Lars Grundemar

Neuropeptide Y Receptor Subtypes, Y1 and Y2

Heterogeneity among NPY (and PYY) receptors was first proposed on the basis of studies on sympathetic neuroeffector junctions, where NPY (and PYY) can exert three types of action: 1) a direct (e.g., vasoconstrictor) response; 2) a postjunctional potentiating effect on NE-evoked vasoconstriction; and 3) a prejunctional suppression of stimulated NE release; the two latter phenomena are probably reciprocal, since NE affect NPY mechanisms similarly. It was found that amidated C-terminal NPY (or PYY) fragments, e.g., NPY 13-36, could stimulate selectively prejunctional NPY/PYY receptors, which were termed Y2-receptors. Consequently, the postjunctional receptors which were activated poorly by NPY/PYY fragments, were termed Y1-receptors. Later work has indicated that the Y2-receptor may occur postjunctionally in selected sympathetic effector systems. The central nervous system appears to contain a mixture of Y1- and Y2-receptors as indicated by functional as well as binding studies. For instance, NPY and NPY 13-36 produced diametrically opposite effects on behavioral activity, indicating the action of the parent peptide on two distinct receptors. Cell lines, most importantly neuroblastomas, with exclusive populations of Y1- or Y2-receptors, have been characterized by binding and second messenger studies. In this work, selective agonists for the two receptor subtypes were used. Work of many investigators has formed the basis for subclassifying NPY/PYY effects being mediated by either Y1- or Y2-receptors. A preliminary subclassification based on effects of NPY, PYY, fragments and/or analogs is provided in Table 6. It is, however, to be expected that further receptor heterogeneity will be revealed in the future. It is argued that mast cells possess atypical NPY/PYY receptors. The histamine release associated with stimulation of the latter receptors may, at least in part, underlie the capacity of NPY as well as of short C-terminal fragments to reduce blood pressure. Fragments, such as NPY 22-36, appear to be relatively selective vasodepressor agents because of their weak vasopressor properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Pitfalls using metalloporphyrins in carbon monoxide research

The proposal that endogenously produced carbon monoxide (CO) may act as a biological messenger has remained controversial. Carbon monoxide is generated by haem oxygenase isoenzymes in the degradation of haem-containing molecules. Certain metalloporphyrins, which are inhibitors of haem oxygenase, have been widely used as pharmacological tools in order to establish a messenger role for CO in the brain and periphery. However, increasing evidence shows that many metalloporphyrins are also associated with a large range of undesired effects, which make the interpretation of results using such compounds very uncertain. In this article, Lars Grundemar and Lars Ny evaluate the properties and describe the nonselective effect profile of such metalloporphyrins.

Neuropeptide Y effector systems: perspectives for drug development

Neuropeptide Y was isolated in 1982 and has since attracted considerable interest. It is widely distributed in central and peripheral neurones and can produce a multitude of biological effects in the brain and the periphery. For example, the peptide has been associated with stimulation of food and water intake, control of mood, and regulation of central autonomic functions. In the periphery, sympathetic neuropeptide Y plays a role as a vasopressor and vasoconstrictor. Neuropeptide Y acts on at least three distinct receptor types, referred to a Y1, Y2 and Y3. This review by Lars Grundemar and Rolf Håkanson focuses on some neuropeptide Y-dependent mechanisms that may be implicated in certain disorders and may be promising targets for drugs active at neuropeptide Y receptors.

Multiple neuropeptide Y receptors are involved in cardiovascular regulation. Peripheral and central mechanisms

1. Neuropeptide Y (NPY) occurs in both the central and peripheral nervous system. In the periphery, NPY coexists with noradrenaline (NA) in perivascular sympathetic fibers. 2. NPY has a vasopressor effect, reflecting direct vasoconstriction of blood vessels and potentiation of the NA-evoked response. NPY also suppresses the release of NA from sympathetic fibers. 3. The post- and pre-junctional NPY receptors are referred to as Y1 and Y2, respectively. They recognize not only NPY but also the homologous gut hormone peptide YY (PYY). 4. The Y1 and Y2 receptors have been characterized in numerous test systems using analogs of NPY/PYY. Already the deletion of the first N-terminal amino acid (NPY 2-36) results in a marked loss of potency at the Y1 receptor. The Y2 receptor is much less dependent upon an intact N-terminus, and a wide range of C-terminal NPY fragments retain quite high potency. 5. Recently, yet another NPY receptor, Y3, that is distinct from Y1 and Y2 in that it recognizes PYY poorly, has been demonstrated in the brainstem and in the periphery. 6. Further attempts to characterize the various receptor types have relied on truncated and substituted analogs of NPY/PYY. Although such studies suggest the existence of at least three types of NPY receptors, the lack of antagonists has represented a problem. 7. Since NPY may regulate cardiovascular functions via peripheral and central receptors its physiological and possibly pathophysiological significance has attracted much attention. 8. The responsiveness to NPY seems to be altered in animal models of hypertension and elevated plasma levels of NPY have been found in patients under various conditions of stress and in primary hypertension. A number of studies have suggested that NPY may be a pathogenetic factor behind primary hypertension. 9. Antagonists for the various NPY receptors would be useful for an analysis of which effects of these peptides are physiologically relevant. It is tempting to predict that both agonists and antagonists of the NPY receptors could be useful as drugs, for instance, in the treatment of primary hypertension.

