The effect of urethane and thiopental sodium on platelet aggregation in vitro and in vivo

Thiopental enhances human platelet aggregation by increasing arachidonic acid release

Conflicting results have been reported regarding the effect of thiopental on aggregation and cytosolic calcium levels in platelets. The present study attempted to clarify these phenomena. Using platelet-rich plasma or washed suspensions, platelet aggregation, thromboxane (TX) B2 formation, arachidonic acid (AA) release, and cytosolic free calcium concentrations ([Ca2+]i) were measured in the presence or absence of thiopental (30–300 µM). Platelet activation was induced by adenosine diphosphate (ADP, 0.5–15 µM), epinephrine (0.1–20 µM) arachidonic acid (0.5–1.5 mM), or (+)-9,11-epithia-11,12-methano-TXA2 (STA2, 30–500 nM). Measurements of primary aggregation were performed in the presence of indomethacin (10 µM). Low concentrations of ADP and epinephrine, which did not induce secondary aggregation in a control study, induced strong secondary aggregation in the presence of thiopental ([Formula: see text]100 µM). Thiopental ([Formula: see text]100 µM) also increased the TXB2 formation induced by ADP and epinephrine. Thiopental (300 µM) increased ADP- and epinephrine-induced 3H-AA release. Thiopental (300 µM) also augmented the ADP- and epinephrine-induced increases in [Ca2+]i in the presence of indomethacin. Thiopental appears to enhance ADP- and epinephrine-induced secondary platelet aggregation by increasing AA release during primary aggregation, possibly by the activation of phospholipase A2.Key words: barbiturates, anesthetics, eicosanoids, phospholipase.

Etomidate and thiopental inhibit platelet function in patients undergoing infrainguinal vascular surgery

BACKGROUND

Postoperative platelet hyperaggregability following general anesthesia has been reported in patients undergoing major vascular surgery. In contrast, since anesthetic agents inhibited platelet function both in vitro and in vivo, an increased risk for postoperative bleedings due to prolonged platelet dysfunction has been discussed. Nevertheless, data describing platelet-affecting properties of induction agents such as etomidate and thiopental in patients undergoing major vascular surgery are lacking.

METHODS

Platelet function was determined at 0, 2, 20, and 200 microg/ml thiopental and at 0, 0.2, 2, 20 microg/ml etomidate in vitro in blood samples drawn from 16 patients suffering from severe occlusive arterial disease. In addition, 30 patients undergoing vascular surgery were investigated before (PRE) and after anesthesia induction (T0) either with etomidate (ETO group, n=16) or thiopental (THIO group, n=14), and 2 h after the beginning of surgery (T2). Platelet function was determined according to platelet aggregation, in vitro bleeding time, and flow cytometric measurements.

RESULTS

In vitro, P-selectin expression was inhibited by etomidate at 2 and 20 microg/ml (-28% and -38%, respectively) and also by thiopental at 200 microg/ml (-27%). In patients undergoing vascular surgery, anesthesia induction in the ETO group resulted in a 31% prolongation of the in vitro bleeding time and an inhibition of ADP- and collagen-induced platelet aggregation (-30% and -17%, respectively) and of P-selectin expression (-25%) at T0. In the THIO group, only ADP-induced platelet aggregation was affected (-16%). At T2, all parameters had reached PRE level again in both groups. Furthermore, in comparison with the THIO group, operation time was significantly prolonged and transfusion volume was significantly increased in the ETO group. In addition, platelet count and hematocrit significantly decreased at T2, whereas levels of tPA, PAI-1, fibrinogen and antithrombin III and partial thromboplastin time remained unchanged in both groups during the study period.

CONCLUSIONS

In the present study, etomidate and, to a minor extent, thiopental offered significant platelet inhibitory properties. Anesthetic-induced platelet inhibition may lead to higher transfusion rates and prolonged operation times. Therefore, anesthetic-related platelet inhibitory properties should be considered when searching for the anesthetic agent of choice, especially in patients with compromised hemostasis and co-existing bleeding disorders.

Platelet function and anesthetics in cardiac surgery: an in vitro and ex vivo study

We studied the effects of the anesthetics commonly used in cardiac surgery on platelet function. Fentanyl, droperidol, succinylcholine, pancuronium, thiopental, and diazepam at therapeutic concentrations were tested for their in vitro effects on the expression of platelet membrane glycoproteins Ib and IIbIIIa (GpIb, GpIIb-IIIa) and of P-selectin in anticoagulated whole blood by flow cytometry. The expression of P-selectin was determined under basal conditions, after the incubation of blood with adenosine diphosphate (ADP) 10 micromol/L, and the stable prostaglandin endoperoxide analog U46619 1 micromol/L. No drug affected the expression of P-selectin in unstimulated and ADP- or U46619-stimulated platelets, with the exception of thiopental, which markedly decreased the U46619-induced expression of P-selectin. Thiopental concentration-dependently inhibited U46619-induced and ADP-induced platelet aggregation, with effects on U46619-induced aggregation at therapeutic concentrations. To assess ex vivo effects, the same platelet markers were also assessed in blood obtained from 10 patients undergoing elective coronary surgery. Compared with basal values, platelet response to U46619 was significantly reduced just after the administration of anesthetic drugs, and the effect persisted for 48 h after surgery. Our study suggests that, at therapeutic concentrations, thiopental inhibits U46619-induced platelet activation both in vitro and ex vivo. The mechanisms responsible of this effect, together with its clinical significance, require further investigation.

IMPLICATIONS

Thiopental inhibited prostaglandin-induced platelet activation at therapeutic concentrations both in vitro and ex vivo in cardiac surgical patients whereas adenosine diphosphate-induced activation was affected only at supratherapeutic drug concentrations. Thus, administration of sodium thiopental may contribute to the in vivo impairment of platelet function in patients undergoing elective cardiac surgery.

Suitability of urethane anesthesia for physiopharmacological investigations. Part 3: Other systems and conclusions

The suitability of urethane anesthesia for physiopharmacological experiments in various systems is briefly reviewed. Urethane anesthesia appears to be suitable for various types of studies on respiratory function and on reflex activation of motility of the urinary bladder and some sections of the intestinal tract. However, urethane produces a variety of potentially disturbing side-effects at endocrine and renal level.