Thomas W. Lameris

Time Course and Mechanism of Myocardial Catecholamine Release During Transient Ischemia In Vivo

BACKGROUND Elevated concentrations of norepinephrine (NE) have been observed in ischemic myocardium. We investigated the magnitude and mechanism of catecholamine release in the myocardial interstitial fluid (MIF) during ischemia and reperfusion in vivo through the use of microdialysis. METHODS AND RESULTS In 9 anesthetized pigs, interstitial catecholamine concentrations were measured in the perfusion areas of the left anterior descending coronary artery (LAD) and the left circumflex coronary artery. After stabilization, the LAD was occluded for 60 minutes and reperfused for 150 minutes. During the final 30 minutes, tyramine (154 nmol. kg(-1). min(-1)) was infused into the LAD. During LAD occlusion, MIF NE concentrations in the ischemic region increased progressively from 1. 0+/-0.1 to 524+/-125 nmol/L. MIF concentrations of dopamine and epinephrine rose from 0.4+/-0.1 to 43.9+/-9.5 nmol/L and from <0.2 (detection limit) to 4.7+/-0.7 nmol/L, respectively. Local uptake-1 blockade attenuated release of all 3 catecholamines by >50%. During reperfusion, MIF catecholamine concentrations returned to baseline within 120 minutes. At that time, the tyramine-induced NE release was similar to that seen in nonischemic control animals despite massive infarction. Arterial and MIF catecholamine concentrations in the left circumflex coronary artery region remained unchanged. CONCLUSIONS Myocardial ischemia is associated with a pronounced increase of MIF catecholamines, which is at least in part mediated by a reversed neuronal reuptake mechanism. The increase of MIF epinephrine implies a (probably neuronal) cardiac source, whereas the preserved catecholamine response to tyramine in postischemic necrotic myocardium indicates functional integrity of sympathetic nerve terminals.

Cyclosporin A Impairs the Nocturnal Blood Pressure Fall in Renal Transplant Recipients

In renal transplant recipients, hypertension and a diminished nocturnal blood pressure fall are frequently found. To investigate whether this diminished nocturnal blood pressure fall is related to the use of cyclosporin A or to other factors, such as the use of glucocorticoids, we measured 24-hour ambulatory blood pressure in 18 renal transplant recipients both before and 16 weeks after conversion from cyclosporin A to azathioprine. Renal blood flow and glomerular filtration rate were estimated from 131I-hippurate and 125I-iothalamate clearances, respectively, and plasma concentrations of renin, atrial natriuretic peptide, norepinephrine, prostaglandin E2, and thromboxane B2 were determined. During cyclosporin A treatment, mean 24-hour blood pressure was 117 +/- 3 mm Hg, and the nocturnal fall in blood pressure was 4 +/- 9 mm Hg. A nondipping diurnal blood pressure pattern was present in 13 patients. After conversion to azathioprine, mean 24-hour blood pressure decreased to 109 +/- 3 mm Hg (P < .001), the nocturnal fall increased to 9 +/- 6 mm Hg, and the number of patients with a nondipping diurnal blood pressure pattern decreased to 9. The nocturnal fall in heart rate (17 +/- 10 beats per minute) during cyclosporin A did not change after conversion. Body weight and plasma concentrations of norepinephrine and renin did not change. Plasma concentrations of prostaglandin E2 and thromboxane B2 decreased after conversion, as did plasma atrial natriuretic peptide. Renal blood flow and glomerular filtration rate increased after conversion. In conclusion, cyclosporin A appears to be involved in the disturbance of the circadian blood pressure rhythm in renal transplant recipients. Although the precise mechanism is unclear. the elevated plasma atrial natriuretic peptide and slightly suppressed plasma renin concentrations suggest that intravascular volume expansion may contribute to the observed hemodynamic alterations.

Cardioprotection in Pigs by Exogenous Norepinephrine but not by Cerebral Ischemia–Induced Release of Endogenous Norepinephrine

