The differential effect of cooling on the responses of splenic capsular and vascular smooth muscle to nerve stimulation and noradrenaline.

The responses of the capsular and vascular smooth muscle of the dog's spleen to splenic nerve stimulation and to infused noradrenaline have been studied in the isolated, blood-perfused preparation at 37 degrees C, at 27 degrees C and again after rewarming to 37 degrees C. It was found that cooling per se had no effect on perfusion pressure but reduced splenic arterial blood flow, and caused no appreciable alteration in spleen volume. The increase in splenic flow resistance in response to nerve stimulation and noradrenaline was significantly greater at 27 degrees C than at 37 degrees C, but the concomitant reduction in spleen volume was significantly reduced. The enhanced effect of splenic nerve stimulation and noradrenaline on splenic flow resistance is discussed in terms of the relative contributions of an increased smooth muscle response and increased blood viscosity. The different effects of cooling on the responses of splenic vascular and capsular smooth muscle to nerve stimulation and noradrenaline are discussed in the context of the effect of cooling on other vascular and non-vascular smooth muscle.