Thomas M. Tagliente

Beneficial effects from β-adrenergic blockade in elderly patients undergoing noncardiac surgery

BackgroundPerioperative β-blockade has been shown to improve long-term cardiac outcome in noncardiac surgical patients. A possible mechanism for the reduced risk of perioperative myocardial infarction is the attenuation of the excitotoxic effects of catecholamine surges by β-blockade. It was hypothe

Atenolol may not modify anesthetic depth indicators in elderly patients — a second look at the data

PurposeDecreased cardiac chronotropic response in elderly patients along with concomitant β-blockade may suppress the autonomic responsiveness to surgical stimulation and subsequently obscure episodes of “light anesthesia”.MethodsWe analyzed post hoc computerized data from our previous study evaluating the effects of perioperative atenolol administration. Bispectral index (BIS) and the performance of routine anesthetic depth indicators were analyzed in 45 patients undergoing abdominal surgery: Group I (n = 12), isoflurane/fentanyl/nitrous oxide in oxygen anesthesia; Group II (n = 16), isoflurane/fentanyl/nitrous oxide in oxygen with 10 mg atenolol intravenously prior to anesthesia; Group III (n = 17), isoflurane/fentanyl/nitrous oxide in oxygen with a maximum end-tidal isoflurane concentration of 0.4 vol.% and incremental doses of atenolol (5 mg intravenously stepwise). In all groups, blood pressure (BP) was maintained within ♂ 20% of preoperatively defined baseline BP and heart rate (HR) between 50–80 beats·min−1. BP, HR, and end-tidal isoflurane were tested for their potential to predict BIS using a previously described statistical model (PK).ResultsAlthough Group III patients received on average 39.5% less isoflurane compared with Group I patients (P = 0.006), and Groups II and III patients received on average 21% less fentanyl compared with Group I patients (P ≤ 0.002), similar levels of intraoperative average BIS values (53–54) were obtained for all groups. Higher BIS values were reached at emergence in atenolol-treated patients. The performance of hemodynamic variables or end-tidal isoflurane to predict BIS was moderate even at critical intraoperative events, but unaffected by atenolol.ConclusionAtenolol reduces anesthetic requirements but may not modify anesthetic depth indicators in elderly patients.RésuméObjectifChez les patients âgés, la diminution de la réponse cardiaque chronotropique, avec un βblocage concomitant, peut supprimer la réactivité autonome à la stimulation chirurgicale et, par la suite, masquer les épisodes “d’anesthésie légère”.MéthodeNous avons analysé les données informatisées de nos études précédentes pour évaluer les effets de l’administration périopératoire d’aténolol. L’index bispectral (BIS) et le rendement des indicateurs habituels de la profondeur de l’anesthésie ont été analysés chez 45 patients de chirurgie abdominale. Le groupe I (n = 12) comportait une anesthésie avec un mélange d’isoflurane/fentanyl/protoxyde d’azote dans de l’oxygène; le groupe II (n = 16), isoflurane/fentanyl/protoxyde d’azote dans de l’oxygène, avec l’administration intraveineuse de 10 mg d’aténolol avant l’anesthésie; le groupe III (n = 17), isoflurane/fentanyl/protoxyde d’azote dans de l’oxygène, dont une concentration téléexpiratoire maximale d’isoflurane de 0,4 vol.%, et des doses progressives d’aténolol (palier de 5 mg intraveineux). Dans tous les groupes, la tension artérielle (TA) a été maintenue à ♂ 20 % de la mesure de base préopératoire et la fréquence cardiaque (FC) entre 50 et 80 battements·min−1. La TA, la FC et l’isoflurane téléexpiratoire ont été évalués pour leur potentiel de prédiction du BIS en utilisant un modèle statistique précédemment décrit (PK).RésultatsMême si les patients du groupe III ont reçu en moyenne 39,5 % moins d’isoflurane que ceux du groupe I (P = 0,006) et les patients des groupes II et III ont reçu en moyenne 21 % moins de fentanyl que ceux du groupe I (P ≤ 0,002), les valeurs moyennes de BIS peropératoires ont été similaires (53– 54) dans tous les groupes. Des valeurs de BIS plus élevées ont été atteintes chez les patients traités avec l’aténolol. La capacité des variables hémodynamiques ou de l’isoflurane téléexpiratoire à prédire le BIS a été modérée même pour des événements peropératoires critiques, mais elle n’a pas été modifiée par l’aténolol.ConclusionL’aténolol réduit les besoins anesthésiques, mais ne modifierait pas les indicateurs de la profondeur de l’anesthésie chez les patients âgés.

