Changes in regional blood flow in response to distension of the uterus in anaesthetised pigs.

The present study was undertaken in anaesthetised pigs to determine the primary reflex effects of distension of the uterus on the peripheral circulation. Experiments were performed in seven pigs anaesthetised with α-chloralose and artificially ventilated. Blood flow in the superior mesenteric, left renal and left external iliac arteries was assessed using electromagnetic flowmeters. Distension of the uterus was performed whilst preventing changes in heart rate and aortic blood pressure by injecting 20 ml of warm Ringer solution in a balloon positioned within the viscus (mean transmural pressure of about 18 mmHg). In each pig, distension of the uterus caused decreases in all measured blood flows. In four pigs, these decreases were graded by step increments of distension. In the seven pigs, the responses of decrease in mesenteric, renal and iliac blood flows were not affected by blockade of β-adrenergic receptors with propranolol, but were abolished by the subsequent blockade of α-adrenergic receptors with phentolamine. The present study showed that distension of the uterus in anaesthetised pigs primarily caused reflex vasoconstriction in the mesenteric, renal and iliac vascular beds. This reflex response was mediated by sympathetic mechanisms which involved α vascular adrenergic receptors.