A strategy for immunohistochemical signal enhancement by end-product amplification

We report a novel strategy, called end-product (EP) amplification, capable of enhancing the sensitivity of immunohistochemical procedures by about an order of magnitude or more. The strategy employs an antibody (anti-EP) to the product generated by the action of horseradish peroxidase on 3,3'-diaminobenzidine (DAB), and can be extended to the products of other enzymes as well, e.g., alkaline phosphatase. Amplification is the consequence of the ability of anti-EP to detect the multiplicity of product moelcules resulting from the turnover of substrate by a single enzyme molecule. The subsequent detection of anti-EP was by biotinylated goat anti-rabbit antibody, followed by avidin-peroxidase and DAB or by avidin-alkaline phosphatase and Vector Red. Further amplification can be accomplished by repeated cycles of the protocol. Anti-EP was produced by immunization with a bovine serum albumin (BSA) conjugate of a soluble polymer of DAB, prepared by a carefully controlled reaction of DAB with horseradish peroxidase and hydrogen peroxide. Coupling to BSA (and to RSA) was accomplished with glutaraldehyde. The titer of anti-EP was established by ELISA. Formalin-fixed, paraffin-embedded sections of five cases of Hodgkin's disease and five tonsils with follicular hyperplasia were immunolabeled for the following lymphoid markers: CD3, CD20, CD30, CD45RA, and CD68. EP amplification with anti-EP was also applied to cases of CMV pneumonia and cerebral toxoplasmosis to determine whether this procedure could improve detection of the infectious agents. Immunolabeling of the primary antibody was performed by the avidin-biotin-peroxidase technique with DAB as the reaction substrate. The specificity of EP amplification was tested by demonstrating binding of anti-EP with Vector Red with the generation of a fluorescence end-point. There was complete congruence in the distribution of the DAB signal and the red immunofluorescence representing EP amplification. The intensity of the DAB signal was increased as much as 16-fold by EP amplification, making possible a reduction in the amount of the primary antibody by as much as 85-90%. Sensitivity also increased with respect to weakly expressed antigens and low concentrations of infectious agents.

Cyclophilin binding to the human immunodeficiency virus type 1 Gag polyprotein is mimicked by an anti-cyclosporine antibody

Human immunodeficiency virus type 1 is unique among retroviruses in that infectivity requires specific incorporation into virions of the cellular protein cyclophilin A through interactions with the Gag polyprotein. Here we show that monoclonal antibody B11 1.4, which recognizes a cyclophilin-binding epitope on cyclosporine, detects denatured or native human immunodeficiency virus type 1 capsid. B11 1.4 does not recognize the capsids of other retroviruses, and binding is inhibited by cyclosporine or by cyclophilin A.

Role of the sympathoadrenal axis in the cardiovascular response to cocaine in conscious unrestrained rats

We investigated the role of peripheral sympathetic neurons and the adrenal medulla in the cardiovascular responses to cocaine in conscious, unrestrained Sprague-Dawley rats. Surgical adrenal demedullation (ADM) and/or chemical peripheral sympathectomy was used to eliminate one or both components of the sympathoadrenal axis. Phentolamine (5 mg/kg i.v.) was used to evaluate whether cocaine elicited epinephrine (EPI) release from the adrenal medulla. Significant EPI release by cocaine would result in "epinephrine reversal" after phentolamine pretreatment. Cocaine (2.5 mg/kg i.v.) was used in all experiments except the dose-response relationship study. In normal rats, cocaine caused a transient increase in mean blood pressure (MBP). Pretreatment with phentolamine reversed this BP response and this depressor effect was blocked by propranolol (2 mg/kg i.v.) suggesting that the pressor effect of cocaine was mediated by EPI. Chemical sympathectomy alone partially inhibited the pressor effect of cocaine, but pretreatment with phentolamine still reversed the residual action of cocaine on MBP at this time. Two weeks after ADM, the effect of cocaine on MBP was not significantly different from that of the sham-operated rats. However, pretreatment with phentolamine inhibited but did not reverse the effect of cocaine on MBP at that time. In rats with both ADM and chemical sympathectomy, cocaine caused only a decrease in MBP that was not blocked by propranolol or atropine methylnitrate, presumably because of its direct depressive actions. Results of this study suggest that both peripheral sympathetic neurons and the adrenal medulla play important roles in the cardiovascular actions of cocaine.

