Preemptive visceral analgesic effect of thoracic paravertebral block on postoperative opioid consumption in patients undergoing laparoscopic cholecystectomy: a prospective, randomized, assessor-blind study / 대한마취과학회지

Background@#The preemptive visceral analgesic effect of regional nerve block has not been adequately investigated to date. We evaluated the preemptive visceral analgesic effect of thoracic paravertebral block (TPVB) in patients undergoing laparoscopic cholecystectomy (LC) in whom pre-incisional rectus sheath block (RSB) was used to minimize somatic surgical pain. @*Methods@#In this prospective, randomized, assessor-blind study, 70 patients scheduled for elective LC were randomly assigned to the pre-TPVB (n = 35) or the post-TPVB (n = 35) group. Both groups received pre-incisional RSB, and patients in the pre-TPVB group received TPVB before skin incision while those in the post-TPVB group received TPVB after skin closure. The primary outcome was the total rescue analgesic consumption (morphine equianalgesic dose) during the 24 h post-surgery. The secondary outcomes were the cumulative analgesic consumption and pain intensity for 24 h after surgery, and adverse events. @*Results@#Pre-TPVB significantly reduced total rescue analgesic consumption (estimated mean [95% CI]) during the 24 h after surgery than post-TPVB (16.9 [14.5, 19.3] vs. 25.3 [22.8, 27.7] mg, estimated difference: -8.3 [-11.8, -4.9], P < 0.001). The cumulative rescue analgesic consumption was significantly lower in the pre-TPVB group from 2–24 h after surgery (P < 0.001). The postoperative pain intensity was significantly lower in the pre-TPVB group as well at 0.5–6 h after surgery. There were no adverse events in both groups. @*Conclusions@#Pre-incisional TPVB conferred a significant preemptive visceral analgesic effect in patients undergoing LC, and significantly reduced the amount of postoperative opioid consumption.

Current clinical application of dantrolene sodium

Dantrolene sodium (DS) was first introduced as an oral antispasmodic drug. However, in 1975, DS was demonstrated to be effective for managing malignant hyperthermia (MH) and was adopted as the primary therapeutic drug after intravenous administration. However, it is difficult to administer DS intravenously to manage MH. MH is life-threatening, pharmacogenomically related, and induced by depolarizing neuromuscular blocking agents or inhalational anesthetics. All anesthesiologists should know the pharmacology of DS. DS suppresses Ca2+ release from ryanodine receptors (RyRs). RyRs are expressed in various tissues, although their distribution differs among subtypes. The anatomical and physiological functions of RyRs have also been demonstrated as effective therapeutic drugs for cardiac arrhythmias, Alzheimer’s disease, and other RyR-related diseases. Recently, a new formulation was introduced that enhanced the hydrophilicity of the lipophilic DS. The authors summarize the pharmacological properties of DS and comment on its indications, contraindications, adverse effects, and interactions with other drugs by reviewing reference articles.

Effects of hydrocortisone-presensitized sugammadex on recovery from neuromuscular blockade induced by rocuronium: a rodent in vivo study

Sugammadex is a specific antagonist of aminosteroidal neuromuscular blocking agents with 1:1 binding to guest molecules. Sugammadex can also bind to other drugs having a steroid component in its chemical structure. In this in vivo experiment, we investigated the differences in the recovery of rocuronium-induced neuromuscular blockade using sugammadex pre-exposed with two different concentrations of hydrocortisone. Methods: The sciatic nerves and tibialis anterior muscles of 30 adult Sprague–Dawley rats were prepared for the experiment. The sciatic nerves were stimulated using a train-of-four (TOF) pattern with indirect supramaximal stimulation at 20 s intervals. After 15 min of stabilization, a 250 μg loading dose and 125 μg booster doses of rocuronium were serially administered until > 95% depression of the first twitch tension of TOF stimulation (T1) was confirmed. The study drugs were prepared by mixing sugamadex with the same volume of three different stock solutions (0.9% normal saline, 10 mg/ml hydrocortisone, and 100 mg/ ml hydrocortisone). The recovery of rats from neuromuscular blockade was monitored by assessing T1 and the TOF ratio (TOFR) simultaneously until T1 was recovered to > 95% and TOFR to > 0.9. Results: In the group injected with sugammadex premixed with a high concentration of hydrocortisone, statistically significant intergroup differences were observed in the recovery progression of T1 and TOFR (P < 0.050). Conclusions: When sugammadex was pre-exposed to a high dose of hydrocortisone only, recovery from neuromuscular blockade was delayed. Delayed recovery from neuromuscular blockade is not always plausible when sugammadex is pre-exposed to steroidal drugs.

