The effects of halothane on the human beta-adrenergic receptor of lymphocyte membranes

The effects of halothane on beta-adrenergic receptor antagonist interaction were studied using the membranes of human lymphocytes as a model. Membrane preparations of lymphocytes were obtained from blood samples withdrawn from seven healthy young volunteers. Beta-receptor studies were performed using (-)125I iodocyanopindolol (125ICP) binding. Non-specific binding was determined in the presence of (-)isoproterenol. Beta-receptor density (Bmax) and the dissociation constant (KD) for 125ICP were determined from saturation curves. Beta-receptor affinity for agonists evaluated by the IC50 (the concentration of isoproterenol required to inhibit 50% of specific 125ICP binding) and the dissociation constant (KL) for isoproterenol was established from competition curves. The effect of halothane 1%, in an air oxygen mixture (oxygen fraction: 0.3) administered by tonometry during ligand membrane incubation, on beta-adrenergic receptor, was compared to that of control experiments not exposed to halothane. Halothane produced a moderate but significant decrease of Bmax (-10%) and a significant increase in non-specific binding (+30%), while KD, IC50, and KL were unchanged. The authors conclude that halothane, in vitro, decreases beta-adrenergic receptor density. This effect could be mediated by an alteration of the receptor in the membrane due to action of halothane on the lipid phase of the membrane.     

Brain cyclic-AMP and possible mechanisms of cerebrovascular dilation by anesthetics in rats

Barbiturates decrease both cerebral metabolic rate (CMR) and cerebral blood flow (CBF) and thereby preserve CBF and CMR coupling. However, many inhalation agents and ketamine uncouple CBF and CMR by virtue of inducing disproportionate increases in CBF. Adenosine 3',5'-monophosphate (cyclic-AMP) reportedly mediates uterine and aortic smooth muscle relaxation by halothane and may also mediate CBF-CMR uncoupling by anesthetics. Therefore, the authors studied the effect of various doses of halothane and ether on brain cyclic-AMP and compared them with the effects of ketamine and pentobarbital anesthesia. Both halothane 1.5 and 2.0 per cent and ether, 2.5 to 7.5 per cent (inspired concentrations) increased whole brain cyclic-AMP above unanesthetized levels (1,046 +/- 75 pmol/g wet brain) in a dose-related manner. Ketamine, 150 mg/kg, ip, increased brain cyclic-AMP twofold, whereas an apparent increase by 60 mg/kg pentobarbital, ip, was not significant. These results show a dose-related effect of ether and halothane on brain cyclic-AMP levels and suggest a causal relationship to their cerebrovasodilatory effects.     

Intravenous dexmedetomidine inhibits cerebrovascular dilation induced by isoflurane and sevoflurane in dogs.

Our aim in this study, performed using a closed cranial window preparation, was to investigate the effect of systemic pretreatment with dexmedetomidine on cerebrovascular response to isoflurane or sevoflurane. After instrumentation under pentobarbital anesthesia, 48 dogs were assigned to one of two groups: the isoflurane group or the sevoflurane group (n = 24 each). Twenty-four dogs received saline (n = 6) or one of three different doses of dexmedetomidine (0.5, 1.0, or 2.0 micrograms/kg) (n = 6 each) i.v. Animals were then exposed to three different minimum alveolar anesthetic concentrations (MACs; 0.5, 1.0, and 1.5) of either isoflurane or sevoflurane. Cerebrovascular diameters were measured at each stage. Pretreatment with dexmedetomidine decreased pial vessel diameters. Both isoflurane and sevoflurane significantly dilated both arterioles and venules in a concentration-dependent manner. Isoflurane- and sevoflurane-induced dilation of cerebral arterioles was significantly attenuated in the presence of dexmedetomidine. The dexmedetomidine-induced attenuation of the vascular responses was not dependent on the dose of dexmedetomidine and was not different between isoflurane and sevoflurane. The vasodilation of cerebral pial vessels induced by isoflurane and sevoflurane could be attenuated by the systemic administration of dexmedetomidine, and this interaction between dexmedetomidine and volatile anesthetics showed no evidence of dose-dependency. Implications: The systemic administration of dexmedetomidine attenuates the dilation of cerebral vessels induced by isoflurane and sevoflurane in pentobarbital-anesthetized dogs. This interaction was not dependent on the clinical (0.5-2.0 micrograms/kg) dose of dexmedetomidine and was not different between isoflurane and sevoflurane anesthesia.     

