Relaxant effects of vasodilator peptides on isolated basilar arteries from stroke-prone spontaneously hypertensive rats

Vasomotor effects of noradrenaline, 5-hydroxytryptamine, angiotensin II, bradykinin, histamine, and acetylcholine on the bat (Rhinolophus ferrumequinum) basilar artery

The responsiveness of the basilar artery to intrinsic vasoactive substances is species-specific and can be a unique characteristic. We investigated the responsiveness of the bat (Rhinolophus ferrumequinum) basilar artery to noradrenaline (NA), 5-hydroxytryptamine (5-HT), angiotensin (Ang) II, bradykinin (BK), histamine (His), and acetylcholine (ACh). NA, 5-HT, Ang II, and BK induced contraction, whereas His and ACh induced relaxation, in a concentration-dependent manner. The NA cumulative concentration-response curve was shifted to the right in parallel with phentolamine (an α-antagonist). However, propranolol, a β-antagonist, had no significant effect. The 5-HT curve was shifted to the right in parallel by ketanserin (a 5-HT₂ antagonist) and methiothepin (a 5-HT₁ and 5-HT₂ antagonist). Losartan (an AT₁ antagonist) shifted the Ang II curve to the right, whereas PD123319 (an AT₂ antagonist) had no significant effect. L-NA, indomethacin, and des-Arg⁹-[Leu⁸]-BK (a B₁ antagonist) did not significantly affect BK-induced contractions. HOE140 (a B₂ antagonist) shifted the BK concentration-response curve to the right. The His curve was shifted to the right weakly by diphenhydramine (an H₁ antagonist) and strongly by cimetidine (a H₂ antagonist). ACh-induced relaxation was significantly inhibited by L-NA, atropine, and pFHHSiD (a muscarinic M₃ antagonist), whereas pirenzepine and methoctramine (muscarinic M₁ and M₂ antagonists, respectively) showed no significant effects. At a resting vascular tone, L-NA-induced contraction and indomethacin induced relaxation. These results suggest that α-adrenergic, 5-HT₁, 5-HT₂, AT₁, and B₂ receptors might be important in arterial contraction, whereas M₃ and H₂ (>H₁) receptors might modify these contractions, inducing relaxation.

Atrial natriuretic peptide and regulation of vascular function in hypertension and heart failure: implications for novel therapeutic strategies

Atrial natriuretic peptide (ANP) plays a pivotal role in modulation of vascular function and it is also involved in the pathophysiology of several cardiovascular diseases. We provide an updated overview of the current appraisal of ANP vascular effects in both animal models and humans. We describe the physiological implications of ANP vasomodulatory properties as well as the involvement of ANP, through its control of vascular function, in hypertension and heart failure. The principal molecular mechanisms underlying regulation of vascular tone, that is natriuretic peptide receptor type A/cyclic guanylate monophosphate, natriuretic peptide receptor type C, nitric oxide system, are discussed. We review the literature on therapeutic implications of ANP in hypertension and heart failure, examining the potential use of ANP analogues, neutral endopeptidase (NEP) inhibitors, ACE/NEP inhibitors, angiotensin receptor blocker (ARB)/NEP inhibitors, the new dual endothelin-converting enzyme (ECE)/NEP inhibitors and ANP-based gene therapy. The data discussed support the role of ANP in different pathological conditions through its vasomodulatory properties. They also indicate that ANP may represent an optimal therapeutic agent in cardiovascular diseases.

Peptidergic and non-peptidergic innervation and vasomotor responses of human lenticulostriate and posterior cerebral arteries

The aim of the present study was to compare in man the innervation pattern and the functional responses to neuronal messengers in medium sized lenticulostriate and branches of the posterior cerebral arteries (PCA). The majority of the nerve fibers found were sympathetic and displayed specific immunoreactivity for tyrosine hydroxylase (TH) and neuropeptide Y (NPY). Only few nerve fibers displayed vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and substance P (SP) immunoreactivity. In both arteries, the contractions induced by noradrenaline (NA), NPY and 5-hydroxytryptamine (5-HT) and the relaxant responses induced by acetylcholine (ACh), VIP and pituitary adenylate cyclase activating peptide-27 (PACAP) as well as CGRP and SP were compared in vitro. In conclusion, there was no major difference in innervation pattern or vasomotor sensitivity (pEC50 and pIC50 values) between the two vessels. However, the general pattern indicates stronger vasomotor responses (Emax and Imax) in the PCA branches as compared to the lenticulostriate arteries which may lend support for the clinical observation of a difference in stroke expression between the two vascular areas.