Background and Purpose— Endogenous norepinephrine release induced by cerebral ischemia may lead to small areas of necrosis in normal hearts. Conversely, norepinephrine may be one of the mediators that limit myocardial infarct size by ischemic preconditioning. Because brief ischemia in kidneys or skeletal muscle limits infarct size produced by coronary artery occlusion, we investigated whether cardiac norepinephrine release during transient cerebral ischemia also elicits remote myocardial preconditioning. Methods— Forty-one crossbred pigs of either sex were assigned to 1 of 7 experimental groups, of which in 6 groups myocardial infarct size was determined after a 60-minute coronary occlusion and 120 minutes of reperfusion. One group served as control (no pretreatment), while the other groups were pretreated with either cerebral ischemia or an intracoronary infusion of norepinephrine. Results— In 10 anesthetized control pigs, infarct size was 84±3% (mean±SEM) of the area at risk after a 60-minute coronary occlusion and 120 minutes of reperfusion. Intracoronary infusion of 0.03 nmol/kg · min−1 norepinephrine for 10 minutes before coronary occlusion did not affect infarct size (80±3%; n=6), whereas infusion of 0.12 nmol/kg · min−1 limited infarct size (65±2%; n=7;P <0.05). Neither 10-minute (n=5) nor 30-minute (n=6) cerebral ischemia produced by elevation of intracranial pressure before coronary occlusion affected infarct size (83±4% and 82±3%, respectively). Myocardial interstitial norepinephrine levels tripled during cerebral ischemia and during low-dose norepinephrine but increased 10-fold during high-dose norepinephrine. Norepinephrine levels increased progressively up to 500-fold in the area at risk during the 60-minute coronary occlusion, independent of the pretreatment, while norepinephrine levels remained unchanged in adjacent nonischemic myocardium and arterial plasma. Conclusions— Cerebral ischemia preceding a coronary occlusion did not modify infarct size, which is likely related to the modest increase in myocardial norepinephrine levels during cerebral ischemia. The infarct size limitation by high-dose exogenous norepinephrine is not associated with blunting of the ischemia-induced increase in myocardial interstitial norepinephrine levels.

Sensitive and specific method for the simultaneous determination of natural and synthetic catecholamines and 3,4-dihydroxyphenylglycol in microdialysis samples

The relatively new technique of microdialysis provides new possibilities for investigating in vivo the functioning of the sympathetic nervous system. The small sample volumes obtained, however, are a great challenge for analytical chemists. We report here a HPLC method for measuring in one run both natural and synthetic catecholamines [dopamine, (nor)epinephrine, alpha-methylnorepinephrine, isoproterenol and epinine] and the intraneuronal metabolite 3,4-dihydroxyphenylglycol in small microdialysis samples after derivatization with the fluorogenic agent 1,2-diphenylethylenediamine. No prior clean-up step is necessary. N-Ethylmaleimide is necessary for preventing an inhibitory action on derivatization occurring in in vivo microdialysis samples. The method can handle large numbers of samples, is sensitive (on-column detection limits 30 to 200 fg) and reproducible (RSD 1 to 7%). Recovery characteristics of the commercial microdialysis probe used (CMA/20) were extensively investigated both in vitro and in vivo at various perfusion rates; for practical purposes a rate of 2 microl/min and sampling at 10-min intervals was found to be workable and to give good and reproducible recoveries (50 to 70%).

