CBF and oxygen metabolism in hemodialysis patients: effects of anemia correction with recombinant human EPO

To investigate the effects of anemia correction with recombinant human erythropoietin (rhEPO) on both cerebral blood flow and oxygen metabolism in hemodialysis (HD) patients, the regional cerebral blood flow (rCBF), oxygen extraction (rOEF), and metabolic rate for oxygen (rCMRO2) were measured by positron emission tomography in five HD patients, and the data were compared with eight nondemented controls who had neither anemia nor uremia. In the HD patients, 1,500 U of rhEPO were administered intravenously three times a week to achieve a 10% increase in hematocrit (Hct) as an absolute value. Before rhEPO administration, the hemispheric rCMRO2 in HD patients was 1.48 +/- 0.09 (SE) ml.min-1.100 ml-1, which was significantly lower than that of 2.18 +/- 0.10 in the controls (P less than 0.01). In contrast, both rCBF and rOEF were significantly greater in the HD patients than the control, being 40 +/- 3 vs. 32 +/- 3 ml.min-1.100 ml-1 for rCBF (P less than 0.02) and 49 +/- 1 vs. 38 +/- 1% for rOEF (P less than 0.001). After treatment with rhEPO, Hct rose significantly from 21 +/- 1 to 31 +/- 1% in HD patients (P less than 0.001). There were significant reductions in both the hemispheric rCBF to 32 +/- 1 ml.min-1.100 ml-1 (P less than 0.01) and rOEF to 42 +/- 1% (P less than 0.01). However, the hemispheric rCMRO2 remained low at 1.58 +/- 0.06 ml.min-1.100 ml-1 even after rhEPO treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of ischemia-induced dopamine release by omega-conotoxin, a calcium channel blocker, in the striatum of spontaneously hypertensive rats: in vivo brain dialysis study

The effect of omega-conotoxin GVIA (CgTX), an N-and L-type voltage-sensitive calcium channel (VSCC) blocker, on the release of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum before and during transient cerebral ischemia in spontaneously hypertensive rats was studied using an in vivo brain dialysis technique. Continuous perfusion of CgTX in the striatum was started 20 min before ischemia and concentrations of dopamine and DOPAC in the dialysate were measured using HPLC with an electro-chemical detector. Before ischemia, both 10 and 100 microM CgTX significantly lowered the concentration of dopamine, to 49% of the basal values. DOPAC concentrations also decreased significantly, by 28 and 17%, respectively. Forebrain ischemia, produced by bilateral carotid artery occlusion, reduced striatal blood flow to less than 6% of the resting value in each group. During 20 min of ischemia, the vehicle group showed a marked increase in dopamine (175 times the basal concentration). In the 10 or 100 microM CgTX perfusion group, in contrast, dopamine release was significantly attenuated, to 38 or 29% of the vehicle group, respectively. DOPAC concentrations decreased during ischemia to 58% of the basal value in the vehicle group and 49% in both CgTX groups. These results indicate that the massive release of striatal dopamine during ischemia depends largely on the influx of extracellular calcium via CgTX-sensitive VSCCs.

Age-related vulnerability to cerebral ischemia in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

We sought to determine the effects of aging on regional cerebral blood flow and ischemic brain damage in transient cerebral ischemia in rats.

METHODS

Five adult (5-6 months) and five aged (18-22 months) female spontaneously hypertensive rats were subjected to 20 minutes of bilateral carotid occlusion and 60 minutes of recirculation under amobarbital anesthesia (100 mg/kg i.p.). Regional cerebral blood flow in the hippocampus and striatum was measured using the hydrogen clearance method. Nine adult and 14 aged rats were subjected to 20 minutes of bilateral carotid occlusion or were sham-operated under ether anesthesia. Seven days after 20 minutes of cerebral ischemia, the rats' brains were perfusion fixed. Ischemic damage in the hippocampus and striatum was graded (0 [normal] to 3 [majority of neurons damaged]).

RESULTS

After 20 minutes of bilateral carotid occlusion, striatal cerebral blood flow decreased to 9.1 +/- 1.5 and 3.9 +/- 2.0 ml/100 g/min in aged and adult rats, respectively, and hippocampal cerebral blood flow decreased to 8.6 +/- 2.4 and 5.7 +/- 2.4 in aged and adult rats, respectively. Although these ischemic cerebral blood flow values were not significantly different between the two age groups, scores for ischemic damage in the hippocampus CA-1 subfield and striatum were significantly higher in aged than in adult rats (p less than 0.05, Kruskal-Wallis' h test with Bonferroni correction).