Interleukin balance and early recovery from anesthesia in elderly surgical patients exposed to β-adrenergic antagonism☆

STUDY OBJECTIVE To determine whether proinflammatory and antiinflammatory cytokines, as measured in blood specimens, would correlate with improved SF-36 physical composite scores observed in elderly surgical patients who were administered perioperative atenolol. DESIGN Post hoc analysis of data from a randomized clinical study. SETTING Department of Anesthesiology, Mount Sinai Medical School, New York. PATIENTS 59 ASA physical status II, III, and IV patients > or =65 years of age, who were scheduled for major elective noncardiac surgery. INTERVENTIONS Patients were randomized to one of three anesthetic regimens to receive 1) perioperative management without beta-adrenergic antagonism, 2) preoperative and postoperative administration of atenolol, or 3) intraoperative atenolol as a major component of the anesthetic regimen. MEASUREMENTS AND MAIN RESULTS Blood samples were drawn perioperatively at seven different time points. Interleukin-1 beta, interleukin-6, interleukin-1ra, and interleukin-10 were measured using enzyme-linked immunosorbent assay (ELISA) kits. Also, recovery from anesthesia and physical/mental well-being (SF-36 questionnaire) were determined perioperatively. Compared with control patients, atenolol-treated patients experienced improved postoperative physical well-being, which paralleled the previously reported faster recovery from anesthesia and a decreased need for perioperative analgesics. Improved postoperative physical well-being of atenolol-treated patients was specifically caused by an ameliorated bodily pain score, a major component of the physical composite score of the SF-36 questionnaire. The cytokine response of these elderly surgical patients was similar to that of younger patients, and the perioperative profile of proinflammatory and antiinflammatory cytokines was not affected by atenolol. CONCLUSIONS Perioperative administration of atenolol to elderly surgical patients markedly improves physical sense of well-being, which coincides with improved postoperative pain control and decreased analgesic requirements. This improvement experienced by patients receiving atenolol is not related to alterations in perioperative cytokine response.

Activation of the 2A –adrenoceptor mediates deceleration of the deaggregation component of the response to ADP or 5-HT in human platelets in vitro

Platelet aggregation requires the concomitant activation of at least one G(i)- and one G(q)-coupled receptor. Epinephrine (EPI) amplifies the response elicited by a number of agonists for platelet aggregation. This study tested the hypothesis that platelet alpha(2A)-adrenoceptor activation causes deceleration of the deaggregation component of the platelet aggregation response when activated concomitantly with the G(q)-coupled adenosine diphosphate (ADP) P2Y(1) or 5-hydroxytryptamine(2A) receptor. The time course of the aggregation response of human platelet-rich plasma following activation of combinations of two or three receptors was assessed by turbidometry using lepirudin anticoagulation. Simultaneous activation of specific two- and three-receptor combinations was achieved using selective antagonists for the P2Y(12) and P2Y(1) receptor subtypes. Steady-state and kinetic parameters, obtained using a four-compartment kinetic model, were used to assess the effects on the net aggregation response. Graded alpha(2A)-adrenoceptor activation was associated with a concentration-dependent decrease of the rate constant of deaggregation. Activation of both ADP receptor subtypes and the alpha(2A)-adrenoceptor produced a concentration-dependent, mutual amplification of the aggregation response. In addition, when three receptors were simultaneously activated, mutual amplification of the aggregation response was observed at physiologically relevant concentrations of epinephrine or norepinephrine (NE) and ADP. We propose that similar to the P2Y(12) receptor, activation of the alpha(2A)-adrenoceptor decelerates the deaggregation component shifting the balance toward increased net aggregation. The effects of EPI and NE on the aggregation response may contribute to the mechanism of increased thrombotic risk present in certain pathophysiological and disease states.Platelet aggregation requires the concomitant activation of at least one G i - and one G q -coupled receptor. Epinephrine (EPI) amplifies the response elicited by a number of agonists for platelet aggregation. This study tested the hypothesis that platelet f 2A -adrenoceptor activation causes deceleration of the deaggregation component of the platelet aggregation response when activated concomitantly with the G q -coupled adenosine diphosphate (ADP) P2Y 1 or 5-hydroxytryptamine 2A receptor. The time course of the aggregation response of human platelet-rich plasma following activation of combinations of two or three receptors was assessed by turbidometry using lepirudin anticoagulation. Simultaneous activation of specific two- and three-receptor combinations was achieved using selective antagonists for the P2Y 12 and P2Y 1 receptor subtypes. Steady-state and kinetic parameters, obtained using a four-compartment kinetic model, were used to assess the effects on the net aggregation response. Graded f 2A -adrenoceptor activation was associated with a concentration-dependent decrease of the rate constant of deaggregation. Activation of both ADP receptor subtypes and the f 2A -adrenoceptor produced a concentration-dependent, mutual amplification of the aggregation response. In addition, when three receptors were simultaneously activated, mutual amplification of the aggregation response was observed at physiologically relevant concentrations of epinephrine or norepinephrine (NE) and ADP. We propose that similar to the P2Y 12 receptor, activation of the f 2A -adrenoceptor decelerates the deaggregation component shifting the balance toward increased net aggregation. The effects of EPI and NE on the aggregation response may contribute to the mechanism of increased thrombotic risk present in certain pathophysiological and disease states.