Catecholamine handling in the porcine heart: a microdialysis approach

Experimental findings suggest a pronounced concentration gradient of norepinephrine (NE) between the intravascular and interstitial compartments of the heart, compatible with an active neuronal reuptake (U1) and/or an endothelial barrier. Using the microdialysis technique in eight anesthetized pigs, we investigated this NE gradient, both under baseline conditions and during increments in either systemic or myocardial interstitial fluid (MIF) NE concentration. At steady state, baseline MIF NE (0.9 ± 0.1 nmol/l) was higher than arterial NE (0.3 ± 0.1 nmol/l) but was not different from coronary venous NE (1.5 ± 0.3 nmol/l). Local U1 inhibition raised MIF NE concentration to 6.5 ± 0.9 nmol/l. During intravenous NE infusions (0.6 and 1.8 nmol ⋅ kg-1 ⋅ min-1), the fractional removal of NE by the myocardium was 79 ± 4% to 69 ± 3%, depending on the infusion rate. Despite this extensive removal, the quotient of changes in MIF and arterial concentration (ΔMIF/ΔA ratio) for NE were only 0.10 ± 0.02 for the lower infusion rate and 0.11 ± 0.01 for the higher infusion rate, whereas U1 blockade caused the ΔMIF/ΔA ratio to rise to 0.21 ± 0.03 and 0.36 ± 0.05, respectively. From the differences in ΔMIF/ΔA ratios with and without U1 inhibition, we calculated that 67 ± 5% of MIF NE is removed by U1. Intracoronary infusion of tyramine (154 nmol ⋅ kg-1 ⋅ min-1) caused a 15-fold increase in MIF NE concentration. This pronounced increase was paralleled by a comparable increase of NE in the coronary vein. We conclude that U1 and extraneuronal uptake, and not an endothelial barrier, are the principal mechanisms underlying the concentration gradient of NE between the interstitial and intravascular compartments in the porcine heart.Experimental findings suggest a pronounced concentration gradient of norepinephrine (NE) between the intravascular and interstitial compartments of the heart, compatible with an active neuronal reuptake (U1) and/or an endothelial barrier. Using the microdialysis technique in eight anesthetized pigs, we investigated this NE gradient, both under baseline conditions and during increments in either systemic or myocardial interstitial fluid (MIF) NE concentration. At steady state, baseline MIF NE (0.9 +/- 0.1 nmol/l) was higher than arterial NE (0.3 +/- 0.1 nmol/l) but was not different from coronary venous NE (1.5 +/- 0.3 nmol/l). Local U1 inhibition raised MIF NE concentration to 6.5 +/- 0.9 nmol/l. During intravenous NE infusions (0.6 and 1.8 nmol. kg(-1). min(-1)), the fractional removal of NE by the myocardium was 79 +/- 4% to 69 +/- 3%, depending on the infusion rate. Despite this extensive removal, the quotient of changes in MIF and arterial concentration (DeltaMIF/DeltaA ratio) for NE were only 0.10 +/- 0.02 for the lower infusion rate and 0.11 +/- 0.01 for the higher infusion rate, whereas U1 blockade caused the DeltaMIF/DeltaA ratio to rise to 0.21 +/- 0.03 and 0.36 +/- 0.05, respectively. From the differences in DeltaMIF/DeltaA ratios with and without U1 inhibition, we calculated that 67 +/- 5% of MIF NE is removed by U1. Intracoronary infusion of tyramine (154 nmol. kg(-1). min(-1)) caused a 15-fold increase in MIF NE concentration. This pronounced increase was paralleled by a comparable increase of NE in the coronary vein. We conclude that U1 and extraneuronal uptake, and not an endothelial barrier, are the principal mechanisms underlying the concentration gradient of NE between the interstitial and intravascular compartments in the porcine heart.

Epinephrine in the Heart Uptake and Release, but No Facilitation of Norepinephrine Release

Background—Several studies have suggested that epinephrine augments the release of norepinephrine from sympathetic nerve terminals through stimulation of presynaptic receptors, but evidence pertaining to this mechanism in the heart is scarce and conflicting. Using the microdialysis technique in the porcine heart, we investigated whether epinephrine, taken up by and released from cardiac sympathetic nerves, can increase norepinephrine concentrations in myocardial interstitial fluid (NEMIF) under basal conditions and during sympathetic activation. Methods and Results—During intracoronary epinephrine infusion of 10, 50, and 100 ng/kg per minute under basal conditions, large increments in interstitial (from 0.31±0.05 up to 140±30 nmol/L) and coronary venous (from 0.16±0.08 up to 228±39 nmol/L) epinephrine concentrations were found, but NEMIF did not change. Left stellate ganglion stimulation increased NEMIF from 3.4±0.5 to 8.2±1.5 nmol/L, but again, this increase was not enhanced by concomitant intracoronary epinephrine infusion. Intracoronary infusion of tyramine resulted in a negligible increase in epinephrine concentration in myocardial interstitial fluid (EPIMIF), whereas 30 minutes after infusion of epinephrine an increase of 9.5 nmol/L in EPIMIF was observed, indicating that epinephrine is taken up by and released from cardiac sympathetic neurons. Although 68% to 78% of infused epinephrine was extracted over the heart, the ratio of interstitial to arterial epinephrine concentrations was only ≈20%, increasing to 29% with neuronal reuptake inhibition. Conclusions—Our findings demonstrate epinephrine release from cardiac sympathetic neurons, but they do not provide evidence that epinephrine augments cardiac sympathoneural norepinephrine release under basal conditions or during sympathetic activation.

Effects of cerebral air embolism on brain metabolism in pigs.

Objectives – Cerebral air embolism was induced in pigs and changes in intracranial pressure (ICP), brain oxygen (PbrO2), brain carbon dioxide (PbrCO2), brain pH (brpH) and glucose, lactate and pyruvate levels were used to characterize this model.