Absence of cellular hypersensitivity in patients with unexplained hepatitis following halothane.

In-vitro tests of cell-mediated immunity were performed using blood obtained from subjects with unexplained hepatitis following halothane anesthesia to determine whether sensitization to potentially antigenic products of halothane metabolism might exist. Both lymphocyte transformation and leukocyte migration-inhibition tests were undertaken in the presence of trifluoroacetylated human serum albumin. All tests in the presence of these potential antigenic complexes were negative. The results support the view that cell-mediated hypersensitivity to trifluoroacetylated proteins does not contribute to the pathogenesis of hepatic dysfunction following halothane anesthesia.     

围术期β肾上腺素受体阻滞剂的应用

β肾上腺素受体阻滞剂为临床上常用的心血管药物,在围术期可用于防治高血压、控制心律失常、治疗慢性心衰、保护和改善心肌功能,从而增强手术耐受力,提高术后生存率。现就β肾上腺素受体阻滞剂在围术期的应用作一探讨。     

The effect of low concentrations of halothane on the cerebrovascular circulation in young children

To determine the effect of halothane on cerebral blood flow velocity measured by transcranial Doppler, 23 healthy young children were studied during surgery. Anaesthesia was induced with thiopental, fentanyl and vecuronium, and maintained with halothane in 70% nitrous oxide in oxygen. A continuous epidural anaesthesia with 0. 25% bupivacaine was performed. End-tidal carbon dioxide pressure, temperature, heart rate and systolic blood pressure were kept constant. Three minimal alveolar concentrations (MAC; 0.5, 1.0 and 1. 5) of halothane were administered in stepwise increases. The cerebral blood flow velocity increased significantly at 1.0 (p < 0. 01) and 1.5 MAC (p < 0.001) compared with the value at 0.5 MAC. No further change in cerebral blood flow velocity was seen between 1.0 and 1.5 MAC. These data show that maximal changes in cerebral blood flow velocity are obtained at 1.0 MAC and that further increases in halothane concentration do not modify the cerebral circulation. It is suggested that young children differ from adults in that the maximal effect of halothane occurs at lower concentrations.     

Deficiency of cardiac beta-adrenergic receptor in streptozocin-induced diabetic rats

The number of beta-adrenergic receptors in cardiac myocytes isolated from rats made diabetic with streptozocin (STZ) for 10 wk was measured by use of a hydrophilic nonselective antagonist [3H]CGP 12177 and was found to decrease to 59% of the number in control rats (P less than .05), without any change in affinity. Similarly, using [125I]iodocyanopindolol as a ligand, we found a decrease in the beta-adrenergic-receptor number on cardiac plasma membrane isolated from the diabetic rats [29% decrease (P less than .05) at 1 wk, 50% (P less than .01) at 3 wk, and 49% (P less than .01) at 10 wk compared with control rats]. However, the serum triiodothyronine level that had been known to modulate the beta-adrenergic-receptor-adenylate cyclase system was decreased in the 1-wk-diabetic rats but not in the 10-wk-diabetic rats compared with each control group. Furthermore, there was no difference in urinary catecholamine excretion between diabetic and control groups. In the 10-wk-diabetic rats, the response of adenylate cyclase to isoproterenol was significantly defective (56% decrease compared with control rats; P less than .05), although both the basal and the forskolin-stimulated maximum adenylate cyclase activities and a half-maximum concentration of isoproterenol for the stimulation of adenylate cyclase were similar in control and diabetic rats. On the other hand, both cholera toxin-dependent and islet-activating protein-dependent [32P]NAD incorporations into cardiac plasma membrane were markedly increased in the diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Absence of antitrifluoroacetate antibody after halothane anaesthesia in patients exhibiting no or mild liver damage

