Cerebrovascular effects of prostaglandin inhibitors in the gerbil

Effect of non-steroid anti-inflammatory drugs on neurovascular coupling in humans

BACKGROUND/AIMS

Neuronal activation induced cerebral blood flow increase was shown in animal experiments to require the presence of functioning cyclooxygenase. Our aim was to study whether widely used, non-steroid anti-inflammatory drugs (NSAIDs), given orally in usual therapeutic doses, inhibit neurovascular coupling in humans.

METHODS

By using a visual cortex stimulation paradigm, the flow velocity response was measured by transcranial Doppler sonography in both posterior cerebral arteries of fifteen young healthy adults. The investigation was repeated in the same subjects after 2-day administration of 3×25 mg indomethacin (indomethacin phase) and 2×550 mg naproxen (naproxen phase). Visual-evoked-potentials were also recorded during the control phase and after administration of NSAIDs.

RESULTS

Basal flow velocity significantly decreased while the pulsatility index increased after administration of either indomethacin or naproxen (p<0.01). Despite unchanged visual-evoked-potentials, the visually evoked flow velocity increase (26±7% in the control phase) significantly declined after administration of indomethacin (19±5%; p<0.01) or naproxen (20±5%; p<0.02).

CONCLUSION

Oral administration of indomethacin or naproxen in their usual therapeutic doses significantly impaired the resting and the visually evoked blood flow regulations in healthy human subjects. Together with stable evoked potentials, our findings indicate disturbance of neurovascular coupling.

The neurovascular coupling bears properties of a feedforward and feedback regulative mechanism

Temporal profiles of mediators involved in the neurovascular coupling bear feedforward and feedback characteristics, which are supported by mathematical modeling of evoked hemodynamic responses. However, cerebral autoregulation was expressed as a feedback control system. Therefore, question of overdetermination of the neurovascular coupling model arises. Addressing this issue, we analyzed both models for their appropriateness in describing the neurovascular coupling. Visually evoked flow velocities were recorded from healthy volunteers (aged 24.7 +/- 1.6 SD; 9 females, 11 males) with transcranial Doppler in the posterior cerebral artery. Control system parameters of the two models were specified according to the least-square-fitting technique. Mean square errors between measured and modeled curves and Akaike's information criterion (AIC) supported the feedforward-feedback model. Mean square differences decreased from 27.2 +/- 37.9 to 2.3 +/- 2 and the AIC from 2.7 +/- 0.6 %(2) to 2 +/- 0.3 %(2). The feedforward element increased the accuracy of the control system model in describing the fast initial response. Biologically, the parameter decreases the initial mismatch between the fast neuronal but slow vascular response because of visual activation.

A control system approach for evaluating somatosensory activation by laser-Doppler flowmetry in the rat cortex

Coupling between functional cortical activity and blood flow is a regulatory principle that adjusts the supply of substrates to the metabolic needs of the tissue. The flow response is usually expressed as the maximum increase over baseline; control system analysis allows the description of the entire time course and the main dynamic features of the regulative principle. In chloralose-anesthetized rats, forepaws were stimulated by trains of electric pulses of 0.3 or 5 ms duration. Blood flow was recorded in the contralateral somatosensory cortex by laser-Doppler flowmetry and correlated with the amplitude of primary somatosensory evoked potentials (SEP). Changes were analyzed by a control system approach. Pulses of 0.3 or 5 ms evoked SEPs of similar amplitude, whereas flow responses differed: 0.3 ms pulses led to a peak and plateau characteristic, 5 ms pulses evoked a plateau characteristic. The flow response evoked by 0.3 ms pulses can be modeled mathematically by an initial feedforward regulative principle followed after some delay by feedback controlled flow stabilization, whereas 5 ms pulses lack the feedforward component. The absence of an electrophysiological difference points to a dissociation between electrophysiological and hemodynamic responses and may be of importance for the understanding of flow coupling.

Gender-related effects of indomethacin on cerebrovascular CO2 reactivity

Prostaglandins are believed to play an important role in the regulation of resting cerebral blood flow and in the vasodilatory response to hypercapnia. Recently, we reported an increased CO2 reactivity (CR) in premenopausal women and, in the past, evidence has accumulated that estrogens might increase basal levels of prostaglandin secretion from endothelial cells. Therefore, one may speculate that gender differences in CR are possibly mediated by higher prostaglandin levels in women. Using transcranial Doppler sonography, we assessed CR before and 90 min after a single dose of 100 mg of indomethacin in 22 healthy volunteers (11 men, 11 women). Before intake of indomethacin, women had a significantly higher CR (4.53+/-0.49 vs. 3.61+/-0.74, P<0.01). Ninety minutes after indomethacin administration, CR decreased to 1.53+/-0.93 in women and 1.60+/-0.92 in men, respectively. The change of CR was 3.00+/-1.29 in women vs. 2.01+/-1.06 in men (P=0.07). For the entire study population, the decrease of CR was linearly correlated with the initial value of CR (rs=0.74, P<0.001). This gender-related difference possibly relates to higher prostaglandin levels as mediators of an increased CR in premenopausal women, although the exact features remain to be clarified.

