Diabetes attenuates the minimum anaesthetic concentration (MAC) and MAC-blocking adrenergic response reducing actions of clonidine in rats

Aortic depressor nerve function examined in diabetic rats by means of two different approaches

The present study examined in anesthetized rats, 5 or 120 days after the onset of streptozotocin-induced diabetes, the aortic depressor nerve (ADN) function by means of pressure-nerve activity curve (fitted by sigmoidal regression) and cross-spectral analysis between mean arterial pressure (MAP) and ADN activity. From the sigmoidal regression curve it was calculated the upper and lower ADN activity plateau, range, average gain and MAP halfway between the lower and upper plateau (MAP50). By means of spectral analysis it was calculated the transfer function magnitude (ratio of ADN activity/MAP) as an index of ADN sensitivity (gain) during induced (withdrawal and reinfusion of blood) slow (0.35 Hz) oscillations of MAP simulating Mayer's waves and spontaneous oscillations (approximately 1.5 Hz) caused by respiratory movement. Diabetic rats exhibited, at 5 or 120 days, lower MAP and heart rate. The parameters calculated by means of the sigmoidal regression curve, as well as the ADN activity gain during slow or spontaneous oscillations of MAP, were similar in diabetic and control rats. In conclusion, it was demonstrated that ADN activity was not altered after 5 or 120 days of experimental diabetes, even though the literature documents, at this time frame of diabetes, a conspicuous derangement of the baroreflex.

Diabetes Mellitus Reduces the Antiarrhythmic Effect of Ion Channel Blockers

We designed the present study to examine whether diabetes mellitus affects the antiarrhythmic effect of flecainide, a sodium channel blocker, E-4031, a potassium channel blocker, and verapamil, a calcium channel blocker, in diabetic rats. The experiments were performed in intact and diabetic rats 2, 4, and 6 wk after administration of streptozotocin. Rats were anesthetized with halothane and monitored continuously for arterial blood pressure and premature ventricular contractions. The arrhythmogenic dose of epinephrine was defined as the smallest dose producing 3 or more premature ventricular contractions within a 15-s period. The arrhythmogenic doses of epinephrine in the presence of flecainide were 8.2 +/- 2.2 (mean +/- sd), 7.4 +/- 6.1, 5.5 +/- 2.8, and 2.0 +/- 0.5 microg/kg in intact and diabetic rats 2, 4, and 6 wk after streptozotocin administration, respectively. Similarly, the arrhythmogenic doses of epinephrine in the presence of E-4031 were 7.7 +/- 2.6, 2.3 +/- 0.7, 2.0 +/- 0.7, and 1.2 +/- 0.5 microg/kg, and those in the presence of verapamil were 8.2 +/- 2.1, 3.1 +/- 1.2, 2.3 +/- 0.9, and 1.5 +/- 0.5 microg/kg. Insulin partially recovered the antiarrhythmic effect of the blockers. We concluded that diabetes mellitus reduces the antiarrhythmic effects of flecainide, E-4031, and verapamil.

Insulin decreases isoflurane minimum alveolar anesthetic concentration in rats independently of an effect on the spinal cord

The observation that insulin supplies an element of analgesia suggests that insulin administration might decrease the concentration of inhaled anesthetic required to produce MAC (the minimum alveolar anesthetic concentration required to eliminate movement in response to noxious stimulation in 50% of subjects). We hypothesized that insulin decreases MAC by directly affecting the nervous system, by decreasing blood glucose, or both. To test these hypotheses, we infused increasing doses of insulin either intrathecally or IV in rats anesthetized with isoflurane and determined the resulting MAC change (assessing forelimb and hindlimb movement separately). Infusion of insulin produced a dose-related decrease in MAC that did not differ among groups. That is, the IV and intrathecal infusions caused similar decreases in MAC at a given infusion rate. Blood glucose concentrations were larger in the rats given insulin with 5% dextrose. However, the percentage change in MAC determined from forelimb versus hindlimb movement did not differ. For a given insulin infusion rate, MAC changes and glucose levels did not correlate with each other, except, possibly, for the most rapid infusion rate, for which smaller glucose concentrations were associated with a marginally larger decrease in MAC. Intrathecal infusions of insulin did not produce spinal cord injury. In summary, we found that insulin decreases isoflurane MAC in a dose-related manner independently of its effects on the blood concentration of glucose. The sites at which insulin acts to decrease MAC appear to be supraspinal rather than spinal. The effect may be due to a capacity of insulin to produce analgesia through an action on one or more neurotransmitter receptors.

IMPLICATIONS

Intrathecal and IV insulin administration equally decrease isoflurane MAC in rats, regardless of the concentration of blood sugar. These findings indicate that although insulin decreases MAC, the decrease is not mediated by actions on the spinal cord.

Diabetes attenuates the hemodynamic stabilizing effects of oral clonidine during off-pump coronary artery bypass surgery

STUDY OBJECTIVE

To investigate the influence of diabetes mellitus on the hemodynamic-stabilizing effect of clonidine during off-pump coronary artery bypass (OPCAB) surgery.

DESIGN

Prospective study.

SETTING

Public, university-affiliated hospital.

PATIENTS

40 patients (32 male, 8 female) scheduled for OPCAB surgery.

INTERVENTIONS AND MEASUREMENTS

Patients were divided into equal groups of diabetic and nondiabetic patients. All patients were given 150 microg oral clonidine 1 hour before induction. Anesthesia was induced and maintained with fentanyl, propofol, and sevoflurane. Propranolol was administered intermittently to maintain an adequate heart rate (HR; 50 to 70 bpm). Preoperative demographic data (fasting blood glucose concentration and hemoglobin A1c), dose of intraoperative drugs (propofol and propranolol), and outcome data (duration of intubation and duration of hospital stay after surgery) were analyzed.

MAIN RESULTS

In the diabetic and nondiabetic groups, the mean (+/-SD) plasma glucose values were 7.8 +/- 2.3 mmoL. L(-1) and 5.4 +/- 0.7 mmoL. L(-1), respectively (p < 0.05), and the mean (+/-SD) HbA1c values were 7.1 +/- 1.3% and 5.2 +/- 0.4%, respectively (p < 0.05). The mean propofol infusion rate was 2.8 +/- 0.9 mg. kg(-1). h(-1) in diabetic patients and 3.1 +/- 1.0 mg. kg(-1). h(-1) in nondiabetics (NS, p > 0.05). The total requirement for propranolol was 5.1 +/- 2.4 mg in diabetic patients and 1.6 +/- 1.1 mg in nondiabetics (p < 0.05).

CONCLUSIONS

Diabetes attenuates the hemodynamic stabilizing effects of preanesthetic oral clonidine in the clinical setting.