Role of endothelial cells in responses of spontaneously hypertensive rat mesenteric arteries to norepinephrine and angiotensins

The role of endothelial cells in the constrictor and dilator responses of mesenteric arteries to infused drugs was evaluated. Fifteen- to seventeen-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) were used. Periarterial sympathetic nerve stimulation (PNS, 6 Hz, 30 sec) elicited greater pressor responses in SHR than WKY. Acetylcholine (ACh, 1.0 microM) lowered the perfusion pressure elevated by norepinephrine (NE, 0.1 microM) significantly more in SHR than WKY. Angiotensin I and II (AI and AII, 1.0 nM) markedly potentiated the PNS-induced constriction in both animals. Collagenase perfusion (Type 1A, 2 mg/ml, 5 ml/min intermittently, for 23 min) significantly diminished the ACh-induced dilation, indicative of endothelium destruction. However, it greatly increased the constrictor effect of NE and AI and AII in SHR and the potentiating effects of AI and AII on PNS-evoked construction in both SHR and WKY, especially in SHR. These results suggest that, while endothelial cells mediate the dilator response to ACh, they are unnecessary for the constrictor and potentiating effects of NE, AI and AII and, in fact, counteract the latter two effects, particularly in the hypertensive rats. Furthermore, the endothelial cell functions promoting the effect of ACh or countering those of NE, AI and AII are in general greater in SHR than WKY.

Serotonin as an alternative transmitter in sympathetic nerves of large cerebral arteries of the rabbit

The distribution of serotonin (5-HT)-like immunoreactive (5-HT-LI) nerves and the potential role of 5-HT as a vasoconstrictor transmitter in large cerebral arteries of the rabbit were examined. 5-HT-LI fibers with weak immunofluorescence were observed in the anterior cerebral, middle cerebral, and basilar arteries when fixed by immersion after dissection from exsanguinated animals. The 5-HT-LI fibers, however, were not detected in these arteries when fixed either in vitro or in situ after first being perfused with Krebs solution in situ to flush the blood component from the lumen prior to dissection. In these arteries, 5-HT-LI nerve fibers with intense immunofluorescence, however, reappeared following incubation with 5-HT in vitro. The intensity of the 5-HT-LI fibers seemed to be proportional to the duration and 5-HT concentration during incubation. Following chronic surgical sympathectomy, 5-HT-LI fibers were not detected in arteries before or after incubation with 5-HT. Transmural nerve stimulation elicited constriction in 50% of the control arterial segments examined. The constriction was not affected by ketanserin but was prevented by guanethidine and chronic surgical sympathectomy. The remaining arterial segments that did not respond on transmural nerve stimulation, however, became constrictive on transmural nerve stimulation following incubation with 5-HT in vitro. The constriction was blocked by ketanserin and clonidine. These results demonstrate that the large cerebral artery of the rabbit brain has extremely sparse or no authentic 5-HT-LI nerves.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered endothelial modulation of vascular tone in aging and hypertension

The role of endothelial cells in modulating the vascular smooth muscle tone in aging and hypertension was examined. Results from in vitro pharmacological studies indicate that vasodilations of rat arteries induced by several dilator agents, such as nitrovasodilators, decrease with advancing age and experimental hypertension. These diminished dilator responses to nitrovasodilators however were not observed in arteries with endothelial cells removed. Furthermore, 8-bromo-cGMP-induced relaxations were not different between arteries with and without endothelial cells and were not affected by hypertension. It appears that the diminished vasodilator responses in aging and hypertension is not initially due to defects in vascular smooth muscle but rather due to an altered modulatory function of the endothelial cells. At different ages and under different pathological conditions, such as hypertension, the ratio of production and/or activities of endothelium-derived relaxing factors and endothelium-derived constrictor factors may vary, and therefore directly or indirectly affect the production of cGMP and smooth muscle tone.

