Neuronal versus endothelial origin of vasoactive acetylcholine in pial vessels

Characterisation of angiotensin II receptors in isolated human subcutaneous resistance arteries

Subcutaneous arteries have been used as a model for resistance arteries, which are potentially involved in enhanced blood pressure (BP) regulation in man. Angiotensin II (Ang II) is an important regulator of tone, acting via type 1 (AT1-) and type 2 (AT2-) receptor subtypes. The aim of this study was to characterise the Ang II receptors in isolated human subcutaneous arteries, using pharmacological and molecular methods.

Subcutaneous arteries were obtained from patients undergoing elective gut surgery and were carefully dissected from the abdominal wall. Cylindrical segments were mounted on two L-shaped metal prongs, one of which was connected to a force-displacement transducer for continuous recording of isometric tension. Concentration-response curves to Ang II were constructed in the presence and absence of various selective AT1-receptor antagonists, candesartan, EXP3174, irbesartan and losartan, and the AT2-receptor antagonist, PD 123319. Responses to Ang II were measured as increases in force (mN) and expressed as a percentage of the response to 60 mM of KCl. Ang II caused a concentration-dependent contraction (pEC50=9.45±0.48, Emax=120±13%). Candesartan and EXP3174 caused concentration-dependent depression of the Emax of Ang II without any major shift of pEC50. Losartan and irbesartan caused a significant, dose-dependent rightward shift of the Ang II contraction-response curve in human subcutaneous arteries. The results show that contractile responses of human subcutaneous arteries are mediated via the AT1-receptor. The AT1-receptor antagonists, candesartan and EXP3174, acted in an insurmountable manner, while losartan and irbesartan were surmountable AT1-receptor antagonists. The AT2-receptor antagonist, PD 123319, (10, 100 nM) had no effect on Ang II-induced contraction. This is supported by the positive identification of mRNA for the human AT 1-receptor by RT-PCR.

Up-regulation of G-protein-coupled receptors for endothelin and thromboxane by lipid-soluble smoke particles in renal artery of rat

Up-regulation of G-protein-coupled receptors (GPCR) plays key roles in renal hypertension and cardiovascular disease pathogenesis. The present study was designed to examine if lipid-soluble cigarette smoking particles (DSP), nicotine and endotoxin (LPS), induce GPCR up-regulation for thromboxane A(2) (TP), endothelin type A (ET(A) ) and type B (ET(B) ) receptors in renal artery, and if intracellular signal mechanisms are involved. Renal artery segments of rats were exposed to DSP, nicotine or LPS, in organ culture for up to 24 hr. The GPCR-mediated contractions were recorded by using a myograph system. Expression of the GPCR was examined by real-time PCR and immunohistochemistry at mRNA and protein levels. Sarafatoxin 6c (S6c, selective ET(B) receptor agonist), endothelin-1 (ET-1, non-selective ET(A) and ET(B) receptor agonist) and 9,11-Dideoxy-9a,11a-methanoepoxy prostaglandin F(2a) (U46619, a TP receptor agonist) induced contractions were significantly increased after the arterial segments exposed to DSP in a concentration-dependent (0.1-0.4 μl/ml) manner, and S6c also induced a time-dependent contraction, compared to control (dimethyl sulfoxide). This was in parallel with enhanced mRNA expression for ET(B) receptor but not ET(A) and TP receptors, while increased protein expression for ET(A) , ET(B) and TP receptors was seen. The specific nuclear factor-kappa B (NF-κB) signal pathway inhibitor BMS345541 was applied to link DSP effects to the GPCR up-regulation. It totally abolished ET(B) receptor up-regulation, but not ET(A) and TP receptor up-regulations. Our results suggest that DSP transcriptionally up-regulated ET(B) receptor expression in rat renal artery via NF-κB signal pathways, whereas up-regulation of ET(A) and TP receptor-mediated contraction may involve post-transcriptional mechanisms.

Lipid-soluble smoke particles upregulate vascular smooth muscle ETB receptors via activation of mitogen-activating protein kinases and NF-kappaB pathways

Cigarette smoke is a strong risk factor for cardiovascular disease. However, the underlying molecular mechanisms that lead to cigarette smoke-associated cardiovascular disease remain elusive. With functional and molecular methods, we demonstrate for the first time that lipid-soluble cigarette smoke particles (dimethylsulfoxide-soluble cigarette smoke particles; DSP) increased the expression of endothelin type B (ET(B)) receptors in arterial smooth muscle cells. The increased ET(B) receptors in arterial smooth muscle cells was documented as enhanced contractility (sensitive myograph technique), elevated levels of ET(B) receptor mRNA (quantitative real-time PCR), and protein expressions (immunohistochemistry and Western blotting). Intracellular signaling was studied with Western blotting and phosphoELISA; this revealed that DSP induced extracellular-regulated protein kinases 1 and 2 (ERK1/2), p38, and nuclear factor-kappaB (NF-kappaB) phosphorylation within 3 h. Blocking ERK1/2, p38, or NF-kappaB activation by their specific inhibitors significantly attenuated the DSP-induced upregulation of ET(B) receptor-mediated contraction and both ET(B) receptor mRNA and protein expression. In addition, dexamethasone abolished the DSP-induced upregulation of ET(B) receptor-mediated contraction. In conclusion, upregulation of ET(B) receptors by DSP in arterial smooth muscle cells involves activation of mitogen-activating protein kinases (ERK1/2 and p38) and the downstream transcriptional factor NF-kappaB pathways.

