Effects of some vasoactive drugs on the vessels of cerebral grey matter in the dog

The cerebrovascular response to norepinephrine: A scoping systematic review of the animal and human literature

Intravenous norepinephrine (NE) is utilized commonly in critical care for cardiovascular support. NE's impact on cerebrovasculature is unclear and may carry important implications during states of critical neurological illness. The aim of the study was to perform a scoping review of the literature on the cerebrovascular/cerebral blood flow (CBF) effects of NE. A search of MEDLINE, BIOSIS, EMBASE, Global Health, SCOPUS, and Cochrane Library from inception to December 2019 was performed. All manuscripts pertaining to the administration of NE, in which the impact on CBF/cerebral vasculature was recorded, were included. We identified 62 animal studies and 26 human studies. Overall, there was a trend to a direct vasoconstriction effect of NE on the cerebral vasculature, with conflicting studies having demonstrated both increases and decreases in regional CBF (rCBF) or global CBF. Healthy animals and those undergoing cardiopulmonary resuscitation demonstrated a dose-dependent increase in CBF with NE administration. However, animal models and human patients with acquired brain injury had varied responses in CBF to NE administration. The animal models indicate an increase in cerebral vasoconstriction with NE administration through the alpha receptors in vessels. Global and rCBF during the injection of NE displays a wide variation depending on treatment and model/patient.

The efficacy of papaverine administration by different routes for the treatment of experimental acute cerebral vasospasm

OBJECTIVE

To compare the effect of papaverine (PPV) by different routes of administration for the treatment of experimental acute cerebral vasospasm.

METHODS

A rabbit model of acute cerebral vasospasm induced by autologous blood injected into the basilar and prepontine cistern was used. The PPV (2mg/kg) was injected either by an intravenous (IV), intra-arterial (IA), intra-cisternal (IC), or combination of intra-arterial and intra-cisternal (IA+IC) routes. Basilar artery diameters were measured before and after vasospasm was induced and after PPV treatment.

RESULTS

Induction of vasospasm reduced basilar artery diameters by more than 50% in all animals. Compared to artery diameters before vasospasm, diameters after PPV treatment via the IV route were only reduced by 0.5+/-4.7%. Other reductions in the diameter included 29.1+/-10.4%, about 1.8+/-3.1%, and about 26.7+/-8.4% in the IA, IC, and IA+IC groups, respectively. However, IA administration of PPV caused obvious side effects.

CONCLUSION

Intra-arterial application of the PPV was the most effective way to treat vasospasm in this study. The efficacy of IC route in our study did not confirm the results of prior study. The possibility of side effects of PPV via the IA route should be considered before clinical application.

Effect on ventilation of papaverine administered to the brain stem of the anaesthetized cat

1. To investigate whether cerebral vasodilatation by itself contributes to the decrease in ventilation as found during brain stem hypoxia the role of cerebral vasodilatation on minute ventilation was investigated in twelve cats anaesthetized with alpha-chloralose-urethane. 2. Cerebral vasodilatation in the medulla oblongata was produced by adding papaverine to the blood perfusing the brain stem. 3. Papaverine at concentrations of 10-35 micrograms per millilitre of blood had an appreciable depressant effect on ventilation. At a concentration of 14.3 micrograms ml-1 the depression in ventilation averaged 0.7 +/- 0.1 l min-1. 4. The ventilatory response to stepwise changes in papaverine concentration could be adequately described with a single exponential function with a time delay. 5. The time constant of the ventilatory response following a step increase in papaverine concentration (134 +/- 15 s) was longer than that of the step decrease (105 +/- 10 s) in concentration (P = 0.034). The time delays of the ventilatory response (88 +/- 21 s and 53 +/- 8 s respectively) were not significantly different (P = 0.126). 6. The ventilatory response to stimulation of the peripheral chemoreceptors by hypoxia and of the central chemoreceptors by hypercapnia was not impaired by papaverine. 7. The results support the hypothesis that cerebral vasodilatation by itself contributes to the decrease in ventilation by brain stem hypoxia.

