The relation between stimulus frequency and the relative size of the components of the biphasic response of the vas deferens to electrical stimulation at different temperatures.

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Abstract
Electrical stimulation of the guinea pig or rat vas deferens (pre- or post-ganglionically) at frequencies from 2.5-40 Hz with trains of stimuli of 30 s duration induced a biphasic response. A rapid contraction (component A) was followed after a brief relaxation by a slower contraction (component B); the 2 phases were seen most clearly with stimulation frequencies of less than 10 Hz. The responses to post-ganglionic stimulation were always larger than those to preganglionic stimulation. In general, at low frequencies component A exceeded component B while at high frequencies component B was the larger. Separation of the 2 components on the basis of their frequency response characteristics was better for rat than for guinea pig vasa. Log frequency-response curves to transmural (post-ganglionic) electrical stimulation and log dose-response curves to noradrenaline were recorded for guinea-pig and rat vasa deferentia at 32.degree., 22.degree. and 12.degree. C. For the guinea pig reduction of bath temperature to 12.degree. C increased the amplitude of component A at 2.5 and 5 Hz; component B could not confidently be distinguished at this temperature. At 22.degree. C there was potentiation of B at lower frequencies and depression of B at higher frequencies. There was no response to noradrenaline at 12.degree. C. At 22.degree. C the response to noradrenaline was increased except to doses at or near the maximum to which the response was reduced. For the rat vas deferens component A was little changed by reduction of temperature. Component B at 12.degree. C was greatly depressed at higher frequencies. The response to noradrenaline was increased to lower doses and decreased to higher doses as the temperature was lowered. The B component of the response of guinea pig vasa at 22.degree. C and rat vasa at 32.degree. C was more sensitive than the A component to inhibition by thymoxamine. Further analysis of the mechanisms underlying the A and B components of the biphasic response may be facilitated by relative isolation of each component by the appropriate selection of parameters of electrical stimulation and of temperature for the species being investigated. The contractions of the B component are similar to, if not identical with, those produced by exogenously applied noradrenaline.