Effects of different sugammadex doses on the train of four ratio recovery progression during rocuronium induced neuromuscular blockade in the rat phrenic nerve hemidiaphragm / 대한마취과학회지

Background@#In this study, we used an ex-vivo model to investigate the recovery pattern of both the train-of-four (TOF) ratio and first twitch tension of TOF (T1), and determined their relationship during recovery from rocuronium-induced neuromuscular blockade at various concentrations of sugammadex. @*Methods@#Tissue specimens of the phrenic nerve-hemidiaphragm were obtained from 60 adult Sprague-Dawley rats. Each specimen was immersed in an organ bath filled with Krebs buffer solution and stimulated with the TOF pattern using indirect supramaximal stimulation at 20-second intervals. After a 30-minute stabilization period, rocuronium loading and booster doses were serially administered at 10-minute intervals in each sample until > 95% depression of T1 was confirmed. Specimens were randomly allocated to either the control group (washout) or to one of five sugammadex concentration groups (0.75, 1, 2, 4, or 8 times equimolar doses of rocuronium to produce >95% T1 depressions; SGX0.75, SGX1, SGX2, SGX4, and SGX8, respectively). Recovery from neuromuscular blockade was monitored using T1 and the TOF ratio simultaneously until the recovery of T1 to > 95% and the TOF ratio to > 0.9. @*Results@#Statistically significant intergroup differences were observed between the recovery patterns of T1 and the TOF ratio (TOFR, p<0.050), except between SGX2 and SGX4 groups. TOFR/T1 values were maintained at nearly 1 in the control, SGX0.75, and SGX1 groups; however, they were exponentially decayed in the SGX2, SGX4, and SGX8 groups. @*Conclusions@#Recovery of the TOF ratio may be influenced by the sugammadex dose, and a TOF ratio of 1.0 may be achieved before full T1 recovery if administration of sugammadex exceeds that of rocuronium.

Malignant hyperthermia and dantrolene sodium / 대한마취과학회지

No abstract available.

Current use of neuromuscular blocking agents and antagonists in Korea: a 2018 survey

BACKGROUND: Neuromuscular blocking agents (NMBAs) and neuromuscular monitoring in anesthetic management are integral for endotracheal intubation, better visualization of the surgical field, and prevention of residual neuromuscular blockade and pulmonary complications. Sugammadex is a drug that reduces risk of residual neuromuscular blockade, with more rapid recovery compared to anticholinesterase. The purpose of this study was to investigate current usage status of NMBAs and antagonist with neuromuscular monitoring, among anesthesiologists in Korea.METHODS: Anesthesiologists working in Korea were invited to participate in an online survey via email January 2–February 28, 2018. The questionnaire consisted of 45 items, including preferred NMBAs, antagonists, neuromuscular monitoring, and complications related to the use sugammadex. A total of 174 responses were analyzed.RESULTS: Rocuronium was a commonly used NMBA for endotracheal intubation (98%) of hospitals, and maintenance of anesthesia (83.3%) in of hospitals. Sugammadex, pyridostigmine, and neostigmine were used in 89.1%, 87.9%, and 45.4% of hospitals. Neuromuscular monitoring was employed in 79.3% of hospitals; however only 39.7% of hospitals used neuromuscular monitoring before antagonist administration. Usual dosage range of sugammadex was 2.1–4 mg/kg in 35.1% of hospitals, within 2 mg/kg in 34.5% of hospitals, and 1 vial regardless of body weight in 22.4% of hospitals. Sugammadex-related complications were encountered by 14.9% of respondents.CONCLUSIONS: This survey indicates several minor problems associated with the use of antagonists and neuromuscular monitoring. However, most anesthesiologists appear to have appropriate information regarding the usage of NMBAs and sugammadex.