[Experimental study on the processed drug of castor seeds in the therapy of pulmonary carcinoma]

In this study, castor seeds were processed by one of the traditional Chinese methods, LD50 was measured and tumor inhition tests in nude mice bearing human pulmonary carcinoma were conducted. The results showed that the processing method was able to lower the toxicity of castor seeds and maintain their antitumor effect, thus providing an experimental basis for oral administration of castor seeds in the therapy of pulmonary carcinoma.

Idiotypic mimicry and the assembly of a supramolecular structure: an anti-idiotypic antibody that mimics taxol in its tubulin-microtubule interactions

Taxol, originally extracted from the bark of the western yew, Taxus brevifolia, is reportedly the first of a new class of anti-cancer agents. It acts by promoting and irreversibly stabilizing microtubule assembly, thus interfering with the dynamic processes required for cell viability and multiplication. With the aim of using immunological techniques to study the mechanism of action of taxol, a monoclonal anti-idiotypic antibody that mimics taxol was prepared, using an auto-anti-idiotypic strategy. It and its Fab fragment inhibited the binding of [3H]taxol to microtubules. Moreover, like taxol, both promoted the assembly of tubulin into microtubules. These findings provide an example of an anti-idiotypic antibody capable of assembling an organized supramolecular structure from soluble cellular components. In addition, it further establishes the ability of anti-idiotypic antibodies to be functional mimics of ligand molecules bearing no structural similarity to immunoglobulins. The variable regions of the antibody have been sequenced. With the exception of the complementarity-determining region 3, the sequence of the heavy chain variable region is strikingly similar to that of an anti-idiotypic antibody raised to anti-insulin. The finding that a polypeptide can mimic taxol raises the possibility that taxol acts as a peptidomimetic compound that interferes with the function of an endogenous polypeptide.

Percutaneous transluminal excimer laser coronary angioplasty. Clinical report of six cases

Six patients with 95% to 100% occluded atherosclerotic lesions underwent percutaneous transluminal excimer laser coronary angioplasty (PTELCA). Among them, 5 were male and 1 was female; their age ranged from 28 to 66 years. Four patients had LAD stenosis and 2 LCX lesions. Acute angiographic and clinical success was achieved in all patients but one, with a success rate of 83.3%. It was demonstrated that PTELCA is a safe and effective therapy for selected patients with coronary artery disease.

Reproductive patterns of the yak. I. Reproductive phenomena of the female yak

The reproductive phenomena of 62 multiparous yaks from two grassland areas were investigated. The lengths of oestrus and the oestrus cycle were 12-36 h and 19-21 days respectively. Ovulation occurred 12-36 h after the end of oestrus. The oestrus and conception rates were 85.5% and 94.3%. The duration of pregnancy ranged from 248 to 258 days. The signs of oestrus, pregnancy and parturition, and the changes of the uterus and ovaries during oestrus and pregnancy are described.

