Cyclooxygenase inhibition and glutamine addition to Cryptosporidium parvum infected calf ileal tissue

Abstract

The research contained herein examines the relationship between Cryptosporidium parvum infection, glutamine administration and cyclooxygenase (COX) inhibition in calf ileal tissue. Ileal mucosa from healthy and C. parvum infected calves was mounted in Ussing chambers and treated with COX inhibitors or glutamine. Radiolabeled isotopes were used to determine the unidirectional flux of 22Na and 36Cl, to calculate net fluxes in response to both treatment and infection. Electrical data was collected, and, in conjunction with the isotope data, aided in the determination of electroneutral versus electrogenic transport.

Treatment of infected tissue with indomethacin (10-6 M), a non-selective COX inhibitor, increased electroneutral Na+ uptake (P< 0.05, ANOVA), whereas selective inhibition of COX-1 (SC-560, 10-6 M) or COX-2 (NS-398, 10-6 M) had no effect. Treatment with SC-560 and NS-398 (10-6 M) yielded similar results to that of the indomethacin treatment, indicating that blockade of both enzymes is required to restore electroneutral Na+ absorption. Exogenous glutamine increased Na+ uptake (P< 0.02, control tissue; P= 0.17, infected tissue; ANOVA), also increasing short circuit current in the infected tissue (Isc) (P< 0.05, ANOVA) suggesting electrogenic Na+-glutamine absorption in the infected tissue. The absence of an electrical response following glutamine administration in healthy tissue suggests stimulation of an electroneutral transport mechanism. Immunohistochemistry revealed the presence of both COX isoforms in healthy and infected tissue. Further, NHE-3 was found in the control, but not in the infected tissue, while NHE-2 was found in neither healthy nor infected tissue. For both COX-2 and NHE-3, Western blot analysis confirmed the immunohistochemical findings. This study indicates that the blockade of both COX isoforms is necessary to release the prostaglandin-mediated inhibition of electroneutral Na+ uptake in C. parvum infected calf ileal tissue. The absence of both NHE-2 and NHE-3 in infected tissue, despite the complete restoration of electroneutral sodium transport following prostaglandin inhibition, suggests the presence of an unidentified sodium transporter in infected calf ileum. Further, glutamine increases Na+ uptake by an electrogenic mechanism in infected tissue and an electroneutral mechanism in healthy tissue.