Abstract
We investigated whether responsiveness to dinucleotide uridine adenosine tetraphosphate (Up&sub4;A) was altered in aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats compared with those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats at the chronic stage of disease. In OLETF aortas, we observed the following: (1) Up&sub4;A-induced contractions were lower than those in the LETO aortas under basal conditions, (2) slight relaxation occurred due to Up&sub4;A, but this was not observed in phenylephrine-precontracted LETO aortas, (3) acetylcholine-induced relaxation was reduced (vs. LETO), and (4) prostanoid release (prostaglandin (PG)F2α, thromboxane (Tx)A&sub2; metabolite, and PGE&sub2;) due to Up&sub4;A was decreased (vs. LETO). Endothelial denudation suppressed Up&sub4;A-induced contractions in the LETO group, but increased the contractions in the OLETF group. Under nitric oxide synthase (NOS) inhibition, Up&sub4;A induced contractions in phenylephrine-precontracted aortas; this effect was greater in the LETO group (vs. the OLETF group). The relaxation response induced by Up&sub4;A was unmasked by cyclooxygenase inhibitors, especially in the LETO group, but this effect was abolished by NOS inhibition. These results suggest that the relaxant component of the Up&sub4;A-mediated response was masked by prostanoids in the LETO aortas and that the LETO and OLETF rats presented different contributions of the endothelium to the response.