Adrenomedullin receptors: pharmacological features and possible pathophysiological roles

Three receptor activity modifying proteins (RAMPs) chaperone calcitonin-like receptor (CLR) to the cell surface. RAMP2 enables CLR to form an adrenomedullin (AM)-specific receptor that is sensitive to AM-(22-52) (AM(1) receptor). RAMP3 enables CLR to form an AM receptor sensitive to both calcitonin gene-related peptide (CGRP)-(8-37) and AM-(22-52) (AM(2) receptor), though rat and mouse AM(2) receptors show a clear preference for CGRP alpha-(8-37) over AM-(22-52). RAMP1 enables CRL to form the CGRP-(8-37)-sensitive CGRP(1) receptor, which can also be activated by higher concentrations of AM. Here we review the available information on the pharmacological features and possible pathophysiological roles of the aforementioned AM receptors.

Adrenomedullin, an autocrine mediator of blood-brain barrier function

Since the discovery that adrenomedullin gene expression is 20- to 40-fold higher in endothelial cells than even in the adrenal medulla, this peptide has been regarded as an important secretory product of the vascular endothelium, together with nitric oxide, eicosanoids, endothelin-1, and other vasoactive metabolites. Cerebral endothelial cells secrete an exceptionally large amount of adrenomedullin, and the adrenomedullin concentration is about 50% higher in the cerebral circulation than in the peripheral vasculature. The adrenomedullin production of cerebral endothelial cells is induced by astrocyte-derived factors. Adrenomedullin causes vasodilation in the cerebral circulation, may participate in the maintenance of the resting cerebral blood flow, and may be protective against ischemic brain injury. Recent data from our laboratory indicate that adrenomedullin, as an endothelium-derived autocrine/paracrine hormone, plays an important role in the regulation of specific blood-brain barrier properties. Adrenomedullin is suggested to be one of the physiological links between astrocyte-derived factors, cyclic adenosine 3'5'-monophosphate (cAMP), and the induction and maintenance of the blood-brain barrier. Moreover, the role of adrenomedullin in the differentiation and proliferation of endothelial cells and in angiogenesis suggests a more complex function for adrenomedullin in the cerebral circulation and in the development of the blood-brain barrier.

The calcitonin receptor-like receptor/receptor activity-modifying protein 1 heterodimer can function as a calcitonin gene-related peptide-(8-37)-sensitive adrenomedullin receptor

The receptor activity-modifying protein (RAMP)/calcitonin receptor-like (CRL) receptor heterodimer is thought to function as a receptor for either a calcitonin gene-related peptide (CGRP) (CRL receptor/RAMP1) or adrenomedullin (CRL receptor/RAMP2 or -3), depending on the RAMP isoform present. We examined the receptor specificity of adrenomedullin-induced increases in cAMP in human embryonic kidney (HEK)293 cells coexpressing human CRL receptor and human RAMP1 or RAMP2. In cells expressing CRL receptor/RAMP1, adrenomedulin-induced increases in cAMP were comparable to those induced by alpha-CGRP, and the CGRP receptor antagonist alpha-CGRP-(8-37), but not the adrenomedullin receptor antagonist adrenomedullin-(22-52), blocked the adrenomedullin-evoked responses. Cells expressing CRL receptor/RAMP2 responded more selectively to adrenomedullin; in this case, the effect was blocked by adrenomedullin-(22-52) but not by alpha-CGRP-(8-37). Real-time quantitative polymerase chain reaction confirmed that cotransfection of CRL receptor and RAMP1 had no effect on the endogenous expression of RAMP2. Thus, CRL receptor/RAMP1 likely functions as an adrenomedullin receptor as well as a CGRP receptor, which may explain why many of the actions of adrenomedullin are potently antagonized by alpha-CGRP-(8-37).

