Inhibited neutrophil functions in patients treated with nifedipine but not with verapamil or diltiazem

Neutrophil functions were studied in patients receiving calcium channel blockers: nifedipine, diltiazem or verapamil. Neutrophils from patients treated with nifedipine showed a significantly lower superoxide generation stimulated by phorbol myristate acetate (PMA) (50 ng mL⁻¹), opsonized zymosan (1 mg mL⁻¹) or formyl-methionyl-leucyl-phenylalanine (FMLP) (10⁻⁷  m ), whereas superoxide generation by neutrophils of patients receiving diltiazem or verapamil showed only a slight and insignificant reduction compared with controls. Similarly, chemotaxis towards 10⁻⁷  m FMLP and phagocytosis were significantly lower in patients receiving nifedipine compared with controls and were only slightly reduced in patients receiving diltiazem or verapamil. Nifedipine was the most efficient drug in inhibiting the rise in intracellular calcium ion concentration ([Ca²⁺]_i) when added in vitro and in neutrophils of patients receiving this drug, whereas verapamil had no significant effect. The correlation between the inhibitory effect of nifedipine on neutrophil function and the elevation of [Ca²⁺]_i suggests that nifedipine inhibits neutrophil functions through its effect on [Ca²⁺]_i. However, it is not the sole mechanism as superoxide generation induced by PMA, an agent that does not induce a rise in [Ca²⁺]_i, is also inhibited. The unique effect of nifedipine in reducing neutrophil functions in vivo suggests its clinical implications concerning response to acute ischaemic myocardial events.     

Differential effects of cromakalim on pancreatic vascular resistance and insulin secretion in vitro

Summary— The effects of the potassium channel opener cromakalim on vascular resistance and insulin output were investigated in vitro within the same experimental preparation, the isolated rat pancreas perfused at a constant pressure with a physiological solution containing 8.3 mM glucose. Cromakalim induced a clear and concentration-dependent dilatory response of pancreatic vessels; the concentration-response curve obtained in the range of 10⁻⁸-10⁻⁵ M had a sigmoidal shape with a linear part between 10⁻⁷ and 10⁻⁶ M. Cromakalim did not inhibit insulin release at these concentrations. These results differ from those obtained with diazoxide, which has been previously shown both to inhibit insulin secretion and induce vasodilatation of the pancreatic vascular bed in a similar range of concentrations (10⁻⁶ – 10⁻⁵ M). The data presented provide evidence for a selective effect of cromakalim on pancreatic vascular resistance. Our present and previous results support the view that cromakalim is effective on K+ channels of vascular smooth muscle that differ from the ATP-sensitive K+ channel opened by diazoxide in insulin-secreting B-cells.     

Effects of cooling and warming on 5-hydroxytryptamine- and acetylcholine-induced contractions of human umbilical vessels: role of nitric oxide

The effects of cooling (to 28 degrees C) and warming (to 41 degrees C) on the vasoconstrictions induced by 5-hydroxytryptamine (5-HT) and acetylcholine (ACh) and the role of nitric oxide in these effects were analyzed in human umbilical artery and vein. 5-HT (10(-9)-10(-4) M) and ACh (10(-9)-10(-4) M) induced concentration-dependent contractions at 37, 28 and 41 degrees C. During cooling, the sensitivity, but not the maximal response, of 5-HT and ACh was significantly higher than at 37 degrees C; and during warming, again the sensitivity, but not the maximal response, of both contractile agents was significantly lower than at 37 degrees C. Neither cooling to 28 degrees C nor warming to 41 degrees C, after treatment with N(G)-nitro-L-arginine methyl esther (L-NAME, 10(-4) M), modify the effect of temperature in both vessels. These results suggest that cooling- and warming-induced responses in human umbilical artery and vein are independent of nitric oxide.     