Forearm vasorelaxation in hypertensive renal transplant patients : the impact of withdrawal of cyclosporine

Objective To determine whether cyclosporine A-induced hypertension in renal transplant recipients is accompanied by impairment of endothelium-dependent vasodilatation, which has been suggested by in-vitro and in-vivo animal experiments. Design and methods In-vivo endothelium-dependent and endothelium-independent vasodilatation, and plasma concentrations of vasoactive hormones in 16 renal transplant patients were determined while they were being treated with cyclosporine A, and 16 weeks later, after their treatment had been changed to azathioprine therapy. The vasodilator response of the forearm vascular bed was measured by strain gauge venous occlusion plethysmography during intra-arterial infusion of acetylcholine (endothelium-dependent vasodilatation) and nitroprusside (endothelium-independent vasodilatation). Postischemic reactive flow was measured after 10 min of arterial occlusion. In addition, plasma concentrations of norepinephrine, and the prostanoids prostaglandin E2 and thromboxane B2, and also concentration of cyclosporine A in blood, were measured. Glomerular filtration rate and renal blood flow were estimated 1 day before the plethysmography study during each treatment period. Results Upon changing from cyclosporine A to azathioprine treatment, mean arterial pressure fell significantly by 12 ± 3% (P < 0.05). Glomerular filtration rate and renal blood flow increased by 13 ± 5 and 19 ± 8%, respectively (both P < 0.05), while renal vascular resistance fell by 48 ± 11% (P < 0.01). Both baseline forearm blood flow and baseline forearm resistance did not change after conversion (5.7 ± 0.7 versus 4.9 ± 0.6 ml/100 ml/min, and 27.3 ± 4.2 versus 26.2 ± 3.2 arbitrary units). The absolute and relative forearm blood flow responses, and forearm vascular resistance responses to infusions of acetylcholine and nitroprusside were similar during treatments with cyclosporine A and azathioprine. Peak postischaemic forearm blood flow was 42 ± 12% higher during cyclosporine A treatment than it was during azathioprine treatment (P < 0.05), but the minimal postischaemic forearm vascular resistance did not differ for these treatments. Plasma prostaglandin E2 and thromboxane B2 levels decreased by 34 ± 7 and 45 ± 8%, respectively, after changing treatment, but norepinephrine levels did not change. Conclusions Our data indicate that cyclosporine A-induced hypertension in renal transplant recipients is not accompanied by an increase in forearm vascular resistance. In addition, changing from cyclosporine A to azathioprine treatment did not cause changes in endothelial vasodilator functioning, although mean arterial pressure decreased significantly. Our results do not support the hypothesis that attenuation of endothelial vasodilator functioning contributes to the development of cyclosporine A-induced hypertension. J Hypertens 16:331–337

Brain glucose and lactate levels during ventilator-induced hypo- and hypercapnia

Objective:  Levels of glucose and lactate were measured in the brain by means of microdialysis in order to evaluate the effects of ventilator‐induced hypocapnia and hypercapnia on brain metabolism in healthy non‐brain‐traumatized animals.

Exogenous angiotensin II does not facilitate norepinephrine release in the heart

Abstract—Studies on the effect of angiotensin II on norepinephrine release from sympathetic nerve terminals through stimulation of presynaptic angiotensin II type 1 receptors are equivocal. Furthermore, evidence that angiotensin II activates the cardiac sympathetic nervous system in vivo is scarce or indirect. In the intact porcine heart, we investigated whether angiotensin II increases norepinephrine concentrations in the myocardial interstitial fluid (NEMIF) under basal conditions and during sympathetic activation and whether it enhances exocytotic and nonexocytotic ischemia-induced norepinephrine release. In 27 anesthetized pigs, NEMIF was measured in the left ventricular myocardium using the microdialysis technique. Local infusion of angiotensin II into the left anterior descending coronary artery (LAD) at consecutive rates of 0.05, 0.5, and 5 ng/kg per minute did not affect NEMIF, LAD flow, left ventricular dP/dtmax, and arterial pressure despite large increments in coronary arterial and venous angiotensin II concentrations. In the presence of neuronal reuptake inhibition and &agr;-adrenergic receptor blockade, left stellate ganglion stimulation increased NEMIF from 2.7±0.3 to 7.3±1.2 before, and from 2.3±0.4 to 6.9±1.3 nmol/L during, infusion of 0.5 ng/kg per minute angiotensin II. Sixty minutes of 70% LAD flow reduction caused a progressive increase in NEMIF from 0.9±0.1 to 16±6 nmol/L, which was not enhanced by concomitant infusion of 0.5 ng/kg per minute angiotensin II. In conclusion, we did not observe any facilitation of cardiac norepinephrine release by angiotensin II under basal conditions and during either physiological (ganglion stimulation) or pathophysiological (acute ischemia) sympathetic activation. Hence, angiotensin II is not a local mediator of cardiac sympathetic activity in the in vivo porcine heart.