Pre- and postsynaptic effects of angiotensins in the femoral artery of spontaneously hypertensive and Wistar-Kyoto rats

The effects of angiotensin I (AI) and angiotensin II (AII) on ring segments of femoral arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) were studied. AI and AII elicited significantly greater direct contractile response in arteries from SHR than those from WKY. These peptides also potentiated the contractile response to transmural adrenergic nerve stimulation (TNS) in both preparations, but to a greater extent in those of WKY than SHR, without potentiating the contractile response to exogenous norepinephrine (NE). The potentiation of the TNS response and direct contraction caused by AI were markedly attenuated by captopril, an AI-converting enzyme inhibitor. Destruction of endothelium failed to alter the contractile response to AI in both WKY and SHR but augmented that to AII in WKY. Isoproterenol and salbutamol produced significant potentiation of TNS response only in arteries of SHR. Yohimbine and prostaglandin F2 alpha potentiated TNS response to a similar extent in arteries of WKY and SHR. These results suggest that AII locally generated from AI can act postsynaptically to cause contraction and presynaptically to promote adrenergic neurotransmission in the isolated rat femoral artery. The AI to AII conversion appears to take place mainly at sites other than endothelial cells. The postsynaptic effect of AII is greater in SHR than WKY, but its presynaptic effect is diminished in SHR unlike some other agents which facilitate adrenergic neurotransmission, and unlike that in mesenteric arteries of SHR.

Endothelial modulation of vascular relaxation to nitrovasodilators in aging and hypertension

Blood vessel responses to relaxant drugs have been reported to change with aging and with the development of hypertension. In view of the requirement of endothelial cells for the activity of many relaxant drugs, we examined the role of the endothelium in the relaxation response of vascular tissue. Aortic and mesenteric ring segments from normotensive and hypertensive rats, ages 5 to 6, 15 to 18 and 30 to 31 weeks, were examined for relaxation to sodium nitroprusside, sodium nitrite, atrial natriuretic factor and 8-bromo-cyclic GMP. Relaxation responses to the nitrovasodilators were reduced progressively with aging in ring segments of Wistar-Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) with intact endothelium; however, intact SHR ring preparations displayed less relaxation to nitrovasodilators at 15 to 18 and 30 to 31 weeks than those of WKYs. Rubbed (endothelium denuded) ring preparations displayed greatest relaxation to nitrovasodilators with no difference being observed between SHR and WKY preparations at any age tested. Relaxation to atrial natriuretic factor and 8-bromo-cyclic GMP was not different between rubbed and unrubbed ring segments or between SHRs and WKYs, indicating no detectable impairment of the overall relaxation response in the vascular smooth muscle of SHRs. These results suggest that the total functional capacity of vascular smooth muscle to relax to nitrovasodilators is not changed with aging or hypertension. However, the endothelial cells exert modulatory influences upon the vascular smooth muscle to reduce overall responsiveness to nitrovasodilators, an effect that is enhanced with aging and the development of genetic hypertension.

Extraneuronal serotonin accumulation in peripheral arteries of the rat

Accumulations of serotonin (5-HT) and norepinephrine (NE) were compared in control and 6-hydroxydopamine (6-OHDA) pretreated rat aorta, mesenteric and tail arteries. The distribution of these amines was corrected by subtracting tissue uptake of tritiated sorbitol in the extracellular space. 5-HT greatly accumulated both in control and 6-OHDA pretreated arteries. In contrast, NE accumulation in mesenteric and tail arteries was substantially decreased after 6-OHDA treatment. In the aorta 6-OHDA pretreatment did not affect the accumulation of both amines. These findings suggest that 5-HT accumulation in these arteries is mainly extraneuronal, and NE mainly neuronal. Since the accumulation of 5-HT in the aorta was not influenced by pretreatment with 10 microM NE, the extraneuronal uptake mechanisms for 5-HT and NE appear to be different.

Altered cerebral vessel innervation in spontaneously hypertensive and renal hypertensive rats

The ultrastructural distributions of sympathetic and non-sympathetic nerve terminals in cerebral arteries of normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and one-kidney, one clip renal hypertensive rats (RHR) were examined. When compared with WKY, the SHR cerebral arteries receive denser sympathetic nerve terminals and fewer non-sympathetic nerve terminals. On the other hand, both sympathetic and non-sympathetic nerve terminals decrease in the cerebral arteries of RHR. These results suggest that the sympathetic vasoconstriction may surpass the non-sympathetic vasodilation in some brain regions of SHR, while the functional significance of cerebral sympathetic vasoconstrictor and non-sympathetic vasodilator nerves may decrease in RHR. The pattern of cerebral vessel innervation differs in different types of hypertension.