Up-regulation of thromboxane A2 receptor expression by lipid soluble smoking particles through post-transcriptional mechanisms

Atherosclerosis is a key factor in vascular disease, and cigarette smoking is a well-known risk factor that may induce an inflammatory response and enhance plaque formation in arteries. Thromboxane (Tx) is one key inflammatory mediator involved in the pathogenesis of cardiovascular disease. The present study was designed to test if lipid soluble smoking particles (DSP) enhance TxA(2) receptor (TP) expression in rat mesenteric arteries, and if intracellular mitogen-activated protein kinase (MAPK) pathways play a role. Organ culture of rat mesenteric arteries in the presence of DSP (0.2 microl/ml for 24h) resulted in markedly elevated contractile responses to the Tx analog U46619, compared with the control DMSO. There was no increase in TP receptor mRNA expression, while the protein expression was significantly enhanced. This up-regulation was not affected by a general transcriptional inhibitor actinomycin D, but was almost completely abolished by cycloheximide, a general translational inhibitor. Dexamethasone, a glucocorticoid, manifested a potent inhibitory effect as well. These results suggest that the up-regulation of TP receptor occurs via post-transcriptional events, and mainly translation. This is supported by experiments with specific inhibitors for c-Jun-NH(2)-terminal kinase (SP600125), extracellular signal-regulated kinase 1 and 2 (PD98059 and U0126) and p38 (SB203580) that had no inhibitory effect on the up-regulation of TP receptors. Collectively, the results show that MAPK pathways are not involved in TP receptor up-regulation. Study on TP receptor mRNA stability showed that during organ culture, the TP receptor mRNA was stable in both DMSO and DSP group, but the latter elicited a tendency to stabilize the TP receptor mRNA at higher level. Thus, post-transcriptional mechanisms are responsible for the up-regulation of TP receptor by DSP, in which enhanced translation is the major cause of the elevated protein expression and the enhanced contraction.

Characterization of K(ATP)-channels in rat basilar and middle cerebral arteries: studies of vasomotor responses and mRNA expression

Changes in the activity of K+ channels represent a major mechanism that regulates vascular tone. Cerebrovascular adenosine 5'-triphosphate-sensitive K+(K(ATP)) channels were characterized in studies of the molecular expression and vasomotor reactivity to different K(ATP) channel openers in rat basilar and middle cerebral arteries. Both arteries showed strong mRNA expression of the subunits of the pore-forming inward-rectifying K+ channel type 6.1 (Kir6.1), Kir6.2 and the connected sulfonylurea receptor (SUR) subunits, SUR1 and SUR2B, while only weak bands for SUR2A were seen. The K(ATP) channel openers induced relaxation of prostaglalndin F2alpha-precontracted isolated basilar and middle cerebral arteries with the order of potency N-Cyano-N-(1,1-dimethylpropyl)-N''-3pyridylguanidine (P-1075)>levcromakalim>N-(4-Phenylsulfonylphenyl)-3,3,3-trifluoro-2-hydroxy-2-methylpropanamide (ZM226600)>pinacidil>diazoxide. The responses induced by levcromakalim, ZM226600 and diazoxide were significantly more potent in basilar arteries than in middle cerebral arteries, while pinacidil and P-1075 were equipotent. Endothelium removal decreased (P<0.05) the sensitivity (pIC50) of basilar arteries, but not of middle cerebral arteries, to pinacidil, levcromakalim, P-1075 and ZM226600. The maximum relaxant response to P-1075 was stronger (P<0.005) in basilar arteries with endothelium than without endothelium. Correlation of the relaxant potency of K(ATP) channel openers in rat basilar and middle cerebral arteries with historical measurements of affinity obtained in COS-7 cell lines expressing either SUR1, SUR2A or SUR2B showed that vasodilatation by K(ATP) channel openers correlated with binding to either the SUR2A or the SUR2B subunit. Glibenclamide was a blocker of relaxation induced by pinacidil, levcromakalim, P-1075 and ZM226600 in basilar arteries. Only a weak antagonistic effect of glibenclamide on pinacidil-, levcromakalim- and ZM226600-induced relaxations was found in middle cerebral arteries. The subunit profile and the observed pharmacological properties suggest that the K(ATP) channels expressed in rat basilar and middle cerebral artery are likely to be composed of SUR2B co-associated with Kir6.1 or Kir6.2. In basilar arteries, but not in middle cerebral arteries, endothelial K(ATP) channels may be involved.

Transcriptional Up-Regulation in Expression of 5-Hydroxytryptamine2A and Transcriptional Down-Regulation of Angiotensin II type 1 Receptors during Organ Culture of Rat Mesenteric Artery

The purpose of this study was to investigate in rat mesenteric artery if there is up-regulation of 5-hydroxytryptamine (5-HT) receptors and angiotensin II receptors and the potential role of protein kinase C activation in the smooth muscle cells during organ culture. Angiotensin II, 5-HT and potassium induced contraction of ring segments without endothelium, monitored by a sensitive in vitro pharmacology method. After the culture of the arterial ring segments for 24 hr, the concentration-contraction curves induced by 5-HT slightly shifted towards to the left with pEC(50) from 6.64+/-0.11 to 6.84+/-0.11 and a significant increase in E(max) from 147+/-11% to 246+/-15% (P<0.05), compared with that obtained in fresh segments. In contrast, the angiotensin II concentration-contraction curve only showed a significant decrease in E(max) from 99+/-10% to 37+/-8%. Specific antagonists for the 5-HT type 2A receptors (5-HT(2A)) and angiotensin II type 1 receptors (AT(1)) demonstrated that the contractions occurred via 5-HT(2A) and AT(1) receptors, respectively. Real-time PCR revealed that the 5-HT(2A) receptor mRNA was up-regulated in parallel with the contractile response while there was a down-regulation of AT(1) receptor mRNA. Transcriptional inhibitor actinomycin D and specific protein kinase C inhibitor Ro31-8220 demonstrated that it was a transcriptional mechanism with involvement of protein kinase C that regulated the enhanced expression of 5-HT(2A) receptors in the mesenteric artery.