Protein C inhibitor directly and potently inhibits activated hepatocyte growth factor activator

Background:  Hepatocyte growth factor (HGF) plays an important role in tissue repair and regeneration. HGF activator (HGFA), a factor XIIa-like serine protease, activates HGF precursor to HGF. The precursor of HGFA, proHGFA, is activated by thrombin generated at sites of tissue injury. It is known that protein C inhibitor (PCI), an inhibitor of activated protein C (APC), also inhibits thrombin–thrombomodulin (TM) complex. Objectives:  In the present study we evaluated the effect of PCI on thrombin-catalyzed proHGFA activation in the presence of TM, and on HGFA activity. Results:  PCI did not inhibit thrombin-TM-mediated proHGFA activation, but it directly inhibited activated HGFA by forming an enzyme inhibitor complex. The second-order rate constants ( m ⁻¹ min⁻¹) of the reaction between HGFA and PCI in the presence or absence of heparin (10 U mL⁻¹) were 4.3 × 10⁶ and 4.0 × 10⁶, respectively. The inhibition of HGFA by PCI resulted in a significant decrease of HGFA-catalyzed activation of HGF precursor. Exogenous HGFA added to normal human plasma formed a complex with plasma PCI, and this complex formation was competitively inhibited by APC in the presence of heparin, but very weakly in the absence of heparin. We also demonstrated using recombinant R362A-PCI that Arg362 residue of PCI is important for HGFA inhibition by PCI as judged from the three-dimensional structures constructed using docking models of PCI and HGFA or APC. Conclusion:  These observations indicate that PCI is a potent inhibitor of activated HGFA, suggesting a novel function for PCI in the regulation of tissue repair and regeneration.     

Assay of human erythrocyte sodium-dependent lithium efflux: the importance of timing of blood sampling

The activity of the human erythrocyte sodium–lithium countertransport (SLC) is stable over long periods in individuals. However, it is becoming increasingly evident that the transport system is susceptible to modulation, both acutely and chronically, by various factors. In this study, the authors observed temporal variation in SLC over a period of 10 h (08.00–18.00 hours) in healthy volunteers. SLC V _max was maximum (0.354 ± 0.051 mmol L⁻¹ cell⁻¹ h⁻¹; mean ± SE) at 'mid-day' and significantly higher than in the morning (0.291 ± 0.035 mmol L⁻¹ cell, h; P  < 0.010). Its value in the evening (0.316 ± 0.042 mmol L⁻¹ cell⁻¹ h⁻¹) was lower than at 'mid-day' ( P  < 0.045) but higher than in the morning ( P  < 0.037). These changes were not accompanied by any significant change in the affinity of the transporter for external sodium, K _m. Changes in SLC V _max did not correlate with the corresponding ones in either plasma cortisol or aldosterone. However, they correlated well with those in plasma renin activity, the correlation between mid-day and a.m. sets of values ( r  = 0.718; P  = 0.019) being better than that between mid-day and p.m. ( r  = 0.688; P  = 0.028). The authors conclude that changes in SLC occur during the day, and this need be taken into account in the planning and execution of studies involving determination of the activity of this transport system.     

Warming and response to contractile agents in calf cardiac vein: role of the nitric oxide

The effects of warming on the response to various contractile agents of calf cardiac vein were studied using 2.5-mm long cylindrical segments. Concentration-response curves for carbachol (10(-9)-3 x 10(-4) m), 5-hydroxytryptamine (5-HT; 10(-8)-3 x 10(-3)), potassium chloride (KCl; 10(-4)-5 x 10(-2) m) and calcium chloride (CaCl2; 10(-4)-10(-2)) were isometrically recorded at 37 and 41 degrees C (warming). During warming the sensitivity, but not the maximal response, of carbachol 5-HT, KCl, and CaCl2 was significantly higher than at 37 degrees C. Warming to 41 degrees C after treatment with NG-nitro-L arginine methyl esther (10(-5) m) did not modify the effect of warming. These results suggest that nitric oxide seems to have no role in the warming-induced responses in calf cardiac vein.     

Mesangial medium with IgA1 from IgA nephropathy inhibits nephrin expression in mouse podocytes

Background  IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA1, and podocyte injury plays an important role in glomerulosclerosis of the disease. Our previous study indicated that medium of mesangial cells co-incubated with aggregated IgA1 (aIgA1), isolated from IgAN patients, down-regulated nephrin expression. Yet the mechanism remains unclear.
Materials and methods  Podocytes were incubated with a medium of mesangial cells co-incubated with aIgA1, which was isolated from IgAN patients, and enalaprilat (10⁻⁵ M), valsartan (10⁻⁵ M) and anti-mouse tumour necrosis factor-α antibody (50 ng mL⁻¹) separately. Nephrin expression in podocytes was measured by real-time polymerase chain reaction and Western blot analysis.
Results  The level of angiotensinogen and angiotensin-converting enzyme mRNAs in podocytes, as well as angiotensin, was also increased by a medium of mesangial cells co-incubated with aIgA1 from IgAN patients( P  <   0·05). Enalaprilat or valsartan partly improved nephrin expression when compared with that by podocytes exposed to the mesangial medium ( P  <   0·05), while the nephrin expression of podocytes with enalaprilat or valsartan was lower than that of podocytes exposed to medium of mesangial cells stimulated by aIgA1 from healthy control ( P  <   0·05). However, anti-mouse tumour necrosis factor-α antibody did not show any improvement in nephrin expression.
Conclusion  Our findings implicate that local renin angiotensin system activation in podocytes is partly involved in down-regulation of nephrin by mesangial medium in IgA nephropathy.     

