Vasodilator action of guinea pig vasoactive intestinal polypeptide (VIP): comparison with common mammalian VIP.

The vascular activity of guinea pig (gp) and common mammalian (p) VIP were compared in anesthetized guinea pigs and dogs. In the guinea pig, intravenous injections of gpVIP and pVIP increased pancreatic blood flow and reduced the systemic arterial pressure and pancreatic vascular resistance in a dose-related manner. There were no significant differences in the vasodilator actions of these two VIPs, indicating that the overall cardiovascular actions of gpVIP and pVIP are similar in guinea pigs. In the dog, gpVIP, when given intra-arterially, was less potent (about 1/4) than pVIP in its action on femoral blood flow, suggesting that the blood vessels of the dog hind leg are more sensitive to its own VIP than to gpVIP. Oxidation of pVIP and gpVIP with H2O2 greatly reduced their vasodilator effects on the femoral arterial blood flow. The vascular effects were restored to control levels by reduction of the oxidized peptides with mercaptoethanol, which suggests that methionine residues of gpVIP and pVIP are important in the vasodilator effect on the femoral arterial bed in dogs.     

Porcine VIP is more potent than guinea pig VIP in relaxing the guinea pig uterine artery

The vasodilator potency of guinea pig VIP (gp VIP) on the guinea pig uterine artery was compared with the potency of porcine VIP (p VIP), which differs in amino acid sequence at four locations. When antioxidants were not used, the two peptides were approximately equipotent in causing relaxation of precontracted vessel segments. Use of the antioxidants ascorbic acid and dithiothreitol resulted in significantly increased potency of both peptides. Porcine VIP was 15 times more potent than gp VIP synthesized by the same method (tBoc), and gp VIP synthesized by tBoc methodology was 2 times more potent than gp VIP synthesized by Fmoc methodology. Therefore, care should be taken in the choice and handling of synthetic peptides when aiming to mimic actions of endogenous peptides.     

The peptidergic innervation of the guinea pig uterine artery in pregnancy

The influence of pregnancy on the density and pattern of the peptidergic innervation of the guinea pig uterine artery was studied. Whole mount stretch preparations of the uterine artery from estrus and late pregnant guinea pigs were processed for the immunohistochemical demonstration of neuropeptide Y (NPY)-, vasoactive intestinal polypeptide (VIP)-, calcitonin gene-related peptide (CGRP)- and substance P (SP)- immunoreactive nerve fibres. In late pregnancy the density of NPY- and CGRP- containing nerve fibres was remarkably decreased, while that of VIP- and SP- immunoreactive nerves showed a moderate reduction. The meaning and the possible physiological relevance of the decreased density of peptide-immunoreactive nerves in the uterine artery in late pregnancy are discussed.     

Differential inhibition by botulinum neurotoxin A of cotransmitters released from autonomic vasodilator neurons

The role of the soluble NSF attachment protein receptor (SNARE) protein complex in release of multiple cotransmitters from autonomic vasodilator neurons was examined in isolated segments of guinea pig uterine arteries treated with botulinum neurotoxin A (BoNTA; 50 nM). Western blotting of protein extracts from uterine arteries demonstrated partial cleavage of synaptosomal-associated protein of 25 kDa (SNAP-25) to a NH2-terminal fragment of approximately 24 kDa by BoNTA. BoNTA reduced the amplitude (by 70-80%) of isometric contractions of arteries in response to repeated electrical stimulation of sympathetic axons at 1 or 10 Hz. The amplitude of neurogenic relaxations mediated by neuronal nitric oxide (NO) was not affected by BoNTA, whereas the duration of peptide-mediated neurogenic relaxations to stimulation at 10 Hz was reduced (67% reduction in integrated responses). In contrast, presynaptic cholinergic inhibition of neurogenic relaxations was abolished by BoNTA. These results demonstrate that the SNARE complex has differential involvement in release of cotransmitters from the same autonomic neurons: NO release is not dependent on synaptic vesicle exocytosis, acetylcholine release from small vesicles is highly dependent on the SNARE complex, and neuropeptide release from large vesicles involves SNARE proteins that may interact differently with regulatory factors such as calcium.     

