Frequency-dependent differences in the responses of the capsular and vascular smooth muscle of the spleen of the dog to sympathetic nerve stimulation.

1. The responses of the capsular and vascular smooth muscle to splenic nerve stimulation have been studied simultaneously in the isolated blood-perfused dog's spleen.2. Low frequencies of splenic nerve stimulation (below 1.0 Hz) caused pronounced contraction of the splenic capsule but little or no constriction of the splenic vascular bed.3. Splenic contraction reached a maximum at stimulation frequencies of 1-2 Hz; maximum vasoconstriction occurred at frequencies of 7-10 Hz.4. The separation of responses of the capsular and vascular smooth muscle was mimicked by close arterial infusions of either adrenaline or noradrenaline.5. The maximum responses of the splenic vascular smooth muscle to nerve stimulation, adrenaline and noradrenaline were not significantly different.6. The maximum reduction in spleen volume to sympathetic nerve stimulation was significantly greater than the maximum response to close arterial noradrenaline.7. The maximum contractions of the spleen to adrenaline and noradrenaline were not significantly different. At concentrations producing submaximal responses adrenaline was more potent than noradrenaline.8. It is suggested that the frequency dependent separation of smooth muscle responses to sympathetic nerve stimulation is due to a different sensitivity of the capsular and vascular smooth muscle to the chemical transmitter noradrenaline.9. The results are discussed in the context of the function of the dog's spleen.