It has been shown that the circulating antibodies, which bind to rat hepatic microsomal proteins obtained after in vivo exposure to halothane, are detectable by immunoblotting in patients with “halothane hepatitis (HH),” and that rabbit immunized anti-sera against trifluoroacetylated rabbit serum albumin (TFA-RSA) recognizes rat microsomal distorted polypeptides in almost the same way as do sera from patients with HH. In this paper, we report first the development of a novel method of synthesizing TFA-RSA using p-nitrophenyl TFA, and second the results of tests for circulating anti-TFA antibodies in the serum of 86 patients who had received halothane anaesthesia and developed no (67 patients) or mild (19 patients, the maximum activity of serum alanine aminotransaminase 519 IU · L^?1) liver damage. Serum was selected from stored sera of post-transfusion patients. The new method of synthesizing TFA-RSA was convenient and was able to be done at neutral pH. Rabbit sera obtained after immunization with the newly synthesized TFA-RSA recognized the same polypeptides (109 kDa, 92 kDa, 80 kDa, 76 kDa, 64 kDa and 59 kDa) as the established anti-sera against TFA-RSA, and these reactions were inhibited in the presence of TFA-lysine. Circulating antibodies were not detected in our patients who had developed no or mild liver damage. The present finding supports the hypothesis that the appearance of circulating antibodies against microsomal distorted proteins are specific to patients with HH. Furthermore, we have shown here that the halothane-induced mild increase in ALT activity is not associated with the appearance of those circulating antibodies, supporting the pathophysiological difference between HH and halothane-induced mild hepatic damage.     

Absence of frequent involvement of modifier of MinAPC in sporadic colorectal cancer

Background: Mutations in the multiple intestinal neoplasia (Min) gene, the mouse homologue of the APC gene, result in the development of intestinal tumors. The degree of tumor expression is suppressed by the modifier of Min (MOM). Alterations in the MOM gene result in markedly increased tumor expression in the mouse. The human homologue of the MOM gene has been mapped to a locus on chromosome 1p35–36, but the role of the MOM gene in the development of human sporadic colorectal cancers has not been defined. Methods: The microsatellite marker D1S199 has been previously mapped to the region of the MOM gene and was used as a primer for PCR amplification. The PCR products were subjected to denaturing electrophoresis and analyzed for loss of heterozygosity (LOH) and the mismatch repair phenomenon (RER) of each tumor compared to its mucosal control. Results: 48 consecutive sporadic colorectal cancers and normal adjacent mucosa were analyzed. LOH was noted in 2 of 48 tumors and the RER phenomenon was noted in 6 of 48 tumors. Thus, 8 of 48 tumors (16.7%) showed alterations in the region of the locus of the MOM gene. There was no association between alterations in this region and TNM stage, disease-free survival, overall survival, or p53 mutation. Conclusions: Although mutation of the APC gene is an integral component of sporadic colorectal carcinogenesis, alteration in the region including the MOM gene does not appear to play a significant role in the development or clinicopathologic behavior of human sporadic colorectal tumors. Presented at the 50th Annual Cancer Symposium of The Society of Surgical Oncology, Chicago, Illinois, March 20–23, 1997.     

AMPA receptor competitive antagonism reduces halothane MAC in rats.

Various subtypes of receptors have been identified for glutamate, an excitatory neurotransmitter. Previous studies have shown that antagonism of glutamate at the NMDA receptors reduces minimum alveolar concentration (MAC) for volatile anesthetics. NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline) is a selective antagonist at the glutamatergic AMPA receptor. The purpose of this experiment was to determine whether AMPA receptor antagonism influences halothane MAC in the rat. Sprague-Dawley rats were anesthetized with halothane in 50% O2/balance N2, tracheally intubated and the lungs were mechanically ventilated. Increasing doses of NBQX were intravenously infused in three groups while the control group was infused with vehicle (D5W). Halothane MAC was then determined by the tail-clamp method. Halothane MAC was log-linearly related to plasma NBQX concentrations (MAC = 0.125 (In plasma concentration NBQX) + 1.035, r2 = 0.77). A maximal 58% reduction of halothane MAC was achieved with an NBQX loading dose of 42 mg/kg followed by a continuous infusion rate of 36 mg x kg-1 x h-1 (control = 1.02 +/- 0.07%; NBQX = 0.43 +/- 0.12%; P < .01). Larger doses of NBQX were not possible because of the poor aqueous solubility of this compound. In a separate experiment, awake rats were randomly assigned to groups based on the dose of NBQX infused. Pa(CO2) and mean arterial pressure were measured at time 0 and at 5 and 30 min after start of NBQX infusion. The infusion was then stopped. Time until recovery of the righting reflex was recorded.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of benzodiazepine receptor antagonism by flumazenil on the MAC of halothane in the rat

