Richard M. Raymond

Insulin Improves Survival in a Canine Model of Acute β-Blocker Toxicity

STUDY OBJECTIVE To compare the efficacy of a novel antidote, insulin, with standard treatments, glucagon and epinephrine, in a canine model of acute beta-blocker toxicity. METHODS Anesthetized dogs were fitted with instruments by means of thoracotomy and vascular cutdown for multiple cardiodynamic, hemodynamic, metabolic, and electrical measures. After basal measurements were taken, animals received intravenous propranolol (.25 mg/kg/minute) continuously for the remainder of the experiment. Toxicity was defined as a 25% decrease in the product of heart rate times mean blood pressure. Thirty minutes after the development of toxicity, toxic measures were taken (treatment 0 minutes), and then the animals (n = 6 each group) received either sham (saline solution), insulin (4 IU/minute with glucose clamped), glucagon (50 micrograms/kg bolus, then 150 micrograms/kg/hour infusion), or epinephrine (1 microgram/kg/minute). Animals were monitored until death or for 240 minutes. RESULTS Propranolol decreased contractility, left ventricular pressure, and systemic blood pressure, and resulted in death of all sham-treated animals by 150 minutes. Six of six insulin-treated, four of six glucagon-treated, and one of six epinephrine-treated animals survived. Survival was greater for insulin-treated animals, compared with either glucagon-treated (P < .05) or epinephrine-treated animals (P < .02) by the log-rank test. Insulin-treated animals were characterized by improved cardiodynamics and hemodynamics, increased myocardial glucose uptake, and decreased serum potassium. CONCLUSION Insulin is a superior antidote compared with glucagon or epinephrine in an anesthetized canine model of acute beta-blocker toxicity.

Effect of endotoxin shock on the clearance of lidocaine and indocyanine green in the perfused rat liver

Endotoxin administration and cecal ligation and puncture produce significant hepatocellular dysfunction when studied in vivo. Specific factors that are present in vivo after endotoxin administration and cecal ligation and puncture, such as alterations in liver blood flow, circulating mediators, and hypoxia, can alter hepatic function. In this study, we used an isolated perfused liver to evaluate the effects of in vivo administration of endotoxin on hepatic function using indocyanine green (ICG) as a global marker of function and lidocaine and its metabolite, MEGX, as specific markers of the CYP450 enzyme system. Endotoxin (Escherichia coli; 45 mg/kg i.p.) was administered to rats followed by a 6-h monitoring before preparation of the isolated in situ perfused liver. Livers from control and endotoxin groups received either ICG (control, n = 6; endotoxin, n = 5) or lidocaine (control, n = 8; endotoxin, n = 8). A separate group of rats (n = 6) received cimetidine (an inhibitor of the CYP450 enzyme system) at a dose of 80 mg/kg daily for 3 days. Livers were perfused via the portal vein by using a single-pass system with a balanced salt solution 6 h after receiving either endotoxin or saline or 24 h after receiving the last dose of cimetidine. After a 40-min stabilization period, ICG or lidocaine was infused via the portal vein until steady-state concentrations were reached in the venous outflow. The total hepatic clearance and intrinsic hepatic clearance for ICG and lidocaine were unchanged in the livers obtained from endotoxin-treated rats. This model could adequately detect CYP450 inhibition because cimetidine-treated rats had significantly lower initial MEGX concentrations (0.63 +/- 0.03 mg/L) compared with control (0.77 +/- 0.03 mg/L) and endotoxin-treated (0.74 +/- 0.04 mg/L) rats. Septic livers had significantly higher initial hepatic oxygen consumption (HVO2) than did control livers (45 +/- 3 microL/min/g vs 82 +/- 9 microL/min/g). The HVO2 remained higher in the septic livers and significantly increased throughout the study, which demonstrated that the livers remained viable and functional. These data indicate that there is no detectable hepatocellular dysfunction after endotoxin shock using ICG, lidocaine, and MEGX in the isolated perfused liver; therefore the dysfunction reported from in vivo studies may be reversible when the liver is removed from the shocked environment.

Effect of amiloride on age-dependent cardiac dysfunction after ischemia/reperfusion in the isolated, perfused rat heart