Differential effect of three cyclooxygenase inhibitors on human cerebral blood flow velocity and carbon dioxide reactivity

BACKGROUND AND PURPOSE

Prostaglandins are believed to play an important role in maintenance of cerebral blood flow and possibly in the vasodilatory response to carbon dioxide. Therefore, the nonsteroidal anti-inflammatory drugs and aspirin, which inhibit cyclooxygenase, might be expected to reduce cerebral blood flow and the response to hypercapnia. This could induce cerebral ischemia in patients with a hemodynamically critical circulation. It would also interfere with the measurement of cerebrovascular reserve using carbon dioxide.

METHODS

The effect of a single dose of indomethacin and of two other cyclooxygenase inhibitors (aspirin and sulindac) on the cerebral circulation was measured using transcranial Doppler ultrasonography of the middle cerebral artery. Seven normal adults were studied in each drug group. Resting blood flow velocity and the responses to hypercapnia and to hyperventilation were measured.

RESULTS

Indomethacin resulted in a fall in basal middle cerebral artery flow velocity from a mean of 48.9 cm/s to 34.0 cm/s (P < .002). It also reduced the vasoconstrictor response to hypocapnia (induced by hyperventilation) from 37.5% to 20.7% (P < .003). There was a nonsignificant reduction in the vasodilatory response to 8% carbon dioxide (mean: predrug, 87.7%; postdrug, 61.0%), with marked intersubject variability. In contrast, basal middle cerebral artery velocity and vasoconstrictor and vasodilatory responses to changes in carbon dioxide were unchanged after aspirin or sulindac administration.

CONCLUSIONS

The lack of effect of aspirin on basal cerebral blood flow velocity and on vasodilatory reserve is reassuring; aspirin will not reduce cerebral blood flow or the response to a reduced perfusion pressure in patients with critically impaired cerebral hemodynamics. However, indomethacin should be avoided in such patients.

Comparison of the effects of NG-nitro-L-arginine and indomethacin on the hypercapnic cerebral blood flow increase in rats

The effects of NG-nitro-L-arginine (NOLAG), an inhibitor of nitric oxide synthase (NOS), and of indomethacin, an inhibitor of cyclooxygenase, on the rise in cerebral blood flow (CBF) accompanying increasing levels of hypercapnia (paCO2 = 40-135 mmHg) were studied in anesthetized rats. CBF was measured by intracarotid injection of 133Xe. Progressive increases in paCO2 of 10 mmHg, at intervals of about 8-10 minutes, were associated with gradual increases in CBF until a paCO2 level of 115 mmHg was reached. No further CBF changes (from the maximum value of 446 +/- 70 ml 100 g-1 min-1) were seen with additional step increase in paCO2. Intracarotid infusion of 7.5 mg/kg NOLAG significantly attenuated the CO2-elicited CBF increase by about 45-65% at paCO2 values below 115 mmHg. Beyond this level, there was a lesser inhibition of about 27-35%. 30 mg/kg NOLAG had essentially the same effect as 7.5 mg/kg NOLAG. 50 mg/kg NOLAG, given intraperitoneally (i.p.) twice daily for 4 days, also caused an attenuated CBF response to CO2, but the inhibitory effect was significantly less than with acute NOLAG administration in the paCO2 range of 61-90 mmHg. Infusion of L-arginine, 1 g/kg/h, prevented the effect of 7.5 mg/kg NOLAG. Indomethacin, 10 mg/kg, i.v. produced a more dramatic attenuation of the response, to the extent that the steady rising curve of CBF as a function of paCO2 was almost completely abolished. With indomethacin, a moderate increase (50%) in CBF was seen at the lowest level of hypercapnia, but raising paCO2 above this level did not result in further increases in CBF. This effect could not be prevented by L-arginine. When combining 7.5 mg/kg NOLAG with 10 mg/kg indomethacin, the response to hypercapnia was totally blocked. The results suggest that NOLAG and indomethacin act through different mechanisms on the hypercapnic CBF response, and that indomethacin is the more powerful inhibitor.