Cerebral blood flow and oxygen uptake in endotoxic shock. An experimental study in dogs

Cerebral blood flow (CBF), cerebral oxygen uptake (CMRO2) and central haemodynamics in anaesthetized dogs with controlled ventilation were studied at intervals for 2 h following an intravenous injection of E. coli endotoxin, 1.0-1.5 mg/kg. CBF showed a 30% decrease within 15 min after the endotoxin administration, while the arterial blood pressure was still not markedly depressed. Autoregulation to arterial blood pressure changes was maintained during endotoxinaemia and the cerebrovascular reaction to changes in arterial carbon dioxide tension (PaCO2) depressed. Normocapnic animals (PaCO2) greater than or equal to 4.0 kPa) showed an increase in CMRO2 of over 40%, that was obvious 1 h after the administration of endotoxin. The intracranial pressure was decreased with 5 min of the administration of endotoxin irrespective of the prevailing arterial blood pressure. Thereafter, it was raised above the control level. Two hours after endotoxin increased protein concentrations in cerebrospinal fluid were seen, results compatible with blood-brain barrier damage and penetration of other substances; e.g. monoamines released during endotoxinaemia could thus be expected to have a direct influence on both cerebral blood flow and metabolism.

Effects of sympathetic stimulation on cerebral and ocular blood flow. Modification by hypertension, hypercapnia, acetazolamide, PGI2 and papaverine

The effect of unilateral, electrical stimulation of the cervical sympathetic chain in rabbits anesthetized with pentobarbital sodium and vasodilated by hypercapnia, acetazolamide, papaverine or PGI2 was investigated to determine to what extent the sympathetic nerves to the brain and the eye cause vasoconstriction and prevent overperfusion in previously vasodilated animals. Evans blue was given as a tracer for protein leakage. Blood flow determinations were made with the labelled microsphere method during normotension and acute arterial hypertension. Hypertension was induced by ligation of the thoracic aorta and in some animals metaraminol or angiotensin was also used. Acetazolamide caused a two to threefold increase in cerebral blood flow (CBF) and hypercapnia resulted in a fivefold increase. CBF was not markedly affected by papaverine or PGI2. In the choroid plexus, the ciliary body and choroid, papaverine and hypercapnia caused significant blood flow increases on the control side. Sympathetic stimulation induced a 12% blood flow reduction in the brain in normotensive, hypercapnic animals. Marked effects of sympathetic stimulation at normotension were obtained under all conditions in the eye. In the hypertensive state the CBF reduction during sympathetic stimulation was moderate, but highly significant in hypercapnic or papaverine-treated animals as well as in controls. Leakage of Evans blue was more frequently seen on the nonstimulated side of the brain. In the eye there was leakage only on the control side except in PGI2-treated animals where 2 rabbits had bilateral leakage. The effect of sympathetic stimulation on the blood flow in the cerebrum and cerebellum in vasodilated animals seems to be small or absent if the blood pressure is normal. In the eye pronounced vasoconstriction occurs under these conditions. In acute arterial hypertension sympathetic stimulation protects both the cerebral and ocular barriers even under conditions of marked vasodilation.

Quantitative changes in regional cerebral blood flow of rats induced by alpha- and beta-adrenergic stimulants