Blind nasal intubation as an alternative to difficult intubation approaches

Airway difficulties are a major concern for anesthesiologists. Even though fiberoptic intubation is the generally accepted method for management of difficult airways, it is not without disadvantages-requires patient cooperation, and cannot be performed on soiled airway or upper airways with pre-existing narrowing pathology. Additionally, fiberoptic bronchoscopy is not available at every medical institution. In this case, we encountered difficult airway management in a 71-year-old man with a high Mallampati grade and a thick neck who had undergone urologic surgery. Several attempts, including a bronchoscope-guided intubation, were unsuccessful. Finally, blind nasal intubation was successful while the patient's neck was flexed and the tracheal cartilage was gently pressed down. We suggest that blind nasal intubation is a helpful alternative in difficult airway management and it can be a lifesaving technique in emergencies. Additionally, its simplicity makes it a less expensive option when advanced airway technology (fiberoptic bronchoscopy) is unavailable.

Blind nasal intubation as an alternative to difficult intubation approaches

Airway difficulties are a major concern for anesthesiologists. Even though fiberoptic intubation is the generally accepted method for management of difficult airways, it is not without disadvantages-requires patient cooperation, and cannot be performed on soiled airway or upper airways with pre-existing narrowing pathology. Additionally, fiberoptic bronchoscopy is not available at every medical institution. In this case, we encountered difficult airway management in a 71-year-old man with a high Mallampati grade and a thick neck who had undergone urologic surgery. Several attempts, including a bronchoscope-guided intubation, were unsuccessful. Finally, blind nasal intubation was successful while the patient's neck was flexed and the tracheal cartilage was gently pressed down. We suggest that blind nasal intubation is a helpful alternative in difficult airway management and it can be a lifesaving technique in emergencies. Additionally, its simplicity makes it a less expensive option when advanced airway technology (fiberoptic bronchoscopy) is unavailable.

Spectral analysis of respiratory-related hemodynamic variables in simulated hypovolemia: a study in healthy volunteers with spontaneous breathing using a paced breathing activity / 대한마취과학회지

BACKGROUND: A dynamic preload index such as stroke volume variation (SVV) is not as reliable in spontaneous breathing (SB) patients as in mechanically ventilated patients. This study examined the hypothesis that spectral analysis of hemodynamic variables during paced breathing (PB) activity may be a feasible index of volume changes and fluid responsiveness, despite insufficient respiratory changes in the preload index during SB activity. METHODS: Blood pressure and stroke volume (SV) were measured in 16 subjects undergoing PB (15 breaths/min), using a Finometer device and the Modelflow method. Respiratory systolic pressure variation (SPV) and SVV were measured and respiratory frequency (RF, 0.2-0.3 Hz) of power spectra of SPV (SPV(RF)) and SVV (SVV(RF)) were computed using fast Fourier transformation. Progressive hypovolemia was simulated with lower body negative pressure (LBNP). Volume challenges were produced by infusion of normal saline and subsequent release of LBNP to baseline. Fluid responsiveness, defined as a >20% increase in SV, was assessed by the area under the curve (AUC) of receiver operating characteristic curves. RESULTS: Graded hypovolemia caused a significant increase in SPV(RF) and a decrease in SVV(RF). During volume expansion, SPV(RF) decreased and SVV(RF) rose significantly. Fluid responsiveness was better predicted with SVV(RF) (AUC 0.75) than with SPV(RF), SPV, or SVV. SVV(RF) before volume challenge was significantly correlated with volume expansion-induced changes in SV (r = -0.64). CONCLUSIONS: These results suggest that RF spectral analysis of dynamic preload variables may enable the detection of volume change and fluid responsiveness in SB hypovolemic patients performing PB activity.

