Local Regulation Of Blood Flow Research Articles

Reaction of the vasa nervorum of the facial nerve during stimulation with neurotransmitters.

The local blood flow of a tissue depends on the pressure difference in the respective vessel system. In approximate terms, the flow of fluid in an arterial vascular system can be described by the Hagen-Poiseuille law based on the laminar flow of a homogeneous fluid in a rigid tube with wettable walls. The flow-time volume prevailing in a vessel is accordingly proportional to the fourth power of the radius. Regulation of local blood flow is therefore very much more effective when increase of the pressure difference.

NO-Synthase-Containing Neurons of the Pig Inferior Mesenteric Ganglion, Part of Them Innervating the Ductus deferens

The presence of nitric oxide-synthase (NOS) in neurons of the porcine inferior mesenteric ganglion (IMG) has been investigated. A minority (about 1-3%) of the neurons were immunoreactive (IR) for NOS, the vast majority of which stained for neuropeptide Y (NPY) but not for tyrosine hydroxylase (TH). A small subpopulation of prevertebral neurons, 1% of which stained for NOS or NADPH-diaphorase (NADPHd), projected to the ductus deferens, as demonstrated by retrograde tracing. Within the wall of the ductus deferens, NOS- or NOS/NPY-IR nerve fibres were found to innervate the smooth muscle or were closely associated with blood vessels. It is therefore suggested that nitric oxide might be involved in the regulation of local blood flow and muscular tone in the wall of the pig ductus deferens.

New insights into the local regulation of blood flow by perivascular nerves and endothelium

Blood flow, particularly in the skin, is essential for the success of plastic surgical operations. This review describes recent studies of the perivascular nerves and vascular endothelial cells which regulate blood flow. Perivascular nerves, once considered simply adrenergic or cholinergic, release many types of neurotransmitters, including peptides, purines and nitric oxide. Cotransmission (synthesis, storage and release of more than one transmitter by a single nerve) commonly takes place. Some afferent nerves have an efferent (motor) function and axon reflex control of vascular tone by these “sensory-motor” nerves is more widespread than once thought. Endothelial cells mediate both vasodilatation and vasoconstriction. The endothelial cells can store and release vasoactive substances such as acetylcholine (vasodilator) and endothelin (vasoconstrictor). The origins and functions of such vasoactive substances are discussed. Endothelial vasoactive substances may be of greater significance in the response of blood vessels to local changes while perivascular nerves may be concerned with integration of blood flow in the whole organism. The dual regulation of vascular tone by perivascular nerves and endothelial cells is altered by aging and conditions such as hypertension, as well as by trauma and surgery. Studies of vascular tone in disease and after denervation or mechanical injury suggest possible trophic interactions between perivascular nerves and endothelial cells. Such trophic interactions may be important for growth and development of the two control systems, particularly in the microvasculature where neural-endothelial separation is small.

Altered local regulation of blood flow and shear rate in renal hypertension.

The purpose of this study was to evaluate acute and chronic autoregulation of blood flow in the cremaster muscle of one-kidney, one-clip (1K1C) hypertensive rats and to investigate alterations of shear stress during the development of hypertension. Unilateral renal artery stenosis and contralateral nephrectomy were performed in half of the rats and a sham operation was carried out in the other half. Mean blood pressure was significantly increased at 1 (38%) and 4 (34%) weeks in 1K1C rats v age-matched controls. Heart rate was significantly increased 15% at 1 week in 1K1C rats but returned to the control level at 4 weeks. Cremaster arteriolar dimensions were measured in vivo by intravital microscopy. Resting diameter of the first-order arteriole (1A) in 1K1C rats was decreased by 25% (P < .05) at 1 week and by 16% at 4 weeks (ns). Measured by the dual-slit technique, total blood flow to the cremaster muscle in 1K1C rats was reduced by 58% (P < .05) at 1 week but was not significantly different from control at 4 weeks. Wall shear rate calculated in the 1A of 1K1C rats was not significantly different from control at 1 week but was elevated 70% (P < .05) at 4 weeks. Therefore, autoregulation of blood flow in skeletal muscle is impaired and/or overridden in the acute phase of 1K1C hypertension. Shear rate, however, did not deviate from the control level until later, which might be the result of impaired function of the endothelium in chronic hypertension.

Molecular aspects of kallikrein and kininogen in the maturing kidney.

