Transport and metabolism of octanoate by the perfused rat kidney

Abstract

These studies were done to determine the capacity of the perfused rat kidney to metabolize and transport the medium-chain fatty acid, octanoate (C8). Use of C8, which is water soluble, facilitated the study of transport, since protein, normally needed to transport long-chain fatty acids in solution, could be omitted from the perfusate. Using a filtering kidney it was found that total metabolism and incorporation of [1-14C]octanoate occurred at a rate of 3.9 +/- 0.3 micromol-g wet wt-1-20 min-1 when the perfusate octanoate was 2.8 mM, and reabsorptive uptake occurred at the rate of 7.5 +/- 1.3 micromol-g wet wt-1-20 min-1 at the same octanoate concentration. Use of a nonfiltering kidney (10% dextran perfusate) allowed quantitation of peritubular octanoate uptake. This peritubular uptake showed saturation above 0.7 mM perfusate octanoate with an apparent transport maximum (Tmax) at 2.1 micromol-g wet wt-1-20 min-1. Many previous experiments have linked renal fatty acid transport with that of the organic anion transport system. The apparent peritubular Tmax observed for octanoate suggests carrier-mediated transport. However, this transport did not appear to be inhibited by other organic acids such as probenecid (1--2 mM) and p-aminohippurate (1--2 mM).

Long Chain Fatty Acid Transport by the Perfused Rat Kidney

“…This is similar to the maximum peritubular uptake ofoctanoate(Cg) which is 2.1 pmol ■ g wet weight'1 • 20 m in'1 [5].…”

“…In this respect, it is of interest that kidneys perfused with octanoate in the absence of albumin showed peritubular fatty acid uptake of the same magnitude as kidneys perfused with palmi tate. In the absence of albumin, octanoate concentration in the lumen reached the same high levels yet no limitation of octa noate entry into cells by way of the luminal membrane was observed [5], In summary, although peritubular up take of palmitate exhibited saturation, sug gestive of carrier-mediated transport, no firm evidence for its transport by way of the OATS was apparent. However, since trans port could not be studied in the absence of metabolism, a role for the OATS cannot be discounted.…”

“…In the present experiments, inhibition of peritubu lar fatty acid uptake by PAH, probenecid, or other LCFA was not observed. Although these represented non-steady-state condi tions, it has been possible to demonstrate inhibition of PAH transport by probenecid under similar conditions [5]. In one experi ment with only trace amounts of l4C-palmitate and 1 mM probenecid, there was a sug gestion that inhibition had occurred.…”

“…exhibited a Tm characteristic of carrier-me diated transport. This uptake could not be inhibited by PAH or probenecid [5]. In vivo studies, however, have demonstrated inhibi tion of nonesterified fatty acid (predomi nantly long chain) uptake by probenecid [6] and some diuretics [6,7], The present studies were done to extend the observations on fatty acid uptake in the perfused kidney to include uptake of long I chain fatty acids (LCFA).…”

Renal Disposition Characteristics of Oligonucleotides Modified at Terminal Linkages in the Perfused Rat Kidney

“…The filtering kidney was prepared by maintaining renal arterial pressure at 70-80 mm Hg by adjusting the perfusate flow rate. The nonfiltering kidney, in which glomerular filtration was inhibited and the uptake of oligonucleotides occurred only from the capillary side, was prepared by tying the ureters, raising the perfusate albumin concentration to 10%, and lowering the renal arterial pressure to 55 mm Hg (Trimble, 1979;Maack, 1980). In this perfusion system, the perfusate flow rate (18.0 ± 2.0 ml/minute), glomerular filtration rate (GFR) (0.4 ± 0.1 ml/min), perfusion pressure (70-80 mm Hg), urine flow rate (50-100 /al/minute), and glucose reabsorption ratio (>90%) were maintained almost constant and were comparable to those reported in other studies (Epstein et al, 1982;Hall and Rowland, 1985).…”