The present in vitro microperfusion study examined whether furosemide has an effect on hydraulic conductivity (Lp X 10(-6) cm/sec.atm) and 14C-urea permeability (Pu X 10(-5) cm/sec) in inner medullary collecting ducts (IMCD) and cortical collecting tubules (CCT) isolated from rat and rabbit kidneys. Furosemide added to the bath fluid decreased arginine-vasopressin (AVP)-stimulated Lp of rat IMCD in a dose-dependent manner, with the threshold effect at 10(-6) M. Furosemide (10(-4) M) reduced Lp from 20.5 +/- 2.3 to 12.1 +/- 1.2 (P less than 0.01) reversibility, but had no effect when added to the perfusate. In addition, furosemide reduced dibutyryl cyclic AMP-stimulated Lp from 20.3 +/- 1.1 to 11.2 +/- 1.6 (P less than 0.01). This effect of furosemide was also observed with indomethacin, a PGE2 synthesis inhibitor. The addition of indomethacin (10(-4) M) to AVP (50 microU/ml) increased Lp from 24.7 +/- 2.3 to 29.7 +/- 2.8 (P less than 0.001), which was reduced to 20.3 +/- 2.6 (P less than 0.001) when furosemide was added to indomethacin in the bath. The inhibitory effect of furosemide on AVP-stimulated Lp was also observed in rabbit IMCD (Lp decreased from 12.8 +/- 0.8 to 5.15 +/- 1.46, P less than 0.02), but it was not observed in the CCT isolated from rabbit kidneys (7.96 +/- 1.87 with AVP vs. 7.94 +/- 1.41 with AVP + furosemide). Furthermore, in rat IMCD the stimulatory effect of AVP on Pu from 7.7 +/- 0.4 to 26.8 +/- 1.3 was reduced by furosemide to 19.7 +/- 1.2 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)