A B S T R A C T Transport of NaCl and water was examined in the rabbit medullary thick ascending limb of Henle (ALH) by perfusing isolated segments of these nephrons in vitro. Osmotic water permeability was evaluated by perfusing tubules against imposed osmotic gradients. In these experiments the net transport of fluid remained at zero when segments of thick ALH were perfused with isotonic ultrafiltrate in a bath of rabbit serum in which the serum osmolality was increased by the addition of either 239±8 mosmol/liter of raffinose or 232±17 mosmol of NaCl indicating that the thick ascending limb of Henle is impermeant to osmotic flow of water. When these tubules were perfused at slow rates with isosmolal ultrafiltrate of same rabbit serum as used for the bath, the effluent osmolality was consistently lowered to concentrations less than the perfusate and the bath. That this decrease in collected fluid osmolality represented salt transport was demonstrated in a separate set of experiments in which it was shown that the sodium and chloride concentrations decreased to 0.79+0.02 and 0.77±0.02 respectively when compared with the perfusion fluid concentrations. In each instance the simultaneously determined transtubular potential difference (PD) revealed the lumen to be positive with the magnitude dependent on the perfusion rate. At flow rates above 2 nl -min1, the mean transtubular PD was stable and equal to 6.70+0.34 mv. At stop-flow conditions this PD became more positive. Ouabain and cooling reversibly decreased the magnitude of this PD. The transtubular PD remained positive, 3.3+ 0.2 mV, when complete substitution of Na by choline was carried out in both the perfusion fluid and the bathing media. These results are interpreted to indicate that Dr. Rocha is

Acute renal failure induced by leptospirosis was studied in 56 patients. A higher frequency of nonoliguric renal failure was observed with lower morbidity and mortality rates than in oliguric forms. In addition, 45% of the patients in this series were hypokalemic, and no hyperkalemic patients were seen. A prospective study in 11 patients showed an initially elevated urinary fractional potassium excretion that fell simultaneously with the high urinary fractional sodium excretion and the urinary K/Na ratio, suggesting an increased distal potassium secretion due to an increased distal sodium delivery consequent to functional impairment of the proximal reabsorption of sodium.

The kidney involvement in leptospirosis appears to be a special form of acute renal failure due to a higher frequency of polyuric forms and the presence of hypokalemia with an elevated urinary fractional excretion of potassium. Using a clearance technique, we detected higher fractional urinary potassium excretion in leptospirotic guinea pigs (26.5 ± 4.7%) than in normal animals (14.1 ± 2,8%, p < 0.05). After blocking distal NaCl reabsorption with furosemide, it was observed that in leptospirotic animals both fractional sodium excretion (40.0 ± 7.4%) and fractional potassium excretion (136.3 ± 32.7%) were higher than in normal animals (20.4 ± 3.8%, p < 0.05, and 43.6 ± 9.0%, p < 0.05, respectively). Microperfusion studies showed that the normal and leptospirotic medullary thick ascending limb had both identical transepithelial potential difference (+ 3.7 ± 0.4 vs. 3.9 ± 0.2 mV) and relative sodium-to-chloride permeability. The same technique showed that the osmotic water permeability (P_osm; 0.9 ± 0.4 × 10^-5 cm/s · atm) and diffusional permeability (34.7 ± 6.6 × 10”5 cm/s) observed in the leptospirotic inner medullary collecting duct (IMCD) in the presence of vasopressin were unchanged, as was also the case for urea permeability (3.74 ± 0.7×10^-5 cm/s). These data show that acute renal failure in leptospirosis is characterized by tubular changes leading to potassium secretion probably due to a decrease in proximal sodium reabsorption. Furthermore, the inability to concentrate urine evidenced by the low P_osm present in leptospirotic animals is due, at least in part, to IMCD resistance to vasopressin.

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A B S T R A C T Calcium and phosphate transport was examined in rabbit thin descending, thin ascending, and thick ascending limbs of Henle by in vitro perfusion of isolated tubular segments. Permeability coefficients for these segments with 45Ca and 32P04 were determined for both lumen-to-bath and bathto-lumen directions. Both the thin descending and thin ascending limbs were found to be relatively impermeable to both 45Ca and 32PO4. In neither segment were we able to show evidence for net transport of calcium or phosphate. In contrast, the thick ascending limb of Henle showed a decrease in calcium lumen-to-bath concentration from 0.97±0.02 to 0.88 +0.02 when perfused at 4.8 nl min-'. 45Ca lumen-tobath and bath-to-lumen fluxes were 19.96+1.05 and 9.89±0.02 peq min-l cm-1, respectively, and the potential difference was +3.8±0.3 mV (lumen positive).The observed calcium flux ratio was significantly higher than that predicted by Ussing's equation. When ouabain was added to the bath the potential difference fell to + 1.1±0.3 mV, whereas the calcium efflux was only slightly diminished (29.5+5.3-23.7+5.1 peq cm-l min-1). Ouabain had no effect on the influx of Ca across the thick ascending limb of Henle. There was no net transport of phosphate across the thick ascending limb. Phosphate permeability was exceedingly low bidirectionally across the thick ascending limb. Our findings indicate: (a) all segments of Henle's loop are relatively impermeable to calcium and phosphate; (b) net transport of phosphate seems to be absent in Henle's loop; (c) net calcium reabsorption, which cannot be explained by Preliminary reports of a portion of this work have been presented at the VI International Congress of Nephrology.1975.

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We examined the action of atrial natriuretic factor (ANF) on Na+ and Cl- transport in in vitro microperfused inner medullary collecting ducts (IMCD) isolated from rat kidneys. First we studied the isotopic fluxes at low perfusion rates (7 nl/min). The results showed that ANF added to bath decreased lumen-to-bath flux (Jl----b) of Na+ and increased Na+ bath-to-lumen flux (Jb----l). This was substantiated by a direct demonstration that ANF reduces net Na+ and Cl- absorption. The effect of ANF on Jl----b and Jb----l of Na+ was also observed at high perfusion rates (25 nl/min). The inhibitory effect of ANF was observed even when Na+ Jl----b was stimulated by vasopressin (VP). ANF (6 x 10(-11) M) added to bath increased Cl- Jb----l and generated a negative lumen potential difference (PD). These two effects were inhibited by furosemide and by the replacement of Na+ by choline and Cl- by SO4(2-) in the bath fluid. These observations are compatible with the existence of a Na(+)-Cl(-)-K+ cotransport mechanism stimulated by ANF. Moreover, the effects of guanosine 3',5'-cyclic monophosphate (cGMP) added to the bath on PD, Jl----b, and Jb----l of Na+ were similar to those observed with ANF. Thus, physiological concentrations of ANF inhibit directly Na+ and Cl- absorption in IMCD by two mechanisms, 1) by increasing cotransport Na(+)-Cl(-)-K+ secretion and 2) by inhibiting NaCl absorption both in the absence and in the presence of VP. These effects on NaCl transport appear to be mediated by cGMP.

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