Effect of age on the contraction of pulmonary venous sphincters in rats.

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Pulmonary veins of rats have regular focal ringlike muscular constrictions (sphincters) that deepen with stimuli, such as head injury, sufficient to cause pulmonary edema. The depth of the individual constrictions on the veins can be determined by casting the pulmonary circulation, fracturing the cast veins at their narrowed points, and measuring the constriction using a scanning electron microscope. A recent study in rats given a blow to the head showed that the venous constriction was attenuated by alpha-adrenergic antagonism, but interaction between the antagonist, the animal body weight, and sex was found. Older, heavier male animals constricted more. To clarify these factors and assess the change in pulmonary venous sphincter contraction with age, 20 female Sprague-Dawley rats aged 5, 10, 15, 20, and 30 wk had their lung vasculature cast with methyl methacrylate. Of the 4 animals in each age group 3 were given a blow to the head to constrict the veins while the plastic was solidifying. The lungs were digested and the casts of the blood vessels were fractured, exposing the constricted portions of the veins. The depths of these focal constrictions were measured. In animals that received the head blow the constrictions were 2.9 +/- 0.3% (5 wk), 4.1 +/- 0.3% (10 wk), 5.8 +/- 0.4% (15 wk), 6.8 +/- 0.4% (20 wk), and 7.1 +/- 0.5% (30 wk) (p < 0.0001). To separate age from weight, a multivariate regression that accounted for venous contraction was carried out. Although head blow, age, and weight were each individually important, the combined model showed age was insignificant (p = 0.9) when weight (p = 0.02) was present.(ABSTRACT TRUNCATED AT 250 WORDS)

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