Date of Award

1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physiology

College

College of Graduate Studies

First Advisor

W. C. Wise

Second Advisor

Rupert L. Green

Third Advisor

James A. Cook

Fourth Advisor

D. G. Priest

Fifth Advisor

Perry V. Halushka

Abstract

A rat fecal peritonitis model of acute intraabdominal sepsis was investigated in order to evaluate the potential role of arachidonic acid metabolites in septic shock. Immunoreactive (i) Thromboxane (Tx) B2, the stable metabolite of TXA2' and i6-keto-PGF1α, the stable metabolite of prostacyclin, were measured by radioimmuonassay. plasma levels of iTXB2 rapidly increased from non-detectable (ND<200 pg/ml) to 1,066 -/+ 194 pg/ml (N=14) 1 hour after feces injection. iTxB2 then increased to 1,695 -/+ 218 pg/ml (N=16) at 4 hours and remained unchanged through 6 hours. Plasma i6-keto-PGF1α increased from ND to 3,777 -/+ 414 pg/ml (N=16) at 1 hour. Four hours after feces, i6-keto-PGF1α levels rose to 6,945 -/+ 732 pg/ml (N=16) then continued to rise to 9,465 -/+ 792 pg/ml (N=7) at 6 hours. Either essential fatty acid deficiency (arachidonic acid depletion) or indomethacin pretreatment (cyclooxygenase inhibition) significantly decreased (P<0.01) the elevations of plasma iTxB2 and i6-keto-PGF1α associated with fecal peritonitis. Thrombocytopenia occurred within 6 hours after injection of feces and was significantly improved (P<0.05) by indomethacin. Elevated fibrin degradation products at 6 hours (18 -/+ 3 µg/ml) were significantly reduced in essential fatty acid deficient (7 -/+ 2 µg/ml; P<0.05) and indomethacin treated (4 -/+ 0.7 µg/ml; P<0.01) rats. Survival time (8.6 -/+ 0.2 hours) was significantly enhanced by essential fatty acid deficiency (10.2 -/+ 0.4 hrs; P<0.01) or indomethacin pretreatment (13.3 -/+ 0.6 hrs; P<0.01). These studies show that fecal peritonitis is associated with increased synthesis of thromboxane A2 and prostacyclin and suggest that these arachidonic acid metabolites may play a role in the pathophysiology of septic shock. To evaluate the pathogenic role of thromboxane (Tx) and prostacyclin (PGI2) in septic shock, the protective efficacy of the Tx synthetase inhibitor, 7(l-imidazolyl) heptanoic acid (7-IHA) and the cyclooxygenase inhibitor, ibuprofen, were assessed during fecal peritonitis in the rat. 7-IHA (60 mg/kg) administered ip 30 minutes prior to feces significantly reduced the plasma level of iTxB2 to ND (P<0.01) at 1 hour and to 508 -/+ 56 pg/ml (P<0.01) at 4 hours after injection of feces. In contrast, the levels of i6-keto-PGF1α, the stable metabolite of PGI2 were significantly elevated by 7-IHA pretreatment from septic control levels to 5,185 -/+ 467 pg/ml (P<0.05) at 1 hour. Plasma i6-keto-PGF1α at 4 hours in 7-IHA treated rats (5,503 -/+ 665 pg/ml) was not different from untreated controls. Ibuprofen (5 mg/kg) administered ip 30 minutes prior to feces significantly decreased both iTxB2 and i6-keto-PGF1α plasma levels to 729 -/+ 99 pg/ml and 1,327 -/+ 251 pg/ml, respectively (P<0.05) at 4 hours. Survival associated with fecal peritonitis was not altered by 7-IGA pretreatment, but was significantly improved (P<0.05) in ibuprofen treated rates. Fibrin degradation products were also significantly decreased (P<0.05) by 7-IHA pretreatment. These results suggest that TxA2 may contribute to the coagulopathies seen in septic shock and that PGI2 may be associated with terminal pathophysiologic events. The final phase of this project investigated the possible synergistic benefit between an antibiotic, gentamicin (GENT), and reduction of arachidonic acid metabolism by pre-administration of indomethacin (INDO) or essential fatty acid (EFA) deficiency. GENT significantly increased mean survival time to 23.8 -/+ 2.6 hours (N=16; P<0.01). GENT + INDO or GENT + EFA deficiency further improved mean survival time and produced long term survivals (>48 hrs) of 35% (N=17) and 30% (N=7) respectively (P<0.01 compared to GENT). GENT pretreatment did not significantly alter plasma iTxB2 levels, however, it selectively decreased i6-keto-PGF1α. For example, i6-keto-PGF1α decreased from 9,465 -/+ 792 pg/ml (N=7) to 2,096 -/+ 1174 pg/ml (N=5; P<0.01) at 6 hours after induction of fecal peritonitis. GENT + INDO pretreatment significantly decreased both iTxB2 and i6-keto-PGF1α to ND (P<0.01). Pretreatment with GENT alone did not reduce fibrin degradation products. These findings are consistent with the concept that TxA2 may play a role in consumptive coagulopathies and PGI2 may be associated with the terminal hypotension seen during septic shock. The effect of GENT on TxA2 and PGI2 production was investigated further. GENT had no observable effect on in vitro endotoxin stimulated production of these arachidonic acid metabolites by cultured rat peritoneal macrophages. GENT significantly reduced the plasma levels of iTxB2 and i6-keto-PGF1α during endotoxin induced shock in rats. These observations support a complex interaction of bacteria, endotoxin, host tissues, and gentamicin with the possible involvement of undescribed mediated factors.

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