Neuropeptide Y-like immunoreactivity of plasma during hypoglycaemia in man

Roles of nuclear NPY and NPY receptors in the regulation of the endocardial endothelium and heart functionThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

It is now well accepted that the heart is a multifunctional organ in which endothelial cells, and more particularly endocardial endothelial cells (EECs), seem to play an important role in regulating and maintaining cardiac excitation–contraction coupling. Even if major differences exist between vascular endothelial cells (VECs) and EECs, all endothelial cells including EECs release a variety of auto- and paracrine factors such as nitric oxide, endothelin-1, angiotensin II, and neuropeptide Y. All these factors were reported to affect cardiomyocyte contractile performance and rhythmicity. In this review, findings on the morphology of EECs, differences between EECs and other types of endothelial cells, interactions between EECs and the adjacent cardiomyocytes, and effects of NPY on the heart will be presented. We will also show evidence on the presence and localization of NPY and the Y1receptor in the endocardial endothelium and discuss their role in the regulation of cytosolic and nuclear free calcium.

Neurohormonal changes in medical students during academic stress

BACKGROUND

Academic stress is a good model of psychological stress in humans and is thus useful for studying psychoneurohormonal changes. The aim of the current study was to examine the effect of academic examination stress on activation of the hypothalamus-autonomic nervous system (HANS) and the hypothalamic-pituitary-adrenocortical (HPA) axis, through the measurements of changes in neuro-hormones during final exams as compared to the pre-exam baseline.

MATERIALS AND METHODS

Forty-eight first- and second-year female medical students participated. Plasma leptin, neuropeptide Y (NPY), nitrite, nitrate, andrenomedullin, cortisol and adrenocorticotropic hormone (ACTH) were measured at baseline and during final examinations.

RESULTS

Plasma levels of cortisol, ACTH, NPY, adrenomedullin, nitrite and nitrate increased during times of academic stress as compared to baseline levels. However, only plasma leptin level was decreased during the academic stress as compared to baseline, probably through a negative feedback mechanism resulting from sympathetic stimulation. The results indicate that both the HANS and HPA are involved in this type of stress and both are activated at the same time.

CONCLUSION

Academic stress induced significant neurohormonal changes. Leptin, NPY, nitrite, nitrate, adrenomedullin, cortisol and ACTH can be considered part of a complex mosaic model of the neuroendocrine system during academic stress.

Region-specific neuropeptide Y overflows at rest and during sympathetic activation in humans

Neuropeptide Y coexists with norepinephrine in sympathetic nerves and is coreleased into the circulation on sympathetic activation. Little is known about the regional release of neuropeptide Y in humans under normal conditions or in pathophysiological situations of sympathetic activation or denervation. We measured plasma neuropeptide Y-like immunoreactivity and norepinephrine concentrations in samples taken from the brachial artery; coronary sinus; and internal jugular, antecubital, or hepatic veins in volunteers aged 20 to 64 years. Regional neuropeptide Y overflow at rest was calculated from venoarterial plasma concentration differences and plasma flow, and norepinephrine spillover was determined by [3H]norepinephrine infusion techniques. Cardiac release of neuropeptide Y and norepinephrine was examined in response to various stressors as well as in clinical models of sympathetic activation, cardiac failure, and denervation after cardiac transplantation. In healthy volunteers, cardiac, forearm, and jugular venous sample neuropeptide Y concentrations were similar to arterial levels. Hepatic vein plasma neuropeptide Y was greater than arterial both at rest (119 +/- 5% of arterial, n = 7) and after a meal (132 +/- 12%, n = 7), with neuropeptide Y overflows of 6 +/- 2 and 11 +/- 2 pmol/min, respectively. In contrast, hepatomesenteric norepinephrine spillover was not significantly increased by feeding. Although coronary sinus plasma norepinephrine concentrations increased significantly with the cardiac sympathetic activation accompanying mental arithmetic, coffee drinking, isotonic exercise, and bicycle exercise, only the latter powerful sympathetic stimulus increased neuropeptide Y overflow. Cardiac failure was associated with increased resting release of both norepinephrine and neuropeptide Y from the heart, whereas postcardiac transplant norepinephrine spillover from the heart was reduced. The net overflow of neuropeptide Y to plasma observed at rest across the hepatic circulation, but not the cardiac, forearm, or cerebral circulations, indicates that the gut, the liver, or both make a major contribution to systemic plasma neuropeptide Y levels in humans. Sympathetic activation by exercise produced a modest increase in cardiac neuropeptide Y overflow but to only approximately 25% of the resting input from the gut and without a change in arterial neuropeptide Y concentration. Plasma neuropeptide Y measurements are less sensitive than those of plasma norepinephrine concentrations as an index for quantifying sympathetic neural responses regulating the systemic circulation.