Mechanisms of extraneuronal serotonin uptake in the rat aorta

The mechanisms of extraneuronal serotonin (5-HT) uptake in the rat aorta were studied. Aortic strips were pretreated with 0.1 mM pargyline and incubated with 0.1 to 9.1 microM 5-HT (5-HT, 0.02-1.60 microgram/ml including [3H]-5-HT, 0.02 microgram/ml) for 1, 2, 3 and 5 min at 37 degrees C. Accumulation of [3H]sorbitol was used to correct for extracellular distribution of this amine. The initial rate of 5-HT uptake was related linearly to the substrate concentration within the tested range. Cocaine, imipramine, desipramine (10 microM each), Na+-free solution and cooling (0 degrees C) inhibited markedly both the 1- and 5-min uptake of 5-HT. Removal of the endothelium did not affect the 5-HT uptake for 1 min but reduced slightly that for 5 min. Corticosterone (10 microM), norepinephrine (10 microM) and 6-hydroxydopamine pretreatment did not affect the uptake of 5-HT. Autoradiography demonstrated that uptake of 5-HT for 5 min in the rat aorta occurs primarily at the smooth muscle cells near the lumen. These results suggest that the rat aorta has a large capacity of cocaine-sensitive extraneuronal uptake of 5-HT. This uptake appears to occur primarily in the muscle layers adjacent to the lumen, suggesting that the muscle cells of the luminal side function differently from those from the adventitial side. The mechanism of the extraneuronal uptake of 5-HT appears to be different from that of norepinephrine and the extraneuronal uptake of 5-HT occurs initially in a nonsaturable mode and later through a Na-dependent, carrier-mediated transport.

Potentiation of pressor responses to serotonin by ketamine in isolated perfused rat mesentery

The effects of ketamine on vasoconstrictor responses to periarterial sympathetic nerve stimulation (PNS), norepinephrine (NE), and 5-hydroxytryptamine (5-HT) were studied in normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The isolated mesenteric arteries were perfused at a constant rate (5 ml/min), and the perfusion pressure was recorded. The pressor responses to PNS (8 Hz, 2 ms, 30 s) were augmented by ketamine (2 X 10(-5) and 10(-4) M) in WKY and SHR. Those to intraarterially infused NE (3 X 10(-10) M) were statistically unaltered. However, in three of seven arterial preparations from WKY and in six of nine preparations from SHR, ketamine (2 X 10(-5) and 10(-4) M) decreased the pressor responses to NE. In contrast, the responses to intraarterial 5-HT (1.3 X 10(-9) mol) were potentiated by ketamine (2 X 10(-5) and 10(-4) M) in SHR and WKY--to a much greater extent in SHR. Fractional release of tritium by PNS from isolated mesenteric arteries previously labeled with 1-[7,8-(3)H]NE (10(-7) M) was unaltered by ketamine (10(-4) M) in SHR and WKY. Cocaine (10(-5) M) prevented the ketamine-induced potentiation of PNS and 5-HT responses. Ketamine as well as cocaine inhibited the accumulations of [3H]5-HT and [3H]NE in intact mesenteric arteries from SHR and WKY to a comparable extent. In tissues denervated by 6-hydroxydopamine, the accumulation of 5-HT was about 70% (WKY) and 60% (SHR) of those in intact tissues, whereas that of NE was about 11% (WKY) and 9% (SHR).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxyhemoglobin inhibition of acetylcholinesterase activity

The effects of human oxyhemoglobin (HbO2), human methemoglobin (MetHb), and porcine serum albumin (PSA) on the activity of acetylcholinesterase (AChE) isolated from Electrophorus electricus were examined. HbO2 produced a dose-dependent reduction in AChE activity. Fifty percent of activity was obtained at 5 microM HbO2, while 95% inhibition was obtained at 50 microM. In this concentration range MetHb and PSA had little effect on esterase activity.

Aztreonam in the treatment of bone and joint infections caused by gram-negative bacilli

Aztreonam was used successfully in 17 of 17 patients with orthopedic infections due to gram-negative bacilli (11, osteomyelitis; six, septic arthritis). Duration of treatment ranged from 14 to 55 days, and the period of follow-up was four to 18 months. Causative organisms included Pseudomonas aeruginosa, Serratia marcescens, Enterobacter gergoviae, Citrobacter diversus, Proteus mirabilis, and Enterobacter aerogenes. Aztreonam was well tolerated. The only definite reactions attributable to aztreonam were asymptomatic increases in serum aspartate aminotransferase (SGOT) and serum alanine aminotransferase (SGPT) in four patients; none of these reactions interfered with completion of therapy. Adverse reactions that were possibly attributable to aztreonam included rash (two patients), diarrhea (one patient), and leukopenia (one patient). All of these patients were receiving antibiotics active against gram-positive organisms in mixed infections in addition to aztreonam. Aztreonam is a promising new monobactam without significant toxicity. It has good activity against gram-negative aerobic bacteria, including P. aeruginosa, and is effective in the treatment of serious infections due to gram-negative aerobes.