The Effects of Superior Cervical Sympathetic Ganglion Block on the Acute Phase Injury and Long Term Protection against Focal Cerebral Ischemia/Reperfusion Injury in Rats / 대한통증학회지

BACKGROUND: Cerebral blood vessels are innervated by sympathetic nerves from the superior cervical ganglia (SCG), and these nerves may influence the cerebral blood flow. The purpose of the present study was to evaluate the neuroprotective effect of superior cervical sympathetic ganglion block in rats that were subjected to focal cerebral ischemia/reperfusion injury. METHODS: Eighty male Sprague-Dawley rats (270-320 g) were randomly assigned to one of two groups (the ropivacaine group and a control group). In all the animals, brain injury was induced by middle cerebral artery (MCA) reperfusion that followed MCA occlusion for 2 hours. The animals of the ropivacaine group received 30microl of 0.75% ropivacaine, and their SCG. Neurologic score was assessed at 1, 3, 7 and 14 days after brain injury. Brain tissue samples were then collected. The infarct ratio was measured by 2.3.5-triphenyltetrazolium chloride staining. The terminal deoxynucleotidyl transferase mediated dUTP-biotin nick-end labeled (TUNEL) reactive cells and the cells showing caspase-3 activity were counted as markers of apoptosis at the caudoputamen and frontoparietal cortex. RESULTS: The death rate, the neurologic score and the infarction ratio were significantly less in the ropivacaine group 24 hr after ischemia/reperfusion injury. The number of TUNEL positive cells in the ropivacaine group was significantly lower than those values of the control group in the frontoparietal cortex at 3 days after injury, but the caspase-3 activity was higher in the ropivacaine group than that in the control group at 1 day after injury. CONCLUSIONS: The study data indicated that a superior cervical sympathetic ganglion block may reduce the neuronal injury caused by focal cerebral ischemia/reperfusion, but it may not prevent the delayed damage.

The Effects of Temperature Monitoring Methods and Thermal Management Methods during Spinal Surgery / 대한마취과학회지

BACKGROUND: The precise measurement of body temperature during anesthesia is important to prevent hypothermia.The aim of this study was to compare the urinary bladder temperature to the esophageal, nasopharyngeal, rectal and skin temperatures, and to compare three heating methods during spine surgery. METHODS: Forty-two patients with ASA physical status I-II, who were scheduled to undergo spine surgery in the prone position, were included in this study.The patients were randomly divided into 4 groups:Group I was treated without any heating methods; group 2, with fluid-warmers; group 3, with forced air-warmers; and group 4, with a combination of both heating methods.After the induction of anesthesia, the esophageal, nasopharyngeal, rectal, urinary bladder and skin temperature was monitored every 15 minute for 3 hours.The urinary bladder temperature was compared to the esophageal, nasopharyngeal, rectal and skin temperatures. RESULTS: The urinary bladder temperature was found to be higher than the esophageal and the nasopharyngeal temperatures (P < 0.01).The urinary bladder temperature of group 3 was higher than that of group 1 at 180 minutes after induction of anesthesia (P < 0.05).The urinary bladder temperature of group 4 was higher than that of group 1 at 150 minutes (P < 0.05), as well as at 165 and 180 minutes (P < 0.05).The skin temperatures of groups 3 and 4 were higher than group 1 (P < 0.001). CONCLUSIONS: The urinary bladder temperature was higher than the esophageal temperature and correlated with the esophageal, nasopharyngeal and rectal temperatures.During spine surgery in the prone position, a forced air-warmer was found to be the most effective but a combination of all the methods tested was found to be even more effective.

