Effects of prostaglandins and the autonomic nervous system on the vasodilatory properties of nitroglycerin in conscious dogs.

This study was designed to assess the respective roles of prostaglandins and the autonomic nervous system in the responses to nitroglycerin (NTG) in conscious dogs. In vivo, NTG (1, 10, and 100 micrograms/kg i.v.) induced dose-dependent decreases in blood pressure and increases in heart rate and cardiac output. Coronary and carotid blood flows increased simultaneously, whereas responses in renal blood flow were biphasic, i.e., an initial decrease was followed by an increase above control at 10 and 100 micrograms/kg. NTG responses were not changed by indomethacin but were affected by chlorisondamine alone or in combination with indomethacin; tachycardia was abolished, and increases in cardiac output after 10 and 100 micrograms/kg were reduced by 26 and 32%, respectively, after ganglionic blockade and by 19 and 32%, respectively, after chlorisondamine plus indomethacin. In addition, increases in carotid blood flow in doses of 100 micrograms/kg were reduced by 88% after chlorisondamine and 83% after chlorisondamine plus indomethacin. Finally, in the presence of chlorisondamine plus indomethacin, NTG induced a more pronounced hypotension associated with a more pronounced renal vasodilation at the highest dose. Independent of indomethacin pretreatment, NTG in vitro induced a dose-dependent relaxation of the carotid, coronary, and renal arteries. Depending on the vascular bed, the reflex and local controls of circulation are affected differently by NTG.