Effects of indomethacin on myogenic contractile activation and responses to changes in O2 and CO2 in isolated feline cerebral arteries

We used an isolated, pressurized, and perfused feline middle cerebral artery preparation to measure how changes in intraluminal pressure and alterations in O2 and CO2 affect vessel diameter and myogenic contractile activation before and after treatment with indomethacin (IND). Vessel diameters were measured over the pressure range 60-140 mm Hg. The arteries were then exposed to low O2 (50 torr) and/or high CO2 (65 torr) and diameters remeasured over the same range. Under control conditions, the arteries exhibited myogenic contractile activation. Exposure to low O2, high CO2, or a mixture of low O2/high CO2, increased vessel diameter but did not change the vessels' myogenic contractile responsiveness to changes in pressure. Arteries exposed to IND decreased in diameter but retained myogenic contractile activity. In the presence of IND, vessels dilated to both low O2 and a mixture of low O2/high CO2, but did not dilate to high CO2 alone. Under all conditions, vessels retained myogenic contractile activity. Results obtained under control conditions and low O2 confirm those of others using similar systems. Myogenic contractile activity in the presence of high CO2 or a mixture of low O2/high CO2 has not been previously reported. The dilation to low O2 but not to high CO2 in the presence of IND suggests that this drug's effects in cerebral arteries are not limited solely to inhibition of prostaglandin synthesis.

Cerebral blood flow and indomethacin drug levels in subjects with and without central nervous side effects

1. Central nervous system (CNS) side effects are observed during treatment with all nonsteroidal anti-inflammatory drugs (NSAIDs) but their effects are more common during treatment with indomethacin. 2. The aim of the study was to elucidate the mechanism of the CNS related side effects of indomethacin. Two groups were obtained, one with (n = 11), and one without (n = 7), CNS symptoms. Cerebral blood flow was measured in these groups with Doppler equipment, indomethacin levels with h.p.l.c. and CNS symptoms graded on a VAS scale. 3. Blood flow was reduced by 18-30% and was most marked 60 min after dose and did not differ between the two groups. The maximum CNS effect coincided with indomethacin peak levels 60-70 min after dose. These results could implicate that CNS symptoms may be related to indomethacin levels in sensitive patients.

Effect of infusion rate of indomethacin on cerebrovascular responses in preterm neonates

Cerebrovascular responses were studied in preterm infants by Doppler ultrasound and cerebral electrical impedance for one hour after intravenous indomethacin infusion for patent ductus arteriosus. Indomethacin in a dose of 0.2 mg/kg body weight was infused over five minutes in one group of infants (20 doses) and over 20 minutes in a second group of infants (16 doses). There were no significant differences between the two groups in birth weight (mean = 1068 g, range 569-1950), gestational age (mean 28.4 weeks, range 25-31), or postnatal age (mean 18.1 days, range 6-42). There was a significant reduction in both the Doppler mean flow velocity in the anterior cerebral artery (mean (SE) -20 (4.2)%) and peak amplitude of cerebral electrical impedance (-26 (3.9)%) within two minutes of starting the indomethacin infusion over five minutes. There was no significant change after the infusion over 20 minutes. There were no significant changes in blood pressure or carbon dioxide tensions after infusion at either rate. The results suggest that infusion of indomethacin over five minutes caused a potentially deleterious reduction in cerebral blood flow. No such reduction occurred when it was infused over 20 minutes.

Mechanism of CO2 response in cerebral arteries of the newborn pig: role of phospholipase, cyclooxygenase, and lipoxygenase pathways

The role of phospholipase, lipoxygenase, and cyclooxygenase pathways in the mechanism of the cerebrovascular response to CO2 and H+ was investigated in newborn piglets. Responsiveness of pial arterioles, 48-206 micron diameter, to inhalation of 6% CO2 and to suffusion of acidic cerebrospinal fluid (CSF, pH = 6.84), adenosine (10(-4) M), or theophylline (10(-2) M) was studied using a closed cranial window. Pial arteriolar diameter was measured using intravital microscopy. Phospholipase inhibitors quinacrine hydrochloride (10(-4) M in CSF) and p-bromophenacyl bromide (10(-4) M in CSF) abolished the CO2 vasodilation from delta diameter = 27 +/- 5% and 28 +/- 3% during baseline to 0 +/- 4% and -1 +/- 1% following the respective inhibitors. Following administration of the cyclooxygenase inhibitor indomethacin (5 mg/kg i.v.), the CO2 response was converted from vasodilation, 31 +/- 6%, to constriction, -4 +/- 1% (p less than 0.001), while the lipoxygenase inhibitor nordihydroguaiaretic acid (2 mg/kg i.v. or 10(-4) M in CSF) augmented the pial arteriolar response to CO2 from 21 +/- 4% to 34 +/- 7% (p less than 0.005). Topical application of superoxide dismutase (40 units/ml CSF) plus catalase (40 units/ml CSF) also appeared to augment the CO2 response. Suffusion of the cortical surface with acidic CSF at constant PCO2 increased pial arteriolar diameter by 11 +/- 2% that was also abolished by indomethacin. Vasodilatory responses to topical adenosine and theophylline were not affected by indomethacin, suggesting specificity for H+ ion-related vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Actions of some prostaglandins and leukotrienes on rat cerebral and mesenteric arteries