Reproductive patterns of the yak. II. Progesterone and oestradiol-17 beta levels in plasma and milk just before the breeding season; also during normal and short oestrous cycles

Concentrations of oestradiol-17 beta and progesterone in plasma and milk of the yak before the first oestrus at the beginning of the breeding season and during normal and short oestrus cycles were measured by radioimmunoassay (RIA). Both oestradiol-17 beta and progesterone were maintained at stable, low levels before the first oestrus. However, oestradiol-17 beta showed a peak, similar to that on the day of oestrus (P > 0.05), about 6 days before the first oestrus and a small progesterone peak was seen 2 days before it. There were three peaks of oestradiol-17 beta in plasma and milk on the day of oestrus [24.57 (SD 11.35) pg ml-1 and 97.84 (SD 26.02) pg ml-1 respectively], and on days 5 and 14 of the cycle. Progesterone levels in plasma and milk were low during oestrus but peaks were seen on day 15 [5.23 (SD 1.02) ng ml-1 and 20.44 (SD 3.64) ng ml-1 respectively]. The patterns of oestradiol-17 beta and progesterone during the short cycle were similar to those during the normal cycle (P > 0.05), but the values were lower. The levels of oestradiol-17 beta and progesterone in milk were about 3 or 4 times higher than those in plasma before the first oestrus, and about 4 or 5 times higher during the normal cycle.

Reproductive patterns of the yak. III. Levels of progesterone and oestradiol-17 beta during pregnancy and the periparturient period

Changes in plasma progesterone and oestradiol-17 beta in yaks during pregnancy and the periparturient period of yaks and in milk during the first month of pregnancy were analysed. The profiles of progesterone were similar for pregnant and non-pregnant yaks within 14 days following oestrus (P > 0.05), but the concentration was significantly higher on day 19 (P < 0.05) and in pregnant yaks tended to increase gradually thereafter. The plasma progesterone decreased rapidly on day 120 (P < 0.05), then increased to reach its maximum of 15.5 (SD 3.74) ng ml-1 on day 210; declined again 20 days before parturition and resumed the same levels at parturition as during mating (P > 0.05). The oestradiol-17 beta levels in plasma and milk increased gradually from day 23 after conception, decreased abruptly on day 60 (P < 0.05), then increased to reach their maximum at parturition of 551.4 (SD 70.86) pg ml-1. The oestradiol decreased again after parturition to the same level as during mating (P > 0.05).

High-contrast channel waveguide switch with two sections of a nematic liquid crystal covering

Theoretical and experimental results for waveguide modes with a distinctive channel waveguide switching geometry are presented from the viewpoint of improving the switching contrast for hybrid-mode propagation. The channel waveguide structure consists of two types of active material covering regions of a nematic liquid crystal; one has a pair of strip electrodes, and the other is without electrodes. An experimental switch is demonstrated to have the contrast ratio of 1430 for the hybrid modes with E(1n)(y) primary components.

Human mononuclear phagocytes express adenosine A1 receptors. A novel mechanism for differential regulation of Fc gamma receptor function

Using monoclonal anti-adenosine A1 receptor antibodies that bind the A1 receptor ligand binding site, we demonstrate that A1 receptors are expressed on cultured monocytes and rheumatoid synovial fluid mononuclear phagocytes. This finding is associated with the acquisition of reactivity with selective adenosine A1 receptor agonists and is temporally coordinated with the induction of adenosine A2 receptors on cultured monocytes. In a rapid, concentration-dependent fashion, these two distinct adenosine receptors modulate Fc gamma receptor-mediated phagocytosis, a response critical to the pathogenesis of immune complex diseases. Occupancy of A1 receptors by N6-cyclopentyladenosine (an A1-specific adenosine analogue) or mAb AA1 (an anti-A1 mAb) results in a potent stimulation that is blocked by adenosine receptor antagonists. This A1 receptor-induced enhancement of Fc gamma receptor-mediated phagocytosis is a consequence of preferential augmentation of Fc gamma RI function, suggesting distinct mechanisms for receptor-effector coupling of Fc gamma receptor families. In contrast, ligation of A2 receptors by A2-specific agonists decreases Fc gamma receptor-mediated phagocytosis in cultured monocytes. The opposing effects of adenosine A1 and A2 receptors allow for a concentration-dependent feed-back loop that responds more rapidly than effects elicited by other endogenous modulators. Low concentrations of adenosine are proinflammatory providing enhanced Fc gamma receptor function via A1 receptors, whereas higher concentrations that can occur with tissue damage are anti-inflammatory providing inhibition via A2 receptors. This rapid and potent modulation of Fc gamma receptor-mediated function suggests that adenosine is an important local regulator of the inflammatory response.

