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In order to study the role of platelet activating factor (PAF) on norepinephrine induced vascular escape and tachyphylaxis, compounds from different pharmacological families sharing PAF-antagonistic activity, were infused in the isolated rabbit kidney perfused with Krebs-Henseleit solution. A natural compound derived from Ginkgo biloba (BN 52020, 1.1 x 10(-6) M), a triazolobenzodiazepine substance (WEB 2170, 1.1 x 10(-6) M) and a dihydropyridine derivative lacking cardiovascular effects (PCA 4248, 2.7 x 10(-6) M), were analysed. The vascular reactivity to three cycles of norepinephrine (1.3 x 10(-6) M), infused in the kidneys treated with each of the PAF- antagonists, were evaluated for vascular escape and tachyphylaxis. The results demonstrated a significant reduction of both regulatory phenomena. A fall in renal vascular escape promoted by PAF antagonists, from a control level of 50.32 +/- 4.61 to 27.64 +/- 8.01% (p0.05), suggests a role for PAF-acether in the vascular adjustment of the mammalian kidney.

Guanylin is an endogenous peptide synthesized by several mammalian species that mimics the effects of a thermostable enterotoxin of Escherichia coli (STa: NTFYCCELCCNPACAGCY) in the gut. We have cloned a lysine-1 derivative of rat guanylin (Lys-1-NTCEICAYAACTGC) and tested its effects on ileal tissue membranes in Ussing chambers and in the isolated perfused rat kidney. Rabbit ileal mucosa membranes were mounted into a Ussing chamber and the effects of Lys-1 guanylin (Lys-1 G) and STa enterotoxin peptide on chloride secretion were determined by changes in short-circuit current (Isc). Lys-1 G (10 to 100 nM) showed a dose-dependent effect on chloride secretion with a maximal response estimated to be 52 microA/cm2. Lys-1 G mimics the effect of STa peptide, but the enterotoxin elicited a greater maximal effect of 120 microA/cm2 (P0.01). Lys-1 G (2.5 micrograms/ml) promoted an increase in both urine flow (from 0.13 +/- 0.07 to 0.40 +/- 0.01 ml g-1 min-1, N = 4; P0.05) and glomerular filtration rate (from 0.68 +/- 0.02 to 0.85 +/- 0.00 ml g-1 min-1, N = 4; P0.01) in the isolated perfused kidney and a reduction of the fractional reabsorption of sodium (from 76.0 +/- 0.03 to 59.5 +/- 0.85%, N = 4; P0.01). These maximal effects were accompanied by intense natriuretic effect observed 30 and 60 min after drug administration. The Lys-1 G analog similar to STa enterotoxin elicited intestinal chloride secretion and a natriuretic effect. These data demonstrate that the cloned peptide analog retains the biological activity of the native hormone and presents activity similar to STa. The properties of Lys-1 G resemble those of a factor formed during perfusion of the hypoxic rabbit kidney and named by us factor natriureticus similis (FNS).

Isolated rabbit kidneys were perfused with Krebs-Henseleit solution in an open system designed to allow study of dose-response relationships. The effects of the cyclooxygenase inhibitor indomethacin and of reserpine on (norepinephrine) noradrenaline (NOR)-induced renal vascular escape were studied. Indomethacin (50 mg/Kg) was given two hours prior to surgery followed by continuous infusion (0.33 mg/min), and blocked renal vascular escape in all doses of NOR tested (10(-7)-10(-4) M) by 70-80%. Reserpine (10 mg/Kg, given 10-12 hours prior to organ perfusion), also suppressed renal vascular escape significantly by 80-90%. We conclude that there is a participation of prostaglandins in noradrenaline induced escape in the perfused rabbit kidney.