Bradykinin receptors: functional similarities in guinea pig gut muscle and mucosa

It is well established that bradykinin can stimulate mucosal electrolyte transport. However, the receptor type which mediates this effect has not been fully characterized. Recent studies have suggested that bradykinin and related kinins may act at two types of receptors designated as B1 and B2. We have determined the effect of bradykinin on electrolyte secretion across guinea pig ileal mucosa and longitudinal muscle in vitro in the presence and absence of D-Phe7-bradykinin (B2 antagonist) and des-Arg9-(Leu8)-bradykinin (B1 antagonist). The B2 antagonist (less than 100 microM) did not affect resting muscle tension or basal electrolyte transport but at 6-30 microM it caused a parallel rightward shift in the concentration-response curves to bradykinin in the mucosa (Ki = 4 microM) and muscle (Ki = 6 microM). Changes in electrolyte transport and muscle contractility evoked by bethanechol and substance P were not affected by the B2 antagonist (30 microM) in either the muscle or the mucosa. Moreover, changes in electrolyte transport and muscle contractility produced by bradykinin were not altered by the B1 antagonist (30 microM). Finally, the B1 agonist des-Arg9-bradykinin (10 nM-1 microM) was not active in either preparation. These data suggest that under normal conditions, ileal secretion and smooth muscle contractility in the guinea pig are regulated by B2-type bradykinin receptors.     

Interaction of NPY and VIP in regulation of myometrial blood flow and mechanical activity

The occurrence, molecular characteristics and biological function of neuropeptide Y (NPY) has been studied in the female genital tract of non-pregnant rabbits. NPY immunoreactivity was demonstrated throughout the genital tract. Maximum concentrations were found in the salpinx (fallopian tube), 570 pmol/g (median) lower within the uterine body (1.5 pmol/g), cervix (2.8 pmol/g) and vagina (3.6 pmol/g). In vitro, NPY had a dose-dependent stimulatory effect on non-vascular smooth muscle (ED50 10(-9) mol/l) as studied by myometrial tension recordings. In vivo, NPY (50 pmol/min.kg) induced a dose-related, non-adrenergic and non-cholinergic decrease in myometrial blood flow. Small C-terminal (NPY31-36) or N-terminal (NPY1-16) fragments of NPY had no effect on myometrial blood flow. NPY was found to interact with the smooth muscle effect of VIP; the presence of VIP (10(-8) mol/l) counteracted the contraction elicited by NPY (10(-8) mol/l) returning the response to control value. VIP and NPY displayed a similar physiological antagonism on myometrial blood flow. There was a clear difference in the response to VIP and NPY as the effect of NPY on myometrial blood flow first appeared after a lag period of 2 minutes whereas the effect of VIP was almost instantaneous. It is concluded that NPY and VIP may interact in the local nervous control of genital functions.     

Receptor binding of guinea pig and pig vasoactive intestinal peptides by rat lung.

Guinea pig vasoactive intestinal peptide (gpVIP) differs from other mammalian VIPs in four of its 28 amino acid residues. In the present study, the gpVIP displaced 125I-labelled pig VIP (pVIP) binding by rat lung membranes with 7.7-fold lower potency than pVIP. Degradation of gpVIP by rat lung membranes, assessed by radioimmunoassay and h.p.l.c., was 1.9-fold greater than that of pVIP. This difference in degradation of the two peptides was not large enough to account for the lower receptor-binding potency of gpVIP. The amino acid residues that distinguish pVIP from gpVIP are likely to contribute to the interaction of VIP with receptors and peptide hydrolases in lung membranes.     

Relative resistance of functional beta2-adrenoceptor-mediated smooth muscle responses to in vitro desensitization.

The effects of in vitro incubation of rat isolated left atria, pulmonary artery rings, and aortic rings with isoprenaline (10(-6) M for 6 h) were examined to compare the degree of desensitization of beta1- and beta2-adrenoceptor-mediated functional responses. The experimental protocols were carefully controlled to exclude influence from persistence of agonist in the tissues after the prolonged exposures, time-dependent changes in tissue sensitivity, and the methods of plotting the data. Concentration-response curves for isoprenaline were constructed before incubation with isoprenaline and, after washout during 1 h, a second curve was obtained. Two protocols were employed: firstly, the preincubation curve was constructed to ensure that a maximum response was obtained (>10(-6) M) and, secondly, the preincubation curve was constructed to a maximum isoprenaline concentration of 10(-6) M. Preincubation curves were corrected for time-dependent changes in sensitivity from sham-incubation control experiments. There was significant desensitization of the beta1-adrenoceptor-mediated positive inotropic responses of the left atria, using both protocols, seen as rightward shifts (dose ratios: 4.48 +/- 1.12 and 8.39 +/- 2.3) of the concentration-response curves and depression of the maximum responses (77.0 +/- 3.2 and 60.8 +/- 5.5%). In contrast, the beta2-adrenoceptor-mediated relaxations of the noradrenaline-constricted pulmonary artery and aorta did not display a significant loss of sensitivity. When the relaxation responses were plotted as a percentage of the noradrenaline-induced tone, there was no significant rightward shift of the concentration-response curves in the pulmonary artery (dose ratios: 2.82 +/- 1.33 and 2.24 +/- 0.62) or aorta (dose ratios: 1.43 +/- 0.62 and 1.31 +/- 0.27) and thus no desensitization.     