Elucidation of a novel epitope of a substrate-inducing monoclonal antibody against the serpin PAI-1

Summary.  Plasminogen activator inhibitor-1 (PAI-1) is the most important physiological inhibitor of plasminogen activators. Inhibition of PAI-1 constitutes a putative strategy for the prevention of cardiovascular disease. The monoclonal antibody MA-8H9D4 inhibits PAI-1 activity by inducing a substrate behavior in PAI-1. To identify the epitope, a rational approach was used to design various PAI-1 alanine mutants ( n  = 16) for evaluation of their affinity. PAI-1-R300A, PAI-1-Q303A and PAI-1-D305A had affinities for MA-8H9D4 of < 10⁵ M⁻¹, 2.0 × 10⁸ M⁻¹ and 2.5 × 10⁸ M⁻¹, respectively, whereas the affinity of wtPAI-1 is 3.3 × 10⁹ M⁻¹. The epitope on the axis of arginine 300, glutamine 303 and aspartic acid 305, located on the loop between α-helix I and β-strand 5A, demonstrates that MA-8H9D4 interferes with the final locking step in the serpin/proteinase interaction, thereby explaining its substrate inducing properties. The location of the epitope as well as the proposed mechanism of action is clearly different from that of other substrate inducing monoclonal antibodies against PAI-1. Elucidation of this novel epitope and the previously unidentified molecular mechanism opens new perspectives for the rational development of PAI-1-neutralizing compounds, as well as for the further exploration of synergistic effects between different PAI-1-inhibiting compounds.     

Vasoactive substances in early dumping syndrome: effects of dumping provocation with and without octreotide

In patients after gastric surgery, early dumping symptoms can be provoked by oral glucose challenge. Octreotide effectively prevents the occurrence of dumping symptoms. We have studied plasma renin activity (PRA), aldosterone and atrial natriuretic peptide (ANP) concentrations in nine patients with early dumping, 10 surgical control subjects and nine healthy control subjects after an oral glucose challenge preceded by either placebo or 25 μg of octreotide subcutaneously (s.c.). In the dumping group, basal PRA was signifi-cantly ( P  < 0.01) higher (3.9 ± 0.6 μg L⁻¹ h⁻¹) than in either surgical or healthy control subjects (1.1 ± 0.3 μg L⁻¹ h⁻¹ and 1.1 ± 0.2 μg L⁻¹ h⁻¹ respectively) and showed a significant rise after glucose ingestion to 5.4 ± 0.9 μg L⁻¹ h⁻¹ that did not occur in control subjects. Aldosterone concentration showed a concomitant rise. In dumping patients, plasma ANP decreased after glucose ingestion from 31 ± 6 ng L⁻¹ to 21 ± 5 ng L⁻¹ ( P  < 0.05). This decrease did not occur in control subjects. Early dumping is associated with an activation of the renin–aldosterone axis and a decrease in plasma ANP, reflecting a hypovolaemic state. Octreotide prevents the occurrence of these changes.     

Low-density lipoprotein-induced formation of nitric oxide by cultured vascular smooth muscle cells of the rat