Deaggregation is an integral component of the response of platelets to ADP in vitro : kinetic studies of literature and original data

Adenosine diphosphate (ADP) is recognized as an important mediator of platelet aggregation. Transient aggregation at low ( h 1 w M), and sustained aggregation at higher ADP concentrations are consistently observed. Dissociation of platelet aggregates has been described and may explain the reversible component of the aggregation response. We hypothesized that the net aggregation response to ADP in vitro results from the concurrent activation of two opposing processes, aggregation and deaggregation. Different purinergic receptor subtypes may mediate these effects. To test this hypothesis and its generalizability, we performed a kinetic analysis of representative published ADP-induced aggregation responses supplemented with original data from our laboratory. A four-compartment kinetic model was used to estimate k 3 , a rate constant of deaggregation. Two model-independent parameters, the magnitude of the aggregation response ( j OD) and the time to reach maximal aggregation ( t peak ) were also assessed. Greater sustained aggregation at higher ADP concentrations was consistently associated with increased j OD and t peak but decreased k 3 values. These relationships were independent of type of platelet preparation or experimental conditions and not due to ADP receptor desensitization. Conversely, blockade of the P2Y 12 receptor subtype (ticlopidine, clopidogrel or 2-MeS-AMP) decreased j OD and t peak but increased k 3 values. This supports the presence of active deaggregation which is decelerated by activation of the P2Y 12 receptor subtype.

Molecular and biochemical evidence for the presence of Type III adenylyl cyclase in human platelets

The isoform(s) of adenylyl cyclase (AC) present in human platelets has not been identified, and evidence supporting a role for AC in platelet aggregation is equivocal. We recently characterized deaggregation as an active component of the platelet aggregation response that may be an important determinant of the extent and duration of aggregation. G i -coupled receptors are linked to the inhibition of AC and are targets of antiplatelet drugs. They also affect platelet aggregation by modulating deaggregation, suggesting a role for AC in modulating this response. The purpose of this study was to identify the AC isoform(s) present in human platelets and to identify its physiological modulators. RT-PCR screening of platelet, buffy coat layer cell and bone marrow megakaryocyte cDNA, and Western blot analysis with AC type III (AC-III) antibodies identified AC-III in platelets and in megakaryocytes. Human platelet AC-III was cloned and expressed in HEK293 cells and its characteristics compared to native platelet AC. Both platelet AC and cloned AC-III required Mg 2+ for activity, were insensitive to Ca 2+ and were G s - and G i -coupled. Zn 2+ and SQ22536 inhibited platelet AC activity. The affinity of SQ22536 was increased with Mg 2+ -related stimulation of AC, while that of Zn 2+ was unchanged, which is consistent with a non-competitive interaction between the two metal ions on AC. The Zn 2+ chelator TPEN reversed the inhibitory effects of Zn 2+ . This study identified AC-III as the predominant AC isoform in human platelets, the activity of which may affect the extent and duration of the net aggregation response by modulating deaggregation.

A modified citrulline assay of NOS activity in rat brain homogenates does not detect direct effects of halothane on the kinetics of NOS activity.

An improved citrulline radioassay of nitric oxide synthase (NOS) activity was developed to study the direct effects of the volatile anesthetic (VA) halothane on the enzyme kinetics of neuronal NOS derived from different regions of the rat central nervous system (CNS). The Vmax of NOS in both soluble cytosolic and membrane bound particulate fractions varied across regions with greatest activity in the cerebellum and least in the spinal cord. In contrast, the Km was not different across regions or in the cytosolic and particulate fractions. Halothane at 0.5, 1, 2 or 3% delivered concentration had no effect on either kinetic parameter of NOS in any of the regions studied indicating that the VAs have no direct effects on NOS activity.