An ANF-like material was detected by radioimmunoassay in the isolated perfused rabbit kidney. The production of ANF-like material after 90 min of perfusion under hypoxia was 3000 pg/ml vs 500 pg/ml under normoxia or control conditions. This material is partially inactivated by heat treatment at 100 degrees C for 5 min and is absorbed on a SEP-PAK column (C18, Waters) but, unlike ANF, cannot be recovered from the column. On Sephadex G25 chromatography, elution in water yielded two active fractions, one corresponding to the solvent front and the second obtained after one column volume. Four fractions with biological activity were eluted with water from Sephacryl 200. Several fractions were tested on rabbit aorta preconstricted with 1 microM phenylephrine, without removal of endothelial cells. Treatment of T84 cells in culture by the crude material promoted a dose-related increase (1:2, 1:5, 1:10) of the generation of cyclic GMP. In contrast to our material, ANF (atriopeptin III, 1 microM-10 fM) failed to activate guanylate cyclase in T84 cells, while the heat-stable E. coli enterotoxin (STa) significantly increased cyclic GMP levels at the dose of 5 microM. We propose that a new ANF/urodilatin/ST-like material was generated by the hypoxic kidney under perfusion, which we name FNS (Factor Natriureticus Similis).

Renal vascular escape is a physiological phenomenon of adaptation that occurs in vascular smooth muscle. It has been described in many preparations subjected to electrical stimulation or treated with vasoactive agents, such as noreprinephrine, angiotensin and vasopressin. We have recently demonstrated that a naturally occurring ginkgolide (BN 52021), which is a PAF antagonist, was able to block norepinephrine-induced escape in perfused rabbit kidney. In the present work other PAF antagonists, such as the ginkgolides BN 52022 and BN 52024, and the synthetic compounds 48740 RP and WEB 2086, were tested. Their effects on renal vascular escape, perfusion pressure and tachyphylaxis were evaluated. They all were shown to block the escape. Among the ginkgolides, BN 52024 is generally recognized as one of the weaker PAF antagonists. However, in spite of this, BN 52024 was able to significantly and simultaneously block renal vascular escape and tachyphylaxis in perfused rabbit kidney infused with norepinephrine.

The uptake of alpha-methyl-D-glucoside by slices of renal cortex was compared in normal and alloxan diabetic rabbits. Alloxanized rabbit tissue showed significantly higher levels of sugar accumulation than normal tissue. Diamide, which is known to oxidize intracellular glutathione (GSH), inhibited the uptake of alpha-methyl-D-glucoside by renal cortical slices. GSH stimulated sugar uptake and was also capable of reversing the inhibition of sugar accumulation caused by diamide. Mercaptoethanol and dithiothreitol, which are commonly used thiol compounds, were not as effective as GSH in stimulating sugar uptake. The level of GSH found in normal and alloxan diabetics rabbit kidneys shows a slightly decreased cortical GSH content in alloxanized animals. One can conclude that GSH participates in sugar uptake in kidney slices from both diabetic and normal rabbits.

Alloxan diabetes promotes, in the rabbit, decrease in sensitivity to norepinephrine (NOR) in the isolated iris dilator muscle at 25 and 37°C in vitro.

Rabbit kidneys were isolated and perfused at 37degrees and 25degrees C with a balanced salt solution and the effects of an alpha agonist and antagonist were tested in several parameters. Perfusion pressure, resistance, perfusate and urine flow, creatinine and PAH clearance, and Na+ and K+ transport were among the parameters studied. At 25degrees C the vascular responses to norepinephrine (NOR) were potentiated in relation to 37 degrees C. Blockade of the reuptake by cocaine and depletion of catecholamines by reserpine was observed to promote a small potentiation of NOR effects on renal vessels as measured by perfusion pressure. This pharmacological treatment compromised kidney function especially after the first 40 min of perfusion, that is to say that after NOR infusion functional parameters were extremely low. During the infusion of NOR there was a decrease in GFR, urinary flow and CPAH, which was even more intense at 25 degrees C. It was concluded that alpha adrenergic receptors are more responsive at 25 degrees C than at 37 degrees C in kidney vascular receptors. There was no difference in regard to alpha blockade at either temperature tested.

Rabbit kidneys were isolated and perfused with a balanced salt solution at 15 degrees C. The effects of norepinephrine (NOR) and phentolamine (P) were tested after fastly or slowly induced cooling. Vascular alpha receptor effects were enhanced by a slow cooling rate (0.6 degrees C/min), but blocked or impaired by a faster cooling rate (6 degrees C/min). Kidney function was severely impaired at this temperature as it would be expected.