Immunohistochemical localization of neuropeptide Y in the guinea pig medulla oblongata. Correlation with VIP and DBH

The immunohistochemical localization of neuropeptide Y (NPY) was correlated with those of dopamine-beta-hydroxylase (DBH) and vasoactive intestinal polypeptide (VIP) by mapping serial 7 micron paraffin sections at three levels of the guinea pig lower brainstem: a) area postrema, b) dorsal motor nucleus of the vagus, and c) nucleus prepositus of the hypoglossal nerve. Based on differences in transmitter expression, three populations of NPY-immunoreactive (IR) neurons were distinguished: NPY-IR catecholaminergic cells (NPY/CA), NPY-IR VIP-ergic cells (NPY/VIP), and NYP-IR cells which were not reactive to either DBH or VIP. Within these populations, size differences among neurons in characteristic locations allowed differentiation among the following subpopulations: NPY/CA neurons in the lateral reticular nucleus--magnocellular part (mean neuronal size 538 micron2) and parvocellular part (318 micron2)-, in the vagus-solitarius complex (433 micron2), and in the dorsal strip (348 micron2); NPY/VIP neurons in the vagus-solitarius complex (368 micron2) and in the nucleus ovalis (236 micron2). Apart from scattered NPY-IR cell bodies in the regions listed above, NPY-IR cell bodies in the lateral portion of the nucleus solitarius and in the caudal part of the spinal nucleus of the trigeminal nerve did not exhibit IR to either DBH or VIP. NPY-IR neurons in the area postrema occurred too infrequently for co-localization studies. The differential distribution of heterogeneous NPY-IR cell subpopulations may reflect the involvement of NPY in a variety of neuronal functions.     

Sodium nitroprusside relaxes goat coronary artery through activation of calcium-dependent K+ channels

In the present investigation we have examined the hypothesis that calcium-dependent K+ channels (K(Ca)) are involved in the sodium nitroprusside (SNP)-induced vasodilatation of goat coronary artery. SNP (10(-9)-3 x 10(-6) M), added cumulatively, relaxed K+ (30 mM)-contracted coronary artery ring segments in a concentration-dependent manner with an EC50 of 1.32 x 10(-7) M (95% CL, 0.93-1.86 x 10(-7) M; n = 21). K(Ca) blocker, tetraethyl ammonium (1 mM) caused a rightward shift in the concentration-response curve of SNP with a corresponding increase in EC50 (1.62 x 10(-6) M; 95% CL, 0.44-6.02 x 10(-6) M, n = 4) of nitro vasodilator. Lowering of extra cellular Ca2+ in the physiological saline solution to 1/4 of normal selectively attenuated the vasorelaxant response of SNP, thereby causing an increase in its EC50 (2.4 x 10(-6) M; 95% CL, 1.23-4.68 x 10(-6) M, n = 4). Exposure of the tissues to high K+ (80 mM) solution, a protocol adopted to reduce the K+ gradient across the cell membrane, markedly inhibited the coronary artery relaxations induced by SNP (EC50, 2.54 x 10(-6) M; 95% CL, 1.31-4.91 x 10(-6) M, n = 4), when compared with tissues contracted with low K+ (30 mM) solution (EC50 7.9 x 10(-8); 95% CL, 4.4 x 10(-8)-1.44 x 10(-7) M, n = 6). The results suggested that a major component of SNP-induced relaxation of goat coronary artery was mediated by K(Ca) channels.     

Dactinomycin is a competitive neurokinin-2 receptor antagonist.

