Glucagon-like peptide-1 (GLP-1), immediately prior to reperfusion, decreases neutrophil activation and reduces myocardial infarct size in rodents.

Glucagon-like peptide-1 (GLP-1) is an incretin that has glucoregulatory effects as well as protective effects in a variety of tissues, including the heart. We hypothesized that GLP-1 may have a direct effect on neutrophils (PMNs) after myocardial ischemia, to ameliorate reperfusion injury. Deeply anesthetized Sprague-Dawley rats underwent 30 min of left coronary artery occlusion followed by 120 min of reperfusion. Immediately prior to reperfusion, rats were treated with either GLP-1 (human rGLP-1, 30 pM/kg/min) or PBS as placebo. GLP-1 significantly decreased myocardial infarct size [73.2±11.7% INF/AAR in PBS (n=4) vs. 15.7 ±5.52% INF/AAR in GLP-1-treated animals (n=5), p<0.05], PMN activation in blood in vivo (fMLP-stimulated CD11b surface expression: PBS 2.78±1.14 vs. GLP-1 1.7±0.21, TFI, p<0.05), and accumulation in myocardium (PBS: 6.52±0.31 vs. GLP-1: 4.78±0.90, n=4-6 animals/group, p<0.05). In addition, we found that GLP-1 mitigated PMN CD11b surface expression in whole rat blood in vitro, an effect that was abolished by GLP-1 receptor blockade (PBS 6.52±0.31 vs. GLP-1 4.78±0.90, TFI, p<0.05). These findings suggest that one mechanism by which GLP-1 decreases reperfusion injury may be the attenuation of PMN-mediated reperfusion injury.

Perflubron emulsion reduces inflammation during extracorporeal circulation.

The recovery from cardiac surgery and cardiopulmonary bypass can be complicated by an acute inflammatory response. Circulating blood through an extracorporeal circuit (ECC) contributes to this complication. Perfluorocarbon-based blood substitutes (PFCs) are under investigation for use as a component of the ECC "prime" solution, because PFCs increase the oxygen-carrying capacity of the diluted blood. Some PFCs may provide the additional benefit of attenuating the ECC-induced inflammatory response. Earlier, we reported that perflubron emulsion (PFE, Alliance Pharmaceutical Corp.) reduced neutrophil (PMN) activation in vivo. However, the potential of PFE to reduce ECC-induced PMN activation has not been investigated. In this study, we used a small-scale ECC model to quantify the extent of PMN activation during circulation and to examine if PFE treatment attenuated PMN activation. ECC circuits were filled with a mixture of blood and Plasmalyte. Two groups were studied: an untreated group containing blood plus PlasmaLyte and a treated group in which some of the Plasmalyte was substituted with PFE (4.5 g/100 ml). Hematology and measures of whole blood PMN activation were made from blood samples taken periodically throughout the 120-min ECC circulation period. We found, for the untreated group, a significant decrease in the number of circulating PMNs and an increase in PMN activation with time. PMN activation was demonstrated as a significant increase in the expression of the PMN adhesion protein CD11b (P < 0.05) and an increase in PMN oxygen free radical production (reactive oxygen species (ROS)). After 120 min of circulation, the PMNs remained capable of a significant response to a second inflammatory stimulus, but PFE treatment significantly attenuated the fMLP-induced increase in PMN ROS at t = 120 min (P < 0.05). These results suggest that PFE may have dual utility in cardiac surgery, to increase oxygen delivery and to serve as an antiinflammatory agent.

Diabetes enhances leukocyte accumulation in the coronary microcirculation early in reperfusion following ischemia.

BACKGROUND: Diabetic hearts are particularly vulnerable to ischemia-reperfusion injury. For leukocytes to participate in ischemia-reperfusion injury, they must first sequester in the microcirculation. The aim of this study was to determine, by direct observation, if early leukocyte deposition was increased in the diabetic coronary microcirculation early in reperfusion following myocardial ischemia. METHODS: Non-diabetic and streptozotocin (STZ)-induced diabetic rat hearts, subjected to 30 min of 37 degrees C, no-flow ischemia, were initially reperfused with blood containing labeled leukocytes. The deposition of fluorescent leukocytes in coronary capillaries and venules was directly visualized and recorded using intravital fluorescence microscopy. In addition, flow cytometry was used to measure CD11b adhesion molecule expression on polymorphonuclear (PMN) leukocytes from non-diabetic and STZ-diabetic rats. RESULTS: In the non-diabetic, control hearts, early in reperfusion, leukocytes trapped in coronary capillaries and adhered to the walls of post-capillary venules. In the diabetic hearts, leukocyte trapping in capillaries and adhesion to venules were both significantly increased (P<0.05). PMN CD11b expression was also significantly increased in the diabetic blood compared to the non-diabetic blood (P<0.05). CONCLUSIONS: Early in reperfusion following myocardial ischemia, leukocytes rapidly accumulate in greater numbers in the coronary microcirculation of the diabetic heart by both trapping in coronary capillaries and by adhering to venules. The enhanced retention of leukocytes in the diabetic coronary microcirculation increases the likelihood of inflammation-mediated reperfusion injury and may explain, in part, the poor recovery of diabetic hearts from an ischemic event.

