鳖心对迷走刺激的时相依赖性反应

THE PHASE--DEPENDENT RESPONSE OF THE HEART TO VAGAL STMULATION IN SOFT--SHELLED TURTLES

在27只毁脑和脊髓的中华鳖上,研究了时相耦联式刺激迷走神经对心率的影响。结果心脏的负变时性反应取决于刺激猝发所在的心动周期时相。首先A-A间期逐渐延长,然后突然缩短。在注射心得安的鳖中,常温下右迷走刺激引起的时相反应曲线的幅度(AT)为1484.10±213.10ms,从最大至最小反应的时相差异为804,00±210.90 ms。AT及(St-A)_(max)(产生最大A-A间期的刺激开始至下一A波开始的间期)直接随AA(最大及最小反应的均值)的改变而改变,皆呈正线性相关,但(St-A)_(min)(产生最小A-A间期的刺激开始至下一A波开始的间期)与AA无显著相关性。冬眠期4只鳖的AT,AA及(St-A)_(min)都显著增大,其中3只鳖在特定时相刺激引起心率加快。左迷走的时相反应明显较小或无作用。 上述反应可被阿托品消除,提示是由于静脉窦起搏细胞在其活动周期的不同时相对迷走传出末梢所释放的ACh的反应性不同所致。

Using cardiac cycle length (A-A interval) as an index, the effect of phase--cou-pled burst of vagal stilmulation on the heart rate were investigated in 27 turtles. Thenegative chronotropic response depended on timing of the stimulus burst within the car-dinc cycle. At first, the A-A interval was lengthened progressively and then showed arapid decrease. The amplitude (AT) of the mean phase--response curve to right vagalstimulus in turtles treated by propranolol at normal temperature was 1484.10±213.10 ms. The minimum--to--maximum phase difference of the response curves was804.00±210.90 ms. Both the AT and (St--A)_(max) of the response curve varied directlywith AA. In contrast, (St-A)_(min) was not influenced by AA. Moreover, it was alsofound that the TFR, AT, AA and (St--A)_(min) in hibernant animals were all higher thanthose in normal ones. However, in three of the six hibernant turtles maximum positivechronotropic response could be elicited at the time when (A--A)_(min) was elicited by vagalstimulation. The results indicated that the phase--dependent response to right vagus inturtles was similar to that in homothermal animals, but significantly different both inthe amplitude of the phase--response and the latency of negative chronotropic response.Since the phase--response was abolished by atropine, not by propranolol, it was suggestedthat the occurrence of phase-response was due to changes of responsiveness of automaticcells to ACh released from the vagus nerve.