Cerebral blood flow was measured with the 14C-ethanol technique in 8 regions (frontal, parieto-temporal and occipital cortex, caudate nucleus, thalamus, cerebellum, mesencephalon, and pons) of rats. The highest flow values (83-89.5 ml/100 g/min) were found in cortical areas, whereas pons had the lowest flow (48 ml/100 g/min). Intravenous infusion of noradrenaline or adrenaline markedly reduced rCBF (by 22-48% of control levels) in all regions except thalamus, mesencephalon, and pons. The noradrenaline-induced reduction was blocked, and the effect of adrenaline reversed, after pretreatment with the alpha-receptor antagonist, phentolamine. Isoprenaline infusion markedly augmented rCBF in thalamus, mesencephalon, pons, and also in the caudate nucleus. The response was reduced by the beta-receptor antagonist, propranolol. The experiments show the presence and heterogenous distribution in the cerebrovascular bed of slpha- and beta-adrenoceptors that can be activated by sympathomimetics given systematically. If noradrenaline was allowed to pass the blood-brain barrier after osmotic opening with urea, an increased regional flow was obtained, probably due to a mechanism where the vasodilator effect secondary to activation of cerebral metabolism predominated over the direct vasoconstrictor effect of the amine.

The effect of papaverine on local tissue PO2 and microflow in cat brain cortex

The effect of intracarotid and intravenous administration of papaverine on local tissue PO2 and microflow in the cat's brain surface was studied. Local tissue PO2 was measured with a multiwire surface electrode polarographically, and microflow by local hydrogen clearance method. The intracarotid infusions were made for 1, 2 and 5 min with doses of 0.1, 0.2 and 0.5 mg/kg/min papaverine, and the intravenous ones for 5 min with doses of 0.2, 0.5 and 1 mg/kg/min. The continuous intracarotid infusions showed that papaverine in the doses used distinctly increased local tissue PO2 and microcirculation of the brain surface. With the doses applied, systemic arterial pressure (SAP) changed little. It slightly decreased only during the 5 min infusions containing 0.5 mg/kg/min. The duration of the effect increased with increases in the duration of the infusion and of the dose. The maximum duration was observed with 5 min infusions and lasted for 10--15 min after drug administration was discontinued. During the i.v. infusions, tissue PO2 and microflow rose less than with intracarotid ones. No redistribution of capillary flow was observed.

Studies on the influence of monoamines on the cerebrovascular response to arterial hypoxia

The cerebrovascular response to arterial hypoxia was studied during blockade of the vascular dopamine receptors and during alpha-adrenergic receptor stimulation and blockade in anaesthetized dogs. Dopamine receptor blockade with pimozide or haloperidol invariably decreased the degree of hypoxic vasodilatation in the brain pointing to a functional role of dopamine in this situation. Alpha-receptor blockade did not change the response, while stimulation of these receptors decreased the dilatory response even in deep arterial hypoxia.

Proposed effects of brain noradrenaline on neuronal activity and cerebral blood flow during REM sleep

We propose that the observed increases of both neuronal activity and cerebral blood flow seen throughout the brain during REM sleep may be effects of decreased central noradrenaline release.

Dynamic response of the intracranial system in the conscious dog to papaverine hydrochloride

The influence of papaverine on the intracranial system of the dog was studied by measuring the pressure-depth-time response for the intact intracranial system, i.e., for the subarachnoid and subpial compartments. This was accomplished by a measurement system which provided an accurate pressure-depth determination and a uniform rate of transducer insertion. Distinct regions of the intracranial system (subarachnoid, transitional, and subpial) were identified from inflections in the pressure response curve. The test parameter, brain relative stiffness (BRS), was obtained by determining the slope of the pressure response values within the subpial region. This parameter is a measure of the "stiffness" or elasticity of bring tissue within the test configuration. A bolus injection of papaverine (1 mg per kilogram, i.v.) caused an increase in the transitional region, a compensatory reduction in the subarachnoid space, and an increase in BRS. It is postulated that at normotensive arterial blood pressure, cerebrovascular expansion caused by papaverine resulted in increased brain tissue elasticity, i.e., an increase in the pressure-depth response for the subpial region. Possible implications for this increase are discussed. Experiments should be conducted in which local blood flow studies are coupled with measurements of brain elastic response.