The effects of some prostaglandins (PG's) and leukotrienes (LT's) on rat middle cerebral, basilar and mesenteric arteries were evaluated in vitro. The order of potency of some prostanoids with respect to their contractile effects in basilar arteries was: U44069 greater than PGF2 alpha greater than PGI2 approximately equal to PGE2 greater than 6-keto-PGE1 greater than 6-keto-PGF1 alpha, whereas 6,15-diketo-PGF1 alpha was inactive. Middle cerebral and basilar arteries were 3-5 times more sensitive than mesenteric arteries to PGF2 alpha. LTD4 and LTC4 were inactive in all three vessel types. PGI2 produced a concentration-related relaxation of similar potency in all three arteries contracted by PGF2 alpha. Arteries preactivated by other agents (K+, noradrenaline, 5-hydroxytryptamine) either failed to relax or inconsistently relaxed after PGI2 application. Among the PGI2 metabolites (6-keto-PGF1 alpha, 6,15-diketo-PGF1 alpha, 6-keto-PGE1), only 6-keto-PGE1 elicited relaxation in the PGF2 alpha-contracted basilar artery. However, the drug potency was significantly smaller than that of PGI2. Nifedipine inhibited the PGF2 alpha-induced contraction by 68% in middle cerebral arteries and by 80% in mesenteric arteries. Exposure to Ca2+-free medium for a time period which almost completely abolished the contractile response to K+ (less than 5% left), reduced the PGF2 alpha-induced contraction by 54, 61 and 85% in middle cerebral, basilar and mesenteric arteries, respectively. The PGF2 alpha-induced contraction of cerebral arteries in Ca2+-free medium was usually composed of a rapidly developing first phase, which levelled off after 1-2 min, and a second slowly developing tonic phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of indomethacin on cardiac output distribution in normal and asphyxiated piglets

We determined the effect of breathing 9% CO2/10% O2/81% N2 (asphyxia) on cardiac output distribution (microspheres) in 4-5 day old unanesthetized, chronically instrumented piglets prior to and following intravenous indomethacin administration. Thirty minutes of asphyxia caused PaCO2 to increase from 35 +/- 2 mmHg to 66 +/- 2 mmHg, PaO2 to decrease from 73 +/- 4 mmHg to 41 +/- 1 mmHg, and pH to decrease from 7.52 +/- 0.05 to 7.21 +/- 0.07. Arterial pressure was increased slightly but cardiac output was not changed significantly. Asphyxia caused blood flow to the brain, diaphragm, liver, heart, and adrenal glands to increase while causing decreases in blood flow to the skin, small intestine, and colon. Blood flows to the stomach and kidneys tended to decrease, but the changes were not significant. Treatment with indomethacin during asphyxia did not alter arterial pressure or cardiac output but decreased cerebral blood flow to the preasphyxiated level and decreased adrenal blood flow about 20%. Indomethacin did not alter blood flow to any other systemic organ. At this time the piglet was allowed to breathe air for 2.5 hr undisturbed. Two and a half hours after indomethacin administration, blood flows to all organs returned to the preasphyxia control levels with the exception of cerebral blood flow which was reduced (93 +/- 13 to 65 +/- 7 ml/100 g X min). Three hours after indomethacin administration, the cerebral hyperemia caused by asphyxia was less (134 +/- 17 ml/100 g X min) than prior to indomethacin (221 +/- 15 ml/100 g X min). Indomethacin did not alter the asphyxia-induced changes to any other systemic organ.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized indomethacin trial for prevention of intraventricular hemorrhage in very low birth weight infants