Neuropeptides in the sympathetic system: presence, plasticity, modulation, and implications

Neuropeptides are ubiquitous in the sympathetic system and modulate transmission at the levels of the intermediolateral cell column, sympathetic ganglia, and neuroeffector junctions. Several neuropeptide-containing pathways from the hypothalamus and medulla modulate excitability of preganglionic neurons. Neuropeptides coexist with norepinephrine or acetylcholine in subpopulations of chemically coded, target-specific sympathetic ganglion neurons. Neuropeptide Y is colocalized in adrenergic vasoconstrictor neurons, whereas vasoactive intestinal polypeptide is colocalized in cholinergic sudomotor neurons. Neuropeptide expression is plastic; during development, neurons that switch from a noradrenergic to a cholinergic phenotype increase expression of vasoactive intestinal polypeptide, somatostatin, and substance P. Preganglionic inputs increase neuropeptide Y and inhibit substance P expression. Sympathetic denervation produces sprouting of sensory fibers containing substance P and calcitonin gene-related peptide in target tissues. Neuropeptides from preganglionic fibers (e.g., enkephalin) and primary afferents (e.g., substance P, vasoactive intestinal polypeptide) modulate transmission in sympathetic ganglia. Neuropeptide Y produces vasoconstriction, prejunctional inhibition of norepinephrine release, and postjunctional potentiation of norepinephrine effects. Plasma neuropeptide Y increases during intense sympathoexcitation, hypertension, and pheochromocytoma. Dystrophic neurites containing neuropeptide Y occur in human sympathetic ganglia during aging, diabetes, and dysautonomia. Sympathetic neuropeptides may thus have important clinical implications.

Preserved insulin secretion and insulin independence in recipients of islet autografts

BACKGROUND

Transplantation of pancreatic islets, rather than whole pancreas, has been introduced as a treatment for diabetes mellitus. We studied five patients ranging in age from 12 to 37 years who had severe chronic pancreatitis for which they underwent total pancreatectomy followed by isolation and hepatic transplantation of their own islets.

METHODS

All patients had remained insulin-independent for 1 to 7 1/2 years after transplantation. The numbers of islets transplanted ranged from 110,000 to 412,000. Islet function was assessed by measuring the plasma insulin responses to intravenous glucose and arginine and the plasma glucagon responses to hypoglycemia and arginine. In one patient, islet function was studied during catheterization of the hepatic vein, portal vein, and splenic artery and by analysis of a liver-biopsy specimen.

RESULTS

After transplantation, the mean (+/- SD) fasting plasma glucose concentration was 122 +/- 47 mg per deciliter (6.8 +/- 2.6 mmol per liter) and the hemoglobin A1c concentration was 6.0 +/- 0.8 percent in the five patients. The values were most abnormal--214 mg per deciliter (11.9 mmol per liter) and 7.3 percent, respectively--in the patient who received only 110,000 islets. The acute plasma insulin responses to glucose and to arginine in the five patients were 23 +/- 13 and 26 +/- 10 microU per milliliter (168 +/- 94 and 184 +/- 70 pmol per liter), respectively, as compared with 58 +/- 6 and 37 +/- 8 microU per milliliter (416 +/- 44 and 267 +/- 61 pmol per liter) in the normal subjects. The peak plasma glucagon responses to insulin and arginine were 21 +/- 4 and 65 +/- 36 pg per milliliter, respectively, as compared with 125 +/- 28 and 156 +/- 99 pg per milliliter in the normal subjects. All five patients had plasma epinephrine but not pancreatic polypeptide responses to hypoglycemia. The results of the hepatic-vein catheterization in one patient indicated that the transplanted islets released insulin and glucagon in response to arginine. Immunoperoxidase staining of this patient's liver-biopsy specimen showed that the islets contained insulin, glucagon, and somatostatin but not pancreatic polypeptide.

CONCLUSIONS

Intrahepatic transplantation of as few as 265,000 islets can result in the release of insulin and glucagon at appropriate times and in prolonged periods of insulin independence.