Sequential alterations in glomerular prostaglandin and thromboxane synthesis in diabetic rats: relationship to the hyperfiltration of early diabetes

Abstract

The present study examined the role of enhanced production of prostaglandin (PG) E2 and 6-keto-PGF1a, the stable metabolite of PGI2, by glomeruli from streptozotocin diabetic rats in the mediation of hyperfiltration. Correlative measurements of insulin clearance (CIn) and glomerular production of PGE2, 6-keto PGF1a and thromboxane (TX) B2 (the stable metabolite of TXA2) were made at two time points, nine to 15 days and 25 to 28 days after streptozotocin. CIn was elevated by 40% to 50% in diabetic rats studied at nine to 15 or 25 to 28 days compared to values in age-matched controls. Basal production of PGE2, 6-keto PGF1a and TXA2 (as reflected by TXB2) and increases in response to A23187 were elevated in glomeruli from nine to 15-day diabetic rats compared to values in control glomeruli. Exogenous arachidonate abolished these differences. Treatment of nine-day diabetic rats with indomethacin (3 mg/kg/d) rapidly (within 24 hours) and reversibly suppressed CIn without altering CIn in control rats. Indomethacin had no effect on plasma glucose in control or diabetic rats. Treatment of nine to 15-day diabetic rats with insulin (10 U/kg/d by osmotic minipump) beginning 24 hours after streptozotocin lowered plasma glucose to values that were not significantly different from control and prevented the rise in CIn. Treatment of diabetic rats with insulin or incubation of glomeruli from untreated diabetic rats with insulin (0.3 mU/mL) for two hours in vitro reduced basal and A23187 induced increases in PGE2, 6-keto PGF1a, and TXB2 to values that were not different from those in control glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)