CONCLUSIONS

We conclude that aging may be a primary factor in the development of greater ischemic neuronal damage observed in aged hypertensive rats.

Effect of blood glucose level in acute cerebral ischemia in spontaneously hypertensive rats--survival and brain pathology

The present study was designed to examine the effect of blood glucose level on survival and pathologic changes of the cortical neuronal cells during and after three-hour incomplete cerebral ischemia, which was induced by bilateral carotid artery ligation in spontaneously hypertensive rats (SHRs). Blood glucose levels were varied by intraperitoneal infusion of 50% glucose (hyperglycemia) or insulin with hypertonic saline (hypoglycemia) or hypertonic saline (normoglycemia). None of the hyperglycemic or normoglycemic animals died during three-hour ischemia, whereas 45% of hypoglycemic animals died (p greater than 0.001). The survival rate for twenty-four hours after recirculation was in the following ascending order: hypoglycemia, normoglycemia, and hyperglycemia. Neither hypoglycemia nor hyperglycemia (38-392 mg/dL) in nonischemic animals developed any morphologic changes in the cerebral cortex. However, both the ischemic and recirculated brains showed various degrees of histologic changes such as shrinkage of the neuronal cells with cytoplasmic vacuoles, perineuronal edema, and swelling of neuropils. Such ischemic damage of the brain was more marked in hypoglycemic animals than in hyperglycemic or normoglycemic ones during ischemia, as well as one hour after recirculation. The results suggest that cerebral ischemia and its outcome become more deleterious in hypoglycemic than in normoglycemic and hyperglycemic states. On the other hand, hyperglycemia is not necessarily a disadvantage in acute cerebral ischemia with or without reperfusion in this model.

[A case of metoclopramide-induced neuroleptic malignant syndrome with cerebrospinal fluid lactic acidosis]

A case of metoclopramide-induced neuroleptic malignant syndrome with cerebrospinal fluid (CSF) lactic acidosis was reported. A 44-year-old Japanese woman noted tarry stool on July 2, 1988 and was treated with metoclopramide and cimetidine for nausea and vomiting. Hydroxyzine pamoate was also administered for insomnia at 3:10 am and she became comatose with muscle rigidity at 3:40-4:30 am on July 3. Tachycardia and high fever (39.5 degrees C) were evident at 8:00 am on July 4. She was transferred to the Kyushu University Hospital. On admission, serum creatine kinase was elevated to 1640 IU/1; MM fraction was 100%. She was diagnosed as malignant syndrome. Cerebrospinal fluid was normocellular with protein 38 mg/dl and glucose 122 mg/dl. Cerebrospinal fluid lactate increased markedly to 3.43 mmol/l, CSF pH was 7.264, HCO3- 14.4 mEq/l, indicating CSF metabolic acidosis. She became afebrile after the 10th hospital day, and gradually but completely recovered within a month. She was discharged on August 16, 1988. The anti-dopaminergic activity of metoclopramide was considered to be primarily responsible for the development of malignant syndrome in this case. Cerebrospinal fluid lactic acidosis seemed to reflect hyperpyrexia or malignant syndrome induced derangement of the brain metabolism.

Prevention of Postanesthetic Shivering with Intravenous Administration of Aspirin

There have been many reports of postanesthetic shivering (PAS); however, the causes have not been defined clearly, and the reported methods of inhibiting PAS are not always available clinically. In the present study, we assessed the effect of the intravenous administration of aspirin on the prevention of PAS in 62 patients undergoing oral or maxillofacial surgery, anesthetized with enflurane-nitrous oxide. Thirty of the patients were randomly selected, and received intravenous aspirin DL-lysine 900 mg (equivalent to aspirin 495 mg) before the end of surgery. No significant differences were noted in the rectal temperatures between the group given aspirin and the control group. Shivering was observed in 17 of the 32 patients of control group. In contrast, shivering was observed in 5 of the 30 patients who received aspirin. This was a statistically significant difference ( P < 0.01). These data indicate that intravenous administration of aspirin significantly inhibited PAS. The finding suggests that PAS is related to prostaglandin synthesis or to the formation of derivatives of arachidonic acid, since aspirin inhibits both the synthesis of prostaglandins and the formation of derivatives of arachidonic acid.

