Effects of noradrenaline on the cerebral blood flow in the dog

Neurochemical underpinning of hemodynamic response to neuropsychiatric drugs: A meta- and cluster analysis of preclinical studies

Functional magnetic resonance imaging (fMRI) is an extensively used method for the investigation of normal and pathological brain function. In particular, fMRI has been used to characterize spatiotemporal hemodynamic response to pharmacological challenges as a non-invasive readout of neuronal activity. However, the mechanisms underlying regional signal changes are yet unclear. In this study, we use a meta-analytic approach to converge data from microdialysis experiments with relative cerebral blood volume (rCBV) changes following acute administration of neuropsychiatric drugs in adult male rats. At whole-brain level, the functional response patterns show very weak correlation with neurochemical alterations, while for numerous brain areas a strong positive correlation with noradrenaline release exists. At a local scale of individual brain regions, the rCBV response to neurotransmitters is anatomically heterogeneous and, importantly, based on a complex interplay of different neurotransmitters that often exert opposing effects, thus providing a mechanism for regulating and fine tuning hemodynamic responses in specific regions.

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.

Effects of various catecholamines on high-energy phosphates of rat liver and brain during hemorrhagic shock measured by 31P-NMR spectroscopy

The effects of dopamine, epinephrine and norepinephrine on energy metabolism as well as intracellular pH in rat liver and brain during hemorrhagic shock were examined by in vivo 31P-NMR spectroscopy. The hemorrhagic shock was induced by arterial bleeding to a mean arterial pressure (MAP) of 30-40 mmHg. Upon the induction of hemorrhagic shock, there was a dramatic fall in adenosine triphosphate (ATP) and a rise in inorganic phosphate (Pi) in the liver. The intracellular pH indicated severe acidosis. However, no change in these parameters was observed in the brain during hemorrhagic shock. After infusion of the above catechollamines following 10 min of hemorrhagic shock, MAP increased to 90-100% of its control value. Only dopamine improved hepatic energy metabolism, whereas brain energy metabolism was not affected by any of them. This suggests that dopamine protects liver function during hemorrhagic shock without affecting brain energy metabolism.

Effects of metabolic pH-alterations on cerebral blood flow and oxygen uptake following E. coli endotoxin in dogs

The aim of the present study was to investigate if metabolic pH-alterations have an influence on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) after an injection of E. coli endotoxin. Following endotoxin in dogs with normal pH a decreased CBF and an increased CMRO2 have earlier been found. Thirteen anaesthetized dogs were subjected to metabolic pH-variations in blood by infusion of hydrochloric acid or sodium bicarbonate. Ten dogs received E. coli endotoxin in a dose of 1 mg.kg-1 bodyweight. CBF, CMRO2 and noradrenaline and adrenaline concentrations in blood and cerebrospinal fluid were measured repeatedly during normoxia and normocarbia. Measurements before endotoxin served as controls, together with three additional animals, where endotoxin was never given. In control measurements pH showed no influence on the variables studied. After endotoxin CBF, CMRO2 and noradrenaline in cerebrospinal fluid increased with decreasing arterial blood pH. The influence exerted by metabolic pH alterations in blood after endotoxin may be explained by hydrogen ions and monoamines passing over a blood-brain barrier (BBB), damaged by endotoxin, into the brain tissue causing vasodilation and neuronal activation.

The effect of chronic propranolol therapy on regional cerebral blood flow in hypertensive patients

In 31 hypertensive patients the effect of chronic oral administration of the beta blocking agent propranolol on regional cerebral blood flow (rCBF) was studied, using the non-invasive 133Xenon inhalation technique. The results of the measurements were compared to the rCBF obtained in an age-matched normal control group. Our study shows that during long-term therapy with low doses of propranolol (less than 120 mg/daily) the rCBF is unaffected, but it is increased significantly if higher doses (greater than 120 mg/daily) are used. In all six patients who served as their own control, as they had basic rCBF measurements before or during low-dose propranolol, the rCBF on high-dose propranolol became significantly increased. The possible mechanisms which may cause the increased rCBF on high-dose propranolol are discussed.