Alterations of the nitric oxide pathway in cerebral arteries from spontaneously hypertensive rats

Hypertension-associated alterations of the nitric oxide (NO) pathway were analyzed in middle cerebral arteries (MCA) from normotensive (WKY) and hypertensive (SHR) rats. The vasoconstrictor response to prostaglandin F2alpha (PGF(2 alpha), 30 and 100 microM) was smaller in MCA from SHR than from WKY. Endothelium-dependent relaxations to bradykinin (1 nM-10 microM) or acetylcholine (10 microM) were similar in MCA from both strains, whereas the endothelium-independent response to sodium nitroprusside (1 nM-0.1 mM) was smaller in MCA from SHR. L-arginine (L-Arg, 10 microM) similarly inhibited the vasoconstrictor responses in both strains; however, the inhibitory effect of 100 microM of L-Arg was greater in MCA from SHR. N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM), but not aminoguanidine (100 microM) or 7-nitroindazole (10 microM), increased basal tone, potentiated the PGF(2 alpha)-induced vasoconstrictor responses and reduced the bradykinin-elicited relaxation in a similar way in MCA from WKY and SHR. N(omega)-nitro-L-arginine methyl ester also antagonized the inhibitory effect of 10 microM of L-Arg. Incubation for 5 h with lipopolysaccharide (10 microg/ml) similarly reduced the response to PGF(2 alpha) in MCA from WKY and SHR; this reduction was antagonized by dexamethasone (1 microM). Cerebral arteries expressed endothelial (eNOS) and neuronal (nNOS) NO synthase similarly in both strains, but inducible NOS (iNOS) expression was more evident in SHR. Lipopolysaccharide increased iNOS expression in both strains to a similar level. The basal constitutive NOS (cNOS) and iNOS activities were similar in arteries from WKY and SHR. Lipopolysaccharide increased iNOS activity only in arteries from SHR. These results indicate that hypertension did not impair endothelial NO production by NOS activation but induced an up-regulation of basal iNOS expression.

Adrenomedullin in the cerebral circulation

The central nervous system requires an effective autoregulation of cerebral circulation in order to meet the critical and unusual demands of the brain. In addition, cerebral microvessels has a unique feature, the formation of the blood-brain barrier, which contributes to the stability of the brain parenchymal microenvironment. Many factors are known to be involved in the regulation of cerebral circulation and blood-brain barrier functions. In the last few years a new potential candidate, adrenomedullin, a hypotensive peptide was added to this list. Adrenomedullin has a potent vasodilator effect on the cerebral vasculature, and it may be implicated in the pathologic mechanism of cerebrovascular diseases. In this review, we describe current knowledge about the origin and possible role of adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Structural alterations of tight junctions are associated with loss of polarity in stroke-prone spontaneously hypertensive rat blood-brain barrier endothelial cells

The mechanisms leading to stroke in stroke-prone spontaneously hypertensive rats (SHRSP) are not well understood. We tested the hypothesis that the endothelial tight junctions of the blood-brain barrier are altered in SHRSP prior to stroke. We investigated tight junctions in 13-week-old SHRSP, spontaneously hypertensive stroke-resistant rats (SHR) and age-matched Wistar-Kyoto rats (WKY) by electron microscopy and immunocytochemistry. Ultrathin sections showed no difference in junction structure of cerebral capillaries from SHRSP, SHR and WKY, respectively. However, using freeze-fracturing, we observed that the blood-brain barrier specific distribution of tight junction particles between P- and E-face in WKY (58.7+/-3.6%, P-face; 41.2+/-5.59%, E-face) and SHR (53.2+/-19. 3%, P-face; 55.6+/-13.25%, E-face) was changed to an 89.4+/-9.9% predominant E-face association in cerebral capillaries from SHRSP. However, the expression of the tight junction molecules ZO-1, occludin, claudin-1 and claudin-5 was not changed in capillaries of SHRSP. Permeability of brain capillaries from SHRSP was not different compared to SHR and WKY using lanthanum nitrate as a tracer. In contrast, analysis of endothelial cell polarity by distribution of the glucose-1 transporter (Glut-1) revealed that its abluminal:luminal ratio was reduced from 4:1 in SHR and WKY to 1:1 in endothelial cells of cerebral capillaries of SHRSP. In summary, we demonstrate that early changes exist in cerebral capillaries from a genetic model of hypertension-associated stroke. We suggest that a disturbed fence function of the tight junctions in SHRSP blood-brain barrier endothelial cells may lead to subtle changes in polarity. These changes may contribute to the pathogenesis of stroke.