In-depth characterization of CGRP receptors in human intracranial arteries

The purpose of the present study was to characterize the effects of human (h) alpha- and beta-calcitonin gene-related peptide (CGRP) on intracranial arteries from man and to investigate the presence of mRNA for the calcitonin receptor like receptor (CRLR) and the receptor activity modifying proteins (RAMPs) 1, 2 and 3, in cerebral and middle meningeal arteries with and without endothelium, in microvessels and in the endothelial cells isolated from the human basilar artery. Reverse transcriptase-polymerase chain reaction (RT-PCR) revealed the presence of CRLR, RAMP 1, RAMP 2 and RAMP 3 in cerebral and middle meningeal arteries with and without endothelium as well as in microvessels and in the endothelial cells. Human and rat alpha- and beta-CGRP, amylin, adrenomedullin and [acetamidomethyl-Cys(2,7)]human CGRP induced strong concentration-dependent relaxation of human cerebral and middle meningeal arteries. Removal of the endothelium neither changed the maximum relaxant response nor the pIC(50) values for alpha- and beta-CGRP as compared to the responses in arteries with an intact endothelium. Human alpha-CGRP-(8-37) caused a shift of h alpha- and h beta-CGRP-induced relaxations in cerebral and middle meningeal arteries. Calculation of pK(B) values revealed that h alpha-CGRP-(8-37) could not significantly discriminate between relaxations induced by h alpha-CGRP (pK(B) around 6.8) and h beta-CGRP (pK(B) around 5.4). There was no significant difference in pK(B) value of h alpha-CGRP-(8-37) on h beta-CGRP-induced relaxation of human cerebral and middle meningeal arteries with and without endothelium. In conclusion, our molecular and pharmacological data support the existence of a single type of CGRP(1) receptors in the human intracranial circulation.

Potent P2Y6 receptor mediated contractions in human cerebral arteries

BACKGROUND

Extracellular nucleotides play an important role in the regulation of vascular tone and may be involved in cerebral vasospasm after subarachnoidal haemorrhage. This study was designed to characterise the contractile P2 receptors in endothelium-denuded human cerebral and omental arteries. The isometric tension of isolated vessel segments was recorded in vitro. P2 receptor mRNA expression was examined by RT-PCR.

RESULTS

In human cerebral arteries, the selective P2Y6 receptor agonist, UDPbetaS was the most potent of all the agonists tested (pEC50 = 6.8 PlusMinus; 0.7). The agonist potency; UDPbetaS > alphabeta-MeATP > UTPgammaS > ATPgammaS > ADPbetaS = 0, indicated the presence of contractile P2X1 P2Y2, P2Y4 and P2Y6, but not P2Y1 receptors, in human cerebral arteries. In human omental arteries, UDPbetaS was inactive. The agonist potency; alphabeta-MeATP > ATPgammaS = UTPgammaS > ADPbetaS = UDPbetaS = 0, indicated the presence of contractile P2X1, and P2Y2 receptors, but not P2Y1 or P2Y6 receptors, in human omental arteries. RT-PCR analysis of endothelium-denuded human cerebral and omental arteries demonstrated P2X1, P2Y1, P2Y2 and P2Y6 receptor mRNA expression. There were no bands for the P2Y4 receptor mRNA in the omental arteries, while barely detectable in the cerebral arteries.

CONCLUSIONS

P2Y6 receptors play a prominent role in mediating contraction of human cerebral arteries. Conversely, no such effect can be observed in human omental arteries and previous results confirm the absence of P2Y6 receptors in human coronary arteries. The P2Y6 receptor might be a suitable target for the treatment of cerebral vasospasm.

BIBN4096BS is a potent competitive antagonist of the relaxant effects of alpha-CGRP on human temporal artery: comparison with CGRP(8-37)

Release of CGRP during migraine may produce harmful dilatation of cranial arteries, thereby possibly causing pain. We have compared the antagonism by BIBN4096BS and CGRP(8-37) of the relaxant effects of alpha-CGRP on rings of human temporal artery. alpha-CGRP relaxed the arteries precontracted with 9 - 24 mM KCl (-logEC50=9.4) nearly as efficaciously as sodium nitroprusside (10 microM). BIBN4096BS (0.1 - 100 nM) antagonized the effects of alpha-CGRP in surmountable manner with slopes of Schild-plots not different from unity. -LogKB values of 10.1 and 10.4 were estimated for BIBN4096BS when administered before or during the KCl-contracture respectively. BIBN4096BS (1 microM) did not modify the relaxant effects of papaverine and sodium nitroprusside. CGRP(8-37) (1 - 10 microM) antagonized the effects of alpha-CGRP in a surmountable manner with slopes of Schild-plots not different from unity. -LogKB values of 6.6 and 6.7 were estimated for CGRP(8-37) administered before or during the KCl-contracture respectively. The high affinity of BIBN4096BS for CGRP receptors of human temporal artery makes it an excellent tool to explore the hypothesis of CGRP-evoked cerebral vasodilation in migraine.

Characterization of CGRP(1) receptors in the guinea pig basilar artery

The purpose of the present study was to characterise receptors mediating calcitonin gene-related peptide (CGRP)-induced relaxation of guinea pig basilar artery. This was done by investigating vasomotor responses in vitro and performing autoradiographic binding studies. We also intended to study the importance of an intact endothelium. Agonist studies showed that peptides of the CGRP family induced relaxation of the guinea pig basilar artery with the following order of potency: human beta-CGRP=human alpha-CGRP>>adrenomedullin=[acetamidomethyl-Cys(2,7)]alpha-human CGRP ([Cys(ACM)(2,7)]CGRP)=amylin. These data are in concord with those of the autoradiographic binding studies that showed displacement of [125I] human alpha-CGRP binding with the following order of potency: human alpha-CGRP=human beta-CGRP>>adrenomedullin=human alpha-CGRP-(8-37)>>Cys(ACM)(2,7)]CGRP. In blockade experiments, the relaxant responses to human alpha- and human beta-CGRP were competitively blocked by the CGRP(1) receptor antagonist human alpha-CGRP-(8-37), while those of adrenomedullin and amylin were blocked non-competitively. In order to examine whether amylin induced relaxation via amylin or CGRP receptors, we studied the antagonistic effect of amylin-(8-37) on the weak relaxant response to amylin and found that it was not blocked by amylin-(8-37). These findings, together with the finding that the CGRP(2) receptor agonist [Cys(ACM)(2,7)]CGRP only induced a weak relaxation in the highest concentrations examined, suggest that the CGRP family of peptides mediate relaxation by CGRP(1)-type receptors. Removal of the endothelium, the addition of N(G)-nitro-L-arginine methyl ester (L-NAME), methylene blue or indomethacin did not affect the concentration-response curves of the CGRP analogues, neither in the presence nor in the absence of human CGRP-(8-37). The study shows the presence of a relaxant CGRP(1) receptor on the smooth muscle cells of guinea pig basilar artery. Various endothelial factors did not influence relaxant responses.

