-8) collected from the urinary bladder may not occur in adequate concentrations to accurately assess the activity of the intrarenal renin-angiotensin system.

Renal tissue angiotensin II: response to infusions of angiotensin I and an angiotensin-converting enzyme inhibitor

A procedure for the collection, processing, extraction, separation, and measurement of renal tissue angiotensin II [ANG-(1-8)] is described. The arterial plasma and renal tissue concentrations of ANG-(1-8) were examined in anesthetized Sprague-Dawley male rats (10 to 12 weeks of age) given an intravenous saline infusion (group 1; n = 6), an intravenous bolus infusion of 0.5 microgram angiotensin I (group 2; n = 6), or an intravenous bolus of an angiotensin-converting enzyme inhibitor (group 3; n = 6). Plasma and renal tissue were collected at the peak mean arterial pressure (MAP) response. The mean (+/- SEM) concentration of ANG-(1-8) in the group given the saline vehicle was 12 +/- 2 fmol/mL in the plasma and 2.4 +/- 0.3 pmol/g in the renal tissue. The angiotensin I bolus significantly increased MAP by 40%. Following the angiotensin I infusion, at the time of peak MAP response, the concentration of the circulating and renal tissue ANG-(1-8) were 12-fold and twofold higher, respectively, compared with the saline vehicle. The angiotensin-converting enzyme inhibitor significantly decreased MAP by 10% and decreased the circulating and renal tissue ANG-(1-8) levels by 75% and 62.5%, respectively, compared with the saline vehicle. The rapid conversion of exogenous angiotensin I to ANG-(1-8) in renal tissue provides direct evidence that renal tissue can generate de novo ANG-(1-8) from a circulating precursor. Furthermore, plasma and renal tissue respond similarly to acute angiotensin-converting enzyme inhibition.

Neurohumoral modulators and sodium balance in experimental heart failure

The acute and chronic interactions of the renal nerves, atrial natriuretic factor (ANF), and mineralocorticoids for the regulation of sodium balance were examined in dogs with an arteriovenous (AV) fistula and the syndrome of high-output heart failure (HOHF) (n = 6). After the AV fistula and bilateral renal denervation, the animals avidly retained sodium for 5-7 days and then regained sodium balance for the subsequent 3 wk. This compensation was associated with the sustained elevations of plasma ANF and the normalization of plasma renin. Subsequent administration of deoxycorticosterone acetate (DOCA) for 10 days produced consistent sodium retention despite additional elevations in plasma ANF. All of these responses were similar to previous studies in AV fistula dogs with intact renal nerves. In a separate part of the study, the renal actions of acute synthetic ANF infusions were examined in these renal-denervated AV fistula dogs before and after DOCA. In the pre-DOCA experiments, ANF infusions at 15, 30, and 100 ng.kg-1.min-1 produced dose-related increases in urinary sodium excretion and significant elevations in creatinine clearance. In the presence of DOCA, urinary sodium excretion was markedly attenuated during identical ANF infusions. The composite results suggest that mineralocorticoids have an important modulatory role for the regulation of sodium balance in experimental HOHF. However, compared with earlier studies in compensated AV fistula dogs with intact renal nerves, the present studies demonstrate that blockade of efferent renal sympathetic nerve activity can restore the natriuretic expression of acute elevations in circulating ANF.

Role of aldosterone in congestive heart failure

Antialdosterone therapy in patients with secondary hyperaldosteronism due to myocardial failure must accomplish the following: (1) reduce or preferably normalize plasma aldosterone levels by blockade of excessive synthesis, (2) antagonize the renal and systemic effects of aldosterone at its receptor sites, and (3) minimize the presence of multiple stimuli to aldosterone secretion. Fulfillment of these goals likely requires the blockade of angiotensin II-induced aldosterone secretion (ie, angiotensin-converting enzyme inhibition) with an antagonist of aldosterone receptors (ie, spironolactone [Aldactone]). Despite the potential for hyperkalemia with this combined use of medications, particularly in patients with impaired renal function, such therapy is likely to attenuate the salt-acquisitive state that is characteristic of myocardial failure.

