Thiacetarsamide depresses relaxation of canine pulmonary artery in vitro.

Little information is available on the primary pharmacological effects of thiacetarsamide on mammalian systems, particularly on blood vessels. The effects of thiacetarsamide on arterial responses was studied in isolated rings from canine pulmonary artery. Vessels were exposed to thiacetarsamide and dose-response relationships were applied to methacholine and nitroglycerin. To rule out non-specific effects of antihelmintics, the effects of two other antifilarial drugs, diethylcarbamazine and ivermectin, were also tested. Thiacetarsamide significantly depressed relaxation of canine pulmonary artery to both methacholine and nitroglycerin, and significantly enhanced constriction to norepinephrine. Neither diethylcarbamazine nor ivermectin altered vascular response. These direct effects of thiacetarsamide on arterial responsiveness may be responsible, in part, for acute pulmonary complications observed in dogs infected with Dirofilaria immitis after adulticide treatment.