Helospectin-like peptides: immunochemical localization and effects on isolated cerebral arteries and on local cerebral blood flow in the cat

Helospectin I and II and helodermin are nonamidated, vasoactive intestinal peptide (VIP)-like peptides, isolated from the salivary gland venom of the lizards Heloderma suspectum and Heloderma horridum. Helospectin I has 38 amino acid residues and differs from helospectin II in that it has an additional serine residue at the C-terminus. Numerous nerve fibers containing helospectin-like immunoreactivity (LI) and a few fibers containing helodermin-LI were present in the adventitia and at the adventitia-media border of cat cerebral arteries. In the sphenopalatine ganglion, numerous nerve cell bodies containing helospectin-LI were seen. Double immunostaining revealed that helospectin-LI nerve cell bodies coexisted with VIP-containing cell bodies. Radioimmunoassay showed high levels of helospectin-LI in extracts of cerebral vessels from the circle of Willis (27.4 pg/mg [wt/wt]). Helospectin I and II and helodermin (10(-10) to 10(-6) mol/L) produced concentration-dependent relaxations of feline middle cerebral arteries amounting to 50% to 80% of precontraction induced by U46619. The maximum effects and the potency were similar to that of VIP. Neither of these peptides elicited endothelium-dependent relaxations. Intracerebral microinjection of helospectin and helodermin produced a moderate concentration-dependent increase of the cerebral blood flow of alpha-chloralose anesthetized cats. The maximum increase (21 +/- 5%) was observed after the injection of 5 microg helodermin, whereas 16 +/- 7% was seen with helospectin I and 19 + 5% with helospectin II. The results suggest that helospectin/helodermin-like peptides co-localize with VIP in perivascular nerve fibers originating in the sphenopalatine ganglion. They seem to have strong and potent vasodilator effects.

Innervation of the human middle meningeal artery: immunohistochemistry, ultrastructure, and role of endothelium for vasomotility

The majority of nerve fibers in the middle meningeal artery and branching arterioles are sympathetic, storing norepinephrine and neuropeptide Y (NPY). A sparse supply of fibers contain acetylcholinesterase activity and immunoreactivity toward vasoactive intestinal peptide (VIP), peptidine histidine methionine (PHM), and calcitonin gene-related peptide (CGRP). Only few substance P and neuropeptide K immunoreactive fibers are noted. Electronmicroscopy shows axons and terminals at the adventitial medial border of the human middle meningeal artery, with a fairly large distance to the smooth muscle cells (>500 nM). Several axon profiles contain vesicles of different types, including putative sensory profiles. The perivascularly stored signal substances, norepinephrine and NPY induced vasoconstrictor. Relaxations were induced by acetylcholine and substance P, and these were significantly reduced in arteries without endothelium, while the responses to norepinephrine, NPY, VIP, PHM, and CGRP were not changed by endothelium removal. Blockade experiments showed that the vasomotor responses to norepinephrine were blocked by prazosin, to NPY by BIBP 3226, acetylcholine by atropin, substance P by RP 67580, and the human alpha-CGRP response by human alpha-CGRP(8-37).

Maintenance of constant blood acetylcholine content before and after feeding in young chimpanzees

We have shown that acetylcholine (ACh) is present in the blood of various species of mammals using a specific, sensitive radioimmunoassay. In the present study, the effect on blood and plasma ACh levels of feeding after overnight fasting was studied in one male and five female 4- to 7-year-old chimpanzees. The mean basal ACh concentrations of the blood and plasma were 3143 +/- 380 and 184 +/- 10 pg/ml (+/-SEM, n = 6), respectively. Feeding each chimpanzee 500 g boiled sweet potatoes as breakfast at 1000 h and tap water given ad libitum did not affect the ACh content of the blood and plasma, and constant values of the blood and plasma ACh contents were observed for 4 h after the feeding. Hematocrit and plasma acetylcholinesterase (AChE) activity were also insensitive to feeding. No correlation was observed between plasma AChE activity and either blood or plasma ACh content. The results of the present study indicate that the blood ACh of chimpanzees is distributed mainly in the blood cell fraction, and that the blood ACh content is not regulated directly by cholinergic nerve activity or by plasma AChE activity.

Oral administration of KW-5092, a novel gastroprokinetic agent with acetylcholinesterase inhibitory and acetylcholine release enhancing activities, causes a dose-dependent increase in the blood acetylcholine content of beagle dogs

Acetylcholine (ACh) was detected in the blood and plasma of beagle dogs using a specific, sensitive radioimmunoassay. The mean basal ACh contents in the blood and plasma of beagle dogs were 451 +/- 65 and 83.5 +/- 12.3 pg/ml (+/- SEM, n = 7), respectively, and were lower than the contents in humans reported previously by our laboratory. Oral administration of KW-5092 (10-30 mg/kg), a gastroprokinetic agent with acetylcholinesterase (AChE) inhibitory and ACh release enhancing activities, caused a dose-dependent increase in the ACh content of both the blood and plasma, as well as several behavioral side effects due to peripheral cholinergic stimulation. The size of the increase in the plasma ACh content at each dose of KW-5092 was greater than that in the blood, indicating that KW-5092 caused the increase in the blood ACh content through elevation of the plasma ACh content, by inhibition of AChE and facilitation of ACh release. These results demonstrate that the blood ACh of beagle dogs is present mainly in the blood cells and to a lesser degree in the plasma, and that KW-5092 increased the blood ACh content mainly by increasing the plasma ACh concentration.