Dactinomycin, a peptide antibiotic from Streptomyces spp., is a classical agent which inhibits DNA replication. In the present study, dactinomycin inhibited specific [125I]NKA binding in rat colon membranes (KI = 1.05 x 10(-5) M) in a competitive manner. Furthermore, dactinomycin caused a parallel rightward shift of the concentration-response curve for the contractions in the rat colon induced by the NK-2 receptor agonist [Nle10]-NKA(4-10). A selective inhibition of NK-2 receptors by dactinomycin was supported by the absence of inhibition of NK-1 receptors activation in guinea pig vas deferens and of NK-3 receptors in rat portal vein. The structural similarity of the cyclic peptide moieties of dactinomycin to L-659,877, a known NK-2 receptor antagonist, can probably account for the present observations.     

Innervation of human omental arteries and veins and vasomotor response to noradrenaline, neuropeptide Y, substance P and vasoactive intestinal peptide

Human omental arteries and veins are supplied with nerve fibers containing noradrenaline (NA) and neuropeptide Y (NPY); these two agents probably co-exist in perivascular sympathetic nerve fibers. Substance P (SP)- or vasoactive intestinal peptide (VIP)-containing fibers could not be detected. In studies on isolated omental vessels NA produced constriction. The results of blockade experiments suggest that human omental arteries are equipped predominantly with alpha 1-adrenoceptors and omental veins with a mixture of alpha 1- and alpha 2-adrenoceptors. NPY at a concentration of 10(-7) M or higher had a weak contractile effect on veins and virtually no effect on arteries. NPY at a concentration of 3 X 10(-8) M shifted the NA concentration response curve to the left in arteries (pD2 = 5.8 for NA versus 6.6. for NA in the presence of NPY; P less than 0.001) but not in veins. Both SP and VIP relaxed arteries precontracted with NA or prostaglandin F2 alpha (PGF2 alpha). The potency of SP as a relaxant agent was similar in arteries and veins; the effect of VIP was elicited at lower concentrations in veins than in arteries.     

Neuropeptide Y (NPY)-like immunoreactivity in guinea pig uterus is reduced during pregnancy in parallel with noradrenergic nerves

Neuropeptide Y (NPY) is a recently discovered neuropeptide with vasoconstrictor effects when given in vivo. It occurs in many sympathetic neurons, where it appears to coexist with noradrenaline (NA). It is wellknown that profound changes in the levels of uterine NA occur in many species during pregnancy. Therefore we have investigated the distribution of catecholamine neurons and NPY by immunohistochemistry in the pregnant and nonpregnant guinea pig uterus. In the virgin uterus NPY-like immunoreactivity was present in nerve fibres and terminals in the smooth muscle layers of the uterine horns and around blood vessels. The distribution of NPY fibres was very similar to that of noradrenergic nerves visualized with antibodies against the catecholamine synthesizing enzyme tyrosine hydroxylase (TH). In the pregnant uterus, NPY- and TH-like immunoreactivity disappeared almost completely. In the cervix, a slight decrease of immunoreactivity was observed, whereas in the ovaries no changes were noted between the pregnant and nonpregnant condition. The results indicate that NPY and catecholamines coexists in the adrenergic neurons of the guinea pig uterus, cervix and ovary and that they vary together in the myometrium during pregnancy. We suggest that NPY may be of functional importance for the pregnant uterus.     

Neuropeptide Y (NPY)-like immunoreactivity in guinea pig uterus is reduced during pregnancy in parallel with noradrenergic nerves

Summary Neuropeptide Y (NPY) is a recently discovered neuropeptide with vasoconstrictor effects when given in vivo. It occurs in many sympathetic neurons, where it appears to coexist with noradrenaline (NA). It is wellknown that profound changes in the levels of uterine NA occur in many species during pregnancy. Therefore we have investigated the distribution of catecholamine neurons and NPY by immunohistochemistry in the pregnant and nonpregnant guinea pig uterus. In the virgin uterus NPY-like immunoreactivity was present in nerve fibres and terminals in the smooth muscle layers of the uterine horns and around blood vessels. The distribution of NPY fibres was very similar to that of noradrenergic nerves visualized with antibodies against the catecholamine synthesizing enzyme tyrosine hydroxylase (TH). In the pregnant uterus, NPY- and TH-like immunoreactivity disappeared almost completely. In the cervix, a slight decrease of immunoreactivity was observed, whereas in the ovaries no changes were noted between the pregnant and nonpregnant condition. The results indicate that NPY and catecholamines coexists in the adrenergic neurons of the guinea pig uterus, cervix and ovary and that they vary together in the myometrium during pregnancy. We suggest that NPY may be of functional importance for the pregnant uterus.     

