Ischemically sensitive abdominal visceral afferents: Response to cyclooxygenase blockade

Ischemically sensitive abdominal visceral afferents are known to reflexly stimulate the cardiovascular system. These nerve endings respond to severe hypoxia as well as to exogenously administered bradykinin and prostaglandins such as PGI₂, PGE, and PGF(2α). We have shown previously that these prostaglandins can sensitize some previously unresponsive afferents to respond to ischemia. To determine if endogenously produced prostaglandins contribute to the observed increase in activity during ischemia, we recorded activity of 6 Aδ- and 23 C-fiber sympathetic afferents in anesthetized cats during 5 min of ischemia before and 15-30 min after intravenous administration of either indomethacin (5 mg/kg) or aspirin (50 mg/kg). Before cyclooxygenase inhibition, we noted repeatable increases of 1.44 ± 0.22 and 1.44 ± 0.36 impulses/s in the Aδ- and C-fibers, respectively, in response to ischemia. After indomethacin or aspirin, these increases were significantly reduced (P < 0.05) in both thinly myelinated and unmyelinated afferents (0.69 ± 0.36 and 0.46 ± 0.21 impulses/s, respectively). In a second protocol, we observed that the activity of six Aδ- and seven C-fibers was significantly reduced by aspirin or indomethacin when a single period of ischemia preceded cyclooxygenase blockade. These data, in conjunction with our previous observations, indicate that prostaglandins significantly contribute to the increased afferent discharge activity associated with ischemia of the abdominal visceral region.