Effect of Superior Cervical Sympathetic Ganglion Block on Brain Injury Induced by Focal Cerebral Ischemia/Reperfusion in a Rat Model / 대한통증학회지

BACKGROUND: Cerebral blood vessels are innervated by sympathetic nerves that originate in the superior cervical ganglia (SCG). This study was conducted to determine the effect of an SCG block on brain injury caused by focal cerebral ischemia/reperfusion in a rat model. METHODS: Male Sprague-Dawley rats (270-320 g) were randomly assigned to one of three groups (lidocaine, ropivacaine, and control). After brain injury induced by middle cerebral artery (MCA) occlusion/reperfusion, the animals were administered an SCG bloc that consisted of 30 microliter of 2% lidocaine or 0.75% ropivacaine, with the exception of animals in the control group, which received no treatment. Twenty four hours after brain injury was induced, neurologic scores were assessed and brain samples were collected. The infarct and edema ratios were measured, and DNA fragmented cells were counted in the frontoparietal cortex and the caudoputamen. RESULTS: No significant differences in neurologic scores or edema ratios were observed among the three groups. However, the infarct ratio was significantly lower in the ropivacaine group than in the control group (P<0.05), and the number of necrotic cells in the caudoputamen of the ropivacaine group was significantly lower than in the control group (P<0.01). Additionally, the number of necrotic and apoptotic cells in theropivacaine group were significantly lower than inthe control group in both the caudoputamen and the frontoparietal cortex (P<0.05). CONCLUSIONS: Brain injury induced by focal cerebral ischemia/reperfusion was reduced by an SCG block using local anesthetics. This finding suggests that a cervical sympathetic block could be considered as another treatment option for the treatment of cerebral vascular diseases.

The Effect of Sevoflurane Anesthesia on the Phase Relationship between Systolic Blood Pressure and Heart Rate / 대한마취과학회지

BACKGROUND: The phase relationship indicates the time delay between the input signal (systolic blood pressure, SBP) and output signal (R-R interval, RRI). In contrast to the awake state, little is known about the effects of general anesthesia on the phase shift. In the present study, we tested the hypothesis that sevoflurane anesthesia causes a phase change between the two signals. METHODS: We assessed changes in phase, coherence, and baroreflex sensitivity between SBP and RRI by the use of transfer function analysis in 50 ASA 1 patients during the awake state and during end-tidal 2% sevoflurane-50% N2O anesthesia. RESULTS: SBP and RRI decreased significantly during sevoflurane anesthesia (P < 0.001). The phase in the low frequency (LF) region remained unchanged, but the phase in the high frequency (HF) region changed significantly from -29.52 +/- 50.70 to 27.28 +/- 80.22 degrees during sevoflurane anesthesia (P < 0.001). Coherence and baroreflex sensitivity between the two signals in the LF and HF regions decreased significantly during sevoflurane anesthesia (P < 0.001, respectively). CONCLUSIONS: We found that in the HF region and not in the LF region, sevoflurane anesthesia provokes the shift of the SBP-RRI phase relationship, suggesting that this change is inconsistent with a vagally mediated response.

Unexpected Massive Bleeding during Liver Transplantation in Patients with Budd-Chiari Syndrome: A case report / 대한마취과학회지

Budd-Chiari syndrome (BCS) is a heterogenous group of disorders characterized by obstruction of hepatic venous outflow. Severe liver cirrhosis and limited cardiac reserve in patients with BCS makes them less tolerant to liver transplantation. We experienced two cases of massive bleeding during living donor liver transplantation in patients with BCS. Blood products and fluids were rapidly infused with a rapid infusion system, final infusion volume in these two patients were 177 L and 193 L, and the use of Cell Savers allowed for the patient's blood products to be saved. The patients were managed successfully and recovered uneventfully with advanced monitoring, including monitoring of their jugular venous oxygen saturation and continuous cardiac output. Therefore, rapid infusion systems and Cell Savers, along with advanced monitoring, are necessary in the event of massive bleeding during liver transplantation.