Kinins are vasoactive paracrine peptides which participate in a wide range of functions, including the regulation of local organ blood flow, systemic blood pressure, transepithelial water and electrolyte transport, cellular growth, capillary permeability and inflammatory response, and pain. The recent introduction of specific bradykinin receptor subtype antagonists has greatly advanced our understanding of the role of the kallikrein-kinin system (KKS) in various physiological and disease states. However, a major gap remains in our knowledge of the role of kinins in early development. In this review, evidence is presented that the developing nephron expresses both tissue kallikrein and kininogen, and that the genes encoding the components of the KKS are subject to considerable developmental regulation. The activity of the intrarenal kinin-generating system is lowest in the developing kidney and increases with age. Completion of nephrogenesis is characterized by a marked surge in intrarenal kallikrein synthesis and gene transcription. Maturation is associated with redistribution of intrarenal kallikrein and its messenger RNA from the inner to outer cortical nephrons following the centrifugal pattern of nephron development. Challenges for the future include delineation of the direct role of kinins in the maturation of renal functions and elucidation of the molecular mechanisms underlying the developmental expression of the KKS.

Helospectin/helodermin-like peptides in guinea pig lung: distribution and dilatory effects.

The lower airways of guinea pigs were analysed for helospectin and helodermin using immunocytochemistry. A moderate supply of helospectin/helodermin-like immunoreactive nerve fibers and few nerve fibers displaying helodermin immunoreactivity was seen in the smooth muscle, around seromucous glands and small blood vessels in the trachea and around bronchi and pulmonary blood vessels. Helospectin I-, helospectin II- and helodermin-induced suppression of smooth muscle responses were analysed using isolated circular segments of trachea and pulmonary arteries of guinea pigs. In both airways and arteries the peptides caused a concentration-dependent relaxation of precontracted segments. The maximal relaxant activity observed was more pronounced in the airways than in the arteries. The effects of the helospectins and helodermin were compared to those of vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), pituitary adenylate cyclase activating peptide (PACAP) and acetylcholine (ACh). All peptides, with the exception of PACAP, caused a total or nearly total relaxation of the precontracted tracheal segments. In the trachea PACAP was significantly more potent than the other five peptides whereas only small potency differences were seen in the pulmonary artery. The relaxant responses to helospectin I, helospectin II and helodermin in the trachea and the intrapulmonary arteries were unaffected by pretreatment with atropine, prazosin, yohimbine, propranolol, mepyramine and cimetidine. Conceivably, nerve fibers containing helospectin and helodermin may play a role in the regulation of airway resistance and in the regulation of local pulmonary blood flow.

Localization of neuropeptide Y and atrial natriuretic peptide in the endothelial cells of human umbilical blood vessels.

The localization of neuropeptide Y (NPY) and atrial natriuretic peptide (ANP) in the endothelial cells of human umbilical blood vessels was studied using the pre-embedding peroxidase-antiperoxidase (PAP) technique for electron microscopy and avidin-biotin-complex (ABC) immunostaining for endothelial cells cultured from umbilical vein. Subpopulations of NPY- and ANP-immunoreactive endothelial cells were present in term umbilical vein and artery. The umbilical vein contained more positive cells than the artery. The percentage of NPY- and ANP-immunoreactive umbilical vein cells in culture was 32% and 44%, respectively, out of a total of 3013 cells examined. The possibility that these potent vasoactive substances located in the endothelial cells of the non-innervated umbilical vessels are involved in the local regulation of blood flow is discussed.

Abnormal baroreceptor-mediated vasodilation of the peripheral circulation in congestive heart failure secondary to idiopathic dilated cardiomyopathy.