Human coronary arteriolar dilation to adrenomedullin: role of nitric oxide and K(+) channels

Adrenomedullin (ADM) is a vasodilator produced by vascular endothelium and smooth muscle cells. Although plasma ADM levels are increased in patients with hypertension, heart failure, and myocardial infarction, little information exists regarding the microvascular response to ADM in the human heart. In the present study we tested the hypothesis that ADM produces coronary arteriolar dilation in humans and examined the mechanism of this dilation. Human coronary arterioles were dissected and cannulated with micropipettes. Internal diameter was measured by video microscopy. In vessels constricted with ACh, the diameter response to cumulative doses of ADM (10(-12)-10(-7) M) was measured in the presence and absence of human ADM-(22-52), calcitonin gene-related peptide-(8-37), N(omega)-nitro-L-arginine methyl ester (L-NAME), indomethacin (Indo), (1)H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, SQ-22536, or KCl (60 mM). ADM dilated human coronary arterioles through specific ADM receptors (maximum dilation = 69 +/- 11%). L-NAME or N-monomethyl-L-arginine attenuated dilation to ADM (for L-NAME, maximum dilation = 66 +/- 7 vs. 41 +/- 13%, P < 0.05). Thus the mechanism of ADM-induced dilation involves generation of nitric oxide. However, neither (1)H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one, SQ-22536, nor Indo alone altered dilation to ADM. High concentrations of KCl blocked dilation to ADM. The magnitude of ADM dilation was reduced in subjects with hypertension. We propose that, in human coronary arterioles, ADM elicits vasodilation in part through production of nitric oxide and in part through activation of K(+) channels, with little contribution from adenylyl cyclase. The former dilator mechanism is independent of the more traditional pathway involving activation of soluble guanylate cyclase.

Vasopeptidase inhibition has potent effects on blood pressure and resistance arteries in stroke-prone spontaneously hypertensive rats

The antihypertensive agent omapatrilat represents a novel approach to antihypertensive therapy, namely vasopeptidase inhibition. Omapatrilat (BMS-186716) concomitantly inhibits neutral endopeptidase and angiotensin-converting enzyme, leading to protection from degradation of natriuretic and other hypotensive peptides in addition to interruption of the renin-angiotensin system. Although the potency of omapatrilat on reduction of blood pressure has been reported, its effects on resistance artery structure and function were unknown. We tested omapatrilat in stroke-prone spontaneously hypertensive rats (SHRSP), a malignant model of hypertension, with the hypothesis that it would improve the structure and endothelial function of mesenteric resistance arteries. Ten-week-old SHRSP were treated orally for 10 weeks with omapatrilat (40 mg/kg per day). Mesenteric arteries (lumen <300 microm) were studied on a pressurized myograph. After 10 weeks, untreated SHRSP had a systolic blood pressure of 230+/-2 mm Hg that was significantly reduced (P<0.05) by omapatrilat (145+/-3 mm Hg). Omapatrilat treatment improved endothelium-dependent relaxation of resistance arteries as elicited by acetylcholine (10(-5) mol/L) but had no significant effect on endothelium-independent relaxation produced by a nitric oxide donor (sodium nitroprusside). This suggested that there existed endothelial dysfunction in SHRSP that was corrected by vasopeptidase inhibition, probably in part caused by the potent blood pressure-lowering effect of omapatrilat. Media width and media/lumen ratio were significantly decreased (P<0.05) by omapatrilat, and a trend (P=0.07) to increase lumen diameter was observed. Vascular stiffness (slope of the elastic modulus versus stress curve) was unaltered by omapatrilat. In conclusion, omapatrilat, acting as a potent antihypertensive agent, may improve structure and endothelial function of resistance arteries in SHRSP, a severe form of genetic hypertension.

