Browsing by Subject "MEAP"
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Item Hemorrhagic Hypotension Alters Circulating and Myocardial Enkephalins and Catecholamines(1994-11-01) Mateo, Zaira; Caffrey, James; Napier, Leslie; Yoshishige, DariceMateo, Zaira, Hemorrhagic hypotension alters circulating and myocardial enkephalins and catecholamines. Master of Science (Biomedical Sciences). November, 1994. A variety of plasma and intrinsic cardiac enkephalins were extracted, chromatographed and assayed under control conditions and during two hours of hemorrhagic hypotension. The animals were anesthetized, instrumented and sufficient blood was withdrawn as required to reduce mean arterial pressure and maintain it at 40 mmHg. Central venous blood samples were obtained 15 minutes before and at 30 minute intervals during the experiment. Arterial blood gases remained stable throughout the experiment while pH declined from above 7.4 to near 7.1. Heart rate rose gradually by 100 bpm. Plasma catcholamines were unchanged during two hour time-controls. Plasma norepinephrine and epinephrine increased by 6 and 100 fold respectively, during the first hour of hypotension and remained high through the second hour. All eight enkephalin immunoreactivities monitored were unchanged during the time-controls. Plasma met-enkephalin (ME) and Peptide-F both gradually increased by 70-100% during the hypotension. Plasma Met-enkephalin-Arg-Phe (MEAP) and Peptide-B concentrations increased 4-5 fold during the same interval. Proenkephalin and other large enkephalin containing peptids though present, were unchanged during hypotension. Myocardial norepinephrine was preferentially concentrated about 3:1 in the atria. Both atrial and ventricular concentrations were reduced by one third or more following two hours of hypotension. Proenkephalin and peptide-B accounted for 75% of the intrinsic enkephalins and their ventricular concentrations were 3 to 4 times atrial concentrations in the same hearts. Intrinsic cardiac MEAP concentrations were 15-25 times higher than comparable ME concentrations in the same myocardial regions. Hypotension produced a significant increase in Peptide-B and proenkephalin compared to controls. The increase was consistent throughout the heart, thus maintaining the preferential concentration in the ventricles. Myocardial ME, MEAP and Peptide-F were largely unchanged in hypotensives compared to time-controls. The data demonstrate the preferential processing and retention of MEAP rather than ME-immunoreactive enkephalins in heart tissue. The data also indicate the responsiveness of MEAP-ir to changes in the circulatory environment and their subsequent appearance in plasma during hemorrhagic hypotension. Prior data suggests that intrinsic cardiac enkephalins may actively regulate either vagal control of the heart or sympathetic control of vasomotor tone.Item Sustained δ1-Opioid Receptor Stimulation Down Regulates δ2-Opioid Receptor Responses(2005-05-01) Deo, Shekhar H.; James L. Caffrey; Michael Smith; H. Fred DowneyDeo, Shekhar., Sustained δ1-opioid receptor stimulation down regulates δ2-opioid receptor responses. Master of Science (Integrative Physiology), May 2005, 49 pp., 2 tables, 8 figures, references, 25 titles. Ultra-low doses of methionine-enkephalin-arginine-phenylalanine (MEAP) improve vagal transmission (vagotonic) and decrease the heart rate by the stimulating δ1-opioid receptors (OR) within the sinoatrial (SA) node. Higher doses of MEAP (5 nmol/min) acting on δ2-opioid receptors interrupt vagal transmission (vagolytic) and reduce the decline in heart rate. Repeated occlusion of the SA node artery produced a vagotonic response during a subsequent prolonged ischemia that was reversed by selective δ1-opioid receptor antagonist, 7-benzylidenaltrexone (BNTX). 2-Methyl-4aα-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aα-octahydro-quinolino[2,3,3-g]isoquinoline (TAN-67); a selective δ1-OR agonist has been used experimentally to mimic ischemic preconditioning in the heart. The following study was designed to test the hypothesis that sustained δ1-opioid receptor stimulation reduces the δ2-opioid receptor response. The cervical vagi were isolated and ligated and the right vagus was stimulated at frequencies chosen to produce a two-step decline in heart rate of about 25 and 50 beats per min (bpm). A microdialysis probe was introduced into the SA node such that the porous window was in the nodal interstitium. In study one, the selective δ2-OR agonist, deltorphin II was introduced (1.67 nmol/min) into the dialysis inflow to evaluate the δ2-OR response before and after the infusion of TAN-67 (1.67 nmol/min). The vagolytic effect (% inhibition) of deltorphin after TAN-67 infusion was significantly reduced during both low (76% to 22%) and high (80% to 21%) frequency vagal stimulation. In study two, BNTX (1.67 