Human mononuclear phagocytes express adenosine A1 receptors. A novel mechanism for differential regulation of Fc gamma receptor function

Using monoclonal anti-adenosine A1 receptor antibodies that bind the A1 receptor ligand binding site, we demonstrate that A1 receptors are expressed on cultured monocytes and rheumatoid synovial fluid mononuclear phagocytes. This finding is associated with the acquisition of reactivity with selective adenosine A1 receptor agonists and is temporally coordinated with the induction of adenosine A2 receptors on cultured monocytes. In a rapid, concentration-dependent fashion, these two distinct adenosine receptors modulate Fc gamma receptor-mediated phagocytosis, a response critical to the pathogenesis of immune complex diseases. Occupancy of A1 receptors by N6-cyclopentyladenosine (an A1-specific adenosine analogue) or mAb AA1 (an anti-A1 mAb) results in a potent stimulation that is blocked by adenosine receptor antagonists. This A1 receptor-induced enhancement of Fc gamma receptor-mediated phagocytosis is a consequence of preferential augmentation of Fc gamma RI function, suggesting distinct mechanisms for receptor-effector coupling of Fc gamma receptor families. In contrast, ligation of A2 receptors by A2-specific agonists decreases Fc gamma receptor-mediated phagocytosis in cultured monocytes. The opposing effects of adenosine A1 and A2 receptors allow for a concentration-dependent feed-back loop that responds more rapidly than effects elicited by other endogenous modulators. Low concentrations of adenosine are proinflammatory providing enhanced Fc gamma receptor function via A1 receptors, whereas higher concentrations that can occur with tissue damage are anti-inflammatory providing inhibition via A2 receptors. This rapid and potent modulation of Fc gamma receptor-mediated function suggests that adenosine is an important local regulator of the inflammatory response.

An improved technique for bloodless hepatic resection on in situ cold perfused liver

An improved technique for bloodless hepatic resection using in situ isolation and asanguinous hypothermic perfusion was described to deal with huge liver tumors involved in the liver hilum, the main hepatic veins and retrohepatic inferior vena cava. The original Fortner's technique was modified, including the choice of incision; semi-isolated perfusion of the liver portion preserved through the single portal vein; suprahepatic outlet of the perfusate and the shortening of the period of hepatic ischemia by reperfusion of hepatic artery prior to the repair or reconstruction of the portal vein. The initial successful experience of the technique applied to 2 pediatric cases with giant liver tumors was reported, and the indications, intraoperative and early postoperative courses were discussed.

Characterization of polyclonal and monoclonal anti-taxol antibodies and measurement of taxol in serum

Anti-taxol antibodies were generated in the rabbit using a taxol-bovine serum albumin conjugate prepared from 2'-succinyltaxol using a mixed anhydride procedure. Immunization with 2'-succinyltaxol-bovine serum albumin gave rise to polyclonal anti-taxol antibodies. By a radioimmunoassay using [3H]taxol, a standard curve gave a 50% inhibitory concentration of 1.0 nM. Taxol levels in human serum could be measured, with the lower limit of detection and measurement being 0.1 nM or 0.085 ng/ml. Two mouse monoclonal anti-taxol antibodies were isolated by immunizing BALB/c mice with the same antigen. One was an immunoglobulin G1 (69E4A8E) and the other was immunoglobulin M (29B7B3C). The specificity of these antibodies was determined by a competitive enzyme-linked immunosorbent assay with taxol and 10 different related derivatives and analogues. 29B7B3C had higher binding affinities for biologically active derivatives and markedly lower affinities for inactive derivatives; i.e., the specificity was consistent with the results of tubulin disassembly and cytotoxicity studies using the same taxol derivatives, making it suitable for screening for taxol or taxol-like compounds in extracts of natural products. 69E4A8E recognized the benzamidocarbamyl group at the C-3' position of taxol and had a lower affinity for other active compounds with different substitutions. Taxol levels in human serum could be detected and measured by 69E4A8E using a competitive enzyme-linked immunosorbent assay. The lower limit of measurement was about 50 nM or approximately 42 ng/ml. Similar measurements could be made by radioimmunoassay.