There is evidence that low-density lipoprotein (LDL) plays a crucial role in atherogenesis. On the cellular level, LDL has been shown to activate a number of mechanisms involved in atherogenesis and vasoconstriction. Local immoderate vasoconstriction is physiologically antagonized by nitric oxide, which is released from the endothelium. To find out whether LDL also influences the synthesis of nitric oxide in vascular smooth muscle cells, both the conversion of arginine to citrulline and the production of nitrite were determined as a measure of nitric oxide formation. After incubation of rat vascular smooth muscle cells with native LDL (25 μg mL⁻¹) for 24 h, the production of both l -[¹⁴C]-citrulline [39 600 (3600) cpm mg⁻¹ cell protein] and nitric oxide [2.95 (0.56) μmol L⁻¹] were about twice and 1.5-fold the amount of the corresonding values in untreated cells (mean ± SD, P  < 0.05, n  = 4). Oxidized LDL was less effective than the native form. The presence of the arginine analogue N ^G-methyl- l -arginine reduced citrulline production dose-dependently but augmented DNA synthesis, both induced by LDL. In addition, the lipoprotein caused a 1.6-fold increase in cyclic GMP production following a 24-h incubation [control = 10.9 (3.8) pmol mg⁻¹ cell protein, P  = 0.016]. The results suggest that native LDL might partly impair its atherogenic potential on the vasculature by stimulating the production by smooth muscle cells of both nitric oxide and cyclic GMP.     

C reactive protein and its determinants in healthy men and women from European regions at different risk of coronary disease: the IMMIDIET Project

Aim:  Differences in C-reactive protein (CRP) levels and its determinants in three European populations at different risk of coronary artery disease (CAD) were studied. Methods:  Subjects were recruited randomly in Limburg (Belgium), Abruzzo (Italy) and south-west (SW) London (England). Results:  Ten-year risk of fatal coronary events (estimated using risk equations provided by the SCORE Project) was lower both in men and women from Abruzzo, intermediate in people from Limburg and higher in subjects from SW London. Within each country, high sensitivity (hs)-CRP levels were higher in the high-risk class in men but not in women. Men from Abruzzo had higher hs-CRP levels than those from Limburg and SW London. Women always had higher hs-CRP levels than men. The strongest hs-CRP determinant was body mass index (BMI, R ² = 0.14) in women and waist circumference (WC, R ² = 0.046) in men. The highest hs-CRP levels were observed in subjects with both high BMI and high WC. Metabolic syndrome was associated with high levels of CRP both in men and women, even after adjustment for confounders. Discussion:  Difference in CRP levels cannot explain the European gradient of CVD risk, although CRP levels are associated with the calculated SCORE risk of fatal coronary events within each country.     

Lack of effect of norepinephrine on cranial haemodynamics and headache in healthy volunteers

Stress is a provoking factor for both tension-type headache and migraine attacks. In the present single-blind study, we investigated if stress induced by norepinephrine (NE) could elicit delayed headache in 10 healthy subjects and recorded the cranial arterial responses. NE at a dose of 0.025 µg kg⁻¹ min⁻¹ or placebo was infused for 90 min and the headache was followed for 14 h. Blood flow velocity in the middle cerebral artery (measured with transcranial Doppler) and diameters of the temporal artery and the radial artery (measured with ultrasound) were followed for 2 h. There were no changes in these arterial parameters after NE. In both treatment groups three subjects developed delayed headaches. Thus, stress by NE infusion did not result in delayed headache.     

Prostaglandin E2 (PGE2) induces headache in healthy subjects

The role of prostanoids in nociception is well established. The headache-eliciting effects of prostaglandin E₂ (PGE₂) and its possible mechanisms have previously not been systematically studied in man. We hypothesized that infusion of PGE₂ might induce headache and vasodilation of cranial vessels. PGE₂ (0.40 µg kg⁻¹ min⁻¹) or saline was infused for 25 min into 11 healthy subjects in a cross-over, double-blind study. Headache intensity was scored on a verbal rating scale from 0 to 10. In addition, we recorded mean flow in the middle cerebral artery (V_MCA) by transcranial Doppler and diameter of the superficial temporal artery (STA) by high-resolution ultrasonography. All 11 subjects reported headache on the PGE₂ day and no subjects reported headache on the placebo day ( P  = 0.001). During the immediate phase (0–30 min) ( P  = 0.005) and the postinfusion phase (30–90 min) ( P  = 0.005), the area under the curve for headache score was significantly larger on the PGE₂ day compared with the placebo day. PGE₂ caused dilatation of the STA (23.5%; 95% CI 14.0, 37.8) and the MCA (8.3%; 95% CI 4.0, 12.6). We suggest that PGE₂ induces headache by activation and sensitization of cranial perivascular sensory afferents.     

