Studies of frequency-dependent inhibition of noradrenaline on the hypogastric ganglion of the guinea pig

Abstract

In previous studies, we showed that selective application of noradrenaline (NA) to the ganglion in the hypogastric nerve-vas deferens preparation of the guinea pig inhibited twitch-like response of the muscle to preganglionic nerve stimulation at low frequencies(stimulation was for period of 2 sec at 2min intervals at frequency of 2 to 50Hz with a pulse duration of 0.1msec), and the ganglion depressant effectiveness of NA increased with decreasing stimulation of frequency. These findings were obtained on the condition that a period of stimulation was held constant. An alteration of frequency in a fixed stimulation-period means change of both the interval between pulses and the number of pulses. The purpose of this study is to elucidate a relationship between these two stimulation parameters and the depressant effect of NA. Since the twitch-like response to the nerve stimulation increased with extending stimulation-period within 2sec and since the same response attained maximum at frequency of 20Hz, the effect of NA was examined on the response to the stimulation at frequency of 2 to 20Hz on the condition that the stimulation-period was within 2sec. When the pulse-number was kept constant and the pulse-interval was altered, NA produced equivalent inhibition of the response. In a fixed pulse-interval, the effectiveness of NA decreased with increasing pulse-number. With the same condition, NA did not block the response to nerve stimulation with a 40pulse train at pulse-interval of 50msec. These results suggest that the depressant action of NA on the guinea-pig hypogastric ganglion is pulse-number dependent.