Innervation of lower airways and neuropeptide effects on bronchial and vascular tone in the pig

Summary The occurrence and distribution of peptide-containing nerve fibres [substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), neuropeptide Y (NPY)] and noradrenergic nerve fibres [tyrosine hydroxylase (TH)- and dopamine beta hydroxylase (DBH)-positive] in the airways of the pig were studied by means of immunohistochemistry. SP- and CGRP-immunoreactive (-IR) nerve fibres were present close to and within the lining respiratory epithelium, around blood vessels, within the tracheobronchial smooth muscle layer and around local tracheobronchial ganglion cells. The content of CGRP- and neurokinin A (NKA)-like immunoreactivity (-LI) measured by radioimmunoassay (RIA) was twice as high in the trachea compared to that in the peripheral bronchi. SP was a more potent constrictor agent than NKA on pig bronchi in vitro. CGRP had a relaxant effect on precontracted pig bronchi. On blood vessels CGRP exerted a relaxant effect that was more pronounced on pulmonary arteries than on bronchial arteries. VIP/PHI-IR fibres were seen in association with exocrine glands and in the tracheobronchial smooth muscle layer. VIP-positive nerve fibres were abundant around blood vessels in the trachea but sparse or absent around blood vessels in the peripheral bronchi. This histological finding was supported by RIA; it was shown that the content of peptides displaying VIP-like immunoreactivity (-LI) was 18 times higher in the trachea compared to peripheral bronchi. VIP was equally potent as CGRP in relaxing precontracted pig bronchi in vitro. Both bronchial and pulmonary arteries were relaxed by VIP. NPY was colocalized with VIP in tracheal periglandular nerve fibres and in nerve fibres within the tracheobronchial smooth muscle layer. NPY was also present in noradrenergic (DBH-positive) vascular nerve fibres. The content of NPY was much higher (15-fold) in the trachea compared to small bronchi. NPY caused a contraction of both pulmonary and bronchial arteries. The bronchial smooth muscle contraction to field stimulation in vitro was purely cholinergic. A non-cholinergic relaxatory effect following field stimulation was observed after bronchial precontraction. Capsaicin had no effect on pig bronchi in vitro.     

Equipotent in vitro actions of alpha- and beta-CGRP on guinea pig basilar artery are likely to be mediated via CRLR derived CGRP receptors

The aim of the present study was to investigate and compare specific in vitro pharmacological actions of human alpha- and beta-CGRP applied as single concentrations to prostaglandin F2alpha precontracted segments of guinea pig basilar artery. To support the suggestion of a possible link between the pharmacological actions of alpha- and beta-CGRP and a specific receptor, we wished to determine whether mRNAs required for the expression of calcitonin receptor-like receptor (CRLR) derived CGRP receptors were present in the guinea pig basilar artery. In the pharmacological experiments we demonstrated an increase in the cAMP content by 2.5-fold and a concomitant significant vasorelaxation of the precontracted basilar artery segments following 1 min of stimulation by 10(-7) M alpha- or beta-CGRP. In another set of experiments, the time course of alpha- and beta-CGRP induced vasodilatation was investigated and concentration dependent responses of the two peptides were demonstrated. No significant differences between the actions of alpha- and beta-CGRP regarding induction of cAMP formation, amount of vasodilatation, time course of vasodilatation and mode of inhibition by the CGRP receptor antagonist, human alpha-CGRP(8-37), could be detected. The presence of mRNA encoding the guinea pig CRLR and the guinea pig CGRP receptor component protein (RCP) in the guinea pig basilar artery was demonstrated by RT-PCR methods. Furthermore, a partial sequence of mRNA encoding the guinea pig CRLR was determined. The expression in this tissue of a CRLR derived CGRP receptor and a functional RCP is therefore likely, and the equipotent pharmacological actions of alpha- and beta-CGRP might be mediated via CRLR derived CGRP receptors.     

