John Pernow

Guanethidine-sensitive release of neuropeptide Y-like immunoreactivity in the cat spleen by sympathetic nerve stimulation

Splenic nerve stimulation (10 Hz for 2 min) caused a perfusion-pressure increase, a volume reduction and an increase in the output of neuropeptide Y-like immunoreactivity (NPY-LI) from the isolated blood-perfused cat spleen. Gel-filtration HPLC analysis revealed that plasma NPY-LI collected during nerve stimulation was similar to the NPY-LI in the spleen and synthetic porcine NPY. Combined propranolol and phenoxybenzamine pretreatment enhanced NPY output upon nerve stimulation by about 60%. Forty percent of the perfusion-pressure increase and 25% of the volume reduction seen during control stimulations remained after adrenoceptor blockade. Guanethidine abolished the release of NPY-LI, the perfusion-pressure increase and the volume reduction normally seen upon splenic nerve stimulation. Infusion of synthetic porcine NPY caused a long-lasting increase in perfusion pressure and a relatively moderate volume reduction. Noradrenaline (NA) both increased perfusion pressure and induced a marked volume reduction. The NPY effects were resistant to adrenoceptor antagonists in doses which abolished the NA response. In conclusion, the present data show that NPY-LI is released upon sympathetic nerve stimulation by a guanethidine-sensitive mechanism. Furthermore, the sympathetic response is partially resistant to adrenoceptor antagonists and NPY has powerful vasoconstrictor effects. This provides further evidence for a role of NPY in sympathetic vascular control.

Glucagon-like peptide-1 relaxes rat conduit arteries via an endothelium-independent mechanism

A lot of interest has engendered in glucagon-like peptide-1 (GLP-1) as an emerging new drug in the treatment of type 2 diabetes. GLP-1 exerts several effects that reduce glycemia in type 2 diabetes patients. We recently also demonstrated that GLP-1 ameliorates endothelial dysfunction in type 2 diabetes mellitus patients with established coronary heart disease, suggesting a new important cardioprotective role for GLP-1. Because hypertension is overrepresented in diabetes and is adversely influencing survival, we have now investigated direct GLP-1 effects on vascular beds in a rat organ bath model. It was found that GLP-1 relaxed femoral artery rings in a dose-response manner. The relaxant effect from GLP-1 was completely inhibited by the specific GLP-1 receptor antagonist, exendin(9-39). Neither the specific nitric oxide (NO) synthase inhibitor, N-nitro-L-arginine, nor removing of endothelium, affected the GLP-1 relaxant effect. In conclusion, we now report a direct vascular action of GLP-1, relaxing conduit vessels independently of NO and the endothelium.

Effect of postconditioning on infarct size in patients with ST elevation myocardial infarction

Background Small studies suggest that postconditioning reperfusion interrupted by brief repetitive cycles of reocclusions, may protect the myocardium in the clinical setting. Objective To test the hypothesis that postconditioning limits infarct size in relation to the area at risk in patients with ST elevation myocardial infarction (STEMI). Methods 76 patients (aged 37–87 years) eligible for primary percutaneous coronary intervention due to STEMI were randomised to standard percutaneous coronary intervention (n=38) or postconditioning, consisting of four cycles of 60 s reperfusion and 60 s of reocclusion before permanent reperfusion (n=38). Results The area at risk was determined from angiographic abnormally contracting segments. Infarct size was quantified from delayed enhancement MRI on days 6–9. Infarct size, expressed in relation to the area at risk, did not differ between the control group (44%; 30, 56) (median and quartiles) and the post-conditioned group (47%; 23, 63). The slope of the regression lines relating infarct size to the area at risk differed between the two groups. Infarct size was significantly (p=0.001) reduced by postconditioning in patients with large areas at risk. The area under the curve and peak troponin T release and CKMB during 48 h did not differ between patients in the control and postconditioning groups. Conclusions This prospective, randomised trial suggests that postconditioning does not reduce infarct size in patients with STEMI in the overall study group. The data indicate that postconditioning may be of value in patients with large areas at risk. Clinical trial registration information Karolinska Clinical Trial Registration (http://www.kctr.se). Unique identifier: CT20080014.

Urotensin II evokes potent vasoconstriction in humans in vivo

The peptide urotensin II (U II) evokes potent vasoconstriction in non‐human primates. In human blood vessels studied in vitro variable effects of U II are reported; vasoconstriction, vasodilatation or no response. It is therefore of importance to determine the vascular effect of U II in humans in vivo. U II (0.1 – 300 pmol min−1) was infused into the brachial artery of nine healthy volunteers. Changes in forearm blood flow (FBF) were determined by venous occlusion plethysmography. U II induced dose‐dependent reduction in FBF. A threshold response was obtained by 1 pmol min−1, and the highest dose of U II (300 pmol min−1) reduced FBF by 31±4% (P<0.01). FBF returned to baseline values within 30 min. This study demonstrates that U II produces potent vasoconstriction in humans in vivo.