Excitatory and inhibitory amino acid changes in ischemic brain regions in spontaneously hypertensive rats

Excitatory (glutamate, aspartate) or inhibitory amino acids (gamma-aminobutyric acid: GABA, taurine) and glutamine contents were examined in acutely induced cerebral ischemia in spontaneously hypertensive rats. At 20 min ischemia most of these amino acids remained unchanged, but glutamine significantly decreased by 14% in the CA3 hippocampal subfield. At 60 min ischemia glutamate significantly decreased by 14% in the CA3, aspartate by 17-26% in the CA3, cingulate cortex, septum and striatum. In contrast, GABA significantly increased by 48-106% in the cortices (frontal, parietal and cingulate), striatum and nucleus accumbens, but insignificantly in hippocampal subfields. Likewise, taurine increased in the parietal cortex and nucleus accumbens. Glutamine showed heterogeneous changes (increase in the nucleus accumbens and decrease in the CA3). Amino acid levels change during ischemia, but their changes are varied in each area, implying that different reaction of amino acids may explain the selective vulnerability to cerebral ischemia.

Cerebral blood flow and oxygen metabolism in patients with vascular dementia of the Binswanger type

We performed clinical and neuroradiologic studies, including positron emission tomography, in five patients with vascular dementia of the Binswanger type. The clinical features of these cases consisted of slowly progressive dementia, together with vascular risk factors such as hypertension and often a history of minor stroke, and characteristic white matter lesions on brain computed tomograms or magnetic resonance images. Digital subtraction angiography of the cervical and intracranial arteries demonstrated no occlusive lesion in any patient. Both cerebral blood flow and the cerebral metabolic rate for oxygen were markedly reduced in the white matter (54-77% of control values), and both were decreased in the parietal (73% of control), frontal (74-80%), and temporal (74-83%) cortices, where no abnormalities were detected by brain computed tomography or magnetic resonance imaging. We conclude that vascular dementia of the Binswanger type may be caused by disconnection between the cerebral cortex and subcortical structures due to ischemic damage in the white matter.

[Monoamine contents and norepinephrine turnover in brain stem nuclei of young and adult spontaneously hypertensive and Wistar-Kyoto rats]

To investigate the brain stem monoamine mechanism in the development and maintenance of hypertension of spontaneously hypertensive rats (SHR), we determined monoamine contents and norepinephrine turnover in discrete brain stem nuclei which are known to relate with cardiovascular control. Specific areas and brain stem nuclei were dissected from serial frozen slices of 300 microns thickness according to the atlas of Palkovits and Jacobowitz. The dissected tissues were homogenized, centrifuged and the supernatants were injected into high performance liquid chromatography with electrochemical detection (HPLC-ECD). Norepinephrine (NE), dopamine (DA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) contents were determined. NE turnover was also determined 2 hour after alpha-methyl-p-tyrosine administration (250 mg/kg, i.p.). In 4-week old SHR, the only significant change observed was decreased NE contents in the nucleus tractus solitarii (NTS). Such decreases in NE contents of the NTS were also found in 8- and 16-week old SHR. However, there were no differences in NE turnover in the NTS between SHR and WKY. Increased NE contents were found in the A1, A5, and nucleus reticularis gigantocellularis (RG) in the later stages (8 and 16 weeks) in SHR. Furthermore, increased NE turnover was seen in the RG of SHR at 16-week old, indicating increased neuronal activity. Dopamine, 5-HT and 5-HIAA showed no consistent changes between SHR and WKY. Increased NE levels were observed in later stages after development of hypertension, suggesting the increased NE in adult SHR may represent a central adaptive change secondary to the established hypertension. Since increased NE levels were consistently found in or around the regions which are known as vasomotor centers, we assume that these increased NE might serve to maintain hypertension or to inhibit a further increase in blood pressure. In contrast, the NE contents were decreased with constant turnover in NTS of SHR aged 4, 8, and 16 weeks. Constant turnover in NE could not compensate for reduced NE in NTS and may lead to a functional reduction or reduced noradrenergic activity. This defect in intrinsic noradrenergic neurons in NTS may trigger the development of genetic hypertension in SHR. In conclusion, the present results demonstrate that NE levels of SHR in the NTS were consistently decreased compared with those of WKY in all age groups. In later stages, increased NE levels were observed in A1, A5 and RG of SHR. These results indicate that brain stem monoamine system, especially noradrenergic neurons, contributes to the development and maintenance of hypertension in SHR.

