Cooling Augments Platelet-Induced Contraction of Peripheral Arteries of the Dog

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Abstract
The effect of cooling on platelet-induced contractions was studied. Rings of canine saphenous arteries were suspended for isometric tension recording in organ baths filled with aerated physiological salt solution. Norepinephrine, 5-hydroxytryptamine and autologous aggregating platelets all caused contractions that were augmented by cooling the bath content from 37.degree. to 24.degree. C. These contractions were inhibited, in a concentration-dependent manner, by the serotonergic antagonist ketanserin. The .alpha.1-adrenergic antagonist, prazosin, in concentrations causing progressive inhibition of contractions evoked by norepinephrine did not affect the response to either 5-hydroxytryptamine or platelets. Aggregating platelets were found to release 5-hydroxytryptamine in sufficient amounts to account for the observed contractions. Pretreatment of platelets with the cyclo-oxygenase inhibitor meclofenamate reduced the amount of thromboxane liberated by aggregating platelets but did not influence evoked contractions. Aggregating platelets may cause contraction of the canine saphenous artery by releasing 5-hydroxytryptamine. Apparently, cooling markedly augments contractions of peripheral arterial smooth muscle caused by aggregating platelets.