Peripheral edema is a major clinical problem in congestive heart failure (CHF). The function of the edema-protective baroreceptor-mediated and local nervous vasoconstrictor reflexes of the lower leg during orthostasis in moderate and severe CHF has largely been unexplored. Baroreceptor-mediated and local nervous regulation of subcutaneous blood flow of the lower leg was studied in healthy subjects and in patients with moderate and severe CHF secondary to idiopathic dilated cardiomyopathy. Blood flow was measured by the local 133Xe washout method in the supine position and during 45 degrees head-up tilt. When the central baroreceptor reflex alone was activated, the changes in subcutaneous blood flow of the heart failure patients in both groups were significantly different from those of the eleven control subjects: blood flow increased 48 +/- 26% in 10 severe and 3 +/- 24% in nine moderate CHF patients compared with the decrease in blood flow of -36 +/- 15% observed in 11 control subjects (p < 0.0001 for both). A highly significant direct association was demonstrated between changes in blood flow and New York Heart Association functional class (p = 0.007) and the left ventricular ejection fraction (p = 0.01). Activation of the baroreceptor and local venoarteriolar axon reflexes simultaneously increased blood flow significantly (30 +/- 9%) in 14 patients with severe CHF, compared with the decrease found in 14 control subjects (-53 +/- 9%) and in the group of 14 patients with moderate CHF (-17 +/- 25%) (p < 0.0001 for both). Patients with CHF secondary to idiopathic dilated cardiomyopathy have an abnormal baroreceptor-mediated vasodilation in subcutaneous tissue of the lower leg during the upright position, which increases with the severity of the disease. The hemodynamic consequence is capillary hypertension and hyperemia in the leg during the upright position that may contribute to the development of edema and to the initiation of structural changes (microangiopathy) demonstrated in the microcirculation.

Evaluation of a rat model for the study of local regulation of intestinal blood flow: ex vivo asanguineous perfusion of the ileal vascular bed

A new model of ex vivo vascularly perfused, isolated rat ileum was developed and evaluated. Segments of distal ileum (approximately 5 cm) from male Wistar rats were isolated on their vascular pedicles. Perfusion through an aortic cannula with oxygenated (95% O 2, 5% CO 2) Krebs solution containing 5% bovine albumin, 5.6 m M glucose, and 25 m M mannitol at 37°C was initiated immediately after interruption of blood flow. The bowel preparations, including the abdominal aorta, were then transferred to a perfusion chamber. Perfusion pressure was maintained by gravity at 40 mm Hg. Flow was measured with an electromagnetic flow probe. The portal vein, together with the lymphatics, drained freely into collection tubes. The bowel lumen was perfused at 0.85 ml/min with isotonic modified Krebs solution containing [ 14C]polyethylene glycol, and the luminal perfusion pressure was monitored. Luminal effluents were collected through a large-bore outlet tubing. As determined by histology, O 2 consumption, vascular reactivity, and mucosal permeability, the preparations were viable for at least 60 min of perfusion. With this model, a vasoconstrictor effect of the α 2-adrenoceptor agonist clonidine was documented for the first time in isolated rat bowel.

Mechanism of action of cerebral epoxyeicosatrienoic acids on cerebral arterial smooth muscle.

Microsomal preparations of cat brain incubated with [14C]arachidonic acid produced epoxyeicosatrienoic acids (EETs) that eluted with the same retention times as synthetically prepared 5,6-, 8,9-, and 11,12-EETs. These compounds dilated serotonin-preconstricted, pressurized cat cerebral arteries in a dose-dependent fashion. Epoxide formation was not found in mitochondrial fractions and was dependent on the presence of NADPH. The maximum effects of 8,9-EET and 11,12-EET were greater than those of 5,6-EET. The cellular basis of this vasodilation was further investigated by examining the effects of 8,9-EET and 11,12-EET on K+ channel activity in vascular muscle cells freshly isolated from cat cerebral arteries. Both 8,9-EET and 11,12-EET increased the frequency of opening, mean open time, and open-state probability of a 98-pS K+ channel recorded in the cell-attached mode with 145 mM KCl in the pipette and 4.7 mM KCl in the bath. Blockade of K+ channel activity with tetraethylammonium attenuated the vasodilatory effects of 11,12-EET on serotonin-preconstricted cat cerebral arteries. These results suggest that endogenously formed EETs may participate in local regulation of cerebral blood flow by dilating cerebral arteries through a mechanism that involves activation of K+ channels.

Competitive inhibition of nitric oxide synthase prevents the cortical hyperemia associated with peripheral nerve stimulation.