Immunoassay of taxol and taxol-like compounds in plant extracts

A mouse monoclonal anti-taxol antibody (69E4A8E) and a rabbit polyclonal anti-taxol antiserum were used to measure taxol levels in plant extracts in a double-blind experiment in conjunction with assays by HPLC. 69E4A8E was previously shown by ELISA to be specific for taxol with only a slight cross reaction with another bioactive compound, cephalomannine; the antiserum, on the other hand, was, by radioimmunoassay (RIA), essentially equally reactive with taxol and cephalomannine. Immunoassays of the plant extracts gave results in agreement with that found by HPLC, suggesting that the antibodies can be used in simple routine procedures for the quantification of taxol or taxol-like compounds in extracts of plants or other potential natural sources.

Evidence for a functional receptor for cyclosporin A on the surface of lymphocytes

Cyclosporin A (CsA) is an immunosuppressive agent that inhibits the synthesis of lymphokines by T lymphocytes at the level of transcription. A cytoplasmic protein, cyclophilin, is the most thoroughly studied CsA-binding protein, but its ubiquitous presence in cells of all types raises questions about its role in immunosuppression. In an attempt to ascertain the presence of a cell surface receptor, we synthesized two polyvalent macromolecular CsA derivatives, CsA-BBa-ovalbumin and CsA-BBa-aminodextran (CBD), from the product of the photochemical reaction of CsA and 4-benzoylbenzoic acid (CsA-BBa). (i) They inhibited the peptidylprolyl cis-trans isomerase activity of cyclophilin and the synthesis of interleukin 2 by phorbol ester-activated EL-4 cells. (ii) CBD also inhibited interleukin 2 secretion by Con A-activated T-cell-enriched mouse splenocytes. 4-Benzoylbenzoic acid (BBa)-aminodextran and aminodextran were inactive. (iii) Direct binding and competition studies with [3H]CsA indicated that CBD does not enter EL-4 cells (i.e., it acted at the surface). (iv) CBD caused agglutination of EL-4 cells, murine B and T lymphocytes, human thymocytes, and two T-cell hybridomas. Agglutination was inhibited by a monoclonal antibody to CsA and by CsA and CsA-BBa, but not by BBa. No agglutination was seen with BBa-aminodextran or aminodextran. HeLa cells, Vero (monkey kidney) cells, a mouse plasmacytoma, COS cells, and a poorly differentiated B-cell lymphoma were not agglutinated. (v) EL-4 cells failed to be agglutinated after treatment with trypsin or chymotrypsin. Specific agglutination was again possible after incubation for 5 h at 37 degrees C in the absence of enzyme. (vi) CBD covalently linked to crosslinked agarose beads inhibited interleukin 2 production by phorbol ester-stimulated EL-4 cells. No activity was seen if cell-to-bead contact was prevented by a 0.02-microns microporous filter that did not interfere with the passage of CBD. Our findings support the presence of a functional receptor on the surface of selected cells of the immune system.