Pharmacological control of local oxygen regulation mechanisms in brain tissue

The effect of several agents active on autonomic nervous system functions was tested on brain oxygen autoregulation parameters. It was found that atropine, propranolol and isoproterenol had no influence in abolishing the measured parameters. Phenoxybenzamine, tolazoline and dibenamine all suppress autoregulation. In an additional experimental series, a phenoxybenzamine infusion was given during O2 breathing. The infusion induced, in most cases, an additional rise in TpO2 (tissue pressure of oxygen, which refers to the partial pressure [in mm Hg] of this gas at the measuring tip of the electrode). It is concluded that an alpha-adrenergic mechanism is part of the autoregulation process. Also, the increase in brain TpO2 induced by 59% O2-5% Co2 breathing seems to be blocked or reversed by alpha-adrenolytic drugs, thus supporting the thinking that the effect of CO2 on cerebral blood flow is at least in part mediated through an alpha-adrenergic response.

Modification of the cerebrovascular response to noradrenaline by bile duct ligation

The effects of intracarotid infusions of noradrenaline on the cerebral vasculature were studied in seven baboons with bile duct ligation. Infusion of 8 mug and 16 mug/min of noradrenaline resulted in a significant decrease in cerebral blood flow in the jaundiced animals. In normal baboons, these doses produced cerebrovascular dilatation. These results indicate that there is an increased cerebrovascular sensitivity to noradrenaline in the obstructive jaundice which follows bile duct ligation. It is postulated that noradrenaline smooth muscle uptake mechanisms are disturbed allowing a greater concentration of the amine at the receptor sites.

Effect of systemic arterial hypotension on the rate of cerebrospinal fluid formation in dogs

✓The rate of cerebrospinal fluid (CSF) production in dogs was measured by ventriculocisternal perfusion with artificial CSF containing inulin. In normotensive animals, the average CSF production was 36 ± 6 µl/min. When the mean arterial blood pressure was reduced to 62 ± 1 mm Hg, the CSF production fell to 22 ± 5 µl/min, a 39% reduction in fluid formation. The authors briefly discuss various hypotheses to explain this reduction.

Effects of catecholamine infusions on cerebral blood flow and oxygen consumption of the isolated perfused dog brain

Our earlier studies revealed a weak alpha-adrenergic and beta-adrenergic activity of the cerebral vessels of the isolated perfused dog brain. The present investigations were undertaken to determine whether vascular adjustments occur in the cerebral circulation during longer periods of catecholamine infusions. The experiments were performed on six isolated canine brains cross perfused from donor dogs. Norepinephrine (2 µg per minute), epinephrine (2 µg per minute), and isoprenaline (0.2 µg per minute) were applied intra-arterially (i.a.) for a period of ten minutes. Total venous outflow, perfusion pressure in the circle of Willis, and venous O 2 saturation were monitored continuously. Cerebral vascular resistance (CVR) and cerebral O 2 consumption (CMRO 2 ) were calculated. Based on the pressure-flow relationship tested in each brain, the indirect effects of catecholamines on CVR caused by autoregulatory influences were calculated and eliminated. During norepinephrine and epinephrine infusions cerebral blood flow (CBF) was found to be decreased by 10.2 ± 6.0% and 4.1 ± 3.3%, respectively, whereas during isoprenaline infusion CBF increased by 9.3 ± 3.6% (mean values ± SD). The maximal changes of CBF were reached in the first or second minute of catecholamine infusion and persisted up to the end of infusion (P > 0.05). After elimination of the indirect effects of catecholamines on CVR, the direct effects on CVR were reduced to about 50% of the original values and remained constant at the level reached during the whole period of infusion. CMRO 2 was not changed (P > 0.05) during infusion of the different catecholamines. Based on these investigations it is assumed that no pronounced vascular adjustments occur in the cerebral circulation during catecholamine infusions.