Hindbrain ischemia produced by bilateral vertebral artery occlusion and moderate hypotension in spontaneously hypertensive rats

Hindbrain ischemia was induced by bilateral vertebral artery occlusion and moderate hypotension in spontaneously hypertensive rats (SHRs). Mean arterial blood pressure was lowered to 80 mmHg in SHRs and to 50 mmHg in Wistar-Kyoto rats (WKYs) by a controlled hemorrhage, and then the vertebral artery was bilaterally occluded through alar foramina of the first cervical vertebra. Following vertebral occlusion, blood flow of the cerebellum was significantly decreased to 9.4 +/- 2.0 mL/100g/min (+/- SEM) while flow of the cerebrum remained at 32.1 +/- 5.4 in SHRs. In contrast, cerebellar blood flow in WKYs was preserved at 24.2 +/- 2.9 mL/100g/min. Brain lactate, pyruvate, and adenosine triphosphate (ATP) were determined in SHRs after sixty minutes of hypotension with or without vertebral occlusion. Although infratentorial metabolites were actually unaltered in rats with hypotension alone, infratentorial lactate and lactate/pyruvate ratio significantly increased to 14.38 +/- 3.61 mmol/kg and 67.7 +/- 12.1, respectively, with a concomitant decrease in ATP in SHRs with hypotension and vertebral occlusion. Bilateral vertebral artery occlusion, together with moderate hypotension, was shown to produce a marked reduction of cerebellar blood flow and to induce ischemic metabolic changes in the infratentorial brain in SHRs.

Regional distribution of DNA and RNA in rat brain: a sensitive determination using high-performance liquid chromatography with electrochemical detection

DNA and RNA contents in 20 brain regions or nuclei of the rat were determined by a highly sensitive method using high-performance liquid chromatography with electrochemical detection. The high DNA and RNA contents were found in the hypothalamic nuclei, especially the median eminence-arcuate nucleus. These results may be available for the preparation of nucleic acids as the regional control.

Striatal glutamic acid and gamma-aminobutyric acid in transient cerebral ischemia in spontaneously hypertensive rats

A massive striatal dopamine release (241-fold increase) was observed in a previous study during acute cerebral ischemia in rats. In this study, extracellular levels of glutamic acid (GLU), gamma-aminobutyric acid (GABA) and lactic acid were simultaneously determined using in vivo brain dialysis in the striatum of spontaneously hypertensive rats during cerebral ischemia and after recirculation. Extracellular GABA levels increased to 932 +/- 75% (mean +/- SEM) of the resting level and GLU increased to 390 +/- 63% during 20 min ischemia. Although ischemia-induced release of GLU and GABA was demonstrated in this study, the degree of increase was smaller than that of dopamine. These findings may be relevant to the pathophysiology of cerebral ischemia in the striatum.

Ischemic flow threshold for striatal dopamine release in rats

To determine the level of cerebral blood flow reduction which causes striatal dopamine release, extracellular dopamine and cerebral blood flow was simultaneously determined using in vivo brain dialysis and a hydrogen clearance method, respectively, in the striatum of spontaneously hypertensive rats before and during experimental cerebral ischemia. The ischemic flow threshold for neurotransmitter dopamine release was found to be 20% of the resting value or 8-10 ml/100g/min of cerebral blood flow, being similar to those for energy and membrane failures.

Acute effects of antihypertensive agents on cerebral blood flow in hypertensive rats

The acute effects of various antihypertensive agents on cerebral blood flow and mean arterial pressure (MAP) were studied in anesthetized (amobarbital 100 mg/kg) spontaneously hypertensive rats. Cerebral blood flow in the cortex and thalamus was measured by the hydrogen clearance method before and during a 60-min i.v. infusion of calcium antagonist (nifedipine), angiotensin converting enzyme inhibitor (captopril) or beta-blocker (propranolol). Nifedipine, 30 or 150 micrograms/kg per h, decreased dose dependently the MAP by 20 or 31%, and concomitantly increased cortical blood flow by 28 or 74%, and thalamic blood flow by 51 or 64%, respectively. Captopril, 10 or 100 mg/kg per h, decreased MAP by 7 or 14%, but changed cerebral blood flow minimally. In contrast, propranolol, 1.0 or 5.0 mg/kg per h, decreased MAP by 13 or 11%, with a concomitant reduction of cortical and thalamic blood flow by 20 or 15 and 33 or 37%, respectively. It is concluded that the changes in cerebral blood flow in response to hypotension are varied by antihypertensive drugs depending on the direct or indirect effect of the drugs (dilatation or constriction) on cerebral vessels. Nifedipine seems to dilate while propranolol constricts cerebral vessels.