Properties of a monoclonal antibody for the detection of abasic sites, a common DNA lesion

The abasic site is one of the most frequent changes occurring in DNA and has been shown to be lethal and mutagenic. An abasic site in DNA can be tagged by reaction with O-4-nitrobenzylhydroxylamine (NBHA), resulting in the formation of an oxime linkage between the abasic site and the NBHA moiety. In order to measure NBHA-tagged abasic sites, a monoclonal antibody was elicited against a 5'-phosphodeoxyribosyl O-4-nitrobenzyl hydroxylamine-BSA conjugate. The antibody was specific for the NBHA residue as demonstrated by hapten inhibition, with IC50 values for 5'-phosphodeoxyribosyl-NBHA, deoxyribosyl-NBHA, ribosyl-NBHA and NBHA of 0.3 microM, 5 microM, 5 microM and 7 microM, respectively. Other haptens examined, including benzylhydroxylamine, 5'-phosphodeoxyribosyl-, deoxyribosyl-, and ribosyl-benzylhydroxylamine, showed no inhibition even at 1 mM. The antibody showed high specificity for NBHA-modified AP sites in DNA and exhibited no cross reactivity with normal DNA bases, otherwise-modified DNA bases or unmodified AP sites. Using a direct ELISA assay, the antibody detected 1 AP site (after NBHA-modification) per 10,000 base-pairs or approximately 10 femtomoles of AP sites in DNA. DNA lesions were detectable in 60Co gamma-irradiated DNA at a dose as low as 10 rad (0.1 Gy) and the production of antibody detectable sites was proportional to the gamma-ray dose. Since NBHA reacts with lesions containing an aldehyde group, the simplicity and sensitivity of the antibody assay should provide a useful method for the quantitation of AP sites or other DNA lesions containing an aldehyde group.

Treatment of hallux valgus in China

This is a review of the treatment of hallux valgus based on the paper material submitted to the First and Second Sino-American Conferences on Foot Disorders held in Beijing in 1987 and 1990. The data consisted of 676 cases (979 feet) from 10 major hospitals in China. There were 122 men and 554 women, giving a male to female ratio of 1:45. Sixty-nine (10%) cases had a family history of hallux valgus and 120 cases (18%) were associated with hammer toe deformity. The age ranged from 16-85 years with an average of 42. Among the 412 female cases (78.5%) at the age of 20-35, 339 (82.3%) had the history of wearing high heeled and narrow tipped shoes. Osteoarthritis changes of the first M-P joint were seen in 31 cases, all above the age of 60. 615 cases (90.9%) were treated surgically for pain relief and only 25 cases (3.7%) at the age of 20-30 had the deformity corrected for cosmetic purpose. The surgical procedures employed were bunionectomy (Silver's operation, 39 feet), Keller's operation (344 feet), McBride's operation (239 feet) and a variety of osteotomies of the first metatarsal (295 feet). Joplin and Lapidus operations were used by one author in 5 and 2 cases respectively. Overall excellent and good results were obtained in 609 cases (90%) during the follow-up of 1-14 years.

Immunological studies of osteoarthritis in bipedal rats

Osteoarthritis (OA) models in bipedal rats were used to study the immune response, including the changes of IgG, antibody dependent cytotoxicity tests toward articular chondrocytes and the matrix. The results revealed significant difference between the bipedal and the quadruped rats. Immunological studies have proved that the OA model of bipedal rats is appropriate for the study of OA.

Characterization of a monoclonal antibody to thymidine glycol monophosphate

A monoclonal antibody specific for thymine glycol (TG) in irradiated or OsO4-treated DNA was obtained by immunizing with thymidine glycol monophosphate (TMP-glycol) conjugated to bovine serum albumin by a carbodiimide procedure. Screening by dot-immunobinding and enzyme-linked immunosorbant assay (ELISA) procedures gave eight clones that bound OsO4- treated DNA. One of them, 2.6F.6B.6C, an IgG2a kappa, was characterized further. Hapten inhibition studies with OsO4-treated DNA showed that the antibody was specific for TMP-glycol. Among the various inhibitors tested, inhibition was in the order TMP-glycol greater than 5,6-dihydrothymidine phosphate greater than TMP greater than thymidine glycol greater than TG. Inhibition by 5,6-dihydrothymidine, thymidine, thymine, AMP, and CMP was negligible. In OsO4-treated DNA, as few as 0.5 TG per 10,000 bp were detectable by direct ELISA. Inhibition assays could detect as few as 1.5 TG per 10,000 bp. The antibody was equally reactive with native or denatured DNA containing TG. Among the X-irradiated homopolymers dC, dA, dG, and dT, only dT reacted with the antibody. Using an ELISA, the antibody could detect damage in irradiated DNA at the level of 20 Gy. Thus the antibody is of potential use in assays for DNA damage caused by X rays or other agents that damage DNA by free radical interactions.