Human neuropeptide Y signal peptide gain-of-function polymorphism is associated with increased body mass index: Possible mode of function

Neuropeptide Y (NPY) has been implicated in the control of food intake and energy balance based on many observations in animals. We have studied single nucleotide polymorphisms (SNPs) within the regulatory and coding sequences of the human NPY gene. One variant (1128 T>C), which causes an amino acid change from leucine to proline at codon 7 in the signal peptide of NPY, was associated with increased body mass index (BMI) in two separate Swedish populations of normal and overweight individuals. In vitro transcription and translation studies indicated the unlikelihood that this signal peptide variation affects the site of cleavage and targeting or uptake of NPY into the endoplasmic reticulum (ER). However, the mutant, and to a lesser extent the wild-type, signal peptide by themselves markedly potentiated NPY-induced food intake, as well as hypothalamic NPY receptor signaling. Our findings in humans strongly indicate that the NPY signaling system is implicated in body weight regulation and suggest a new and unexpected functional role of a signal peptide.

Effects of various neuropeptide Y/peptide YY fragments on electrically-evoked contractions of the rat vas deferens

1 The effects of various neuropeptide Y (NPY) and peptide YY (PYY) fragments on electrically‐evoked twitches in the rat isolated vas deferens were studied and compared with the effects of full length NPY and PYY. The aim was to identify the shortest NPY/PYY fragments that are capable of suppressing the contractions. 2 NPY (1–36) and C‐terminal fragments of NPY (from 11–36 to 22–36) suppressed the electrically‐evoked twitches in a concentration‐dependent manner. On the whole there seemed to be a gradual lowering of the pIC50 values with progressive shortening of the NPY fragments (except for fragments 16–36 and 22–36 that had rather high pIC50 values). NPY 23–36, 24–36 and 25–36 suppressed the twitches at high concentrations (3 μm). NPY 26–36 was without effect as were C‐terminal carboxy‐deaminated NPY and glycine extended NPY (NPY‐Gly‐Lys‐Arg). 3 PYY (1–36) and C‐terminal fragments of PYY (from 11–36 to 23–36) suppressed the electrically‐evoked twitches in a concentration‐dependent manner. PYY 1–36 was more potent than any of the fragments. There was a tendency for shorter fragments to have lower pIC50 values. PYY 24–36 and 25–36 suppressed the twitches at high concentrations (3 μm). PYY 26–36 was without effect. 4 The findings suggest that the 12 C‐terminal amino acid residues of NPY and PYY are the minimum length required to activate the Y2‐receptor.

Localization and activity of haem oxygenase and functional effects of carbon monoxide in the feline lower oesophageal sphincter

