Heparin interferes with the biological effectiveness of atriopeptin

Heparin-Coated Left Heart Bypass: Renal Function and Hormonal Response

The effect of partial (50 mI/min/kg) left heart bypass (LHBP) on renal function, plasma renin activity (PRA), aldosterone, arginine vasopressin and atrial natriuretic peptide (ANP) response was studied in ten anesthetized, open-chested mongrel dogs (weight 23-50 kg) over a period of 6 h. Standard equipment with systemic heparinization (control), initially 300 IU/kg, was employed in five dogs, and heparin-coated equipment without additional heparin in the other five (heparin coated). Urine was continuously collected through a transurethral catheter. Urine samples and pulmonary artery blood samples for hormonal assays were taken at preset intervals before and during LHBP. The results in each group were summarized as median (25th-75th) and compared using the Mann-Whitney U test. In the control group higher blood loss required higher volume substitution. Urine output was maintained in heparin coated and slightly decreased at 3-4 h in control LHBP. Creatinine clearance at 3-5 h and free-water clearance at 3-6 h were significantly higher with heparin-coated LHBP. PRA, aldosterone and vasopressin peaked at 1-2 h of LHBP similarly in both groups, not exceeding the values before perfusion. PRA and aldosterone response was sustained during 6 h and the percentage changes corrected for hemodilution indicated a stronger response with standard equipment. Vasopressin concentrations were slightly but significantly higher in the control group at 1 and 6 h of perfusion. Corrected for hemodilution, vasopressin percentage changes were not different in the two groups. ANP, despite atrial unloading, rose similarly in both groups. There was a tendency to poorly sustained ANP response (control > heparin-coated) after 6 h of perfusion. In conclusion, preserved renal function and attenuated hormonal response during canine partial LHBP are results of better hemostasis and circulatory integrity of perfusion without systemic heparinization.

Perioperative changes in plasma brain natriuretic peptide concentrations in patients undergoing cardiac surgery

The plasma concentrations of brain natriuretic peptide (BNP), a cardiac hormone, were measured in 30 consecutive adult patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) during the perioperative period. BNP concentrations remained unchanged until 6 h after the cessation of bypass, and were elevated 12, 24, and 48 h post-bypass (P < 0.0001 versus baseline). They had returned to the baseline values when measured 3 weeks postoperatively. The preoperative plasma BNP concentration correlated significantly with the left ventricular ejection fraction (r = -0.895). The peak plasma BNP concentration 24 h after bypass correlated with the cardiac index (r = -0.64), stroke volume index (r = -0.62), injection rate of dopamine hydrochloride (r = 0.65), and aortic crossclamp time (r = 0.57). There was also a significant correlation between the preoperative BNP concentration and the plasma BNP concentration 24 h post-CPB. These findings led us to conclude that the plasma concentrations of BNP become markedly and acutely elevated after cardiac surgery with CPB, and reflect the state of left ventricular function. Moreover, the severity of acute heart failure after cardiac surgery can be predicted by the preoperative plasma BNP concentration.

Plasma concentration of human brain natriuretic peptide in patients on hemodialysis

The plasma concentration of immunoreactive human brain natriuretic peptide (ir-BNP) was measured in 40 patients on hemodialysis (HD) and in 12 healthy subjects. Immunoreactive human atrial natriuretic peptide (ir-ANP) was also measured. The mean (+/- SE) plasma ir-BNP concentration in the patients before HD (18.4 +/- 3.4 fmol/mL) was markedly higher than that in the control group (0.39 +/- 0.08 fmol/mL). The plasma ir-BNP level was significantly decreased by HD from 18.4 +/- 3.4 fmol/mL to 10.5 +/- 2.2 fmol/mL (P < 0.001), but the latter value was still higher than the upper limit of the normal range for our laboratory. There were significant correlations between the plasma ir-ANP level and the mean blood pressure before HD (P < 0.05) and between the HD-induced changes in plasma ir-ANP level and mean blood pressure (P < 0.001). These correlations were not observed between the plasma ir-BNP level and mean blood pressure. The plasma ir-BNP level correlated with the cardiothoracic ratio and this correlation was closer to that between the plasma ir-ANP level and cardiothoracic ratio. Ultrasound echocardiographic studies in 13 patients revealed that the pre-HD state of high cardiac output was correlated by HD in association with decreases in plasma ir-BNP and ir-ANP levels. Correlations were observed between the pre-HD ir-ANP level and the interventricular septal thickness index (r = 0.68, P < 0.05) and between the change in ir-BNP level and that in left atrial diameter (r = 0.806, P < 0.001). In conclusion, BNP levels were high in HD patients compared with the control subjects and were decreased during HD. In addition, BNP and ANP levels correlated with several parameters of volume change and cardiac status.