Citral inhibits cell proliferation and induces apoptosis and cell cycle arrest in MCF-7 cells

Many natural components of plants extract are studied for their beneficial effects on health and particularly on carcinogenesis chemoprevention. In this study, we investigated the effect of citral (3,7-dimethyl-2,6-octadienal), a key component of essential oils extracted from several herbal plants, on the proliferation rate, cell cycle distribution, and apoptosis of the human breast cancer cell line MCF-7. The effects of this compound were also tested on cyclo-oxygenase activity. Citral treatment caused inhibition of MCF-7 cell growth (IC₅₀-48 h: 18  ×  10⁻⁵  m ), with a cycle arrest in G₂/M phase and apoptosis induction. Moreover, we observed a decrease in prostaglandin E₂ synthesis 48 h after citral treatment. These findings suggest that citral has a potential chemopreventive effect.     

Elevated cell-associated levels of interleukin 1β and interleukin 6 in inflamed mucosa of inflammatory bowel disease

The aim of this study was to investigate the involvement of the monocyte-derived cytokines interleukin 1β (IL-1β), interleukin 6 (IL-6) and tumour necrosis factor-α (TNF-α) in idiopathic inflammatory bowel disease. Endoscopic biopsies of normal and inflamed intestinal mucosa were obtained from patients with ulcerative colitis ( n  = 11) and with Crohn's disease ( n  = 10). Intestinal mucosal cells were isolated by collagenase digestion. Cell viability, morphology and CD14 expression were determined. To measure cell-associated cytokine levels, cells were lysed and analysed for IL-1β and TNF-α in specific radioimmunoassays and for IL-6 using a biological assay. Compared with mucosal cells from control patients without inflammatory bowel disease the inflamed intestine in ulcerative colitis and Crohn's disease displayed markedly enhanced levels of IL-1β (median 245 pg 10⁻⁶ cells, range 30–1275) and IL-6 (median 22 U 10⁻⁶ cells, range 1–298). Non-inflamed mucosa in patients with ulcerative colitis and Crohn's disease did not shown elevated levels of IL-1β (median 50 pg 10⁻⁶ cells, range 33–90) or IL-6 (mean below detection limit of assay, i.e. 1 U 10⁻⁶ cells). In contrast, no clear cut difference between inflamed and non-inflamed mucosa could be detected for TNF-α. High tissue levels of IL-6 were associated with a high endoscopic grade of local inflammation. These results suggest that the monocyte-derived cytokines IL-1β and IL-6 are mediators of inflammation in inflammatory bowel disease.     

Citrate metabolism by human platelets

As part of a study on the utilization of substrates by platelets in defined media the metabolism of citrate was measured, since citrate is a common anticoagulant of nearly all such media, and is also an intermediate of oxidative metabolism. Human platelets transferred from plasma to an artificial medium by gel filtration, were incubated with [¹⁴C]citrate at 22 °C and labelled carbon dioxide produced was measured during short-term incubations of 2 h. Citrate (1 m m ) was oxidized to carbon dioxide at low (0.3 nmol per 10⁹ platelets h⁻¹) but significant rates, and the oxidation was decreased by the presence of an alternative substrate (acetate) in the medium. There was, however, no significant conversion of citrate to glycogen. It was calculated that under normal storage conditions of platelet concentrates for transfusion purposes, the amount of citrate used cannot decrease citrate concentrations sufficiently to bring about platelet activation.     

短时间一氧化氮吸入对心肌缺血／再灌注损伤的保护机制研究

目的探讨短时间吸入NO对心肌缺血／再灌注损伤的保护机制。方法60只雄性wistar大鼠随机分为三组（Ⅰ、Ⅱ、Ⅲ组）,每组20只,通过腹腔注射氯胺酮（120mg／kg）和咪达唑仑（10mg／kg）施行麻醉,同时给予人工通气。结扎左冠状动脉导致心肌缺血10min后开放,再灌注24h。Ⅰ组为对照组,Ⅱ、Ⅲ组分别在再灌注前5min、60rain吸入10％的NO,再灌注24h后结扎左冠状动脉,注入荧光剂,心脏离体冰冻切片,HE染色,测量心肌梗死范围,取大鼠血液和组织中的NO代谢产物定量检测。结果大鼠吸收NO的速度（6．35±0．24）min内基本成线性分布,后趋于稳定。吸入NO后红细胞中的S-亚硝基硫醇、N-亚硝胺和亚硝酰基亚铁血红素水平均明显增加。再灌注前的5min、60min吸入NO的心肌梗死范围较未吸入NO分别减少28％、31％。结论短时间吸入NO能够明显减少心肌再灌注损伤的范围,提示短时间吸入NO对心肌缺血／再灌注也同样有很好的保护作用。其机制可能是迅速通过血液从肺到心脏的NO代谢产物以生物活性形式发挥作用。     