Operative technique for carcinoma of the oesophagus after distal subtotal gastrectomy: a new method using the residual stomach to reconstruct the alimentary tract

The stomach is the organ most often chosen for substitution following resection of the oesophagus for carcinoma and this method has given good results. The mode of reconstruction of the alimentary tract in oesophageal cancer patients with previous distal gastrectomy presents a surgical problem. Usually the colon or jejunum is chosen as an alternative for substitution in such patients. We report a new technique used in our unit on 30 patients with previous distal subtotal gastrectomy. This involves using the residual stomach for reconstruction and transposing the spleen and tail of the pancreas into the left thoracic cavity in order to preserve the blood supply to the stomach. The entire procedure is performed through the left chest. We explored 35 patients originally, but five were found to be unresectable at operation. Of the remaining 30 patients, the tumour locations were: upper thoracic (1), midthoracic (24) and lower thoracic (5). The anastomotic sites were: above aortic arch (23), below aortic arch (5) and neck (2). The technical success of this procedure was good with no deaths in the immediate post-operative period. There were three anastomotic leakages which all healed after thoracic drainage and a feeding jejunostomy.

Oxygen free radical in human osteoarthritis

The xanthine oxidase catalysed release of superoxide free radicals (O2-) from endogenous hypoxanthine was determined in homogenates of synovium obtained from three groups of patients, those undergoing primary or revision total hip replacement (THR) for osteoarthritis and those undergoing arthroscopy of the knee for semilunar disc injuries. The concentrations of hypoxanthine in homogenates obtained during THR were found to be significantly higher than those in the group with semilunar disc injuries. The results suggest that there is a greater predisposition to free radical release and tissue damage in osteoarthritis.

Dexmedetomidine produces a hypnotic-anesthetic action in rats via activation of central alpha-2 adrenoceptors

Dexmedetomidine, a highly selective and potent alpha-2 adrenoceptor agonist, reduces halothane anesthetic requirements by over 90% in rats. The present study examined whether dexmedetomidine produces a hypnotic-anesthetic action in rats. Dexmedetomidine induced a hypnotic-anesthetic state in rats characterized by loss of righting reflex at doses greater than or equal to 0.1 mg/kg. This response was dose-dependent between 0.1 and 3 mg/kg. Alpha-2 adrenoceptor antagonists that cross the blood-brain barrier (antipamezole and idazoxan) decreased the hypnotic-anesthetic action of dexmedetomidine in a dose-dependent fashion. In contrast, the alpha-2 antagonist, L-659,066, which does not penetrate into the CNS did not affect dexmedetomidine-induced hypnosis. Antagonists for the other adrenoceptors not only failed to reduce the hypnotic-anesthetic action of dexmedetomidine but in some cases even potentiated this effect. Thus, prazosin, an alpha-1 adrenoceptor antagonist, significantly enhanced the hypnotic-anesthetic property of dexmedetomidine. Antagonists with beta-2 receptor blocking properties also enhanced dexmedetomidine-induced hypnosis. Selective beta-1 receptor antagonists did not affect the hypnotic action of dexmedetomidine. These results suggest that dexmedetomidine produces a hypnotic-anesthetic action in rats via activation of central alpha-2 adrenoceptors.