PULMONARY VENOUS SPHINCTER CONSTRICTION IS ATTENUATED BY ALPHA-ADRENERGIC ANTAGONISM

Pulmonary veins of rats have regular thin bands of constriction (sphin cters) that deepen when the animals are given a blow to the head that is sufficient to cause pulmonary edema. Pulmonary edema caused by a st imulus to the brain is attenuated by alpha-adrenergic blockade. This s tudy tested the hypothesis that alpha-adrenergic antagonism decreases this contraction in pulmonary veins. Male and female Sprague-Dawley ra ts were given prazosin, an alpha1-specific antagonist, phentolamine, a combined alpha1- and alpha2-antagonist, or saline 10 min before their lungs were cast and they were given a blow on the head. The casts wer e fractured, causing the veins to break at the site of the constrictio n. Depth of contraction expressed as a percentage was 1 minus the rati o of the inner (constricted) and outer (total) diameters of the vein a t the fracture. Resin that escaped the vascular space to cast alveoli and lymphatics was also measured. The average contraction of the veins at the site of the sphincters was 7.9 +/- 1.1% in the saline group, 5 .4 +/- 0.7% in the phentolamine group, and 4.8 +/- 0.7% in the prazosi n group (p < 0.05), although about a third of the constrictions were l ess than 2% in all groups. Arteries had no contraction. Contraction wa s greater in heavier and male animals, which were variables that inter acted with the agent the animals were given in a multivariate analysis . Contrary to the hypothesis, lymphatic casts were greater in the anim als receiving alpha-blockers (p < 0.001). This study shows that the de pth of the constriction of the sphincters of the veins can be measured and that alpha-adrenergic antagonists reduce it, but they increase ly mphatic casting.