Interaction between diltiazem and halothane or enflurane in the canine blood-perfused papillary muscle and sinoatrial node preparations cross-circulated by chronically instrumented conscious donor dog.

Interaction of cardiovascular effects of diltiazem with those of halothane or enflurane was estimated in the canine isolated papillary muscle and sinoatrial node preparations perfused by arterial blood of the chronically instrumented conscious and halothane- or enflurane-anesthetized donor dog, into which diltiazem was infused i.v. at a rate of 20 micro g/kg/min for 60 min. One hour after diltiazem infusion, in the conscious donor dog, mean arterial pressure (MAP) and heart rate (DHR) were decreased to 84 +/- 3 and 84 +/- 2% and PQ interval (PQ) was prolonged to 148 +/- 5%, while in the isolated preparations, developed tension (DT) of the papillary muscle and sinoatrial rate (SAR) were decreased to 68 +/- 3 and 74 +/- 3% and blood flow (BF) was increased to 155 +/- 5% (n = 10). On the other hand, halothane (0.8%) anesthesia per se decreased MAP, DHR, DT and SAR to 89 +/- 8, 84 +/- 3, 79 +/- 3 and 89 +/- 5% (n = 7) of each basal value in conscious state 20 min after the inhalation. During halothane anesthesia, the same dose of diltiazem infused decreased MAP to 74 +/- 4 (n = 7), DHR to 66 +/- 4 (n = 6), DT to 62 +/- 7 (n = 7) and SAR to 69 +/- 1% (n = 3) of each value suppressed by halothane itself. Meanwhile, enflurane (1.7%) anesthesia itself decreased MAP, DHR, DT and SAR to 81 +/- 3, 85 +/- 2, 81 +/- 2 and 88 +/- 2% (n = 10) of each basal value in conscious state 30 min after enflurane inhalation. During enflurane anesthesia diltiazem decreased MAP to 74 +/- 3 (n = 10), DHR to 67 +/- 3 (n = 8), DT to 45 +/- 5 (n = 10) and SAR to 74 +/- 6% (n = 3) of each value under enflurane anesthesia alone. PQ interval of the donor dog heart was prolonged by halothane alone to 111 +/- 5% (n = 7) and by enflurane alone to 110 +/- 2% (n = 10) of the value before each anesthesia, and then diltiazem prolonged PQ interval to 160 +/- 8% (n = 6) and 174 +/- 10% (n = 8) of each value suppressed by the anesthetic itself during halothane- or enflurane-anesthesia, respectively. The second degree AV conduction block was induced in 1 of 7 halothane- and in 2 of 10 enflurane-anesthetized donor dogs, respectively. The sinus arrest was induced by diltiazem in 4 of 7 sinoatrial node preparations under halothane and in 7 of 10 ones during enflurane anesthesia. Moreover, plasma concentration of diltiazem 60 min after the start of infusion was 556 +/- 121 ng/ml in conscious dogs and tended to increase to 752 +/- 101 ng/ml in enflurane anesthetized donor dogs (n = 4), but there was no significant difference between two values (0.05 < P < 0.1). These results indicate that effects of diltiazem could be potentiated during halothane or enflurane anesthesia by elimination of compensatory reflex noted in conscious state, and that the negative inotropic effect of diltiazem was enhanced by enflurane anesthesia due to unknown mechanisms which probably include a slight but insignificant increase in plasma concentration.