Adrenomedullin: potential in physiology and pathophysiology

Adrenomedullin (ADM), a 52-amino acid ringed-structure peptide with C-terminal amidation, was originally isolated from human pheochromocytoma. ADM mediates vasodilatory and natriuretic properties through the second messenger cyclic adenosine 3',5'-monophosphate (cAMP), nitric oxide and the renal prostaglandin system. ADM immunoreactivity and its gene are widely distributed in cardiovascular, pulmonary, renal, gastrointestinal, cerebral and endocrine tissues. ADM is also synthesized and secreted from vascular endothelial and smooth muscle cells. When injected intravenously, ADM increases flow rates predominantly in organs in which the ADM gene is highly expressed, suggesting that ADM acts as a local autocrine and/or paracrine vasoactive hormone. In addition, ADM is a circulating hormone and its plasma concentration is increased in various cardiorenal diseases such as hypertension, chronic renal failure and congestive heart failure. Current evidence suggests that ADM plays an important role in fluid and electrolyte homeostasis and cardiorenal regulation, however further investigations are required to address the importance of ADM under various physiological and pathophysiological conditions.

Coexpression of receptors for adrenomedullin, calcitonin gene-related peptide, and amylin in pancreatic beta-cells

Three receptors have been characterized by their ability to bind adrenomedullin (AM): L1, RDC1, and CRLR. Immunohistochemical analysis and RT-PCR showed that all three receptors are expressed by the insulin-producing cells of the islets of Langerhans. RDC1 and CRLR in the presence of particular modifying proteins can also bind calcitonin gene-related peptide (CGRP). Such data suggest that the inhibitory effect caused by both AM and CGRP on insulin secretion is mediated by a direct interaction with the beta-cell. We also identified receptors for amylin, the third member of the AM peptide family, in mouse insulin-secreting cells. The beta-cells located closer to the periphery of the islets had a stronger immunoreactivity for the AM/ CGRP receptors. This observation could be related to a paracrine mechanism, given the proximity of AM- and CGRP-secreting cells (F and delta-cells, respectively), which are located at the periphery of the islets. Interestingly, the smooth muscle cells in the pancreatic vasculature expressed only RDC1, which is in agreement with physiological data showing that AM functions in the cardiovascular system are mainly mediated through a CGRP1 receptor. These data further implicate AM and the other components of its peptide family as important regulators of insulin release.

Stimulation of bradykinin B2-receptors on endothelial cells induces relaxation and contraction in porcine basilar artery in vitro

1. The aim of the present study was to characterize the subtypes of bradykinin (BK) receptors that evoke the relaxation and contraction induced by BK and to identify the main contracting and relaxing factors in isolated porcine basilar artery by measuring changes in isometric tension and a thromboxane (TX) metabolite. 2. Endothelial denudation completely abolished both responses. [Thi5,8, D-Phe7]-BK (a B2-receptor antagonist) inhibited the BK-induced relaxation and contraction, whereas des-Arg9, [Leu8]-BK (a B1-receptor antagonist) had no effect. 3. L-nitro-arginine (L-NA, a nitric oxide synthase inhibitor) completely inhibited BK-induced relaxation. Indomethacin (a cyclo-oxygenase inhibitor) completely and ONO-3708 (a TXA2/prostaglandin H2 receptor antagonist) partially inhibited BK-induced contraction, whereas OKY-046 (a TXA2 synthase inhibitor) and nordihydroguaiaretic acid (a lipoxygenase inhibitor) did not. 4. In the presence of L-NA, the contractile response to BK was inhibited by indomethacin or ONO-3708 and was competitively antagonized by [Thi5,8, D-Phe7]-BK (pA2=7.50). In the presence of indomethacin, the relaxant response to BK was inhibited by L-NA and was competitively antagonized by [Thi5,8, D-Phe7]-BK (pA2=7.59). 5. TXA2 release was not induced by BK-stimulation. 6. These results suggest that the endothelium-dependent relaxation and contraction to BK in the porcine basilar artery is mediated via activation of endothelial B2-receptors. The main relaxing factor may be NO and the main contracting factor may be prostaglandin H2.