Neuropeptide Y: presence in perivascular noradrenergic neurons and vasoconstrictor effects on skeletal muscle blood vessels in experimental animals and man

The presence of neuropeptide Y (NPY)-like immunoreactivity (-LI) in sympathetic perivascular nerves and the functional effects of NPY and noradrenaline (NA) on vascular tone were studied in skeletal muscle of various species. A dense network of NPY-LI was found around arteries and arterioles but not venules in the gluteus maximus muscle of man, gracilis muscle of dog, tenuissimus muscle of rabbit and quadriceps muscle of cat, rat, guinea pig and pig. The distribution of NPY-immunoreactive (-IR) nerves was closely correlated to the presence of tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH)-positive fibers, two markers for noradrenergic neurons. Double-staining experiments revealed that NPY- and TH-IR as well as NPY- and DBH-IR nerve fibers around arteries and arterioles were identical. The veins and venules, however, lacked or had a very sparse innervation of NPY-, TH- and DBH-positive fibers. The NPY- and TH-IR nerves in quadriceps muscle of the guinea pig were absent after treatment with 6-hydroxydopamine. Lumbosacral sympathetic ganglia from the same species contained many NPY-positive cells which were also TH- and DBH-IR. NPY-LI was also detected by radioimmunoassay in extracts of skeletal muscle from guinea pig, rabbit, dog, pig and man as well as of lumbosacral sympathetic ganglia. The content of NPY-LI in skeletal muscle was relatively low (0.1-0.4 pmol/g), whereas lumbosacral sympathetic ganglia had a much higher content (48-88 pmol/g). NPY (10(-7) M) contracted arterioles in the tenuissimus muscle of the rabbit to a similar extent (by 65%) as NA (10(-6) M), as studied by intravital microscopy in vivo. NPY had no effect on the corresponding venules while NA caused a slight contraction of these vessels. In vitro studies of small human skeletal muscle arteries and veins revealed that NPY was more potent than NA in contracting the arteries, and the highest concentration of NPY (5 x 10(-7) M) caused a contraction of a similar magnitude as NA 10(-5) M. NA contracted veins from human skeletal muscle, while NPY had only small effects. It is suggested that NPY, together with NA, could be of importance for sympathetic control of skeletal muscle blood flow.     

Contractile and dilatory action of neuropeptides on isolated human mesenteric blood vessels

Neuropeptide Y (NPY), substance P (SP), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), lysyl-bradykinin, somatostatin, Met- and Leu-enkephalin were tested for their smooth muscle activity in isolated human mesenteric arteries and veins. Only NPY regularly contracted both arteries and veins. Alpha-adrenergic and 5-HT2 antagonists did not affect the response. Somatostatin contracted the veins, but not the arteries, in a variable but concentration-dependent way. The other neuropeptides were without contractile effect. CGRP, bradykinin, and SP regularly dilated, in a concentration-dependent way, both arteries and veins precontracted with prostaglandin F2 alpha or uridine triphosphate. CGRP and bradykinin were the most potent dilators. VIP and somatostatin usually caused a moderate dilatation in the arteries, whereas in the veins, somatostatin was without dilatory effect and the VIP-induced dilatation was irregular. In both types of vessels Met-enkephalin seldom gave any significant dilatation, and no response occurred in the presence of Leu-enkephalin or NPY. The SP-antagonist (D-Arg, D-Trp, Leu)-SP (spantide) caused a dextal shift of the concentration-response curves for SP, in the case of the arteries also including a reduced maximum effect.     

The cloned guinea pig neuropeptide Y receptor Y1 conforms to other mammalian Y1 receptors.

We have cloned the guinea pig neuropeptide Y (NPY) Y1 receptor and found it to be 92-93% identical to other cloned mammalian Y1 receptors. Porcine NPY and peptide YY (PYY) displayed affinities of 43 pM and 48 pM, respectively. NPY2-36 and NPY3-36 had 6- and 46-fold lower affinity, respectively, than intact NPY. Functional coupling was measured by using a microphysiometer. Human NPY and PYY were equipotent in causing extracellular acidification with EC50 values of 0.59 nM and 0.69 nM, respectively, whereas NPY2-36 and NPY3-36 were about 15-fold and 500-fold less potent, respectively, than NPY. The present study shows that the cloned guinea pig Y1 receptor is very similar to its orthologues in other mammals, both with respect to sequence and pharmacology. Thus, results from previous studies on guinea pig NPY receptors might imply the existence of an additional Y1-like receptor sensitive to B1BP3226.