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Guanylin and uroguanylin are peptides that bind to and activate guanylate cyclase C and control salt and water transport in many epithelia in vertebrates, mimicking the action of several heat-stable bacteria enterotoxins. In the kidney, both of them have well-documented natriuretic and kaliuretic effects. Since atrial natriuretic peptide (ANP) also has a natriuretic effect mediated by cGMP, experiments were designed in the isolated perfused rat kidney to identify possible synergisms between ANP, guanylin and uroguanylin. Inulin was added to the perfusate and glomerular filtration rate (GFR) was determined at 10-min intervals. Sodium was also determined. Electrolyte dynamics were measured by the clearance formula. Guanylin (0.5 microg/ml, N = 12) or uroguanylin (0.5 microg/ml, N = 9) was added to the system after 30 min of perfusion with ANP (0.1 ng/ml). The data were compared at 30-min intervals to a control (N = 12) perfused with modified Krebs-Hanseleit solution and to experiments using guanylin and uroguanylin at the same dose (0.5 microg/ml). After previous introduction of ANP in the system, guanylin promoted a reduction in fractional sodium transport (%TNa+, P<0.05) (from 78.46 +/- 0.86 to 64.62 +/- 1.92, 120 min). In contrast, ANP blocked uroguanylin-induced increase in urine flow (from 0.21 +/- 0.01 to 0.15 +/- 0.007 ml g-1 min-1, 120 min, P<0.05) and the reduction in fractional sodium transport (from 72.04 +/- 0. 86 to 85.19 +/- 1.48, %TNa+, at 120 min of perfusion, P<0.05). Thus, the synergism between ANP + guanylin and the antagonism between ANP + uroguanylin indicate the existence of different subtypes of receptors mediating the renal actions of guanylins.

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 (P < 0.01). 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; P < 0.05) and glomerular filtration rate (from 0.68 +/- 0.02 to 0.85 +/- 0.00 ml g-1 min-1, N = 4; P < 0.01) 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; P < 0.01). 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).

Toxin A peptide from Clostridium difficile caused damage and secretion in the intestinal mucosa. These effects are mediated in part by pro-inflammatory substances. In order to evaluate and compare the biologic effect of toxin A on renal vascular, glomerular and tubular functions, we studied this toxin in isolated rat kidneys. Isolated kidneys from adult male Wistar rats (260-320 g) were perfused with Krebs-Henseleit solution containing 60 mg/ml dialyzed bovine serum albumin. We studied the effect of toxin A peptide (3.2 x 10(-6) M, injected into perfusate) on glomerular filtration rate (GFR), urinary flow rate (UF) and total sodium reabsorption (TNa+, %). All experiments were preceded by a 30-min basal period, and in another group of kidneys the time course of the variables was followed without toxin infusion for unpaired control. Toxin A (TxA) reduced the perfusion pressure (PP), from PPcontrol/30min = 124.89 +/- 1.91 to PPTxA/120min = 88.13 +/- 5.1 mmHg (N = 6, P < 0.01) with a maximal effect at 120 min after toxin infusion. TxA also caused a significant decrease in GFR with maximal effect at 90 min after toxin infusion (GFRcontrol/30min = 0.53 +/- 0.05 to GFRTxA/90min = 0.30 + 0.05 ml min-1g-1; N = 6, P < 0.01). TxA did not alter renal tubular sodium transport when compared with a control without toxin infusion. In addition, toxin-treated kidneys caused a time-dependent increase in urinary flow from UFcontrol/30min = 0.16 +/- 0.08 to UFTxA/120min = 0.35 +/- 0.1 ml min-1g-1 (N = 6, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)