Evidence for selective effects of chronic hypertension on cerebral artery vasodilatation to protease-activated receptor-2 activation

BACKGROUND AND PURPOSE

Protease-activated receptor-2 (PAR-2) can be activated after proteolysis of the amino terminal of the receptor by trypsin or by synthetic peptides with a sequence corresponding to the endogenous tethered ligand exposed by trypsin (eg, SLIGRL-NH(2)). PAR-2 mediates nitric oxide (NO)-dependent dilatation in cerebral arteries, but it is unknown whether PAR-2 function is altered in cardiovascular diseases. Since hypertension selectively impairs NO-mediated cerebral vasodilatation in response to acetylcholine and bradykinin, we sought to determine whether PAR-2-mediated vasodilatation is similarly adversely affected by this disease state.

METHODS

We studied basilar artery responses in Wistar-Kyoto rats (WKY) (normotensive) and spontaneously hypertensive rats (SHR) in vivo (cranial window preparation) and in vitro (isolated arterial rings). The vasodilator effects of acetylcholine, sodium nitroprusside, and activators of PAR-2 and protease-activated receptor-1 (PAR-1) were compared in WKY versus SHR. Immunohistochemical localization of PAR-2 was also assessed in the basilar artery.

RESULTS

Increases in basilar artery diameter in response to acetylcholine were 65% to 85% smaller in SHR versus WKY, whereas responses to sodium nitroprusside were not different. In contrast to acetylcholine, vasodilatation in vivo to SLIGRL-NH(2) was largely preserved in SHR, and SLIGRL-NH(2) was approximately 3-fold more potent in causing vasorelaxation in SHR versus WKY in vitro. In both strains, responses to SLIGRL-NH(2) were abolished by N(G)-nitro-L-arginine, an inhibitor of NO synthesis. Activators of PAR-1 had little or no effect on the rat basilar artery. PAR-2-like immunoreactivity was observed in both the endothelial and smooth muscle cells of the basilar artery in both strains of rat.

CONCLUSIONS

These data indicate that NO-mediated vasodilatation to PAR-2 activation is selectively preserved or augmented in SHR and may suggest protective roles for PAR-2 in the cerebral circulation during chronic hypertension.

Receptors mediating CGRP-induced relaxation in the rat isolated thoracic aorta and porcine isolated coronary artery differentiated by h(alpha) CGRP(8-37)

1 Receptors mediating CGRP-induced vasorelaxation were investigated in rat thoracic aorta and porcine left anterior descending (LAD) coronary artery and anterior interventricular artery (AIA), using CGRP agonists, homologues and the antagonist h(alpha) CGRP(8-37). 2 In the endothelium-intact rat aorta, h(alpha) CGRP, h(beta) CGRP, rat beta CGRP and human adrenomedullin caused relaxation with similar potencies. Compared with h(alpha) CGRP, rat amylin was about 25 fold less potent, while [Cys(ACM2,7)] h(alpha) CGRP and salmon calcitonin were at least 1000 fold weaker. 3 H(alpha) CGRP(8-37) (up to 10(-5) M) did not antagonize responses to h(alpha) CGRP, h(beta) CGRP or rat beta CGRP (apparent pKB <5). Peptidase inhibitors did not increase either the effect of h(alpha) CGRP or [Cys(ACM,2,7)] h(alpha) CGRP, while h(alpha) CGRP(8-37) remained inactive. Endothelium-dependent relaxation produced by h(alpha) CGRP was accompanied by increases in cyclic AMP and cyclic GMP, that were not inhibited by h(alpha) CGRP(8-37) (10(-5) M). 4 In porcine LAD and AIA, h(alpha) CGRP produced relaxation in an endothelium-independent manner. H(alpha) CGRP(8-37) competitively antagonized h(alpha) CGRP responses (pA2 6.3 and 6.7 (Schild slope 0.9+/-0.1, each), in LAD and AIA, respectively). In LAD artery, h(alpha) CGRP-induced relaxation was accompanied by increases in cyclic AMP that were inhibited by h(alpha) CGRP(8-37) (10(-7)-10(5 )). 5 In conclusion, the antagonist affinity for h(alpha) CGRP(8-37) in porcine coronary artery is consistent with a CGRP1 receptor, while the lack of h(alpha) CGRP(8-37) antagonism in rat aorta could suggest either a CGRP receptor different from CGRP1 and CGRP2 type, or a non-CGRP receptor.