Keratocyte survival following a controlled-rate freeze

One of the major drawbacks of cryorefractive surgery is the delay in the postoperative recovery of corneal clarity. The authors have hypothesized that this delay is due to the death of graft keratocytes caused by the freezing process, and the need for subsequent repopulation by host keratocytes to restore corneal clarity. By using a slow, controlled-rate freeze on a modified Barraquer cryolathe, the authors are able to maintain keratocyte viability in the graft corneal tissue, as assessed by standard histologic methods and by collagenase digestion. Maintenance of keratocyte viability results in the rapid return of corneal clarity following lamellar keratoplasty in the rabbit, with few of the histopathologic changes seen following standard rapid freezing of corneal tissue.

Pubertal growth in diabetics

Mean values for two variables of the pubertal growth spurt, peak height velocity and age at peak velocity, of children attending the diabetic clinic in Bristol are reported. The growth spurt was normal both in timing and intensity in boys, but the peak velocity was reduced and age at peak velocity more variable among girls.

Autonomic innervation of cerebral blood vessels decreases in renal hypertensive rats

The ultrastructural distribution of the autonomic nerves of brain arteries was investigated in renal (one-kidney, one clip) hypertensive and normotensive Wistar-Kyoto rats. Sympathetic and nonsympathetic nerve terminals were found only in the adventitial layer of brain arteries of renal hypertensive and normotensive rats. In both normotensive and renal hypertensive rats the total nerve endings were dense in anterior cerebral artery, moderately dense in middle cerebral artery, and sparse in basilar artery. In normotensive rats, nonsympathetic nerves outnumbered sympathetic nerves in anterior cerebral, middle cerebral, and basilar arteries. In renal hypertensive rats these two types of nerve terminals in close apposition to smooth muscle decreased in anterior cerebral and basilar arteries, while those in middle cerebral arteries remained unchanged. These results suggest that the potential neurogenic control of cerebral blood vessels as well as the trophic effect of sympathetic nerves on brain blood vessels may decrease in renal hypertensive rats. As this finding contrasts with that in spontaneously hypertensive rats, the pattern of innervation in brain arteries may differ in different types of hypertension.

Evidence for the presence of cholinergic nerves in cerebral arteries: an immunohistochemical demonstration of choline acetyltransferase

The presence of cholinergic nerves in cerebral arteries of several species was investigated by an immunohistochemical method using antibodies against choline acetyltransferase (ChAT). In cats, pigs, rats, and dogs, ChAT immunoreactivities were found to be associated with large bundles and single fibers in the circle of Willis and anterior cerebral, middle cerebral, and basilar arteries. In the rabbit, the ChAT-immunoreactive (ChAT-I) nerves were also observed in the circle of Willis and anterior and middle cerebral arteries, but only few or none were found in the basilar and vertebral arteries. The ChAT-I nerves were found only in the adventitial layer of vessels examined. Superior cervical ganglionectomy did not appreciably affect the distribution of ChAT-I nerves. These results indicate the presence of cholinergic nerves in cerebral arteries. The distribution pattern of ChAT-I nerves was different from that of vasoactive intestinal polypeptide (VIP)-like-immunoreactive nerves and acetylcholinesterase-positive nerves. The possible coexistence of ChAT and VIP-like substance in the same neuron is discussed.

Treatment of gram-negative infections with aztreonam

Twenty-one patients with serious gram-negative infections were treated with aztreonam. Twenty of these were clinical and microbiologic cures; there was one clinical improvement with microbiologic persistence. No bacteria became resistant. Cure rates were: bone and joint (11 of 11); skin and soft tissue (six of six); pneumonia (two of two); perinephric abscess (one of one); and intra-abdominal abscess (zero of one). The bacteria responsible for these infections included Pseudomonas aeruginosa (12), Serratia marcescens (two), Enterobacter gergoviae (three), Enterobacter aerogenes (two), Escherichia coli (one), Citrobacter diversus (one), and Hemophilus influenzae (one). Aztreonam was well tolerated. Significant serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase elevations developed in three patients, but none was symptomatic and all resolved after therapy was stopped. Two patients in whom a rash developed were receiving other antibiotics (vancomycin and metronidazole), making the cause of the rash unclear. Diarrhea developed in a single patient with Pseudomonas osteomyelitis, who also was receiving cefazolin for Staphylococcus aureus superinfection of his decubitus ulcer. Aztreonam was highly effective against gram-negative bacilli, including P. aeruginosa. The only clear-cut side effect was an asymptomatic rise in serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase levels in three patients.