Effects of vasopressin on human renal arteries

The effects of vasopressin were studied in isolated rings from branches (2–3mm in external diameter) of human renal arteries obtained from 18 patients undergoing nephrectomy for non-obstructive neoplasia. In arterial rings under resting tension, vasopressin produced concentration-dependent and endothelium-independent contractions with an EC₅₀ of 9.1×10⁻¹⁰molL⁻¹. The vasopressin V₁ receptor antagonist d(CH₂)₅Tyr(Me)AVP (10⁻⁶molL⁻¹) displaced the control curve to vasopressin 564-fold to the right in a parallel manner. In precontracted arterial rings and previously treated with the V₁ antagonist (10⁻⁶molL⁻¹) vasopressin caused endothelium-independent relaxation. The relaxation to vasopressin was reduced significantly by indomethacin (10⁻⁶molL⁻¹) and unaffected by the V₁/V₂ receptor antagonist desGly d(CH₂)₅- d -Tyr(Et)ValAVP (10⁻⁶molL⁻¹) or by N ^G-nitro- l -arginine methyl ester (10⁻⁴molL⁻¹). These observations indicate that vasopressin is primarily a constrictor of human renal arteries by V₁-receptor stimulation. Vasopressin causes prostaglandin-mediated dilatation of human renal arteries only if V₁-receptor blockade is present. The effects of vasopressin on human renal arteries may be relevant in those clinical situations characterized by increased plasma vasopressin levels.     

Delayed migraine-like headache in healthy volunteers after a combination of acetazolamide and glyceryl trinitrate

Glyceryl trinitrate (GTN) is a pro-drug dissociating nitric oxide throughout the body. It dilates cephalic arteries without increasing cerebral blood flow (CBF). GTN induces headache in healthy volunteers and migraine attacks in migraineurs. Acetazolamide (Az) increases CBF but does not dilate cerebral arteries. The hypothesis tested here was that Az, by dilating cerebral arterioles but not arteries and thereby decreasing pulsatile stretching of the wall of the large arteries and their perivascular sensory nerves, would reduce or prevent the GTN-induced headache We tested this hypothesis in 14 healthy volunteers. In a randomized, double-blind, cross-over study, they were pretreated with Az or placebo followed on both study days by a GTN infusion of 0.5 µg kg⁻¹ min⁻¹ for 20 min. Headache was scored on a verbal rating scale and a headache diary was kept for 12 h. Mean blood velocity of the middle cerebral artery was measured (transcranial Doppler). Our hypothesis was disproved, as Az did not decrease GTN-induced headache. Unexpectedly but interestingly, GTN combined with Az induced more delayed headache than GTN alone. Furthermore, a migraine-like headache was observed in three volunteers, who did not develop migraine after GTN alone. The fact that a suitable pharmacological intervention may trigger migraine in individuals with no prior migraine may suggest that the ability to develop migraine without aura is a quantitative genetic trait.     

Calcitonin gene-related peptide is released from capsaicin-sensitive nerve fibres and induces vasodilatation of human cerebral arteries concomitant with activation of adenylyl cyclase

The vasomotor effects of calcilonin gene-related peptide (CGRP) analogues have been studied in circular segments of fresh human cereoral arteries obtained at neurosurgical operations using a sensitive in vitro system. Human a-CGRP, human b-CGRP, rat a-CGRP and rat b-CGRP induced strong and potent relaxation of precontracted circular vessel segments. The I_max (maximum relaxant effect) to human calcitonin was low and the pD₂ (concentration for half maximum effect) 7.7 was much lower than that of CGRP. The CGRP-1, antagonist human a-CGRP_8–37 blocked the response to human a-CGRP but not to human b-CGRP, while the putative antagonist [Tyr]CGRP_28–37 did not. Capsaicin (10⁻¹⁵ - 10⁻⁸ M) caused relaxation of the cerebral arteries by 22% of precontract on. Pre-treatment with 10⁻⁶ M human a-CGRP_8–37 inhibited this relaxation. Human a-CGRP increased the cyclic AMP content of human cerebral arteries in a concentration-dependent manner. This increase in adenylyl cyclase activity was blocked by human a-CGRP_8–37. The results suggest that CGRP-1 receptors coupled to adenylyl cyclase are present in human cerebral arteries.