Institute of Tropical Medicine, Nagasaki University
Abstract
Adult Wistar male rats were used for this experiment. Spinal cord was transected between the C_7 and Th_1 vertebrae under anesthetic condition. After the surgical operation, rats were reared in a warm room (30℃) as chronic spinal rats, and experiment was also performed in a climatic chamber (30℃, 60% r.h.). During the experiment, conscious spinal rats were placed in a small wire-mesh cage. Propranolol hydrochloride (Prop., 8mg/kg; β-adrenergic antagonist) was injected intraperitoneally. Rectal temperature (Tre), tail skin temperature (Ttail) and ambient temperature (Ta) were detected by thermistor probes and recorded simultaneously. In some cases, in addition to such parameters mentioned above, heart rate (HR) calculated by electrocardiogram (ECG) and arterial blood pressure (BP) through the femoral catheter were also recorded. As the index of the tail blood flow, the difference (dTtail) between Ttail and Ta was calculated (dTtail=Ttail-Ta). A sustained decrease in dTtail for 50 min was observed after the Prop. injection in Group-A (S<1W; less than 1 week (W) after the spinalization, N=6), Group-B (1W<S<2W, N=10) and Group-C (2W<S, N=6). In Group-A, mean dTtail was 1.5±0.3℃ before the injection and 0.8±0.3℃ (p<0.05) at 30 min after the injection, mean Tre was 36.3±0.2℃ before the injection and 36.2±0.2℃ (not significant) at 30 min after the injection. In Group-B, mean dTtail was 1.3±0.4℃ before the injection and 0.2±0.2℃ (p<0.01) at 30 min after the injection, mean Tre was 37.2±0.3℃ before the injection and 37.2±0.3℃ at 30 min after the injection. In Group-C, mean dTtail was 1.6±0.4℃ before the injection and 0.5±0.4℃ (p<0.05) at 30 min after the injection, mean Tre was 38.2±0.6℃ before the injection and 38.8±0.7℃ (p<0.05) at 30 min after the injection. By the Prop. injection HR decreased markedly and it stayed at the low level of about 300 beats/min. Mean HR was 394±25 beats/min before the injection, and 292±13 beats/min at 10 min, 285±13 beats/min at 20 min, 285±19 beats/min at 30 min (p<0.05). Arterial BP did not change or slightly increased from just after the injection. Mean value of BP was 82±6 mmHg before the injection, 82±8mmHg at 30 min after the injection. After intraperitoneal injection of the physiological solution, neither BP nor Tre changed. From these results it is assumed that decrease of dTtail after the Prop. injection in chronic spinal rats is due to the vasoconstriction in the tail but not due to the reduction in temperature of circulating blood. The possible explanations for this phenomenon were discussed, as follows; 1, an enhancement of α-adrenergic vasoconstrictor effect by β-adrenergic antagonist 2, the sympathetic reflex triggered by the hemodynamic changes after administration of β-adrenergic antagonist. However from these results, it is difficult to concluded decisively and to explain the underlying mechanisms of the phenomenon. It remains to be solved whether the vasoconstrictor nerves were involved in this response or not in chronic spinal rats