Activation of G i -coupled receptors releases a tonic state of inhibited platelet aggregation

Single-receptor pharmacology does not satisfactorily explain the physiology of the ADP-induced platelet aggregation response. It has been shown that, in addition to G q -coupled receptor activation, one G i -coupled receptor, either the ADP P or the f -adrenoceptor, is required for elicitation of aggregation. The underlying mechanism of this action, however, has not been elucidated. By systematically assaying the entire time course of the aggregation and its fade using two methods of aggregometry, we have investigated the role of graded activation of these two G i -coupled receptors. We demonstrate that constant activation of either of two G q coupled receptors, the ADP P2Y 1 or the 5-HT 2A , and incremental activation of either of the two G i -coupled receptors, tightly regulates the aggregation response in vitro , through the apparent release of a tonic inhibition of platelet aggregation. This tightly regulated release of inhibition, which appears analogous to the phenomena of disinhibition observed in the central nervous system, may be instrumental for the continuous adaptation of the aggregation response to variable physiological conditions.

Agonist concentration-dependent differential responsivity of a human platelet purinergic receptor: pharmacological and kinetic studies of aggregation, deaggregation and shape change responses mediated by the purinergic P2Y1 receptor in vitro

Platelet shape change (SC), aggregation and deaggregation responses are integral components of hemostasis that are elicited and modulated in vivo by the simultaneous activation of several membrane receptors. Selective activation of the purinergic P2Y1 receptor in vitro elicits a sustained SC and a small, transient aggregation response that is reversed rapidly by a robust deaggregation response (Platelets 2003; 14: 89). Using a kinetics-based turbidimetric approach to study the modulation of these concurrent components of human platelet responses, we demonstrate that these P2Y1 receptor-related responses and a number of their kinetic and steady-state characteristics are differentially elicited and modulated. P2Y1 receptor agonist concentrations that elicited aggregation (pEC50 for ADP, 2-MeSADP; 5.88, 6.69) were 10-fold greater than those that elicited SC (7.33, 7.67). The magnitude of the aggregation response was agonist concentration-dependent, saturable and was associated with an agonist concentration-dependent deceleration of the deaggregation response. Gi-coupled receptor (α2A-adrenoceptor, EP3 and P2Y12 receptors) agonists also enhanced aggregation through deceleration of the deaggregation response, and an inhibitor of PI3K activity (wortmannin) inhibited aggregation through acceleration of the deaggregation response. Neither treatment affected the extent or the kinetics of the SC response. The aggregation but not the SC response was rapidly desensitized by P2Y1 receptor activation by ADP. The affinity of the selective P2Y1 receptor antagonist, A3P5P, was independent of the response measured and is consistent with the presence of a single P2Y1 receptor subtype. The differential characteristics and modulation of the SC and aggregation responses by a single receptor support the idea that different signaling pathways activated at different occupancy states of the same receptor underlie the two responses. P2Y1 receptor-mediated platelet aggregation and SC responses provide a convenient model for studying the phenomenon of agonist-directed signaling by differential occupancy of the same membrane receptor.

Concurrent responses elicited by isolated activation of platelet G q -coupled receptors, in vitro : a novel approach for their separation and analysis

This study tested the hypothesis that aggregation mediated by activation of a single G q -coupled receptor can be studied quantitatively if four concurrent but distinct components of the observed platelet response, autocrine stimulation, shape change (SC), aggregation and deaggregation, are separately measured. Responses mediated by two G q -coupled receptors, the TXA 2 and the P2Y 1 , were assayed by a novel, kinetics-based turbidimetric approach. Blocking the autocrine stimulation with a cocktail of receptor antagonists revealed rapid and sustained SC that largely masked the aggregation. Mathematical removal of the SC contribution from the changes in optical density indicated that selective activation of either the TXA 2 or the P2Y 1 receptor was sufficient to induce a small aggregation ( j OD = 0.1-0.2) that was reversed rapidly by a concurrent deaggregation. Model-derived rate constants of SC, aggregation and deaggregation described the observed complex time course of their concurrency well. Laser light scattering aggregometry confirmed the rapid deaggregation of platelet aggregates following TXA 2 or P2Y 1 receptor-mediated formation. Saturable concentration response curves of net aggregation were elicited at EC 50 values 6-15 higher than those of SC. The utility of this approach was further demonstrated by the separation of the four components of the response mediated by concurrent 5-HT 2A and f 2A -adrenoceptor activation, as well as the P2Y 1 and f 2A -adrenoceptor, and the autocrine stimulation and SC mediated by the 5-HT 2A receptor. We propose that the novel approach described here is necessary to study the receptor pharmacology and the kinetics of concurrent platelet responses in vitro as demonstrated by platelet aggregation elicited by selective activation of the TXA 2 or the P2Y 1 receptors.