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 calcitonin gene-related peptide (CGRP) analogues have been studied in circular segments of fresh human cerebral arteries obtained at neurosurgical operations using a sensitive in vitro system. Human alpha-CGRP, human beta-CGRP, rat alpha-CGRP and rat beta-CGRP induced strong and potent relaxation of precontracted circular vessel segments. The Imax (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 alpha-CGRP8-37 blocked the response to human alpha-CGRP but not to human beta-CGRP, while the putative antagonist [Tyr]CGRP28-37 did not. Capsaicin (10(-15)-10(-8)M) caused relaxation of the cerebral arteries by 22% of precontraction. Pre-treatment with 10(-6)M human alpha-CGRP8-37 inhibited this relaxation. Human alpha-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 alpha-CGRP8-37. The results suggest that CGRP-1 receptors coupled to adenylyl cyclase are present in human cerebral arteries.

Localization and synthesis of acetylcholine in human leukemic T cell lines

In order to clarify the origin of acetylcholine (ACh) in human blood, we measured the content and synthesis activity of ACh in several human leukemic cell lines. The intracellular ACh content determined by a specific and sensitive radioimmunoassay in the human leukemic T cell lines, HSB-2, MOLT-3, and CEM, was 79.6, 36.2, and 9.5 pmol/10(6) cells, respectively. These values were 9-70-fold higher than those of other cell lines, including a helper T cell line, Jurkat. Stimulation of HSB-2 and MOLT-3 by phytohemagglutinin (PHA) increased both the intracellular content and release of ACh into the culture medium, but did not influence the intracellular content and release of ACh in CEM. ACh synthesis activity was found in all the T cell lines tested. Bromoacetylcholine (100 microM), a choline acetyltransferase (ChAT) inhibitor, and bromoacetyl-L-carnitine (100 microM), a carnitine acetyltransferase (CarAT) inhibitor, decreased ACh-synthesizing activity in MOLT-3, and HSB-2 and CEM, by about 50% and 30%, respectively, indicating that both ChAT, and to a lesser extent CarAt, are involved in ACh synthesis in T cells. These results suggest that T lymphocytes have the potential to synthesize and release ACh, which may play a role in regulating T cell-dependent immune responses.

Peptidergic innervation of guinea-pig brain vessels: comparison with immunohistochemistry and in vitro pharmacology in rostrally and caudally located arteries

The peptidergic innervation of the guinea-pig basilar artery and the posterior, middle and anterior cerebral arteries were studied by means of immunohistochemical and image analysis techniques using whole mount preparations. An in vitro pharmacological study was performed to correlate the distribution of peptide-containing nerves and the action of neuropeptides on vessel segments from the same vascular regions. The overall distribution of perivascular nerve fibres was demonstrated using an antiserum to the general neuronal marker protein gene product 9.5 (PGP 9.5) and the percentage immunostained area of total vessel wall area occupied by PGP-containing nerves, in each of the basilar, posterior and middle cerebral arteries, was set at 100% and used to determine the relative density of specific populations of autonomic and sensory nerve fibres. In all four cerebral arteries, the majority of nerve fibres possessed neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity, occupying 6.2-13.3% and 5.8-7.5% of the total vessel wall area, respectively. Vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin-gene-related peptide (CGRP) were detected at lower densities. The pharmacological study performed on small circular segments with an intact endothelium revealed that, in all four cerebral arteries, NPY was a more potent constrictor than noradrenaline (NA). The rank order of potency for relaxant agents was CGRP = SP > VIP > ACh in the PCA and MCA, and SP = CGRP > VIP > ACh in the BA and ACA. The correlation between immunostained nerve area and the agonist potency suggested that the denser the peptidergic nerve-supply, the lower the sensitivity to the agonist.

Microvessels isolated from brain: localization of muscarinic sites by radioligand binding and immunofluorescent techniques

The present investigation was carried out to determine the extent to which muscarinic acetylcholine receptors (mAChRs) in vascular and perivascular structures were colocalized with glial fibrillary acidic protein (GFAP)-positive structures. To this aim, an immunocytochemical approach on free-floating cryosections and isolated microvessels obtained from rat brain was performed to study the possible colocalization of immunostaining with the anti-mAChR protein antibody (M35) and an anti-GFAP antibody. Double-labeling experiments were carried out by fluorescent techniques. Confocal microscopic observations of GFAP and M35 immunoreactivities on free-floating sections showed a high degree of colocalization on astrocyte processes associated with large vessels or capillaries. This pattern suggests that muscarinic receptors are associated with astrocytic endfeet. Confocal microscopic observations of immunoreactivity from isolated cerebral microvessels strengthen this conclusion since double-labeling of M35 and GFAP showed that perivascular astrocytic structures remained attached to the isolated microvessels and were present on vascular segments showing M35 immunoreactivity. In another set of experiments, the specific binding of [3H]quinuclidinylbenzylate ([3H]QNB) to isolated microvessel membrane preparations from cerebral cortex, caudate nucleus, thalamus, and cerebellum showed that a constant binding yield (20% in bovine and 40% in rat) was observed for microvessels compared with the corresponding brain region. According to our immunocytochemical results, the astrocytic membrane remaining attached to microvessels may account for the majority of the muscarinic binding to isolated microvessels. [3H]QNB binding values found in isolated microvessels cannot therefore be considered as artifacts without any link with vascular function. Taken together, the present study strengthens the idea that the muscarinic receptors may be implicated in the functional relationship between glial and vascular structures.

Cholinergic and vasoactive intestinal polypeptidergic innervation of the cerebral arteries

Acetylcholine and vasoactive intestinal polypeptide are not only two vasoactive agonists that predominantly induce a vasodilatation of the cerebral arteries, but also correspond to neurotransmitters that innervate the various anatomical segments of the cerebral vasculature. The distinct patterns of the cerebrovascular cholinergic and vasoactive intestinal polypeptidergic innervation, their neurochemistry, in vitro and in vivo pharmacology, as well as the putative pathophysiological implications of these neurotransmission systems are critically summarized on the basis of the most recently published literature.