Cerebral hemodynamics, oxygen uptake and cerebral arteriovenous differences of catecholamines following E. coli endotoxin in dogs

In experimental endotoxic shock in dogs, a decrease in cerebral blood flow and an increase in cerebral metabolic rate of oxygen (CMRO2) have been shown to occur. In this situation the blood levels of adrenaline and noradrenaline are markedly elevated. The aim of the present study was to investigate whether a cerebral uptake of circulating catecholamines with a possible influence on CMRO2 takes place in the brain. In eight anaesthetized dogs, arterial blood, superior sagittal sinus blood and cerebrospinal fluid were analyzed for the concentrations of adrenaline, noradrenaline and dopamine before and up to 4 h after an injection of E. coli endotoxin 1.0-1.5 mg . kg-1. The blood levels of adrenaline and noradrenaline, but not dopamine, increased in response to the endotoxin. From about 30 min after the endotoxin injection, arteriovenous adrenaline and noradrenaline differences indicating a cerebral uptake were most often seen. Increased concentrations of noradrenaline, adrenaline and dopamine in cerebrospinal fluid were observed. Noradrenaline gave the highest concentrations and these were correlated to the CMRO2. In some animals the blood and cerebrospinal fluid concentrations of adrenaline seemed to be related. These results indicate that catecholamines might be of importance for the development of an increased CMRO2 in endotoxic shock.

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.

The effects of high dose methylprednisolone or fluid volume expansion on cerebral haemodynamics and oxygen uptake in endotoxic shock. An experimental study in dogs

E coli endotoxin has been shown to decrease cerebral blood flow (CBF) and increase cerebral metabolic rate of oxygen (CMRO2) in normocapnic dogs. The aim of this study was to investigate the effects of different clinical treatments on the cerebral and central circulation already under the influence of endotoxin. Thus the animals were treated with either methylprednisolone or a lactated Ringer's solution. CBF, CMRO2 and intracranial pressure were followed. Central haemodynamic parameters, i.e. cardiac output, aortic pressure and pulmonary artery pressure, were also measured. Five dogs were given methylprednisolone (Solu-Medrol) 30 mg/kg 90 min after the endotoxin injection. Following this drug there were no significant changes in CBF when compared to controls. The primarily increased CMRO2 did, however, show a transient decrease. Five animals were treated with a lactated Ringer's solution. (Ringerdex), 30 mg/kg, given intravenously over 20 min starting 90 min after the endotoxin injection. In these animals, the cardiac output as well as CMRO2 returned to the values before endotoxin. CBF did not increase significantly.

Influence of intravenously administered catecholamines on cerebral oxygen consumption and blood flow in the rat

In order to study effects of catecholamines on cerebral oxygen consumption (CMRo2) and blood flow (CBF), rats maintained on 75% N2O and 25% O2 were infused i.v. with noradrenaline (2, 5, or 8 microgram.kg-1.min-1) or adrenaline (2 or 8 microgram.kg-1.min-1) for 10 min before CBF and CMRo2 were measured. In about 50% of animals infused with 2--8 microgram.kg-1.min-1 of noradrenaline, CMRo2 (and CBF) rose. However, there was no dose-dependent response, and CMRo2 did not exceed 150% of control. The effects of noradrenaline in a dose of 5 microgram.kg-1.min-1 on CMRo2 and CBF were blocked by propranolol (2.5 mg.kg-1). In animals infused with adrenaline (8 microgram.kg-1.min-1) CMRo2 was doubled and, in many, CBF rose 4- to 6-fold. It is concluded that, when given in sufficient amounts, catecholamines have pronounced effects on cerebral metabolism and blood flow, the effects of adrenaline on CMRo2 and CBF resembling those observed in status epilepticus.

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.

The pressure-flow relations of the canine brain in acute mechanically induced arterial hypertension at different levels of cerebral blood flow

Cerebral pressure-flow relations were studied in anaesthetized dogs during acute arterial hypertension, induced by compression of the thoracic aorta. In one group of animals steady state measurements were made with the radioactive gas elimination method. In another group the immediate changes of blood flow at a blood pressure change, as indicated by variations in the cerebral venous oxygen saturation, were studied with continuous oximetric analyses of the superior sagittal sinus blood. The initial blood flow was varied by variations of the arterial carbon dioxide tension of injections of papaverine. At low or normal blood flows autoregulation was efficient up to pressures around 180-200 mmHg, while at higher flows the upper autoregulatory pressure limit was found at lower blood pressures. Above the autoregulatory limit-irrespective of the control flow level-there was a rise in blood flow and a decrease in cerebrovascular resistance.