Prostaglandin synthesis by the lateral cochlear wall under streptomycin influence

The synthesis of 4 prostaglandins (PGs), PGD2, PGE2, PGF2 alpha and PGI2, detected as 6keto PGF1 alpha in the guinea pig lateral cochlear wall (LW) was investigated under streptomycin treatment. Animals underwent daily injections of the antibiotic at dosages of 20, 100 and 200 mg/kg body weight. Prostaglandins were detected 1, 5 and 10 days after drug administration using radioimmunoassay. Under aminoglycoside administration a general reduction of PG-synthesis was evident, which was highest for PGI2. Already after 5 days of treatment the PGI2-synthesis was decreased down to 50% under the lowest drug dosage. The highest antibiotic dosage induced an abrupt decline of PGI2 synthesis, down to 26%, in animals with the longest duration of treatment. The significant synthesis reduction of PGI2 was followed by PGE2. The reduction of PG-synthesis seems to be influenced rather by duration than dosage of drug administration. The decreased synthesis of PGs under streptomycin treatment is interpreted as an inhibition of cell membrane phospholipids, the phosphoinositides. This assumption becomes plausible since the phospholipids represent endogenous precursors of the PG-synthesis.