Cerebral blood flow and metabolism in normotensive and hypertensive patients with transient neurologic deficits

We used positron emission tomography to examine retrospectively the effects of blood pressure on regional cerebral blood flow and oxygen metabolism in seven normotensive and eight hypertensive patients with a history of transient neurologic deficits. In the hypertensive patients, a decrease in regional cerebral blood flow was closely related to blood pressure; these changes were most pronounced in the supratentorial structures, especially the striatum and thalamus. In contrast, the regional cerebral metabolic rate for oxygen was less related to blood pressure. Consequently, the regional oxygen extraction fraction was increased in the hypertensive patients, while regional cerebral blood volume and the regional cerebral blood flow volume ratio were unchanged. Multivariate regression analysis confirmed that hypertension was an independent factor affecting regional cerebral blood flow. The analysis also disclosed that age, sex, hematocrit, smoking, and PaCO2 affected regional cerebral blood flow. These findings suggest that the hemodynamic reserve in hypertensive individuals is reduced, which may predispose them to cerebral ischemia and perhaps stroke, even during small decreases in cerebral perfusion pressure.

Effect of thromboxane synthetase inhibitor on cerebral circulation and metabolism during experimental cerebral ischemia in spontaneously hypertensive rats

The protective effect of thromboxane synthetase inhibitor, OKY-046, on brain ischemia was studied in spontaneously hypertensive rats. Cerebral ischemia was developed by bilateral carotid artery ligation (BCL) for 1 or 3 h and thereafter, circulation was restored for 15 min. OKY-046, 5 or 30 mg/kg, or saline as control was administered i.v. before BCL. Neither blood pressure nor blood gases were altered by OKY-046 or saline injection. During BCL, cerebral cortical blood flow was reduced to 25 and 15% of the resting value at 30 and 60 min, respectively, and these changes were not different among the groups. In rats with ischemia longer than 1 h, the blood flow was well preserved by OKY-046, 30 mg/kg, to 10-17% of the resting level, thus significantly higher than that (less than 5%) in non-treated rats. After 15 min recirculation, the supratentorial lactate level was lower and adenosine triphosphate (ATP) was higher in OKY-046-treated rats than in the saline-treated ischemic rats. Plasma thromboxane B2 was increased markedly in 1 h ischemic-reperfused rats without treatment and the increase was almost completely inhibited by OKY-046. In contrast, 6-keto-prostaglandin F1 alpha was increased 8.5-fold after ischemia and the increase was not affected by the treatment. OKY-046 seems to have an antiischemic effect on acutely induced cerebral ischemia. Selective inhibition of thromboxane A2 production and an inversely high level of prostaglandin I2 may be an important contribution to protection of the microcirculation during ischemia and preservation of ischemic cerebral metabolism.

[A case of a two-chambered right ventricle associated with aneurysm of the sinus of Valsalva]

A 51-year-old male with a two-chambered right ventricle associated with an aneurysm of sinus of Valsalva, who underwent successful surgical repair without ventriculotomy, is reported. Preoperative right ventriculogram revealed that the right ventricle was divided by the anomalous muscle bundle, and the aneurysm of sinus of Valsalva growing from the right coronary sinus protruded just below the pulmonary valve. The right ventricular pressure was 107/10 mmHg and the pressure gradient between the right ventricle and the pulmonary artery was 88 mmHg. Trans-pulmonary arterial resection of the aneurysm of Valsalva sinus was performed and the anomalous muscle bundle was successfully removed through the pulmonary arteriotomy and the right atrial incision. Post-operative right ventricular pressure dropped to 42 mmHg, and there was no stenosis in the right ventricle.

[A case of 72-year-old female with congenital esophago-bronchial fistula]

A 72-year-old female with congenital esophago-bronchial fistula is reported. She had complained of cough attack during meals and repeated pneumonia since childhood. A chest x-ray film showed chronic bronchitis in the right lower lung field. Esophagogram revealed a fistula between the esophagus and the right lower lobe bronchus. Resection of the right lower lobe and removal of the fistulous tract were successfully performed. Histological examination of the resected fistula with slight inflammatory change showed muscle layer and transitional zone between the stratified squamous epithelium of esophagus and the ciliated columnar epithelium of bronchus. This is the oldest case in the Japanese literature.

