Variations in Vascular Reactivity Produced by Season, Cold Stress and Immaturity; Role of Thyroid and Adrenal Cortex

Abstract

Seasonal variations in the reactions of over 500 isolated adult swine carotid arteries studied by a plethysmographic technic over a 30-month period in a single laboratory are described. In winter (Nov. through Apr.) vasoconstriction to epinephrine and acethylcholine is shorter and the reaction to histamine is longer than in summer. The arteries of swine of <12 kg. and of thyroidectomized swine have a pattern of vascular reactivity similar to winter-killed adult swine. In the vessels from the thyroidectomized swine this pattern reverted to normal when DL-thyroxine was added to the perfusate. Acute cold stress did not duplicate the seasonal changes. The histamine response in arteries of adrenalectomized pigs was prolonged; cortisone (2:106) shortened this reaction to normal. No changes occurred in the reaction of these arteries to epinephrine or acetylcholine. Inhibition of amino oxidase, cholinesterase and histaminase resulted in an increase . in the % vasoconstriction and duration of the reaction of normal isolated arteries to L-epinephrine, acetylcholine and histamine, respectively. Evidence is presented suggesting that the seasonal and age variations in vascular reactivity may be partially due to variations in the tissue level of thyroid hormone.