The effect of intracarotid infusion of dexamethasone and 5-hydroxytryptamine on cerebral blood flow and metabolism in baboons

Preoperative high dose methylprednisolone attenuates the cerebral response to deep hypothermic circulatory arrest

OBJECTIVE

The aim of this study was to assess the effects of preoperative high dose methylprednisolone on cerebral recovery following a period of deep hypothermic circulatory arrest (DHCA).

METHODS

Sixteen 1-week-old piglets were randomized to placebo (n=8), or 30 mg/kg intramuscular methylprednisolone sodium succinate (MPRED) given at 8 and 2 h before induction of anaesthesia. All piglets underwent cardiopulmonary bypass, cooling to 18 degrees C, 60 min of circulatory arrest followed by 60 min of reperfusion and rewarming. The radiolabelled microsphere method was used to determine the global and regional cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO(2)) at baseline before DHCA and after 60 min of reperfusion.

RESULTS

In controls, mean global CBF (+/-1 standard error) before DHCA was 53.7+/-2.4 ml/100 g per min and fell to 23.8+/-1.2 ml/100 g per min following DHCA (P<0.0001). This represents a post-DHCA recovery to 45.1+/-3.3% of the pre-DHCA value. In the MPRED group recovery of global CBF post-DHCA was significantly higher at 63.6+/-5.2% of the pre-DHCA value (P=0.009). The regional recovery of CBF in the cerebellum, brainstem and basal ganglia was 80, 75 and 69% of pre-DHCA values in the MPRED group respectively compared to 66, 60 and 55% in controls (P<0.05). Global CMRO(2) in controls fell from 3.9+/-0.2 ml/100 g per min before to 2. 3+/-0.2 ml/100 g per min after DHCA (P=0.0001). This represents a post-DHCA recovery to 58.6+/-4.4% of the pre-DHCA value. In the MPRED group, however, recovery of global CMRO(2) post-DHCA was significantly higher at 77.9+/-7.1% of the pre-DHCA value (P=0.04).

CONCLUSIONS

Treatment with high dose methylprednisolone at 8 and 2 h preoperatively attenuates the normal cerebral response to a period of deep hypothermic ischaemia. This technique may therefore offer a safe and inexpensive strategy for cerebral protection during repair of congenital heart defects with the use of DHCA.

Methylprednisolone attenuates inflammation, increase of brain water content and intracranial pressure, but does not influence cerebral blood flow changes in experimental pneumococcal meningitis

We investigated the effect of methylprednisolone on pathophysiological alterations in experimental pneumococcal meningitis. Untreated rats injected with pneumococcal cell wall components after hydrolization with M1 muramidase (PCW-M) developed an increase of regional cerebral blood flow (rCBF; 165.0 +/- 12.8%, baseline 100%, mean +/- S.E.M.), brain water content (79.23 +/- 0.10%), intracranial pressure (ICP; 11.9 +/- 1.0 mmHg) and white blood cell (WBC) count in the cerebrospinal fluid (CSF) (2,709 +/- 482 cells/microliters) within 8 h after intracisternal (i.c.) challenge. Pretreatment with methylprednisolone or administration of methylprednisolone 4 h after i.c. challenge significantly attenuated the increase of brain water content (78.88 +/- 0.08% and 78.82 +/- 0.05%, resp.), ICP (7.7 +/- 1.1 mmHg and 4.9 +/- 0.8 mmHg, resp.) and CSF WBC count (1,257 +/- 168 cells/microliters and 976 +/- 105 cells/microliters, resp.). However, methylprednisolone did not inhibit the increase of rCBF (163.5 +/- 13.7% and 160.9 +/- 6.8%, resp.), whereas dexamethasone significantly attenuated microvascular changes. Hypercapnia-induced reactivity of cerebral vessels tested 8 h after i.c. injection was preserved in all groups. In conclusion, we found that methylprednisolone significantly attenuated the increase of brain water content, ICP and CSF WBC count, but had no effect on microvascular changes during the early phase of experimental pneumococcal meningitis.