With combined microdialysis and hydrogen clearance techniques for simultaneous local delivery of drugs and blood-flow measurement in the rat hindlimb sensory-motor cortex, we examined the role of nitric oxide in cerebral blood-flow regulation during sciatic nerve stimulation. Infusion of 1 mM nitric oxide synthase antagonist, N eta-nitro-L-arginine methyl ester (L-NAME), blocked the cortical blood-flow response to sciatic nerve stimulation (152 +/- 43 ml.min-1.100 g-1 of tissue in controls and 73 +/- 11 ml.min-1.100 g-1 in the presence of L-NAME; P less than 0.05). Addition of 10 mM L-arginine to the dialysate containing L-NAME partially restored the hyperemic response to nerve stimulation (125 ml.min-1.100 g-1). L-NAME also produced a decrease in baseline cerebral blood flow when compared with the control (66 +/- 14 ml.min-1.100 g-1 vs. 93 +/- 25 ml.min-1.100 g-1). We conclude that nitric oxide from activated neurons participates in the local regulation of cortical blood flow in response to sciatic nerve stimulation and also in the maintenance of basal cortical blood flow.

Endothelium-dependent dilation to L-arginine in isolated rat skeletal muscle arterioles.

The vascular actions of L-arginine (L-Arg) were studied in isolated, pressurized first-order rat cremaster muscle arterioles (93 +/- 2.9 microns) bathed in a Krebs bicarbonate-buffered solution, pH 7.4, equilibrated with 21% O2-5% CO2. Arterioles were studied before and after either the administration of NG-nitro-L-arginine (L-NNA, 10(-3) M), an inhibitor of the synthesis of endothelium-derived relaxing factor (EDRF), or the removal of the endothelium. Acetylcholine (ACh, 10(-8) and 10(-6) M), sodium nitroprusside (SNP, 10(-8) M) and phenylephrine (PE, 10(-7) M) evoked dilation and constriction, respectively. L-Arg, (10(-5)-10(-3) M) the precursor of EDRF, evoked dose-dependent arteriolar dilation; whereas D-arginine (D-Arg, 10(-5)-10(-3) M) was without any significant effect. Administration of L-NNA significantly reduced basal diameters and significantly inhibited the arteriolar dilations to both ACh and L-Arg but had no effect on the dilation to SNP. Removal of the arteriolar endothelium with air inhibited dilations to both ACh and L-Arg, had no effect on responses to SNP, and potentiated vasoconstrictor responses to PE. These findings suggest that in skeletal muscle arterioles the dilations to ACh and L-Arg are endothelium dependent and that microvascular endothelium modulates constrictor responses to PE. Thus EDRF may play an important role in the local regulation of arteriolar resistance and blood flow.

Preretinal pH changes in the rabbit under conditions of light and dark

Preretinal pH was measured in the avascular region of 19 rabbit retinas during alternating cycles of light and dark, using a miniature, needle-type pH electrode. In 14 experiments with the rabbits breathing room air, cyclic changes in pH, decreasing in the dark and increasing in the light, were observed. The transition from light to dark caused a mean pH decrease of 0·047 ± 0·029 U ( n = 14). An inversion of the light/dark pH response was observed in five experiments. In three of these, the effect was induced by having the rabbits breathe 100% O 2. In the five rabbits showing a reversed response, a mean pH increase of 0·034 ± 0·025 pH U was observed in the dark; light-ON caused a decrease of 0·035 ± 0·025 pH U. The direction of the preretinal pH change is thought to be the net effect of light/dark-induced changes in the metabolism of the photoreceptors and inner retinal layers (defined for the purpose of this paper as the region between the outer synaptic layer and the inner limiting membrane). In six separate experiments, retinal metabolism was assessed by measuring preretinal PO 2 during alternating cycles of light and dark while the rabbits breathed room air. Oxygen tension declined from a mean of 14·5 ± 6·2 ( s.d.) mmHg in the light to 10·1 ± 5·4 ( s.d.) mmHg in darkness, and increased from a mean of 10·9 ± 5·1 ( s.d.) mmHg in darkness to 15·4 ± 5·8 ( s.d.) mmHg in the light. The time courses of the pH and the PO 2 changes were similar. These observations suggest that, in the presence of low retinal PO 2, the rapid increase in photoreceptor metabolic activity accompanying dark adaptation leads to accumulation of hydrogen ions in the inner retinal and preretinal vitreous, an effect that may play a role in the local regulation of retinal blood flow.