Gonadotrophin responses to GnRH in precocious puberty treated with GnRH analogue

The gonadotrophin releasing hormone analogue Buserelin was given by intranasal spray to 13 children with precocious puberty. The LH responses to GnRH reverted to prepubertal levels in the boys on 200-400 micrograms daily of the analogue while doses of 400-1200 micrograms daily were needed to suppress the girls. The significance of this apparent sex difference is uncertain.

Erythrocyte extracts enhance neurogenic vasoconstriction of dog cerebral arteries in vitro

Cerebral blood vessels of the dog have been shown to receive vasodilator and constrictor nerves. In isolated ring arterial preparations, neurogenic vasodilation was blocked while neurogenic vasoconstriction was potentiated by hemolysates isolated from hemolyzed erythrocytes. These results suggest that an overall increase in cerebral neurogenic vasoconstriction may occur in vivo following subarachnoid hemorrhage. The significance of this finding in the pathogenesis of cerebral vasospasm is discussed.

Altered cerebral vessel innervation in the spontaneously hypertensive rat

Autonomic innervation in the cerebral arterial walls of adult male spontaneously hypertensive rats and of normotensive Wistar-Kyoto rats was studied. When examined by fluorescence microscopy, dense catecholamine fluorescence was observed in anterior cerebral and middle cerebral arteries of both Wistar-Kyoto and spontaneously hypertensive rats. However, vertebral and basilar arteries and small pial arteries of Wistar-Kyoto rats received extremely sparse or no catecholamine fluorescence, whereas, in the respective regions of spontaneously hypertensive rats, catecholamine fluorescence was found to be significantly elevated. The endogenous norepinephrine content was also higher in cerebral arteries of spontaneously hypertensive than of Wistar-Kyoto rats. When examined ultrastructurally (potassium permanganate fixation), the incidence of granular vesicle-containing nerves, indicative of sympathetic nerves, was found to be significantly elevated in all cerebral arteries of spontaneously hypertensive rats examined. In contrast, the agranular vesicle-containing nerve, indicative of nonsympathetic nerves, with close synaptic cleft distance (less than 2 micron) was found to decrease or remain unchanged in the cerebral arteries of spontaneously hypertensive rats. These results suggest that cerebral sympathetic vasoconstriction may become more prominent than nonsympathetic vasodilation in spontaneously hypertensive rats. This finding lends further credence to the previous in vivo findings that cerebral sympathetic vasoconstrictor nerves become more functional and exhibit a protective effect against brain lesions during hypertension. The potential roles of neurogenic components involved in cerebral blood flow autoregulation are also discussed.

Indoleaminergic mechanisms in brain vessels; localization, concentration, uptake and in vitro responses of 5-hydroxytryptamine

Immunocytochemical studies have revealed the presence of 5-HT-containing nerve fibres in all parts of the cerebrovascular bed (arteries, arterioles and veins) of mouse, rat, guinea-pig, rabbit and cat. Biochemical measurements (using HPLC) revealed substantial concentrations of 5-HT and 5-HIAA in the pial vessels of the rat, rabbit, cat and man, the amounts corresponding well with the density of the perivascular nerve supply. The uptake of 3H-5-HT was studied in arteries removed from the circle of Willis in rats. Maximum uptake was reached after 15 min of incubation at 37 degrees C and plateaued at 30 min. The reaction was temperature-dependent and found to be absent if performed at 0 degrees C. Pharmacological experiments on isolated middle cerebral and basilar arteries showed that vessels from rat and dog were contracted by approximately 90% upon administration of 5-HT, whereas vessels from guinea-pig, rabbit, cat and man were contracted by 40 to 60% relative to 124 mM K+. The EC50 values in the different species varied by between 1.5 X 10(-7) M (rat) and 3 X 10(-9) M (dog). The 5-HT-induced contractions were blocked by the 5-HT antagonists, methysergide, methergoline and ketanserin. Transmural nerve stimulation (TNS) of the rabbit basilar artery revealed a tetrodotoxin sensitive constriction whereas TNS of cat and dog middle cerebral arteries caused a tetrodotoxin-sensitive relaxation. The relaxation was not significantly attenuated until high doses of methergoline (3 X 10(-6) M) or ketanserin (3 X 10(-5) M) had been given.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoactive intestinal polypeptide-like substance: the potential transmitter for cerebral vasodilation

In vitro pharmacological studies demonstrated that exogenously applied vasoactive intestinal polypeptide (VIP) relaxes the smooth muscle cells of cat cerebral arteries, whereas substance P constricts them. Ultrastructural-immunocytochemical techniques show that a VIP-like substance is present in the large granular vesicles of nonsympathetic nerve axons and terminals in the cerebral arterial walls. These results provide strong evidence in favor of the hypothesis that a VIP-like substance is the transmitter for vasodilation in cerebral blood vessels.