We admitted 48 preterm neonates (600 to 1250 gm birth weight, normal 6-hour echoencephalograms) to a randomized prospective indomethacin or placebo trial for the prevention of neonatal intraventricular hemorrhage. Beginning at 6 postnatal hours, indomethacin or placebo was administered intravenously every 12 hours for a total of five doses. Cardiac ultrasound studies to assess the status of the ductus arteriosus were performed at 6 postnatal hours and on day 5. Urinary output, serum electrolytes, and renal and clotting functions were monitored. No differences in birth weight, gestational age, Apgar scores, or ventilatory needs were noted between the two groups. Six infants given indomethacin had intraventricular hemorrhage, compared to 14 control infants (P = 0.02). The indomethacin-treated group had significant decreases in serum prostaglandin values 30 hours after the initiation of therapy. The overall incidence of patent ductus arteriosus was 82% at 6 postnatal hours; 84% of the indomethacin-treated infants experienced closure of the ductus, compared to 60% of the placebo-treated patients. Closure of the ductus was not related to incidence of intraventricular hemorrhage. We speculate that indomethacin may provide some protection against neonatal intraventricular hemorrhage by acting on the cerebral microvasculature.

Prostanoids in cortical subarachnoid cerebrospinal fluid and pial arterial diameter in newborn pigs

These studies were designed to investigate the relationship between cerebral prostanoid synthesis and pial arterial caliber in chloralose-anesthetized newborn pigs with normal blood gases and pH and during combined arterial hypoxia and hypercapnia. Piglets less than 5 days old were equipped with closed cranial windows to allow direct observation of pial vessels, application of prostaglandin E2, and sampling of cortical subarachnoid cerebrospinal fluid. We found that prostanoids accumulate in cerebrospinal fluid on the cortical surface. The only prostanoid detected in arterial blood was 6-keto-prostaglandin F1 alpha [442 +/- 74 pg/ml (radioimmunoassay)]. Only small quantities of 6-keto-prostaglandin F1 alpha (214 +/- 53 pg/ml) and thromboxane B2 (122 +/- 18 pg/ml) were found in cerebrospinal fluid from the cisterna magna. Higher concentrations of 6-keto-prostaglandin F1 alpha (1056 +/- 159 pg/ml), thromboxane B2 (229 +/- 64 pg/ml), and prostaglandin E2 (4235 +/- 269 pg/ml) were found in cortical subarachnoid fluid. In contrast to arterial and cisternal concentrations, the concentrations of 6-keto-prostaglandin F1 alpha, thromboxane B2, and prostaglandin E2 in cortical subarachnoid fluid were increased reversibly by ventilation with 9% carbon dioxide, 10% oxygen, (6-keto-prostaglandin F1 alpha, 5436 +/- 1576 pg/ml; thromboxane B2, 694 +/- 122 pg/ml; and, prostaglandin E2, 12,455 +/- 3688 pg/ml). Further, pial arteries dilated in response to topical application of prostaglandin E2 at the concentration that was found in cortical subarachnoid fluid during combined hypoxia and hypercapnia. Systemic administration of indomethacin trihydrate (5 mg/kg) markedly reduced cortical subarachnoid fluid prostanoid concentrations and attenuated the pial artery vasodilation induced by combined hypoxia and hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)

Beagle puppy model of intraventricular hemorrhage. Effect of superoxide dismutase on cerebral blood flow and prostaglandins

Intraventricular hemorrhage (IVH) represents a major problem for preterm neonates and is thought to occur secondary to alterations in cerebral blood flow (CBF) to damaged germinal matrix tissues. Many investigators believe that both local CBF and changes in capillary morphology and permeability may be partially controlled by prostaglandins. To evaluate this hypothesis, the authors have studied the effects of superoxide dismutase (SOD), a known free-radical scavenger, on newborn beagle pups that were randomly assigned by computer to four groups consisting of either SOD- or saline-pretreated animals that underwent either insult by hemorrhagic hypotension/volume reexpansion or no insult. Prostaglandin levels were determined prior to and 60 minutes following the administration of the solutions, and carbon-14 iodoantipyrine autoradiography was performed for determination of CBF. It was demonstrated that, although SOD significantly decreased the incidence of IVH in this model (p less than 0.05), it caused no alterations in baseline CBF or prostaglandin levels. In addition, SOD did not prevent either the systemic blood pressure changes or the alterations in CBF found in response to a hemorrhagic hypotensive insult. The authors propose that neonatal IVH results from a combination of factors, one of which is prostaglandin-mediated alterations in CBF to a damaged capillary matrix.