Hypercapnic vasodilatation in isolated rat basilar arteries is exerted via low pH and does not involve nitric oxide synthase stimulation or cyclic GMP production

The relaxant effect of hypercapnia (15% CO2) was studied in isolated circular segments of rat basilar arteries with intact endothelium. The nitric oxide synthase inhibitor nitro-L-arginine (L-NOARG) and the cytosolic guanylate cyclase inhibitor methylene blue (MB), significantly reduced this relaxation by 54% and 70%, respectively. The effect of L-NOARG was completely reversed by L-arginine. Blockade of nerve excitation with tetrodotoxin (TTX) had no affect on the 15% CO2 elicited vasodilatation. Measurements of cGMP in vessel segments showed no significant increase in cGMP content in response to hypercapnia. L-NOARG and MB, but not TTX, significantly reduced the basal cGMP content in cerebral vessels. Adding 1.5% halothane to the incubation medium did not result in a significant increase in cGMP content. Lowering the pH by cumulative application of 0.12 M HCl resulted in relaxation identical to that obtained by lowering the pH with 15% CO2. In vessel segments in which the endothelium had been removed beforehand 15% CO2 induced relaxation that was not different from that seen in vessels with intact endothelium. L-NOARG had no affect in endothelium denuded vessels. The results suggest that high CO2 elicits vasodilatation of isolated rat basilar arteries by a mechanism independent of nitric oxide synthase (NOS) activity. The markedly reduced basal cGMP levels in cerebral vessels by L-NOARG and MB suggest that there exists a basal NO formation in the cerebral vessel wall.

The blood-brain barrier in vitro: the second decade

Ever since the discovery of Paul Ehrlich (1885 Das Sauerstoff-bedürfnis des Organismus: Hirschwald, Berlin) about the restricted material exchange, existing between the blood and the brain, the ultimate goal of subsequent studies has been mainly directed towards the elucidation of relative importance of different cellular compartments in the peculiar penetration barrier consisting the structural basis of the blood-brain barrier (BBB). It is now generally agreed that, in most vertebrates, the endothelial cells of the central nervous system (CNS) are responsible for the unique penetration barrier, which restricts the free passage of nutrients, hormones, immunologically relevant molecules and drugs to the brain. After an era of studying with endogenous or exogenous tracers the unique permeability properties of cerebral endothelial cells in vivo, the next generation, i.e. the in vitro blood-brain barrier model system was introduced in 1973. Recent advances in our knowledge of the BBB have in part been made by studying the properties and function of cerebral endothelial cells (CEC) with this in vitro approach. This review summarizes the results obtained on isolated brain microvessels in the second decade of its advent.

Glial cells in coculture can increase the acetylcholinesterase activity in human brain endothelial cells

The elements of the cholinergic system (acetylcholinesterase and choline acetyltransferase) and butyrylcholinesterase were studied in human cortical capillary samples, brain-derived endothelial cell cultures and glial cell cultures. It was shown that the elements of the cholinergic system are present in the microvessels, but the choline acetyltransferase activity may be due to contamination with cholinergic nerve terminals since no choline acetyltransferase could be demonstrated in endothelial cell cultures. The present results revealed that the activity of acetylcholinesterase is reduced in the cortical endothelial cell cultures after longer culture times, while butyrylcholinesterase activity is not altered. In a system where endothelial cells were cocultured with embryonic human brain astroglial cells for 12 days in vitro, the acetylcholinesterase activity was increased 2-fold. These results support a glial influence on the enzyme activity of the cerebral endothelium.

Periendothelial acetylcholine synthesis and release in bovine cerebral cortex capillaries

Choline acetyltransferase (ChAT) activity is present in isolated cerebral capillaries, where it has been considered to be a marker for perivascular cholinergic nerve terminals. However, ChAT-like immunoreactivity has been visualized in endothelial cells. This finding raised the possibility that at least part of the biochemically detected ChAT has a nonneuronal origin. To evaluate the relative contribution of endothelial cells and nerve fibers to the total acetylcholine (ACh)-synthesizing capacity of cerebral capillaries, ChAT activity and ACh release were measured in capillaries and in purified endothelial cells isolated from bovine cerebral cortex. Isolated capillaries showed ChAT activity, which was inhibited by 2-benzoylethyl trimethylammonium to the same extent as cerebral ChAT. When preincubated with [3H]choline, these capillaries presented a calcium-dependent enhancement in tritium release upon electrical field stimulation. Purified endothelial cells had minor ChAT activity and lacked the ability to release tritium in response to electrical stimulation, although the endothelial markers alkaline phosphatase, gamma-glutamyltranspeptidase, and 1,1'-dioctadecyl-1,3,3',3'-tetramethyl-iodocarbocyanide perchlorate-labeled acetylated low-density lipoprotein uptake were fully preserved. These data indicate that, within isolated cerebral capillaries, ACh is synthesized and released by a periendothelial structure. The fact that ACh release is provoked by electrical stimulation and by a calcium-dependent mechanism strongly suggests that cerebrovascular ACh has a neuronal origin.

Acetylcholine levels and choline acetyltransferase activity in rat cerebrovascular bed after uni- or bilateral sphenopalatine ganglionectomy

Endogenous acetylcholine (ACh) levels and choline acetyltransferase (ChAT) activity were measured in several vascular segments (major cerebral arteries, cortical pial vessels, and peripheral arteries) and nervous tissues [including the sphenopalatine ganglion (SPG)] in the rat. The effects of uni- or bilateral surgical ablation of the SPG, a putative origin of the cholinergic cerebrovascular innervation, were investigated on these two specific cholinergic markers at various postoperative times. ChAT activity and ACh levels were enriched in the cerebral as compared to the peripheral arteries. Among the cerebrovascular tissues tested, ACh levels were particularly high in the circle of Willis and the vertebrobasilar segments and, to a lesser extent, in the middle cerebral artery. Lower levels were found in the small pial vessels and choroid plexus. Overall, ChAT activity measured in different arterial beds paralleled the distribution of ACh. Following uni- or bilateral removal of the SPG, slight reductions (18-36%, statistically not significant) were observed in ChAT activity in rostral cerebral arteries and pial vessels overlying the frontal cortex. Similarly, bilateral ganglionectomy resulted in minor decreases (11-22%, not significant) in the cerebrovascular contents of ACh in these same vascular segments. These results clearly show that the SPG does not or only partly contributes to the cholinergic fibers that supply the cerebrovascular bed.