1 In the feline lower oesophageal sphincter (LOS), the distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)−‐1 and −2 was studied by immunohistochemistry and confocal microscopy, the HO activity was measured and the possible role for CO as a mediator of relaxation was investigated. 2 HO‐2 immunoreactivity was abundant in nerve cell bodies of the submucosal and myenteric plexus. Approximately 50% of the HO‐2‐containing myenteric cell bodies were also nitric oxide synthase‐ and vasoactive intestinal peptide (VIP)‐immunoreactive. In addition, HO‐2 immunoreactivity was seen in nerve fibres, in non‐neuronal cells dispersed in the smooth muscle and in arterial endothelium. HO‐1 immunoreactivity was confined to non‐neuronal cells in the smooth muscle, similar to those positive for HO‐2. 3 Activity of HO, measured as CO production, was observed in LOS homogenates at a rate of 1.00±0.05 nmol mg−1 protein h−1. This production was inhibited by the HO inhibitor, zinc protoporphyrin‐IX (ZnPP). 4 In isolated circular smooth muscle strips of LOS, developing spontaneous tone, exogenously administered CO evoked a concentration‐dependent relaxation reaching a maximum of 93±3%. This relaxation was accompanied by an increase in cyclic GMP, but not cyclic AMP levels. The relaxant response was attenuated by methylene blue, but unaffected by tetrodotoxin. Repeated exposure to CO resulted in a progressive reduction of the relaxant response. 5 ZnPP caused a rightward‐shift of the concentration‐response curves for the relaxant responses to VIP, peptide histidine isoleucine, and pituitary adenylate cyclase activating peptide 27. 6 ZnPP and tin protoporphyrin‐IX (another inhibitor of HO) did not affect nonadrenergic, noncholinergic relaxations induced by electrical field stimulation. Nor did ZnPP affect relaxations induced by 3‐morpholino‐sydnonimine or forskolin. 7 The present findings, showing localization of HO immunoreactivity to both neuronal and non‐neuronal cells of the feline LOS, ability of LOS to produce CO and a relaxant effect of CO in circular LOS muscle, suggest a role for CO as a peripheral messenger.

Suppression by neuropeptide Y of capsaicin-sensitive sensory nerve-mediated contraction in guinea-pig airways

1 In the present study we have examined whether neuropeptide Y (NPY) interferes with non‐adrenergic, non‐cholinergic nerve‐mediated contractions and relaxations in the guinea‐pig airways. In these experiments we have used ring preparations of bronchi and trachea, incubated in the presence of atropine, propranolol and indomethacin (each 1 μm). 2 The contractile response to electrical stimulation of non‐adrenergic, non‐cholinergic nerve fibres was suppressed by NPY and NPY 13–36 in a concentration‐dependent manner, these agents having similar inhibitory potencies. NPY caused a more complete inhibition than the C‐terminal fragment. 3 NPY affected neither the basal tension nor the substance P‐evoked contraction in the bronchi and trachea and did not interfere with nerve‐mediated, non‐adrenergic relaxation in the trachea. 4 On the basis of these results, it is suggested that NPY may act on the terminals of sensory neurones in the airways to prevent antidromic, excitatory neurotransmission by inhibiting transmitter release.

Characterization of Receptor Types for Neuropeptide Y and Related Peptides

The structurally related peptides neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) are neuronal and/ or endocrine messengers that are involved in a variety of physiological processes. NPY and PYY are able to evoke potent biological effects as well as modulating responses to other transmitters. In many biological systems, NPY and PYY, but not PP seem to activate the same receptors. Because of the wide distribution of NPY in the central and peripheral nervous system compared to that of PYY, many of these actions have been attributed to NPY.

Neuropeptide Y, peptide YY and C-terminal fragments release histamine from rat peritoneal mast cells

1 Neuropeptide Y (NPY) and peptide YY (PYY) seem to act on at least two receptor sybtypes, Y1 and Y2. The Y1‐receptor requires the whole C‐terminally amidated NPY/PYY molecule whereas the Y2‐receptor in addition recognizes C‐terminal fragments of the two peptides. The present study was designed to elucidate whether NPY and related peptides were able to release histamine from isolated peritoneal mast cells of the rat. 2 NPY, NPY 15–36, NPY 22–36, NPY 26–36 and desamido‐NPY evoked a concentration‐dependent release of mast‐cell histamine. The pEC15 values for NPY 15–36 and NPY 22–36 were higher, while the pEC15 value for NPY 26–36 was lower than that for NPY. At the highest concentration tested (0.1 mm), NPY and its C‐terminal fragments released between 30 and 40% of the total histamine content. At the same concentration desamido‐NPY released about 20%. 3 PYY and PYY 15–36 also evoked a concentration‐dependent release of mast‐cell histamine. PYY was more effective than PYY 15–36 since, at 0.1 mm, PYY released about 33%, while PYY 15–36 released about 15% of the total histamine content. Pancreatic polypeptide (PP) and the Y1‐receptor‐selective agonist [Pro34]NPY were virtually inactive. 4 The effect profile of the NPY/PYY‐related peptides suggests that they act on the mast cells by a mechanism that does not involve either of the receptor subtypes hitherto described. The kinetics of the NPY‐evoked histamine release may suggest that positively charged amino acid residues of NPY/PYY release mast‐cell histamine by a non‐receptor mechanism, as has been suggested for substance P and other basic peptides.