Cerebrospinal fluid lactate in patients with diabetes mellitus and hypoglycaemic coma

Cerebrospinal fluid (CSF) lactate and pyruvate concentrations were determined in 20 patients with diabetes mellitus but without disturbance of consciousness and five who recovered from hypoglycaemic coma. CSF lactate was slightly but significantly higher in diabetes mellitus (1.78, SEM 0.04 m mol/l) than that in 15 control subjects (1.40, SEM 0.05 m mol/l). In those who recovered from hypoglycaemic coma, CSF lactate was markedly elevated to 2.45-4.43 m mol/l. CSF glucose concentrations, however, were substantially the same between treated hypoglycaemic and diabetes mellitus groups. These findings indicate that CSF lactate levels increase with glycaemic levels in diabetes mellitus owing to enhanced glucose influx into glycolytic pathway of the brain, and also increases in treated hypoglycaemic coma probably due to mitochondrial dysfunction or damage.

[Coronary bypass surgery in patients 70 years of age and older]

Twenty-six patients 70 years of age and older who underwent elective coronary artery bypass grafting were analyzed. These patients were compared with 76 patients under 70 years of age. The results obtained were as follows. The aged group had significantly greater incidences of preoperative pulmonary and renal complications. Preoperative cardiac function in the aged group was not different from that in the younger one. The incidence of left main trunk stenosis among the aged group (31%) was twice that in the younger one (15%). Then mean number of grafts was 3.0 in both groups. There were no significant differences in the operation time, anoxic arrest time, and extracorporeal circulation time between these two groups. Although the operative mortality rate in the aged group (11.5%) was higher than that (2.6%) in the younger one, the difference was not significant. Postoperative cerebral, respiratory and renal complications were more common in the aged group. However, the incidences of these complications were not different between these two groups. Surgical mortality and morbidity were improved in the latter half of the patients of the aged group, in whom only one operative death was observed and there was no life-threatening postoperative complication. Symptomatic improvements in survivors were remarkable. Thus, we conclude that coronary artery bypass grafting can be performed with acceptable risk in patients 70 years of age and older.

[A case of coexisting descending thoracic aortic aneurysm and atypical aortic coarctation treated successfully by surgery using the thromboexclusion method]

The thromboexclusion method was successfully applied to a 43-year-old male with aortitis syndrome. Preoperative aortogram showed a fusiform aneurysm of the descending aorta just below the left subclavian artery and atypical coarctation of the descending aorta distal to this aneurysm. Pressure gradient across the stenosis was about 70 mmHg. The technique of flow reversal and thromboexclusion was performed in this patient because of severe calcification in the aortic arch and the entire descending aorta. A long extra-anatomical bypass between the ascending aorta and the infrarenal abdominal aorta was made, and a permanent aortic clamp was placed across the aorta at the left subclavian artery. Hypertension in the arm disappeared immediately after the operation, and postoperative catheterization revealed no pressure gradient between the ascending and the abdominal aorta. Computed tomogram performed 18 days after the operation and aortogram done 44 days postoperatively disclosed thrombi formation in the aneurysm.

Involvement of brain stem noradrenergic neurons in the development of hypertension in spontaneously hypertensive rats

This study attempted to investigate the possible involvement of the brain stem noradrenergic system in the development of hypertension in spontaneously hypertensive rats. Steady-state norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid concentrations and norepinephrine turnover were determined in the individual brain stem nuclei using high performance liquid chromatography with electrochemical detection. Decreased norepinephrine contents in the nucleus tractus solitarii in spontaneously hypertensive rats compared with Wistar-Kyoto rats at the age of 4, 8, and 16 weeks were demonstrated. In later stages (8 and 16 weeks), increased norepinephrine levels were observed in the nucleus reticularis gigantocellularis, the A1 and A5 areas. Norepinephrine turnover was not different between spontaneously hypertensive rats and Wistar-Kyoto rats in the nucleus tractus solitarii at the age of 4 and 16 weeks and increased in the nucleus reticularis gigantocellularis of spontaneously hypertensive rats at 16 weeks. Our results indicate that altered norepinephrine metabolism in the specific brain stem nuclei, especially the consistently decreased norepinephrine in the nucleus tractus solitarii of spontaneously hypertensive rats, contribute to the development of genetic hypertension.