Acetaminophen, Phenacetin and Dipyrone Do Not Modulate Pressor Responses to Arachidonic Acid or to Pressor Agents

In contrast to nonsteroidal anti-inflammatory drugs (NSAIDs), the nonopioid analgesics phenacetin, acetaminophen and dipyrone exhibit weak anti-inflammatory properties. An explanation for this difference in pharmacologic activity was provided by the recent discovery of a new cyclooxygenase isoform, cyclooxygenase (COX)-3, that is reported to be inhibited by phenacetin, acetaminophen and dipyrone. However, COX-3 was found to be a spliced variant of COX-1 and renamed COX-1b. Although recent studies provide evidence for the existence of this new COX isoform, it is uncertain whether this COX-3 (COX-1b) isoform, or putative acetaminophen-sensitive pathway, plays a role in the generation of vasoactive prostaglandins. NSAIDs increase systemic blood pressure by inhibiting the formation of vasodilator prostanoids. Angiotensin II, norepinephrine and other vasoconstrictor agents have been reported to release prostaglandins. It is possible that this acetaminophen-sensitive pathway also modulates pressor responses to these vasoconstrictor agents. Therefore, the purpose of the present study was to determine whether this acetaminophen-sensitive pathway plays a role in the generation of vasoactive products of arachidonic acid or in the modulation of vasoconstrictor responses in the pulmonary and systemic vascular bed of the intact-chest rat. In the present study, the nonopioid analgesics did not attenuate changes in pulmonary or systemic arterial pressure in response to injections of the prostanoid precursor, arachidonic acid, to the thromboxane A2 mimic, U46619, or to angiotensin II or norepinephrine. The results of the present study do not provide evidence in support of a role of a functional COX-3 (COX-1b) isoform, or an acetaminophen-sensitive pathway, in the generation of vasoactive prostanoids or in the modulation of responses to vasoconstrictor hormones in the intact-chest rat.