Neuropeptide Y-like immunoreactivity in adrenaline cells of adrenal medulla and in tumors and plasma of pheochromocytoma patients

The occurrence of neuropeptide Y (NPY)-like immunoreactivity (LI) in the adrenal gland of several species as well as in tumor tissue and plasma from pheochromocytoma patients was investigated. NPY-LI was present in chromaffin cells of the adrenaline type in all species investigated except in the pig, as demonstrated by a colocalization of NPY-LI and the adrenaline-synthetizing enzyme phenylethanolamine N-methyltransferase (PNMT). NPY-LI in the adrenaline cells of the cat was clearly separated from the neurotensin-LI in the noradrenaline dopamine-beta-hydroxylase-positive, PNMT-negative cells. NPY-LI seems to co-exist with enkephalin-like material in the chromaffin cells. In addition, NPY-LI was present in nerves both within the adrenal cortex and medulla. The highest levels of NPY-LI were found in mouse and cat, while only a very low amount of NPY-LI was present in the pig adrenal. Characterization of the adrenal NPY-LI by reversed-phase high-performance liquid chromatography revealed that the main peak was similar to porcine NPY. In addition, two minor peaks of NPY-LI were present. High levels of NPY-LI were found in plasma and tumors from the pheochromocytoma patients. During manipulation of the tumors upon surgical removal, there was a marked increase in plasma NPY-LI in parallel with the raise in catecholamines and in blood pressure. At least two forms of NPY-LI were present in plasma and tumor extracts from pheochromocytoma patients with the main peak corresponding to porcine NPY. Since NPY exerts vasoconstrictor effects, it may be postulated that NPY contributes to the adrenal cardiovascular response and to the hypertension seen in pheochromocytoma patients.

Vasoconstrictor effects in vivo and plasma disappearance rate of neuropeptide Y in man

Vascular effects of neuropeptide Y (NPY) and noradrenaline (NA) were studied in six human volunteers. Systemic infusion of human NPY for 40 min (5 pmol X kg-1 X min-1) increased arterial plasma NPY-like immunoreactivity (NPY-LI) from 12 +/- 2 to 356 +/- 30 pM. This concentration caused no systemic cardiovascular effects. The disappearance curve for NPY-LI was biphasic; the slopes of the two phases corresponding to half lives of 4.1 +/- 0.4 and 20 +/- 2 min respectively. Close i.a. infusion of human NPY in the forearm caused a slowly developing and dose dependent decrease in forearm blood flow (FBF) and increase in venous tone with maximal values of 44 +/- 6 and 235 +/- 81% of control respectively at 5 nmol X min-1. The corresponding values for NA (5 nmol X min-1) were 21 +/- 9 and 489 +/- 78% of control. A threshold concentration for a decrease in FBF was obtained at a plasma NPY-LI of 3.7 +/- 0.6 nM. The decrease in FBF caused by NPY was maintained for a much longer period compared to that of NA.

Neuropeptide Y and sympathetic vascular control in man.

A parallel increase in systemic plasma levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) was found during thoracotomy and surgery involving cardiopulmonary bypass in man. Thus, plasma levels of NPY-LI increased from 29 +/- 4 pmol/l before anaesthesia to 59 +/- 10 after thoracotomy and to 87 +/- 8 pmol/l upon cardiopulmonary bypass. The corresponding NA levels increased from 1.3 +/- 0.1 nmol/l before anaesthesia to 3.0 +/- 0.6 and 4.2 +/- 5 nmol/l after thoracotomy and cardiopulmonary bypass, respectively. A significant correlation was found between plasma levels of NPY-LI and NA during the operation but not between NPY-LI and adrenaline. The NPY-LI in human plasma was found to be similar to synthetic porcine NPY on reversed phase high performance liquid chromatography. Human submandibular arteries contained high levels of NPY-LI (24 +/- 3 pmol/g). In in vitro experiments on isolated human submandibular arteries, NPY in low concentrations (1000 pmol/l) was found to potentiate the contractile effects of NA or transmural nerve stimulation and to exert vasoconstrictor activity per se in higher concentrations. The calcium-entry antagonist nifedipine abolished both the NPY-induced contractions and the enhancement of NA-evoked contractions. NPY depressed the nerve stimulation-evoked 3H-NA release from human submandibular arteries via a prejunctional mechanism which was resistant to nifedipine. NPY contracted human mesenteric veins and renal arteries, but not mesenteric arteries. In conclusion, NPY seems to be co-released with NA upon sympathetic activation in man. Furthermore, NPY exerts both pre- and postjunctional effects on sympathetic control of human blood vessels.