An evaluation of the renal protective effect of manidipine in the uninephrectomized spontaneously hypertensive rat

The effects of calcium antagonism on the development and progression of renal disease are controversial. To address this problem, studies were performed on young, uninephrectomized spontaneously hypertensive rats (SHRs) with the dihydropyridine calcium antagonist, manidipine, to assess its effect on the early pathogenesis of focal glomerulosclerosis. Male SHRs underwent uninephrectomy at age 10 to 11 weeks and were subsequently assigned to no treatment (control), a predetermined subvasodepressor (low) dose of manidipine (2.5 mg/kg body weight), or a predetermined antihypertensive (high) dose of manidipine (20 mg/kg body weight). All animals received a diet containing 0.4% sodium and 23% protein. Serial determinations of body weight, systolic tail cuff pressure, and 24-hour urinary excretion of creatinine, sodium, and protein (UprotV) were made at 1- to 6-week intervals, for a total treatment period of 12 weeks. In final experiments plasma was obtained for creatinine, angiotensin I, and angiotensin II determinations, and renal tissue was harvested for histologic and morphometric analysis. Compared with the untreated control, low-dose manidipine therapy had no effect on body weight, systolic blood pressure, creatinine clearance, UprotV, renal histologic findings, glomerular volume, or plasma angiotensin I or II concentrations. In contrast, high-dose manidipine therapy decreased systolic blood pressure from 194 +/- 3 to 160 +/- 4 mm Hg (p < 0.01). Creatinine clearance and UprotV were unchanged. Although body weight was not different, kidney weight was higher. However, mean glomerular volume was lower. More importantly, the prevalence of mesangial expansion with proliferation was lower: 6.7% (control) versus 2.8% (high-dose manidipine) (p < 0.01). Finally, plasma angiotensin I and angiotensin II concentrations did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone and antialdosterone therapy in congestive heart failure

The pathophysiologic cycle that links myocardial failure with the appearance of congestive heart failure is not fully understood. It is clear, however, that an activation of several neurohormonal systems and the interplay between kidneys, adrenal glands, and heart contribute to abnormal sodium and water homeostasis. Aldosterone, the body's most potent mineralocorticoid hormone, contributes to intravascular and extravascular volume expansion, and thus to the appearance of symptomatic failure. Antialdosterone therapy in patients with secondary hyperaldosteronism due to heart failure must achieve one or more of the following goals: reduce or, preferably, normalize plasma aldosterone levels by limiting synthesis; antagonize the renal and systemic effects of aldosterone at its receptor sites; and eliminate or minimize the multiple stimuli to aldosterone secretion.

Captopril enhances renal responsiveness to ANF in dogs with compensated high-output heart failure

The systemic hemodynamic, hormonal, and renal effects of chronic angiotensin-converting enzyme inhibition (CEI) with captopril and the responses to synthetic atrial natriuretic factor (ANF) infusions in the presence and absence of captopril were examined in normal dogs (n = 6) and in dogs with an arteriovenous (AV) fistula and compensated high-output heart failure (n = 6). This experimental model is characterized by normalization of the circulating renin-angiotensin-aldosterone system (RAAS) and persistent elevations in central filling pressures and plasma ANF. In both normal and AV-fistula dogs, oral captopril for 1 wk at 35 mg.kg-1.day-1 in three divided doses produced progressive reductions in arterial and atrial pressures (P less than 0.05), plasma ANF (P less than 0.05), and aldosterone (P less than 0.05). After 1-2 days of a modest increase in urinary sodium excretion (UNaV) (P less than 0.05), all of the dogs regained and maintained sodium balance during captopril administration. On the 8th day of the captopril regimen, synthetic ANF was infused at 15 and 30 ng.kg-1.min-1 for 75-min periods each. Control infusion experiments were performed in the same animals before captopril administration. The normal dogs exhibited dose-related elevations in UNaV (P less than 0.05) that were not augmented with captopril (P greater than 0.05). In contrast, in the AV-fistula dogs the observed renal unresponsiveness to synthetic ANF in the control experiments was reversed with chronic CEI, and ANF-induced UNaV achieved levels comparable to those obtained in the normal animals.(ABSTRACT TRUNCATED AT 250 WORDS)

ANF and the renin-angiotensin system in the regulation of sodium balance: longitudinal studies in experimental heart failure