Dexamethasone prevents cerebral infarction without affecting cerebral blood flow in neonatal rats

BACKGROUND AND PURPOSE

We recently demonstrated that pretreatment with the synthetic glucocorticoid dexamethasone prevents hypoxic-ischemic brain damage in neonatal rats. Presently, we examine whether this protective effect of dexamethasone is due to an improvement in local cerebral blood flow.

METHODS

Neonatal rats were treated with either vehicle or 0.1 mg/kg i.p. dexamethasone 24 hours before hypoxia-ischemia (right carotid artery occlusion +3 hours of 8% O2). Cerebral blood flow was measured with [14C]iodoantipyrine autoradiography after either 2 (n = 17) or 3 (n = 15) hours of hypoxia-ischemia. Additional animals (n = 20) were perfusion-fixed 3 days after hypoxia-ischemia. The area of cerebral pathological changes was measured from hematoxylin and eosin-stained coronal sections taken at three different levels.

RESULTS

Pathological outcome differed between groups. In vehicle-treated rats, sections from anterior, mid, and posterior portions of the cerebrum all had extensive infarction or cellular necrosis ipsilateral to the occlusion (mean areas of damage were 62.6 +/- 10%, 70.2 +/- 9%, and 54.2 +/- 8%, respectively). However, in dexamethasone-treated animals, brain damage in sections at corresponding levels was minimal (0%, 1.6 +/- 2%, and 1.5 +/- 1%, respectively; p < 0.0002). In contrast to the pathological results, cerebral blood flow was equivalent in the dexamethasone- and vehicle-treated groups. After either 2 or 3 hours of hypoxia, cerebral blood flow was reduced 60-80% ipsilateral to the carotid artery occlusion in animals treated with either vehicle or dexamethasone.

CONCLUSIONS

Despite ischemic levels of cerebral blood flow, pretreatment with dexamethasone prevents cerebral damage in neonatal rats. Instead of improving local cerebral perfusion, dexamethasone presumably acts via peripheral or central glucocorticoid receptors to produce some alteration in the brain that decreases its susceptibility to hypoxia-ischemia.

Regional alterations in blood-to-brain transfer of alpha-aminoisobutyric acid and sucrose, after chronic administration and withdrawal of dexamethasone

The effect of dexamethasone administration and withdrawal was studied with respect to blood-brain barrier function. The tracers alpha-[3H]aminoisobutyric acid (AIB) (MW 104) and [14C]sucrose (MW 342), which have a low permeability across the intact endothelium, were simultaneously injected intravenously in rats treated with dexamethasone and placebo-treated control animals or in rats in which dexamethasone treatment was discontinued 3 days before the experiment. Unidirectional transfer constants (Ki) were determined in discrete brain regions. Steroid administration reduced the rate of influx of AIB and sucrose, whereas discontinuation of drug resulted in an increased permeability. These findings suggest that when exposure to glucocorticoids is prolonged, the efficiency of medical treatment of CNS diseases may decrease due to reduction of drug delivery to CNS. Thus, these experimental findings may have particular importance in the clinical setting of drug administration when considering the combination of steroids with other drugs, and may aid in understanding better the pathogenesis of some types of brain edema seen in patients from whom corticosteroid therapy has been withdrawn.

Electromechanical coupling in feline basilar artery in response to serotonin

This study was undertaken to define some of the cellular mechanisms of action of serotonin on cerebral vascular muscle. Application of serotonin to cat basilar artery resulted in a dose dependent depolarization and contraction beginning at 10(-8) M. The correlation coefficient relating the degree of force development with the change in membrane potential (Em) was 0.98. Excess K+ depolarized these vascular muscle cells with a slope (between 10 and 100 mM [K]0) of 54 mV/decade. When the muscle cells within this artery were depolarized by only 7 mV by addition of excess K+ there was a significant reduction in force development in response to serotonin. When the membrane was depolarized from -63 to -40 mV the mechanical response to serotonin was reduced by around 50%. Steady state current/voltage curves demonstrated a reduction in input resistance suggesting that serotonin's mechanism of depolarization is not due to a reduction in gk. These data demonstrate that serotonin contracts cat basilar artery through mechanisms involving vascular muscle cell depolarization and that factors which influence the level of Em will markedly effect the contractile response to serotonin.