An immunohistochemical study of endothelial cell heterogeneity in the rat: observations in "en face" Häutchen preparations

"En face" sheets of endothelium, in which cellular spatial relationships were maintained, were prepared from proximal pulmonary and femoral arteries and aortae of the Wistar rat, in order to visualise patterns of heterogeneity in populations of endothelial cells. These preparations, termed Häutchen, were immunolabelled with antibodies to angiotensin II, endothelin and Factor-VIII-related antigen, and visualised by an avidin/biotin peroxidase complex. Clusters of cells, which accounted for approximately 30% of the total endothelial cell population, and which were positively immunostained for angiotensin II, were found perpendicular to the longitudinal axis of the aorta and femoral artery. Cells in the pulmonary artery were immunonegative for angiotensin II. The majority of cells in all three vessels were immunopositive for endothelin; groups of intensely stained cells were present in both the femoral artery and aorta, but not in the pulmonary artery. Immunoreactivity to Factor-VIII-related antigen was heterogeneous, with intensely stained amorphous patches of endothelial cells present in the femoral artery and aorta. Häutchen preparations present an opportunity for the investigation of endothelial cell heterogeneity, both within and between vessels; this may provide a basis for the interpretation of the heterogeneity of endothelium-dependent responses in vessels of differing origin.

Evidence that calcitonin gene-related peptide contributes to the capsaicin-induced relaxation of guinea pig cerebral arteries

Pretreatment with capsaicin caused a depletion of substance P (SP)-, neurokinin A (NKA)- and calcitonin gene-related peptide (CGRP)-like immunoreactivity (-LI) from the trigeminal ganglion, dura mater and cerebral arteries. The effect of capsaicin on isolated basilar arteries of guinea pig resulted in a biphasic relaxant response of histamine precontracted vessels. The first phase of the capsaicin-induced relaxation was absent in capsaicin-treated guinea pigs. Furthermore, repeated administration of capsaicin decreased the first but not the second phase of relaxation, supporting the view that a stored agent was released, while the second phase probably was due to a direct effect of capsaicin per se. The biphasic effect was not modified by the SP antagonist Spantide in a concentration that blocks tachykinin response (3.10(-6) M), nor by removal of the endothelium. There was no significant difference in pD2 values (-log concentration eliciting half maximum relaxation) between relaxations induced by SP, NKA, neurokinin B, neuropeptide K or CGRP in capsaicin pretreated as compared to vehicle-treated animals. These results are in support of the assumption that CGRP is involved in the capsaicin-induced relaxation caused by release of vasoactive agents from sensory afferent nerves.

Synthesis and release of acetylcholine by cultured bovine arterial endothelial cells

Using cultured endothelial cells prepared from bovine carotid artery, and a specific radioimmunoassay for acetylcholine (ACh), the synthesis and release of ACh by vascular endothelial cells were investigated directly. ACh content in the culture medium after 24 h of incubation in the presence of isoflurophate, a nonspecific cholinesterase inhibitor, was about 16 times higher than that in endothelial cells, indicating that ACh synthesized inside the cells was released rapidly. The presence of ACh in the culture medium was further confirmed qualitatively using high-performance liquid chromatography with an electrocapture detection. These results represent the first direct evidence that endothelial cells can synthesize and release ACh, suggesting the possibility that ACh acts not only as a neurotransmitter but also as an autacoid under certain conditions.

Selective age-related changes in neuronal markers and smooth muscle reactivity in cerebrovascular beds of Fischer 344 rats

Choline accumulation, choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities were measured simultaneously in various cerebrovascular beds and brain areas from Fischer 344 rats aged 4.5 and 22 months. A slight (25%) but not significant decrease in choline accumulation was observed concomitantly with a significant increase (187%, p less than 0.05) in ChAT activity in the major cerebral arteries of the 22-month-old rats. In small cortical pial vessels and selected brain regions, cholinergic and GABAergic biochemical markers remain unaltered in aged rats. The vasomotor reactivity of the basilar artery was investigated in rats of 4.5, 12, 22 and 30 months of age. In the 22-month-old rats, maximal responses to 5-hydroxytryptamine (-25%, no significant) and prostaglandin F2 alpha (-30%, p less than 0.05 by ANOVA) were less intense as compared to other age-groups despite preserved contractile responses to dopamine, uridine triphosphate or a depolarizing concentration of K+. Relaxations induced by histamine, acetylcholine, noradrenaline, adenosine and somatostatin were strictly comparable among the different age-groups. The sensitivity of the basilar artery to all vasoactive agents failed to demonstrate any correlation with age. Our study suggests that cerebrovascular cholinergic and GABAergic markers undergo minor and selective changes with increasing age. Further, basilar artery vasomotor functions appeared relatively spared by the aging process despite age-related selective decreases in contractile responses to 5-hydroxytryptamine and prostaglandin F2 alpha.

Activation of endothelial L-arginine pathway in resistance arteries. Effect of age and hypertension

In conduit arteries, nitric oxide is formed from L-arginine in the endothelium and released after stimulation with acetylcholine. The contribution of the L-arginine pathway and the effects of age and hypertension on endothelium-dependent vascular regulation were studied, using a video dimension analyzer, in pressurized and perfused mesenteric resistance arteries of 8- and 16-20-week-old Wistar-Kyoto and spontaneously hypertensive rats. Norepinephrine and phenylephrine caused contractions, which were similarly augmented after removal of the endothelium. NG-Monomethyl-L-arginine, an inhibitor of nitric oxide formation, augmented the contraction, but less than endothelial removal. Acetylcholine caused endothelium-dependent relaxations that were much more pronounced with intraluminal than with extraluminal application. NG-Monomethyl-L-arginine, methylene blue, and hemoglobin only partially inhibited the response. With aging, the endothelium-dependent inhibition of the response to norepinephrine decreased in Wistar-Kyoto rats; in spontaneously hypertensive rats this inhibition was smaller as compared with age-matched Wistar-Kyoto rats. In Wistar-Kyoto rats, the difference between intraluminal and extraluminal activation became more pronounced in adult rats. In the adult but not the young spontaneously hypertensive rats, the response to intraluminal but not extraluminal acetylcholine was reduced as compared with Wistar-Kyoto rats. Thus, in mesenteric resistance arteries of the rat, nitric oxide is released from L-arginine under basal conditions and after stimulation with acetylcholine but only in part accounts for endothelium-dependent responses. With aging and hypertension, the inhibitory effects of the endothelium against norepinephrine-induced contractions decrease. In hypertension, the intraluminal but not extraluminal activation of the release of endothelium-derived relaxing factors is impaired.

