Vasopressin induced myocardial depression in neurally mediated and not due to impaired coronary blood flow

Felypressin-induced reduction in coronary blood flow and myocardial tissue oxygen tension during anesthesia in dogs

PURPOSE

To determine whether felypressin reduced myocardial tissue oxygen tension (PmO2).

METHODS

Seven open-chest dogs were studied under nitrous oxide and isoflurane anesthesia. Hemodynamic variables including heart rate (HR), blood pressure (BP), mean pulmonary arterial pressure (MPAP), PmO2 and coronary blood flow (CBF) were continuously recorded. After baseline measurements, felypressin was infused at 0.15, 0.3, 0.6 and 1.0 IU x hr(-1) in a successive manner. Hemodynamic variables were evaluated at 3, 6, 9 min after the start of each infusion.

RESULTS

Felypressin caused reductions in CBF and inner layer PmO2 (int-PmO2). Decreases in CBF (-23%, P< 0.05) and int-PmO2 (-8%, P<0.05) observed at low dose (0.15 1U x hr(-1)) were not accompanied by changes in BP and HR. Negative correlations between cumulative doses of Felypressin (mIU x kg(-1)) and CBF (% change from base line) (r = -0.69, P<0.05) or int-PmO2 (% change from base line) (r = -0.48, P<0.05) were observed.

CONCLUSION

Felypressin reduced PmO2 along with minimal changes in HR and BP.

Differential effects of arginine vasopressin on isolated guinea pig heart function during perfusion at constant flow and constant pressure

8-Arginine vasopressin (AVP) is a powerful coronary vasoconstrictor as well as peripheral vasoconstrictor, but AVP also is reported to have negative cardiac inotropic and chronotropic effects in vitro and in vivo. Our aim was to examine the direct effects of coronary vasoconstriction by AVP on cardiac function and metabolism in isolated guinea pig hearts perfused either at a constant perfusion pressure (CPP) of 55 mm Hg or at a constant coronary flow (CCF) equal to the initial natural flow at constant pressure. Coronary vasoconstriction was elicited by perfusing hearts with increasing concentrations of AVP in random order. Variables assessed were atrial heart rate (HR), atrioventricular (AV) conduction time, left ventricular pressure (LVP), coronary flow, inflow and outflow O2 tensions, O2 delivery (Do2), oxygen consumption (MVo2), percentage oxygen extraction (%O2E) and cardiac efficiency (HR-LVP/MVo2). We found that AVP increased coronary vascular resistance more at CCF than at CPP. The decrease in coronary flow, as a function of AVP at CPP, produced concentration-dependent decreases in heart rate, LVP, and MVo2, a decrease in Do2/MVo2, increases in AV conduction time and %O2E, and no significant change in cardiac efficiency. In contrast, the increase in perfusion pressure as a function of AVP at CCF caused no change in HR and AV conduction time, much smaller decreases in LVP and Do2/MVo2, a smaller increase in %O2E, an increase rather than a decrease in MVo2, and a decrease in cardiac efficiency. Our results indicate that larger decreases in HR, LVP, MVo2, and Do2/MVo2, and the larger increases in AV conduction time and %O2E with the AVP-induced decrease in CF at CPP are consistent with myocardial depression resulting from reduced global perfusion. However, cardiac efficiency was maintained at CPP because the decreased HR and LVP product (cardiac work) matched the decrease in MVo2. At CCF, AVP did not directly produce myocardial depression, but the small time-dependent decrease in LVP over time was not matched by the increase in MVo2, so that cardiac efficiency was not maintained. The demonstration of an increase in MVo2 despite no change or a decrease in cardiac work by coronary vasoconstriction with AVP at CCF, but not at CPP, suggests that cardiac O2 use is dependent more on maintenance of CF, despite increased resistance to perfusion, rather than on maintenance of perfusion pressure. Our data agree that Gregg's phenomenon results from a hydraulic effect to distend coronary vasculature because when flow is not allowed to decrease during vasoconstriction, MVo2 increases even though HR is unchanged and LVP is slightly decreased. This is supported by the finding that AVP does not increase coronary vascular resistance during CCF as much as during CPP, so that O2 supply is better maintained to match MVo2.

Effects of terlipressin on hemodynamics and oxygen content in conscious portal vein stenosed and cirrhotic rats receiving propranolol

Terlipressin is used in patients with variceal bleeding but its effects in patients receiving beta-adrenergic antagonists are unknown. In this study, the hemodynamic effects of terlipressin were evaluated in conscious portal hypertensive rats which had previously received a single dose of propranolol. Moreover, oxygen content and acid-base status were studied. In portal vein stenosed and cirrhotic rats, the addition of terlipressin (0.05 mg/kg) to propranolol (0.4 mg/kg) produced a decrease in portal pressure of 34% and 17%, respectively, and in portal tributary blood flow of 46% and 42%, respectively. In cirrhotic rats, however, the decrease in portal pressure was not significantly different when propranolol was combined with terlipressin than when propranolol was administered alone. Cardiac index also further decreased after terlipressin administration. In both groups of rats, these values were similar to those observed after terlipressin alone. In portal vein stenosed rats but not in cirrhotic rats, arterial pH was significantly lower following the combination of propranolol plus terlipressin than following saline, propranolol or terlipressin alone. In conclusion, terlipressin further reduces both portal pressure and cardiac index in rats with portal hypertension receiving beta-blockers. In portal vein stenosed rats but not in cirrhotic rats, the addition of terlipressin to propranolol induces acidemia. This study suggests that terlipressin might further reduce portal pressure in patients with portal hypertension treated with beta-blockers.

Simultaneous infusion of nitroglycerin and nitroprusside to offset adverse effects of vasopressin during portosystemic shunting

In the present study, 52 patients with cirrhosis, portal hypertension, and variceal hemorrhage underwent either an elective or an emergency side-to-side portacaval shunt operation. Vasopressin was infused intravenously at 60 units/hour from just prior to abdominal incision until completion of the anastomosis. Eight of 35 patients who received vasopressin alone (23 percent) tolerated increased doses of 75 to 90 units/hour to obtain hemostasis. Four of 52 patients required simultaneous infusion of sodium nitroprusside to correct systemic hypertension. An additional 15 percent reduction in portal venous pressure occurred in these patients. Eleven of 13 patients with vasopressin-induced myocardial ischemia responded to simultaneous infusion of nitroglycerin. Further prospective studies are indicated to adequately delineate the dose and duration of therapy with either nitroprusside or nitroglycerin for simultaneous administration with intravenous vasopressin.

Vascular vasopressin receptors

1. Vascular vasopressin receptors are understood because of the specific application of each major technical advance in pharmacology; this review shows that isolated organs, whole animal preparations, hormone synthesis, radioligand binding, and human studies have all played their part. 2. Even so, neither vascular vasopressin receptor heterogeneity nor occupancy-response relationships are fully understood; by way of comparison far more is known about alpha-adrenoceptors. 3. The biochemical pharmacology of vascular vasopressin receptor activation is still in its infancy. Whilst the second messenger molecules resulting from vascular vasopressin receptor activation appear to be component(s) of the pathways of phosphoinositide metabolism, technical difficulties have led investigators to study similar vasopressin receptors in other tissues. 4. It is not certain, for example, that results from hepatic vasopressin receptor studies can be automatically extrapolated to vascular smooth muscle. 5. Lastly, the directions that vascular vasopressin research might take are speculated on. It is not known whether the vascular vasopressin receptor is itself a polymer, whether receptor heterogeneity could be exploited in the clinical uses of vasopressins, nor whether vasopressins are co-released with other neurotransmitters.