The effects of a benzodiazepine receptor agonist and an antagonist on the MAC of halothane required to achieve anesthesia were evaluated to explore the possible functional interaction between halothane and the benzodiazepine receptor. Rats were anesthetized with halothane and then administered midazolam (a benzodiazepine agonist) and/or flumazenil (a benzodiazepine antagonist). Flumazenil in doses of 0.1 mg/kg and 1.0 mg/kg was found to have no effect on the MAC of halothane. Midazolam (1.0 mg/kg) lowered the MAC of halothane by 37%. This decrease in MAC was inhibited by coadministration of flumazenil. The absence of an increase in the MAC of halothane in the presence of flumazenil suggests that halothane does not interact with the benzodiazepine receptor, directly or indirectly, to produce its anesthetic action.     

Identification and characterization of a beta-adrenergic receptor in hamster Sertoli cells

Sertoli cells cultured from immature hamsters contain a beta-adrenergic receptor which is coupled to the cAMP second messenger system. Thus, isoproterenol, epinephrine, and norepinephrine, which act via beta-adrenergic receptors, all stimulate cAMP accumulation in Sertoli cells cultured for 4-5 days. This cAMP response to isoproterenol is inhibited stereospecifically by the beta-receptor blocker, propranolol. It is also sensitive to inhibition by beta-adrenergic antagonists in this order of potency: nonspecific beta receptor antagonists, propranolol, timolol, hydroxypindolol greater than beta 1 selective antagonists, oxyprenolol, metoprolol much much greater than beta 2 selective antagonist, butoxamine. Butoxamine was at least 1000-fold less sensitive than either the nonspecific or the beta 1 selective antagonists at inhibiting the response of either isoproterenol (nonspecific), dobutamine (beta 1 selective) or zinterol (beta 2 selective). The hamster Sertoli cell beta receptor is, therefore, predominantly of the B1 subtype. This beta receptor mediated increase in cAMP is sensitive to homologous desensitization and is stimulated synergistically by forskolin. In addition, Seroli cells freshly isolated from immature hamsters contain an active beta receptor. However, this beta receptor mediated increase in cAMP is dependent on the type of trypsin used in the cell preparation. In agreement with Kierszenbaum et al (1985), freshly isolated Sertoli cells from immature rats never responded to the catecholamines regardless of the type of trypsin used; indicating an important physiologic difference between rat and hamster Sertoli cells.     

Increased beta-adrenergic receptor density in an experimental model of cardiac transplantation

We examined beta-adrenergic receptor density, basal, maximal isoproterenol and fluoride-stimulated adenylate cyclase activities, and morphologic characteristics of rabbit and rat native and heterotopic isograft cardiac tissue. Four weeks after graft placement there were only subtle histologic differences between native and graft tissue. Membrane preparations from isografts of rabbits demonstrated increases in beta-receptor density (maximum [3H]DHA binding = 111 +/- 19.3 fmol/mg versus 52.4 +/- 4.9 in native hearts, p less than 0.05). In a small number of experiments, rat isografts also demonstrated a suggestive increase in beta-receptor density (69.8 +/- 7.1 fmol/mg versus 40.2 +/- 7.3 in native hearts). Isoproterenol-stimulated adenylate cyclase activity was greater in rabbit graft hearts (3.98 +/- 0.20 X basal activity) than in native tissue 2.67 +/- 0.16 X basal activity, p less than 0.05). We conclude that cardiac denervation may lead to a postsynaptic form of beta-adrenergic supersensitivity that is due to an increase in beta-receptor density.