The Protective Effect of Ischemic and Hypoxic Preconditioning on Hypoxic-ischemic Brain Injury in the Neonatal Rat: 1H Magnetic Resonance Spectroscopic Study / 대한마취과학회지

BACKGROUND: A brief episode of cerebral ischemia confers transient ischemic tolerance to a subsequent ischemic challenge. We examined the effect of ischemic and hypoxic preconditioning in the neonatal rat. METHODS: Seven-day old Sprague-Dawley rat pups were divided into three groups:control (n = 53), ischemic preconditioning (n = 51), and hypoxic preconditioning (n = 48). For ischemic preconditioning, the right common carotid artery was occluded for 10 min. Rats in the hypoxic preconditioning group were kept under hypoxic (8% oxygen/92% nitrogen) conditions for 4h. Twenty-four hours after the preconditioning, rats from all groups were exposed to the right common carotid artery ligature, followed by 2.5 h of hypoxia. Lipid/N-acetyl aspartate (Lip/NAA) and lipid/creatine (Lip/Cr) ratios from 1H MR spectroscopy and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) were evaluated as measures of apoptosis 1 and 7 days after hypoxic-ischemic injury. RESULTS: In the ischemic and hypoxic preconditioning groups, the Lip/NAA and Lip/Cr ratios and the numbers of TUNEL-positive cells were significantly lower than those in the control group (P < 0.05), but there were no significant differences between the two preconditioning groups. CONCLUSIONS: These results suggest that ischemic and hypoxic preconditioning in the neonatal rat attenuate the apoptosis that is caused by hypoxic-ischemic brain injury.

Influence of Repeated Exposures to Hypobaric Chamber on Acute Hypoxia Tolerance / 항공우주의학회지

BACKGROUND: Acute hypoxia tolerance has been evaluated by the time of useful consciousness, subjective symptoms, cardiovascular changes, visual deterioration, psychological performance, and so forth. But these methods are either subjective, lacking strict objectivity, or too demanding to collect sufficient data. Pulse oximeter monitoring has come to be used not only in hospitals but in the aviation environment. This noninvasive oxygen monitoring apparatus warrants a highly objective analysis to investigate acute hypoxia tolerance. METHODS: Eight healthy male volunteers (20-25 years old) were exposed three times to a simulated altitude of 25,000 ft (7,620 m) at intervals of 7 days. We monitored arterial oxygen saturation (SaO2) and pulse rate by a pulse oximeter. The duration from taking the mask off to the time of 60% SaO2 was regarded as acute hypoxia tolerance. The venous hemoglobin concentration was measured a day before exposure to hypoxia. A questionnaire on the 14 subjective hypoxic symptoms was obtained after hypobaric chamber training. RESULTS: There were neither differences of acute hypoxia tolerance, hemoglobin concentration, nor pulse rate according to the repeated exposure of hypoxia. Four symptoms of sleepiness, fatigue, flushing and thinking impairment were sustained regardless of repeated exposures to hypoxia. But the incidence of symptoms of ear pain, anxiety, abdominal pain were reduced according to the repeated hypoxia. CONCLUSION: With pulse oximeter monitoring there was no difference between the values of time of 60% SaO2 in repeated exposures to hypoxia. The incidence of some subjective symptoms was reduced according to the repeated exposures to hypoxia.