Arginase as a potential target in the treatment of cardiovascular disease: reversal of arginine steal?

Functional integrity of the vascular endothelium is of fundamental importance for normal vascular function. A key factor regulating endothelial function is the bioavailability of nitric oxide (NO). Recently, the enzyme arginase has emerged as an important regulator of NO production by competing for l-arginine, which is a substrate for both arginase and NO synthase. Increased activity of arginase may reduce the availability of l-arginine for NO synthase, thus reducing NO production, increasing formation of reactive oxygen species, and leading ultimately to endothelial dysfunction. Increased activity and expression of arginase have been demonstrated in several pathological cardiovascular conditions, including hypertension, pulmonary arterial hypertension, atherosclerosis, myocardial ischaemia, congestive heart failure, and vascular dysfunction in diabetes mellitus. Experimental studies have demonstrated that inhibition of arginase under these conditions increases NO bioavailability, reduces oxidative stress, improves vascular function, and protects against ischaemia-reperfusion injury. Initial clinical interventional studies are also promising. The purpose of this review is to discuss the role of arginase in cardiovascular pathologies, its contribution to the development of several cardiovascular disease states and the feasibility of using arginase inhibition as a therapeutic strategy.

Neuropeptide Y and Sympathetic Neurotransmissiona

The coexistence of neuropeptide Y (NPY) with noradrenaline (NA) in perivascular nerves as well as in sympathetic nerves to muscle in the heart, spleen and vas deferens suggests a role for NPY in autonomic transmission. Sympathetic nerve stimulation or reflexogenic activation in experimental animals or man are associated with NPY release as revealed by overflow mainly upon strong activation. This difference between NPY and NA secretion may be related to the partly separate subcellular storage whereby NPY seems to be exclusively present in the large dense-cored vesicles. The NPY secretion is likely to be regulated by the local biophase concentrations of NA acting on prejunctional alpha-2-adrenoceptors since alpha-2 agonists inhibit and antagonists enhance NPY overflow, respectively. Furthermore, after NA has been depleted by reserpine, the nerve stimulation-evoked release of NPY is enhanced leading to a progressive depletion of tissue content of NPY. Exogenous NPY binds to both pre- and postjunctional receptors, inhibits NA and NPY release, enhances NA-evoked vasoconstriction and induces vasoconstriction per se. The prejunctional action of NPY which is especially noticeable in the vas deferens may serve to reduce transmitter secretion upon excessive stimulation. The long-lasting vasoconstriction evoked by sympathetic stimulation in several tissues including skeletal muscle, nasal mucosa and spleen, which remains in animals pretreated with reserpine (to deplete NA) combined with preganglionic denervation (to prevent the concomitant excessive NPY release and depletion), is mimicked by NPY and highly correlated to NPY release. Under these circumstances the NPY content in the local venous effluent reaches levels at which exogenous NPY evokes vasoconstriction.

Endothelin in myocardial ischaemia and reperfusion

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide derived from vascular endothelial cells. ET-1 can also be produced by other cell types such as smooth muscle cells and cardiomyocytes. Plasma levels of ET-1 are elevated during several different cardiovascular disorders like atherosclerosis, myocardial infarction and congestive heart failure. During and following myocardial ischaemia and reperfusion, the myocardial production and release of ET-1 is stimulated and the coronary constrictor response to ET-1 is enhanced. These findings all favour a pathophysiological role for ET-1 in the development of ischaemia/reperfusion injury. Accordingly, by using different pharmacological tools (monoclonal antibody, ET converting enzyme inhibitor or ET receptor antagonists) that block the biological actions of ET-1, myocardial ischaemia/reperfusion injury has been demonstrated to be reduced in experimental animal models, in terms of both reduction in final infarct size and improved recovery of myocardial performance and coronary flow. However, some studies have shown no cardioprotective effects of ET receptor antagonists. Possible explanations for these apparently conflicting results are differences in animal species used, route and timing of drug administration, experimental protocol and chemical nature of the antagonists. The potential mechanisms underlying the cardioprotective effects of ET antagonists are discussed and include prevention of no-reflow, inhibition of ET-induced neutrophil activation, abolishment of direct pro-ischaemic actions of ET on myocytes, and interruption of interference of ET with the renin-angiotensin system.