Determinants of coronary effects of atrial natriuretic factor in dogs

The direct vascular action of atrial natriuretic factor (ANF) is unclear. In coronary vasculature, vasodilation has been reported as well as vasoconstriction. Doses of ANF, baseline plasma ANF levels and interference with the renin-angiotensin system might account for the controversy. We tried to further analyse determinants of the effect of ANF on coronary blood flow in anaesthetized dogs. The chest was opened and the left anterior descending coronary artery cannulated and perfused at constant normal (= 76 +/- 5 mmHg, n = 10) or reduced (= 37 +/- 3 mmHg, n = 10) pressure from the femoral arteries. At normal coronary perfusion pressure, ANF (1 ng kg-1 i.c.) reduced coronary flow from 30.7 +/- 4.2 to 26.9 +/- 4.0 ml min-1 (P less than 0.05). This effect was no longer significant at reduced coronary perfusion pressure (4.9 +/- 0.8 vs. 4.6 +/- 0.7 ml min-1). ANF (1 ng kg-1 i.c.) reduced coronary blood flow in correlation with baseline plasma ANF levels (r = 0.77, P less than 0.001). However the large variability of the constrictor effect of ANF in the rather small range of baseline plasma ANF, weakens the importance of this result and suggests other additional determinants. ANF (100 ng kg-1 i.c.) significantly increased coronary blood flow by 16-23% (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of hypothermic cardiopulmonary bypass on atrial natriuretic factor levels

Atrial natriuretic factor (ANF) is a peptide released from the heart in response to atrial distension. This peptide causes diuresis, vasodilatation, decreased blood pressure, and antagonizes the renin-aldosterone and antidiuretic hormone neuraxes. The influence of cardiopulmonary bypass and cardiac surgery on the circulation and release of ANF is unknown. Plasma ANF concentrations were therefore determined in patients undergoing coronary artery revascularization (CABG) and mitral valve replacement (MVR). Peptide levels were unchanged following anaesthetic induction. Plasma ANF concentrations decreased significantly during hypothermic (less than or equal to 28 degrees C) cardiopulmonary bypass in both patient groups. After 60 minutes of cardiac bypass, ANF declined from (mean +/- SEM) 512 +/- 132 to 20 +/- 6 pg.ml-1 (P less than 0.05) during MVR, and from 178 +/- 41 to 110 +/- 48 pg.ml-1 during CABG (P less than 0.05). Rewarming during bypass was associated with an increase in ANF concentration in both groups. Heparin anticoagulation and protamine reversal had no effect on immunoreactive ANF levels. In patients undergoing CABG, there was a linear relationship between plasma ANF concentration (pg.ml-1) and right atrial pressure (mmHg) prior to cardiopulmonary bypass (r = 0.86, P less than 0.005). However, one and three hours after cardiopulmonary bypass there was no significant relationship between right atrial pressure and ANF plasma levels. These results suggest that reduction in plasma ANF concentration occurs during hypothermic cardiopulmonary bypass. Furthermore, the proportional relationship between atrial distension and circulating ANF concentration was altered following cardiac surgery.

Strategies for the in vivo inhibition of endogenous atriopeptin

Pharmacological strategies have been employed to manipulate the response to atriopeptin (AP-28; ANF 99-126) in rats. These approaches include: heparin infusion which blocks the natriuresis-diuresis produced by exogenous AP infusion or by acute volume expansion; and autoimmune rats with endogenous antibody that blocks the natriuresis-diuresis produced by administration of exogenous AP or by acute volume expansion in anesthetized rats. Administration of the pressor analog 1-deamino-arg8-vasopressin (dAVP) to rats produces an elevation in systemic and right atrial blood pressure and markedly increases atriopeptin blood levels. The dAVP also produces a delayed natriuresis-diuresis which is effectively blunted in the autoimmune or heparin treated rats. The above approaches provide tools, in the absence of a specific receptor antagonist, with which to validate the intrinsic involvement of AP in physiological, pharmacological, or pathophysiological events.