Over the last three decades the role of the renin-aldosterone axis for the renal conservation of sodium has become well established. In the last several years information has accumulated to indicate that ANF is an important complementary hormonal system involved in the elimination of sodium surfeit. Evidence has been presented to suggest that ANF and the renin-aldosterone axis function in an integrated manner for the regulation of sodium balance, with their primary actions exerted in the postprandial and postabsorptive phases, respectively. It is interesting that this hormonal integration continues to be operational during the compensated stage of experimental heart failure but at the expense of a higher level of activity of the ANF system. The significance of ANF as a compensatory mechanism in chronic heart failure remains to be fully elucidated, although the available longitudinal data in experimental animal models suggest that the role of ANF in the maintenance of sodium balance should be most apparent during the early and mild stages of heart failure, before a marked reduction in cardiac performance leads to an excessive activation of the renin-aldosterone axis that in turn can effectively override the natriuretic actions of ANF.

Renal effects of ANF (95-126), a new atrial peptide analogue, in dogs with experimental heart failure

Atrial natriuretic factor 95-126 [ANF (95-126)] is a novel 32 amino acid peptide which is thought to originate from the kidney. The systemic hemodynamic and renal effects of equimolar doses of intravenous synthetic ANF (95-126) and synthetic alpha ANF (99-126) were examined in normal dogs (n = 6) and in dogs with an arteriovenous (AV) fistula and chronic compensated high-output heart failure (n = 5). ANF (95-126) and alpha ANF (99-126) were infused at 5 and 10 pmol/kg/min for 75-min periods each. In the normal and AV fistula dogs the two peptides similarly decreased mean arterial pressures and right atrial pressures (P less than .05). Creatinine clearance and urinary volume excretion increased (P less than .05) in the normal dogs with both peptides, but only ANF (95-126) produced significant elevations (P less than .05) of these two parameters in the AV fistula animals. With the highest infusion dose, ANF (95-126) increased urinary sodium excretion to at least twice the levels observed with alpha ANF (99-126) in both groups of dogs (P less than .05). The decreases in plasma renin and aldosterone were comparable for the two peptides in both groups of animals. These results indicate that ANF (95-126) is more potent than alpha ANF (99-126) for the promotion of a natriuresis, particularly in AV fistula dogs with compensated high-output heart failure, in which the sodium excretory actions of alpha ANF (99-126) were attenuated markedly.

The atrial natriuretic factor hormonal system in the regulation of sodium excretion in dogs with experimental heart failure

In response to a meat meal containing 125 mEq of sodium, conscious dogs (n = 5) with an arteriovenous (AV) fistula and chronic compensated heart failure exhibited temporally related increases in postprandial plasma immunoreactive atrial natriuretic factor (iANF), right atrial pressure, and sodium excretion. In separate experiments, two weeks of dietary sodium restriction produced similar marked stimulation of renin and aldosterone both in normal dogs (n = 5), and in AV fistula dogs (n = 5) with chronic high circulating levels of ANF. Plasma iANF did not change (P greater than .05) in either group. These results suggest that the ANF system is involved in the postprandial regulation of sodium excretion in the AV fistula dogs with compensated heart failure. In the postabsorptive state, however, the activity of the renin-aldosterone axis is closely related to dietary sodium intake and appears to function independently of the ANF system for the prevention of sodium loss.

Intrarenal metabolism of angiotensin II

This study investigated the intrarenal metabolism of circulating angiotensin II. Mean arterial pressure (MAP), renal hemodynamics, and the arterial, renal venous, and renal tissue concentrations of the angiotensin octapeptide [ANG-(1-8)] were examined following the constant intra-arterial infusion of tritiated angiotensin II [( 3H]ANG-(1-8)] in graded doses of 0.5, 2.0, and 2.5 ng.kg-1.min-1 in five uninephrectomized, anesthetized female dogs. The infusion of [3H]ANG-(1-8) had no significant effect on MAP, glomerular filtration rate, renal blood flow, or urine flow rate. The mean degradation rate of intra-arterially infused [3H]ANG-(1-8) was 72%. The net renal venous plasma concentration of ANG-(1-8) was greater than that predicted from the degradation rate of [3H]ANG-(1-8). High concentrations of ANG-(1-8) were measurable in all renal tissues. However, [3H]ANG-(1-8) was not detectable in any renal tissue. These observations suggest that ANG-(1-8) in the renal venous effluent was derived, in part, de novo from intrarenal generation. Likewise, renal tissue ANG-(1-8) was derived de novo from intrarenal generation.