Growth and endocrine function after treatment for medulloblastoma

Children with medulloblastoma in Bristol are treated surgically and with craniospinal irradiation, and in some cases chemotherapy. Thirteen medium or long term survivors were investigated to determine their growth and endocrine function. Their rate of growth was considerably reduced through the first year of their illness and after spinal irradiation spinal growth was poor. Nine children developed growth hormone deficiency. They were clinically euthyroid but 7 had raised basal thyroid stimulating hormone values. Gonadal function was abnormal in all but the youngest child. The rate of survival is increasing in children with medulloblastoma but this is associated with appreciable endocrine abnormalities. Some of these problems are present shortly after treatment ends but others may develop later and long term surveillance is therefore essential.

Prostaglandin isosteres. 2. Chain-modified thiazolidinone prostaglandin analogues as renal vasodilators

Chain modification of a thiazolidinone prostaglandin isostere has led to the production of 4-[3-[3-[2-(1-hydroxycyclohexyl)ethyl]-4-oxo-2-thiazolidinyl]propyl] benzoic acid (5b) which at 1 mg/kg po in the conscious dog causes a 70% increase in renal blood flow over control values with a duration of action exceeding 5 h. Preliminary testing indicates that 5b has a relatively specific action on the vasculature of the kidney. The enantiomers of 5b have been separated and the renal vasodilatory activity has been found to be entirely a property of the R-(+) enantiomer.

Norepinephrine and acetylcholine transmitter mechanisms in large cerebral arteries of the pig

This study examines, using an in vitro tissue bath technique, the nature of the transmitter mechanism(s) in the pig cerebral artery. Of the arteries with intact endothelium, about 25% relaxed on application of acetylcholine (ACh) at low concentration (3 × 10−7 to 3 × 10−6 M) and constricted at concentrations exceeding 10−5 M. The remaining arterial preparations either constricted (61%) or exhibited no response (14%) at any concentration of ACh tested (3 × 10−7 to 3 × 10−3 M). On the other hand, none of the arteries without endothelium relaxed at any concentration of ACh tested (3 × 10−7 to 3 × 10−3 M); of these, 90% constricted and 10% exhibited no response. These results show that ACh-induced cerebral vasodilation is dependent on endothelial cells and the direct action of ACh on the vascular smooth muscle cells is constriction. Contrary to findings in the large cerebral arteries of the cat and several other species, about 90% of the pig cerebral arteries, with or without endothelium, dilated upon application of norepinephrine (NE) at low concentration (10−7 to 3 × 10−5 M) and constricted at concentrations exceeding 3 × 10−5 M. The NE dose–response relationships were not different in arteries with and without endothelial cells, indicating that the NE-induced vasodilation was independent of the endothelial cells. The relaxation and constriction were blocked by the respective β- and α-receptor antagonists, suggesting that both responses resulted from direct stimulation by NE of β and α receptors on the smooth muscle cells. Transmural nerve stimulation (TNS) consistently induced vasodilation of the arteries whether or not the endothelial cells were present. The vasodilation was abolished by tetrodotoxin (TTX) and cold storage denervation. The TNS-induced vasodilation was not smaller in arteries without endothelium than in those with endothelium. This suggests that TNS-induced vasodilation was independent of the endothelial cells. When examined histochemically, the pig cerebral artery exhibited rich catecholamine fluorescence. Biochemical assays indicate that NE is the primary catecholamine. However, the TNS-induced vasodilation was not affected by atropine, guanethidine, or propranolol, nor prevented by reserpine. It is suggested that an as yet unidentified transmitter is responsible for the TNS-induced vasodilation. Results of this study suggest that the nerve-released ACh is a potential vasoconstrictor transmitter and that NE is a potential vasodilator transmitter in the large cerebral artery of the pig. The neurogenic control of the pig cerebral circulation may be different from that of other species, including humans.