Endothelium-derived nitric oxide: the endogenous nitrovasodilator in the human cardiovascular system

The L-arginine pathway within endothelial cells in the blood vessel wall is the source of production of the endogenous nitrovasodilator, nitric oxide (NO). NO is released under basal conditions and in response to various stimuli such as shear stress and in response to platelet-derived products, coagulation factors and hormones. NO is the mediator of endothelium-dependent relaxation in the circulation and exerts its effects by activating soluble guanylyl cyclase in vascular smooth muscle, which in turn leads to the formation of cyclic guanosine monophosphate (cGMP) and to relaxation. In addition to its effects on vascular smooth muscle, NO is also released abluminally to interact with circulating platelets. Increases in cGMP in platelets are associated with a decreased adhesion and aggregation of cells. Thus, endothelium-derived NO, through its vasodilator and anti-aggregatory properties, prevents vasospasm and thrombus formation in the circulation and thereby helps to maintain blood flow to vital organs such as the heart. Therapeutic nitrates also exert their effects by releasing NO from their molecules and activating soluble guanylyl cyclase. Their effects are particularly pronounced in arteries without endothelium and are reduced in the presence of the basal formation of endothelium-derived NO in intact arteries. The lower basal formation of endothelium-derived NO in veins, as compared to arteries, contributes to the greater sensitivity of venous circulation to nitrates. Thus, the endothelial L-arginine pathway plays an important protective role in the local regulation of blood flow and through its vasodilator and antiplatelet properties.

Pituitary adenylate cyclase activating peptide (PACAP) in guinea-pig lung: distribution and dilatory effects

The lower airways of guinea-pigs were analyzed for pituitary adenylate cyclase activating peptide (PACAP) using immunocytochemistry. In the trachea a moderate supply of PACAP-immunoreactive nerve fibers occurred around smooth muscle bundles, glands and small blood vessels. In the lung, PACAP-immunoreactive nerve fibers were distributed around small glands and bronchi. A rich supply of PACAP immunoreactive nerve fibers was found around blood vessels in the lungs. PACAP-suppressed smooth muscle responses were analysed using isolated circular segments of trachea, pulmonary arteries and aorta of guinea-pigs. In both airways and arteries PACAP caused a concentration-dependent relaxation of precontracted segments. The maximal relaxation effects were more pronounced in the airways than in the arteries while the order of potency was aorta > pulmonary artery > trachea. The effect of PACAP was compared to those of acetylcholine (ACh) and vasoactive intestinal peptide (VIP). In the pulmonary artery the vasomotor responses expressed as maximal dilatation had the order: ACh > VIP = PACAP while the order of potency was PACAP = VIP > ACh . In the trachea, PACAP was slightly more potent than VIP. The relaxatory responses to PACAP in the trachea and the intrapulmonary arteries were unaffected by pretreatment with atropine, prazosin, yohimbine, propranolol, mepyramine, cimetidine and Spantide. Removal of the endothelium abolished PACAP-induced vascular relaxation. Conceivably, PACAP-containing nerve fibers play a role in the regulation of airway resistance and local blood flow.

The endothelial L-arginine/nitric oxide pathway and the renal circulation

Endothelial cells contain an enzyme(s) which produces nitric oxide from L-arginine in response to a variety of mechanical stimuli as well as to autacoids and local and circulating hormones. Nitric oxide is a potent vasodilator and inhibitor of platelet function; it exerts its effects via activation of soluble guanylate cyclase and subsequent formation of cyclic 3'-5'-guanosine monophosphate. In the kidney, activation of the endothelial L-arginine pathway is associated with increases in renal blood flow, diuresis and natriuresis, while the glomerular filtration rate remains constant. The activity of the endothelial L-arginine pathway is impaired in hypertension and during chronic therapy with cyclosporine A. In addition, diabetes and atherosclerosis impair this pathway. Thus, the endothelial L-arginine pathway plays an important role in the local regulation of blood flow. Alterations in the activity of this pathway may play an important role in the pathophysiology of hypertension and renal disease.

Chaos in blood flow control in genetic and renovascular hypertensive rats

Hydrostatic pressure and flow in renal proximal tubules oscillate at 30-40 mHz in normotensive rats anesthetized with halothane. The oscillations originate in tubuloglomerular feedback, a mechanism that provides local blood flow regulation. Instead of oscillations, spontaneously hypertensive rats (SHR) have aperiodic tubular pressure fluctuations; the pattern is suggestive of deterministic chaos. Normal rats made hypertensive by clipping one renal artery had similar aperiodic tubular pressure fluctuations in the unclipped kidney, and the fraction of rats with irregular fluctuations increased with time after the application of the renal artery clip. Statistical measures of deterministic chaos were applied to tubular pressure data. The correlation dimension, a measure of the dimension of the phase space attractor generating the time series, indicated the presence of a low-dimension strange attractor, and the largest Lyapunov exponent, a measure of the rate of divergence in phase space, was positive, indicating sensitivity to initial conditions. These time series therefore satisfy two criteria of deterministic chaos. The measures were the same in SHR as in rats with renovascular hypertension. Since two different models of hypertension displayed similar dynamics, we suggest that chaotic behavior is a common feature of renal vascular control in the natural history of the disease.

