Short-term stimulation of cellular autophagy by furosemide in the thick ascending limb of Henle's loop in the rat kidney.

In an effort to investigate the functional relationship between cell-specific work and intracellular degradative processes, the effect of furosemide on cellular autophagy was investigated in two different portions of the nephron, namely, the thick ascending limb of Henle's loop (TAL), which is a main target of this drug, and the proximal convoluted tubule (PCT) as a reference structure. Eight male adult rats were treated with furosemide (60 mg/kg body weight, s.c.). Eight control animals received physiological saline. 1 to 4 h after the injections the animals were killed by perfusion fixation. Small specimens of kidney tissue from the inner stripe of the outer medulla and from the outer cortex were processed for electron microscopy; they were investigated morphometrically for volume fraction and numerical density of autophagic vacuoles (AVs). A significant increase of both parameters (volume fraction: 0.42 x 10(-4) to 1.09 x 10(-4); numerical density: 4.2 x 10(5)/mm3 to 15.5 x 10(5)/mm3) was seen under the influence of furosemide in TAL cells, whereas PCT cells did not show a significant increase in volume fraction or any increase in numerical density of AVs. These data suggest that the functional unloading of TAL, via blocking of the Na+-2Cl- -K+ co-transport by furosemide, results in adaptative "structural unloading", i.e., an increased sequestration of cytoplasmic components into AVs, within a short-time interval.