Enhanced Bradykinin-Stimulated Prostaglandin Release in the Acutely Inflamed Guinea Pig Gallbladder Is Due to New Synthesis of Cyclooxygenase 1 and Prostacyclin Synthase

Abstract

Background.Our previous studies have shown that acute gallbladder (GB) inflammation increases endogenous bradykinin (BK)-stimulated prostaglandin (PG) release and inhibits guinea pig (GP) GB contractility. This study examines the hypothesis that exaggerated PG release following BK stimulation in the inflamed guinea pig GB is due to new protein synthesis of cyclooxygenase 1 (COX-1) and prostacyclin synthase (PS).Materials and methods.Male Hartley GPs (450–550 g) were anesthetized and underwent common bile duct ligation (BDL, a model of acute inflammation). GBs were harvested after 3 days from BDL and control groups. Tissue slices were prepared and placed in oxygenated tissue culture medium at 37°C for 1 h (basal) and for a second hour in medium alone (carrier, Car), medium plus 10−6M BK, or medium plus 10−6M BK plus cycloheximide 100 μg/ml (BK + CX). The medium was assayed for net release of 6-keto-PGF1α(PGI2metabolite), thromboxane B2(TxB2), PGE2, leukotriene B4(LTB4), and C4(LTC4) by enzyme immunoassay and data are reported as nanograms per milligram of protein. GB tissue from control and BDL groups was examined for COX-1, COX-2, PS, and inducible nitric oxide synthase (iNOS) content by Western blot analysis, analyzed by densitometry, and reported as densitometry units.Results.All data were analyzed by ANOVA andttest and reported as means ± SEM,N≥ 5. BK increased the release of PGI2and PGE2from the control group and markedly exaggerated release of PGI2and PGE2from the BDL GP gallbladder. This exaggerated PGI2and PGE2release was greatly diminished by inhibition of new protein synthesis with cycloheximide. TxB2, LTB4, and LTC4showed no significant differences between any groups. COX-1 and PS contents were significantly elevated in the BDL group compared with control. COX-2 and iNOS were not present in control or BDL GBs.Conclusions.These data suggest that the enhanced BK-stimulated PG release seen in the acutely inflamed GP gallbladder is due to the synthesis of new COX-1 and PS enzymes.