Choline Acetyltransferase Activity Associated with Cerebral Cortical Microvessels Does Not Originate in Basal Forebrain Neurons

Cerebral cortical microvessels are innervated by cholinergic fibers that are probably involved in the regulation of local cerebral blood flow and blood-brain barrier permeability. The possibility exists that the cholinergic terminals associated with the cortical microvasculature belong to neurons from the nucleus basalis magnocellularis (NBM), where 70% of the cortical cholinergic projections originate. To test this hypothesis, ibotenic acid (25 nmol) was injected unilaterally in the NBM in rats, and 14 days later, choline acetyltransferase (ChAT) activity was measured in the frontoparietal cortex and in a blood vessel fraction isolated from this region. Lesions of the NBM resulted in a 50% decrease of cortical ChAT as compared with control or sham-operated hemispheres; however, no changes were observed in the ChAT activity associated with cortical microvessels. These results indicate that, in rat cerebral cortex, the perivascular cholinergic terminals do not originate in the basal forebrain.

The involvement of endothelium‐derived relaxing factor in the regulation of renal cortical blood flow in the rat

1. In the present study the role of endogenous nitric oxide (NO) was investigated, in the regulation of renal cortical blood flow (RCBF) in vivo in anaesthetized rats under conditions in which prostacyclin involvement had been eliminated. 2. Infusions of the NO synthesis inhibitor NG-monomethyl-L-arginine (MeArg) at 1 or 3 mg kg-1 min-1, i.v., produced significant decreases in RCBF of 29 +/- 7% and 35 +/- 5%, respectively. These effects were reversed by co-infusion of a 3 fold excess of L-arginine (L-Arg). 3. Similarly, intravenous infusion of N omega-nitro-L-arginine methyl ester (NO2Arg) at 30 or 300 micrograms kg-1 min-1 attenuated RCBF by 21 +/- 4% or 53 +/- 4%, respectively, and these effects were reversed by L-Arg (3 or 10 mg kg-1 min-1, i.v.). Most importantly, a low dose of NO2Arg (30 micrograms kg-1 min-1, i.v.), while having no pressor effect, considerably reduced RCBF, indicating that basal release of NO is important for the maintenance of renal cortical blood flow. 4. MeArg (3 mg kg-1 min-1, i.v.) or NO2Arg (300 micrograms kg-1 min-1, i.v.) inhibited endothelium-dependent acetylcholine (ACh, 10 micrograms kg-1 min-1, i.v. for 3 min) increases in RCBF in an L-Arg reversible manner, but did not affect endothelium-independent (dopamine 10 micrograms kg-1 min-1, i.v., for 3 min) increases. Endothelin- 1 (1 nmol kg-1, i.v.), when given as a control for the vasoconstrictor effects of MeArg and NO2Arg, produced a slight inhibition of the ACh-induced increase in RCBF, but this effect was significantly weaker than that produced by MeArg or NO2Arg. 5. Our findings suggest that MeArg and NO2Arg inhibit basal and ACh-stimulated release of NO in the renal cortical vasculature. Thus, endogenous NO formation may play an important role in the local regulation of renal cortical blood flow.

Effect of carbon dioxide and oxygen on endothelin production by cultured porcine cerebral endothelial cells.

We have previously reported the production of endothelin, a potent vasoconstrictor peptide, by porcine cerebral microvessel endothelia and suggested its important role in the regulation of local blood flow within the brain. In our present study, radioimmunoassay with anti-porcine endothelin antiserum revealed that endothelin, produced by cerebral microvessel endothelia grown on a filter, is released mainly to the basement membrane side, not the vascular lumen side. This finding suggests that endothelin constricts arterioles locally where it is produced by endothelia. We also found that cerebral microvessel endothelia produce less endothelin under low oxygen pressure and more endothelin under low carbon dioxide pressure. Our results suggest that endothelin has a role in the regulation of cerebral blood flow in response to oxygen and carbon dioxide pressure.