Evidence for the direct effect of adrenergic drugs on the cerebral vascular bed of the unanesthetized goat

Despite considerable research, the question of whether adrenergic drugs exert direct effects on the cerebral circulation has remained unresolved. With the development of a method for monitoring continuously the entire blood flow to one hemisphere in the unanesthetized goat, we have been able to study this problem directly. The effects of epinephrine, norepinephrine, and isoproterenol administered by close intra-arterial injection were investigated in 15 goats in which an electromagnetic flowmeter had been implanted previously on the internal maxillary artery, which, in this animal, provides the sole blood supply to a hemisphere. Both epinephrine and norepinephrine (0.1 to 5.0 µg) produced dose-dependent reductions in cerebral blood flow, a decrease of 55 ± 3% (SEM) occurring with the highest dose. Alpha receptor blockade of the ipsilateral hemisphere with phenoxybenzamine totally or partially abolished this cerebral vasoconstriction. Isoproterenol (0.01 to 1.0 µg) produced dose-dependent increases in cerebral blood flow, an increment of 75 ± 6% occurring with the highest dose. Beta blockade with propranolol totally or partially abolished the cerebral vasodilation induced by isoproterenol. Thus, epinephrine, norepinephrine, and isoproterenol exert powerful direct effects on the cerebral circulation of the unanesthetized goat, and these effects appear to be mediated by alpha and beta receptors.

Papaverine hydrochloride and experimental hemorrhagic cerebral arterial spasm

Chronic hemorrhagic spasm of the basilar artery was produced in beagle dogs by introducing blood into the cisterna magna. Spasm was evaluated by means of vertebral angiography. Papaverine hydrochloride was administered intravenously, intracisternally as well as intra-arterially. The intracisternal route was the more effective in combating spasm but the effect was transitory. The results suggest that the treatment of spasm by chemical means in subarachnoid hemorrhage using agents currently available would require continuous topical application.

Effects of intrahypothalamic and intraventricular norepinephrine and 5-hydroxytryptamine on hypothalamic blood flow in the conscious rabbit

Hypothalamic blood flow (HBF) was measured in the conscious rabbit using a 133 xenon clearance technique. The effects of intrahypothalamic norepinephrine (NE) and 5-hydroxytryptamine (5-HT) were determined by adding these compounds to the 133 xenon-in-saline injectate, in varying concentrations. NE produced dose-dependent changes in flow; 1 µg/m injection caused a mean increase in HBF of 55%, while doses of 10, 20, 40 and 200 µg/injection reduced HBF by mean values of 26%, 17%, 20% and 29% respectively. The constrictor effect of NE 40 µg/injection was prevented by the addition of phenoxybenzamine 50 µg/injection. Intrahypothalamic injections of 5-HT (20, 40 and 80 µg/injection) caused increases in mean HBF of 24%, 54% and 69% respectively. Injections of NE into the lateral cerebral ventricles caused an increase in HBF; 5-HT produced a variable response, but mean values for HBF tended to be lower after the injection. There were no changes in mean arterial blood pressure or arterial Pco 2 . It is concluded that NE and 5- HT have an action on hypothalamic resistance vessels when applied from the adventitial side, and that, in the case of NE, the response is dose dependent, and the vasoconstrictor effects may be mediated by alpha receptors in hypothalamic vessels.

The effect of intra-arterial papaverine on the regional cerebral blood flow in patients with stroke or intracranial tumor

The effect of intracarotid injection of 10 mg of papaverine on regional cerebral blood flow was measured in 27 patients. Most of the patients had cerebral infarction or intracranial neoplasm. The intra-arterial 133 Xenon injection method was used and 16 or 35 regions of the diseased hemisphere were monitored. In patients without focal flow abnormalities an average flow increase of 93% followed the injection. In patients with focal abnormalities of cerebral blood flow the intra-arterial injection of papaverine produced a decrease in focal flow or less increase in flow than normal. It is concluded that vasodilator therapy presumably decreased flow in pathological tissue and that such treatment should not be employed in the therapy of cerebrovascular disease.