Spinal Symptoms in Aviators and Their Relationship to Aircraft Types / 항공우주의학회지

BACKGROUND: By frequent G-exposures cervical and lumbar spinal symptoms may be the factors to limit their flying performance and causes of acute and chronic spinal diseases. We examined not only the frequency and degree of spinal symptoms but inter-relationship between these symptoms and several factors according to aircraft type. METHODS: We surveyed 244 ROKAF aviators by questionnaires attending aerospace-medical aviator physiology class of aeromedical center. RESULTS: Exposured gravities are 8.23, 6.02, 5.89 and 5.38 +Gz in pilots of F-16, F-5, F-4 and trainer aircraft respectively. Pilots of trainer aircraft were most frequently exposured to a gravity in a month. 72.5% of F-16 aviators had neck pain and 82.6% of trainer aircraft low back pain. Spinal symptoms limited checking 6 in about 55% of aviators and air combat maneuver in over 30% of aviators. CONCLUSION: To improve combat performance by alleviation of spinal symptoms aircraft aviators may rest sufficiently and had better keep a correct posture while +Gz exposures. We need to invent stretching exercises for relaxing muscle stress and correct seating frame of aircraft. Skilled medical team and instruments for physiotherapy also needed in airbases.

Difference of Hypoxia Tolerance with Reference to Sex

BACKGROUND: Time of useful consciousness is related with various factors including smoking, age, sex, drug, and temperature. It is still unclear whether acute hypoxia tolerance is different between male and female. METHOD: We included 32 healthy students (male, n=16; female, n=16) volunteered to participate in this study. The blood hemoglobin concentration was measured at a day before flight. With high altitude rapid decompression flight training chamber, flight to simulated altitude of 25,000 ft was performed after nitrogen extraction breath. At 25,000 ft, heart rate and arterial O2 saturation (SaO2) were measured by using pulse oximeter after taking off oxygen mask. We compared the duration from mask-off to the time at 60% SaO2 between male and female and correlated the time at 60% SaO2 with hemoglobin concentration. RESULTS: The duration from mask-off to SaO2 reaching 60% were significantly longer in the male group. There was a linear relationship between hemoglobin concentration and time at 60% SaO2. CONCLUSION: Acute hypoxia tolerance differs from the two sexes and the difference of hemoglobin concentration is one of possible causative factors of this difference.

Altered cerebral vasomotion with decreased CGRP level in pial arteries of spontaneously hypertensive rats

The study aims to identify the mechanism (s) underlying the altered vasodilatory responses of the pial artery of spontaneously hypertensive rats (SHR) under a hypothesis that calcitonin gene-related peptide (CGRP) exerts a modulator role in the autoregulation of cerebral blood flow (CBF). The animals were divided into four groups: 1) Sprague-Dawley rats (SDR), 2) Wistar rats (WR), 3) SHR with high blood pressure (BP gtoreq 150 mmHg), and 4) SHR with normotensive BP (ltoreq 150 mmHg). The lower limit of CBF autoregulation in SHR shifted to a higher BP (82.8 +/- 9.3 mmHg, P < 0.05) than that in SDR (58.9 +/- 5.7 mmHg). In SHR, whether the BP levels were high or normotensive, the vasodilator responses to a stepwise hypotension were significantly attenuated unlike with SDR and WR. When artificial cerebrospinal fluid (CSF) containing capsaicin (3 X 10-7 M) was suffused over the cortical surface, a transient increase in pial arterial diameter was observed in the SHR with high or normotensive BP. In contrast, SDR and WR showed a large increase in diameter, and the increase was sustained for over 10 minutes. In line with these results, the basal releases of CGRP-like immunoreactivity (CGRP-LI) in the isolated pial arteries from SHR with high and normotensive BP were 12.5 +/- 1.4 and 9.8 +/- 2.8 fmole/mm2/60 min (P < 0.05), while those from SDR and WR were 25.5 +/- 3.1 and 24.6 +/- 3.1 fmole/mm2/60 min, respectively. The isolated basilar arteries showed similar results to those of the pial arteries in SHR. Thus, it is summarized that, in the SHR, the reduced autoregulatory vasodilator responses to stepwise hypotension and capsaicin may be, in part, ascribed to the decreased release of CGRP from the perivascular sensory nerve fibers of the pial arteries, and that altered vasomotor activity in SHR may not be related with the hypertensive tone.