nmol/min), a selective δ1-OR antagonist was mixed with TAN-67 (1.67 nmol/min) in an equimolar ratio and introduced into the dialysate inflow. By blocking the effects of TAN-67, BNTX preserved the deltorphin response suggesting that the earlier attrition of the response was mediated by δ1-receptor activity. In study three, TAN-67 was omitted to perform a time control study. Unexpectedly, some loss of δ2-response was apparent in the absence of added TAN-67, So study 4 was designed in which BNTX (1.67 nmol/min) was infused for the period of time similar to that of saline in study 3. Like study 2, BNTX prevented the loss of the deltorphin response, suggesting that the attenuated response seen in study 3 was also mediated by δ1-activity. Two additional studies were conducted to determine the effects of TAN-67 alone and the duration of the experiment without prior exposure to deltorphin. Another time control was conducted in which the initial deltorphin evaluation prior to the vehicle treatment was omitted. In that study (Study 5) a very robust vagolytic response was observed when deltorphin was first tested after 2.5 hours. In study six, TAN-67 was substituted for saline and the subsequent δ2-evaluation at 2.5 hour was eroded compared to that in study 5. When BNTX was added to deltorphin after erosion of the vagolytic response, the vagolytic response was not restored. This observation support the conclusion that sustained δ1-stimulation desensitizes or down regulates δ2-mediated responses through a heterologous mechanism. Collectively the six studies support the conclusion that the loss of δ2-mediated vagolytic response was a result of reduction in the number of δ2-receptors mediated by sustained δ1-receptor stimulation.Item Vagotonic Effects of Enkephalin Are Not Mediated by Sympatholytic Mechanisms(2005-05-01) Barlow, Matthew A.; James L. Caffrey; H. Fred Downey; Glenn DillonBarlow, Matthew A., Vagotonic Effects of Enkephalin are not Mediated by Sympatholytic Mechanisms. Master of Science (Biomedical Sciences), May, 2005, 50pp. 1 table, 10 illustrations, bibliography. This study examined the hypothesis that the vagotonic and sympatholytic effects of cardiac enkephalins are independently mediated by different receptors. In study one, the heart rate response to increasing doses of the δ-receptor opioid, MEAP was determined during nerve stimulation. MEAP was administered by microdialysis into the interstitium of the canine sinoatrial node during sympathetic (right ansa subclavia) and parasympathetic (right cervical vagus) stimulation. This protocol was conducted to illustrate that the vagotonic effect of MEAP was independent of any simultaneous sympatholytic activity that might be intrinsic to MEAP. The right cardiac sympathetic nerves were isolated as they exited the stellate ganglion and were stimulated at frequencies selected to produce an intermediate increase in heart rate (HR) of approximately 35 bpm. The cervical vagi were ligated and the right vagus nerve was stimulated at frequencies related to produce a two-step decline in heart rate of approximately 25 and 50 bpm. Dose response relationships were constructed by recording the change in heart rate during nerve stimulation as the dose of MEAP was increased in 5-min steps from 0.05 pmoles/min to 1500 pmoles/min. A significant increase in vagal transmission was observed during the administration of δ-agonist, MEAP at 0.5 pmoles/min as evident by a greater decline in heart rate. The sympathetically mediated tachycardia was unaltered at this or any other dose of MEAP. In study two, a similar dose response relationship was constructed with the κ-opioid receptor agonist, U-50488H to illustrate an independent sympatholytic effect and to verify its κ-receptor character. U-50488H gradually suppressed the sympathetic tachycardia with a significant effect obtained at the highest dose (1500 pmoles/min). U-50488H had no effect on vagally mediated decreases in heart rate. Surprisingly the sympatholytic effect of U-50488H was not reversed by withdrawal of the agonist or by addition of the κ-antagonist, norBNI. Study three was conducted to determine whether the sympatholytic effect to U-50488H could be prevented by co-administration of norBNI. NorBNI blocked the sympatholytic effect of the U-50488H throughout 90 min of exposure. When norBNI was discontinued after 90 min and U-50488H was continued alone, its sympathetic effect reappeared within 30 min. Collectively these observations support the hypothesis that the vagotonic influence of MEAP was independent of sympathetic transmission and sympathetic transmission was unaltered by MEAP. Furthermore the observed sympatholytic effect of U-50488H was mediated independently by κ-receptors. The sympatholytic effect of sustained κ-receptor stimulation appears to evolve gradually into a functional state not easily reversed.