Regional blood-brain barrier permeability changes after restoration of blood flow in postischemic gerbil brains: a quantitative study

A quantitative technique utilising [14C]alpha-aminoisobutyric acid as a tracer was used to study cerebrovascular permeability in 22 Mongolian gerbils. Seven other animals were used to measure cerebral blood volumes. Global cerebral ischaemia was produced by temporary bilateral carotid artery occlusion (60 min) in 16 gerbils that were sacrificed at 1, 2, and 3 h following reperfusion. The blood-to-brain transfer constant was significantly increased after 2 h of reperfusion in the ischaemic zones and also in structures, like the cerebellum, not supplied by the carotid artery and not ischaemic during the vessel occlusion. The blood-brain barrier (BBB) alterations were coincident with the onset of ischaemia--induced seizures that were accompanied by sudden "spikes" of systemic blood pressure. Epilepsy may play an important role in the development of BBB damage in this ischaemic model, and this factor must be considered in the interpretation of BBB damage data in gerbils.

Effects of indomethacin on rCBF during and after focal cerebral ischemia in the cat

The effect of indomethacin on rCBF was studied in cats anesthetized with Nembutal either under resting conditions or with temporary middle cerebral artery (MCA) occlusion. RCBF was measured by the microsphere method. In control animals (n = 3), indomethacin (4 mg/kg, i.v.) significantly reduced rCBF by about 25% in both cortex (from 44 +/- 6 to 32 +/- 3 ml/100 g/min, p less than 0.001) and white matter (from 36 +/- 4 to 26 +/- 2 ml/100 g/min, p less than 0.001). After MCA occlusion rCBF was markedly decreased in the sylvian region ipsilateral to occlusion (ischemic core) (from 38 +/- 4 to 14 +/- 2 ml/100 g/min in cortex, 4 animals). Although pretreatment with indomethacin (4 mg/kg) (4 animals) 30 min prior to occlusion did not alter rCBF during ischemia, a marked enhancement of reactive hyperemia was observed in the ischemic core immediately upon reperfusion following 2 h occlusion (54 +/- 11 untreated vs 95 +/- 13 treated, p less than 0.05). In the delayed postischemic period, namely 2 h after recirculation, rCBF still remained to be higher in the animals treated with indomethacin (40 +/- 6 untreated vs 96 +/- 9 treated, p less than 0.001). Such an effect of indomethacin for ameliorating postischemic blood flow in both the immediate and delayed period was less prominent in the adjacent area (penumbra) ipsilateral to occlusion. In the contralateral hemisphere, indomethacin caused slight reduction in rCBF during ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chronic cigarette smoking on cerebrovascular responsiveness to 5 per cent CO2 and 100 per cent O2 inhalation

Effects of chronic cigarette smoking on cerebrovascular responsiveness of volunteers at risk for stroke and not at risk for stroke were evaluated by serial measurements of cerebral blood flow using the 133Xe inhalation method. Resting gray matter blood flow values (Fg) measured while breathing room air were compared with Fg values measured during inhalation of either 5 per cent CO2 in air or 100 per cent O2. Changes in Fg values during inhalation of 5 per cent CO2 were used to estimate cerebral vasodilator capacitance, and those during inhalation of 100 per cent O2 were used to estimate cerebral vasoconstrictor capacitance. Results indicated that chronic cigarette smokers have both reduced vasodilator (P less than 0.01) and reduced vasoconstrictor (P less than 0.02) capacitance when compared with nonsmokers of the same ages regardless of whether or not other risk factors for stroke were present. Vasodilator capacitance to 5 per cent CO2 inhalation was reduced among smokers compared with nonsmokers of the same age by 48 per cent in non-risk subjects and 56 per cent in risk-factored subjects, while vasoconstrictor capacitance to 100 per cent O2 inhalation among smokers was decreased by 24 per cent in non-risk subjects and 34 per cent in risk-factored subjects. In risk-factored subjects, combined effects of smoking and other risks appeared to be additive.

Beagle puppy model of intraventricular hemorrhage. Effect of indomethacin on local cerebral glucose utilization

The newborn beagle puppy has been demonstrated to provide a good model for neonatal intraventricular hemorrhage (IVH). A study was designed to determine if indomethacin can prevent IVH, and if indomethacin would produce changes in local cerebral glucose utilization (LCGU). By computerized random design, newborn beagle puppies were pretreated with either indomethacin (a known inhibitor of prostaglandin synthetase) or saline, and then assigned either to receive a hemorrhagic hypotension/volume reexpansion insult or to receive no insult. Pretreatment with indomethacin produced a marked drop in the incidence of IVH as well as significant alterations in the blood pressure responses to the hemorrhagic hypotension/volume reexpansion insult. Carbon-14 autoradiography was used to determine LCGU: no alterations were demonstrated in cerebral metabolism in uninjured pups pretreated with indomethacin compared to saline-pretreated animals. In addition, although the hemorrhagic hypotension/volume reexpansion insult produced marked alterations in LCGU in both groups of traumatized pups, indomethacin prevented the changes in LCGU in the germinal matrix and white matter that were found in the saline-pretreated animals.