Effects of exercise training on responses to central injection of CRF and noise stress.

The purpose of this study was to test the hypothesis that the cardiovascular and sympathoadrenal responses to acute environmental stress are attenuated by exercise training. Furthermore, we tested the hypothesis that the cardiovascular and sympathoadrenal responses to intracerebroventricular (ICV) administration of corticotropin-releasing factor (CRF) would be attenuated by training. Conscious, unrestrained, male Sprague-Dawley rats assigned to either a treadmill trained (16-26 m/min, 30-60 min/day, 5 days/week) or nontrained (16-26 m/min, 10 min/day, 1 day/week) group were studied. After 8-10 weeks of training, maximal oxygen uptake was significantly higher in the trained (108 +/- 3 ml/kg/min) vs. the nontrained (94 +/- 4 ml/min/kg) group. There were no significant differences in baseline mean arterial pressure, heart rate and plasma catecholamine levels associated with training. Trained rats exhibited significantly attenuated elevations in arterial pressure (20 +/- 3 vs. 36 +/- 2 mmHg for nontrained) and heart rate (-3 +/- 3 vs. 12 +/- 5 beats/min for nontrained) in response to acute noise stress. Twenty minutes after ICV administration of CRF, blood pressure (trained = 119 +/- 2 mmHg, nontrained = 127 +/- 2 mmHg), heart rate (trained = 408 +/- 8 beats/min, nontrained = 424 +/- 10 beats/min), plasma norepinephrine levels (trained = 757 +/- 54 pg/ml, nontrained = 775 +/- 100 pg/ml) and plasma epinephrine levels (trained = 266 +/- 29 pg/ml, nontrained = 225 +/- 42 pg/ml) were significantly elevated in both trained and nontrained groups. CRF-induced elevations of blood pressure, but not heart rate or plasma catecholamine levels, were significantly attenuated in the trained group.(ABSTRACT TRUNCATED AT 250 WORDS)

Central nervous effects of CRF and angiotensin II on cardiac output in conscious rats.

Studies were performed to determine whether the central nervous system actions of corticotropin-releasing factor (CRF) and angiotensin II (ANG II) on systemic arterial pressure are mediated, in part, through changes in cardiac output (CO). Changes in CO after intracerebroventricular administration of ANG II and CRF were assessed in conscious unrestrained rats bearing pulsed Doppler flow probes on the ascending aorta. Intracerebroventricular injection of CRF (0.15 nmol) increased arterial pressure (15-20 mmHg), heart rate (70-100 beats/min), and CO (25-35%) without significantly affecting total peripheral resistance. Intracerebroventricular injection of ANG II (0.1 nmol) produced similar elevations of arterial pressure (15-20 mmHg). However, the ANG II-induced pressor response was attended by significant decreases in heart rate (20 beats/min) and CO (10-15%) and significant increases in total peripheral resistance (30-40%). The results of these studies demonstrate that CO, as assessed by pulsed Doppler flow probe methodology, may be influenced significantly and differentially by central nervous system administration of CRF and ANG II.

Central nervous system cardiovascular actions of CRF in sinoaortic-denervated rats.

Studies were performed in unrestrained conscious Sprague-Dawley rats to examine the central nervous system (CNS) mechanism by which corticotropin-releasing factor (CRF) produces simultaneous elevations of arterial pressure and heart rate. To test the hypothesis that CRF inhibits ongoing impulse transmission through and/or transmitter release from the CNS terminations of baroreceptor afferents, the cardiovascular effects of intracerebroventricular administration of CRF were compared in rats subjected to prior sham surgery (Sham) or sinoaortic denervation (SAD). Resting levels of arterial pressure and heart rate were elevated after SAD. In addition, SAD resulted in greater chronotropic sympathetic tone and reduced chronotropic parasympathetic tone as assessed by intravenous injections of atropine methyl nitrate and DL-propranolol. Intracerebroventricular administration of CRF in both surgical groups elicited significant increases in arterial pressure and heart rate, although a tendency for reduced tachycardic responses after SAD was apparent. Pretreatment with atropine or propranolol revealed that both the parasympathetic and sympathetic nervous systems contribute to CRF-induced heart rate responses in both surgical groups. These results suggest that ongoing baroreceptor afferent transmission is not requisite for the expression of CRF-induced cardiovascular changes. Thus it is unlikely that CRF elevates arterial pressure and heart rate through an exclusive action at the CNS terminations of baroreceptor sensory fibers.