This study was intended to compare the cardiac consequences of ischemia/reperfusion and amiloride treatment in immature (2-3 wk), juvenile (4-6 wk), and adult (3-5 mo) rats using an isolated, perfused heart model. Male immature, juvenile, and adult rats were anticoagulated and anesthetized. Hearts were harvested and coronary arteries were perfused on a Langendorff apparatus via retrograde perfusion of the aorta at a constant coronary flow (initially determined by perfusing the heart at 50 mm Hg perfusion pressure) with oxygenated Krebs-Henseleit-Bicarbonate (KHB) solution. Left ventricular peak systolic (LVPSP) and end diastolic (LVEDP) pressures were measured via a balloon-tipped catheter placed in the left ventricle through the mitral valve. Following a 20-30 min stabilization period, hearts underwent 30 min of normothermic ischemia and were then reperfused with Krebs-Henseleit-Bicarbonate alone for 30 min, or Krebs-Henseleit-Bicarbonate containing 500 microM amiloride for 5 min followed by Krebs-Henseleit-Bicarbonate alone for 25 min (n = 6/age group). Left ventricular generated pressure was calculated (left ventricular peak systolic-left ventricular end diastolic) and used as a measure of ventricular function. All hearts demonstrated a decrease in generated pressure, respectively, from preischemic levels at 15 and 30 min of reperfusion, although this decrease was significantly less for the immature hearts. Ischemia/reperfusion injury was attenuated by amiloride in adult and juvenile hearts, whereas ischemia/reperfusion injury was worsened by amiloride in immature hearts. Although immature hearts were relatively resistant to ischemia/reperfusion injury compared with adult and juvenile hearts, the presence of amiloride during reperfusion resulted in more severe ventricular dysfunction in immature hearts. These data suggest a differential age-dependent mechanism of sarcolemmal ion exchange in response to ischemia/reperfusion.

The effects of colchicine treatment on wound healing in a caustic murine injury model.

OBJECTIVE The present study determined the effects of colchicine on wound repair in a murine model of dermal chemical injury. METHODS Standardized 4.15 cm2 circular lesions were induced on the dorsum of adult male mice with NaOH. Five minutes of IN or 3N caused lesions of graded depth. Mice received colchicine (1 mg/kg) or phosphate-buffered saline intraperitoneally in equivalent volumes. Treatment began immediately postinjury and was continued on an alternating day schedule for 14 days. Wound size was measured every third day postinjury. On day 15 postinjury, wounds were histologically graded for depth of injury, degree of fibrosis, inflammatory cell response, and revascularization. All histological determinations and wound measurements were performed in a blinded fashion. RESULTS All mice had a similar initial wound size and completed the experimental protocol. In dermal wounds of superficial depth, colchicine-treated mice (n = 20) had a larger wound size during days 6 through 9 of the experimental trial when compared to phosphate-buffered saline-treated mice (n = 18). In the deeper wounds, there were no significant differences in wound size between colchicine and phosphate-buffered saline-treated groups. Colchicine (n = 54) did not affect the degree of fibrosis at all depths of injury vs phosphate-buffered saline treatment in mice (n = 55). The degree of wound revascularization was less in colchicine-treated mice (n = 54) than phosphate-buffered saline-treated mice (n = 55). CONCLUSION Colchicine did not improve wound healing in an alkaline-induced dermal injury.

Cardiac Ischemia-Reperfusion Injury: Preliminary Study of the Effect of Sarcolemmal Na+/H+ Exchange Blockade in the Isolated Heart in Two Age Groups of Young Rats ♦ 381

Cardiac Ischemia-Reperfusion Injury: Preliminary Study of the Effect of Sarcolemmal Na+/H+ Exchange Blockade in the Isolated Heart in Two Age Groups of Young Rats ♦ 381

Direct effects of lithium chloride (LiCl) on cardiac function in the isolated, spontaneously beating rat heart. ♦ 353

Direct effects of lithium chloride (LiCl) on cardiac function in the isolated, spontaneously beating rat heart. ♦ 353

Insulin Is a Superior Antidote for Cardiovascular Toxicity Induced by Verapamil in the Anesthetized Canine

Because of its positive inotropic effects that are independent of cyclic AMP, insulin was compared to epinephrine and glucagon as a novel treatment for cardiac toxicity from verapamil. Twenty-four alpha-chloralose-anesthetized mongrel canines of either sex were instrumented to monitor standard hemodynamic and cardiodynamic parameters and maximum elastance at end systole, via the transit-time technique, as our index of contractility. Toxicity was induced by 0.1 mg/kg/min of verapamil (i.v.), until 50% reduction in mean arterial blood pressure or complete AV dissociation for 30 min. This was followed by continuous infusion of 1.0 mg/kg/hr of verapamil during one of four treatment protocols: 1) control (0.9% NaCl, 2.0 ml/min); 2) epinephrine (1.0 micrograms/kg/min); 3) hyperinsulinemic-euglycemic (HIE) clamp (recombinant insulin at 4.0 U/min with 20% dextrose, arterial glucose clamped); or 4) glucagon (0.2-0.25-mg/kg bolus infusion followed by 150-micrograms/kg/min infusion). Treatments were continued until death or 240 min after which time surviving animals received a 3.0-mg/kg additional bolus of verapamil. Verapamil decreased all hemodynamic parameters during titration. All controls died within 85 min. All treatments tended to improve hemodynamics; however, HIE significantly improved maximum elastance at end systole, left ventricular end diastolic pressure and coronary artery blood flow vs. other treatments (P < .05, repeated measures). Glucagon transiently restored sinus rhythm (four animals), but in all cases reverted to A-V dissociation, coincident with sharp decreases in circumflex artery blood flow and contractility.(ABSTRACT TRUNCATED AT 250 WORDS)