Role of prostaglandins in the response of the cerebral circulation to carbon dioxide in conscious rabbits

The role of prostaglandins in maintenance of resting cerebral blood flow (CBF) and in cerebral vasodilatation during hypercapnia remains controversial. The effect of indomethacin, a cyclo-oxygenase inhibitor, on CBF and cerebrovascular resistance (CVR) was examined in conscious animals. Regional and total CBF were measured with radioactive microspheres, and the efficacy of blockade of prostaglandin synthesis by indomethacin was examined by the cranial window method. CBF was measured in conscious rabbits with 15-μm radioactive microspheres during normocapnia (Pco2 ≈ 30 mm Hg) and hypercapnia (Pco2 ≈ 60 mm Hg), before and after intravenous administration of indomethacin (10 mg/kg) or vehicle (n = 6 for each). Thus, each animal served as its own control. CBF was 84 ± 6 and 190 ± 27 (mean ± SE) ml/min/100 g during normocapnia and hypercapnia, respectively, before indomethacin, and 78 ± 5 ml/min/100 g during normocapnia and 180 ± 16 ml/min/100 g during hypercapnia following indomethacin. Thus, indomethacin did not change normocapnic CBF. In addition, cerebrovascular responses during hypercapnia did not vary between the indomethacin and vehicle groups. Indomethacin did not attenuate increases in blood flow in any area of the brain, except slightly to cerebellum during hypercapnia. Indomethacin did not affect CVR during normocapnia or hypercapnia. The topical application of arachidonic acid (75 and 150 μg/mg), dissolved in cerebrospinal fluid, dilated pial arteries in a dose-dependent fashion. Intravenous administration of indomethacin (10 mg/kg) blocked vasodilatation produced by arachidonic acid by 87% (p < 0.05). Thus, indomethacin, at a dose that effectively inhibits prostaglandin synthesis, did not change resting CBF or CVR or attenuate the increase in CBF or decrease in CVR during hypercapnia. These findings suggest that prostaglandins do not contribute significantly to regulation of the cerebral circulation during normocapnia and hypercapnia.

Beagle puppy model of intraventricular hemorrhage. Effect of indomethacin on cerebral blood flow

The newborn beagle puppy has been demonstrated to provide a good model for neonatal intraventricular hemorrhage (IVH). A study was designed to determine if indomethacin can prevent IVH and if indomethacin would produce changes in cerebral blood flow (CBF). Newborn beagle puppies were randomized by computer into two groups: one was pretreated with indomethacin, a known inhibitor of prostaglandin synthetase, and the other was saline. The dogs in both groups were then assigned either to undergo hemorrhagic hypotension/volume reexpansion insult or to receive no insult. Twenty percent of all pups receiving indomethacin and undergoing the insult experienced IVH, compared to 71% of the pups undergoing insult that had been pretreated with saline. Significant alterations in the blood pressure responses to the hemorrhagic hypotension/volume reexpansion insult were noted in the former group compared to the saline-pretreated pups subjected to insult. Finally, employing carbon-14 autoradiography for the determination of CBF, it was demonstrated that indomethacin decreases resting CBF of the newborn beagle pups and, in indomethacin-pretreated animals subjected to insult, prevents the increases in CBF seen in the saline-pretreated traumatized pups.

Simultaneous determination of regional cerebral blood flow and blood--brain glucose transport kinetics in the gerbil

Cerebral blood flow (CBF) and unidirectional transport of glucose from blood to brain were measured simultaneously in four brain regions of the pentobarbital-anesthetized gerbil. The method consisted of the intravenous injection of a bolus containing [14C]butanol and [3H]glucose, followed by continuous withdrawal of arterial blood and sampling of brain 25 s later. CBF was lowest in the cerebral cortex (50 ml 100 g-1 min-1), highest in the brainstem (89 ml 100 g-1 min-1), and intermediate in the basal ganglia and cerebellum (66 and 69 ml 100 g-1 min-1, respectively). The kinetics of blood-to-brain glucose transport were measured in animals whose blood glucose concentration had been altered by glucose or insulin injections. The half-saturation constant for glucose transport (Km) was similar in all brain regions (7.37-8.14 mM), while the maximal rate of transport (Vmax) was lowest in the cerebral cortex (1.55 mumol g-1 min-1) and significantly higher in the basal ganglia, cerebellum, and brainstem (1.81-2.02 mumol g-1 min-1). These values for CBF and glucose transport are similar to those reported in the literature for other pentobarbital-anesthetized animals. The method provides a simple and rapid technique for determining the effect of ischemia and alterations in CBF on blood-to-brain glucose transport.