Small pial vessels, but not choroid plexus, exhibit specific biochemical correlates of functional cholinergic innervation

In an attempt to provide the biochemical foundations for a putative cholinergic innervation of small pial vessels and choroid plexus, we have assessed their ability to specifically accumulate choline, synthesize and release acetylcholine (ACh) in response to depolarization. Our results show that both small pial vessels and choroid plexus avidly accumulate choline via a sodium-dependent mechanism which could be inhibited by hemicholinium-3 (IC50 in pial vessels = 47.8 microM). Light microscopic examination of radioautographs from vessels incubated with [3H]choline revealed two distinct sites of accumulation in the vessel wall. One site probably corresponded to nerve terminals and the other was closely associated with the endothelial cells. In small pial vessels, a major proportion (60%-70%) of the choline acetyltransferase (ChAT) activity could be inhibited by 4-naphthylvinylpyridine (4-NVP), a potent inhibitor of neuronal ChAT; and, following either K+ or veratridine depolarization, a Ca2(+)-dependent release of authentic [3H]ACh could be measured. In contrast, the choroid plexus exhibited a rather low ChAT activity which was not inhibited by 4-NVP and no release of ACh could be detected in this tissue following depolarization. Altogether, the results of the present study show that (1) small pial vessels exhibit all the most selective biochemical markers that are characteristic of cholinergic nerves; (2) [3H]choline in pial vessels can be accumulated in non-neuronal elements which probably correspond to the endothelial cells; and (3) the choroid plexus failed to exhibit convincing biochemical markers that would attest in favor of a functional cholinergic innervation.(ABSTRACT TRUNCATED AT 250 WORDS)

Origins and pathways of choline acetyltransferase-positive parasympathetic nerve fibers to cerebral vessels in rat

The presence of cholinergic nerve fibers in the brain vasculature has been a matter of controversy, partly due to the lack of a reliable histochemical marker. Accordingly, no distinct information about the origin and pathways for such fibers has been available. In the present study on the rat pial vasculature, utilizing a choline acetyltransferase (ChAT) antibody, which is able to demonstrate this enzyme in peripheral nervous tissue, evidence was obtained for an innervation by cholinergic fibers of large pial arteries. Vasoactive intestinal polypeptide (VIP) was present in or in close association with these fibers. By the aid of the retrograde axonal tracer True Blue (TB) applied to the middle cerebral arterial wall, such fibers were shown to originate in a subgroup of ChAT-positive cells in the sphenopalatine, otic, and internal carotid ganglia, which, in addition, contained VIP. The ChAT-positive pial nerve fibers were few in relation to the VIP-immunoreactive fibers, as was also illustrated by the few TB-positive cells in the ganglia that were ChAT positive as compared with the number of cells that were VIP positive. Only a small population of ChAT-containing neurons in these ganglia appeared to project to the pial vessels. The pathway from the sphenopalatine ganglion is via a membranous structure on the medial orbital wall, through the ethmoidal foramen, and along the internal ethmoidal artery to reach the circle of Willis. The fibers from the internal carotid and otic ganglia probably bridge to the internal carotid artery in the carotid canal, those from the otic ganglion after an initial course in the lesser superficial petrosal nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Extraneuronal localization of acetylcholine and its release upon nicotinic stimulation in rabbits

A study was undertaken to examine the origin of plasma acetylcholine (ACh). The ACh content of blood cells was about 25 times higher than that of plasma in normal rabbits (3,722 vs 140 pg/ml blood, n = 7). Plasma ACh content in rabbits having antibody against ACh was about 80 times higher than in normal rabbits, while no difference was observed in the ACh content of blood cells between the groups. Nicotine (100 micrograms/kg, i.v.) produced a significant increase in plasma ACh content and a decrease in the ACh content of blood cells in normal rabbits. These data demonstrate that a large amount of ACh is localized in blood cells and that a considerable proportion of plasma ACh originates from blood cells, suggesting that ACh acts not only as a neurotransmitter but also as an autacoid.

Parasympathetic nerves in penile erectile tissue of the rat contain choline acetyltransferase

Choline acetyltransferase (ChAT), a biochemical marker of cholinergic neurons, was measured in the erectile tissue of intact rats and in rats in which postganglionic fibers from the pelvic plexus were interrupted. ChAT activity in the denervated erectile tissue fell by 56% compared to control tissues. Acetylcholinesterase positive (AChE+) nerves also fell by about 48%. Penile neurons distal to the lesion probably account for the residual ChAT activity and remaining AChE+ nerve fibers in erectile tissue. These results indicate that acetylcholine is an important neurotransmitter in the regulation of penile erection.

Influx of a choline analog to dog brain measured by positron emission tomography

The influx of the 11C-labeled choline analog pyrrolidinocholine into tissue was measured in the brain of three dogs by positron emission tomography (PET). During the first 90 s after the intravenous bolus injection of the tracer, transfer of tracer from plasma to tissue was unidirectional. The influx constant for pyrrolidinocholine into intracranial tissue, Kin, was 0.017 ml/g/min (0.008 SD), and the initial volume of distribution, V0, was 0.08 ml/g (0.03 SD). The influx constant was at least five times larger than the value expected if simple diffusion were to account for tissue uptake. The method presented in this paper can be used to investigate the availability of plasma choline and its analogs to the living human brain and other tissue in degenerative diseases affecting the cholinergic system, and to provide in vivo information on a choline transport system.