Effect of OKY-1581, a thromboxane synthesis inhibitor, on the platelet aggregation and vasodilation induced by injury of mouse pial arterioles

OKY-1581 (sodium [E]-3-[4-(3-pyridylmethyl)-phenyl]-2-methylacrylate) is a known inhibitor of thromboxane synthesis, a class of agents thought potentially useful in treating conditions characterized by platelet aggregation. Doses of 10, 100, and 300 mg/kg were administered intraperitoneally to mice 1 h before their pial vessels were injured by a combination of light from a filtered mercury lamp and intravascular sodium fluorescein. In this model platelet aggregation and arterial dilation are produced. Pretreatment with OKY-1581 had no effect except at the 300-mg/kg dose, which enhanced aggregation as manifested by a decrease in the time required for the noxious stimulus to initiate aggregation. In addition the dilation increased in magnitude as compared with that in controls. The latter result is compatible with a decreased synthesis of thromboxane, a known constrictor of cerebral vessels. However, the enhancement of aggregation by a high dose of OKY-1581 was unexpected and paradoxical. The data do not support the use of thromboxane synthesis inhibitors as therapy for conditions caused by platelet aggregation, but the results may be dependent upon the species, the vascular bed, or the method used to induce aggregation.

Prostaglandin inhibition and cerebrovascular hemodynamics in normal and ischemic human brain

Indomethacin is a potent inhibitor of prostaglandin synthesis. Indomethacin effects on cerebral blood flow (CBF) in normal subjects and patients with ischemic cerebrovascular disease were measured by133Xe inhalation method and compared. Thirteen normal subjects with muscle contraction headaches were tested and compared to three groups of patients with ischemic cerebrovascular disease: (1) a transient ischemic attack (TIA) group, consisting of 8 patients, (2) a recent cerebral infarction group consisting of 10 patients with recent stroke (within 2 months), and (3) a chronic cerebral infarction group, consisting of 10 patients with remote stroke (exceeding 2 months). From the three groups, 7 patients with internal carotid artery occlusion also underwent superficial temporal artery to middle cerebral artery (STA-MCA) bypass; this group was tested before and after the operative procedure. Indomethacin induced significant CBF reductions in the TIA and chronic cerebral infarction groups but there were no significant effects in the recent cerebral infarction group and many showed paradoxical increases. Plotting indomethacin-induced CBF changes according to the time course of cerebral infarction indicated that abnormal responses gradually returned toward normal within 16 weeks. Indomethacin-induced CBF changes were measured prospectively in patients undergoing STA-MCA bypass. Indomethacin had no significant effect on CBF before the procedure, but significantly reduced CBF (i.e., mean CBF became reduced) after surgery. Comparison of the time course for recovery of indomethacin-induced CBF responses in non-operated cases indicated that the post-operative difference in response could be due to the natural history of the disease rather than to surgery. Present studies confirm that prostaglandins play an important part in cerebral vascular control in man, and that these agents are temporarily deranged following acute cerebral infarction, which may account for temporary alterations in regional cerebrovascular responsiveness to 5% CO2and 100% O2inhalation after stroke.

Effects of prostaglandins on the cerebral circulation in the coat

The role of prostaglandins in producing cerebrovasodilation during hypercapnia was tested in goats. Cerebral blood flow (CBF) changes with increasing arterial PCO2 were measured before and after prostaglandin synthesis inhibition with indomethacin or ibuprofen. Both drugs produced significant decreases in CBF under control anesthetized conditions but had no significant effect on the cerebrovascular response to increased arterial PCO2. The effects of direct intracerebrovascular infusion of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) and prostacyclin were also measured. In the dose range tested (0.1-1) microgram/min) PGF2 alpha had no significantly greater than that produced by PGE2. The effectiveness of each compound in producing cerebrovascular changes is consistent with the endogenous distribution of prostaglandins within the brain. These results suggest that prostaglandins, particularly PGI2, may be important in modulating cerebrovascular tone but have no role in increasing CBF during hypercapnia.