BTCI enhances guanylin-induced natriuresis and promotes renal glomerular and tubular effects

Af Carvalho,Ms Santos-Neto,Sm Freitas,Mc Fonteles,Nrf Nascimento,Hsa Monteiro,L Morhy

doi:10.1590/s1519-69842008000100021

Abstract

Guanylin and uroguanylin are small cysteine-rich peptides involved in the regulation of fluid and electrolyte homeostasis through binding and activation of guanylyl cyclases signaling molecules expressed in intestine and kidney. Guanylin is less potent than uroguanylin as a natriuretic agent and is degraded in vitro by chymotrypsin due to unique structural features in the bioactive moiety of the peptide. Thus, the aim of this study was to verify whether or not guanylin is degraded by chymotrypsin-like proteases present in the kidney brush-border membranes. The isolated perfused rat kidney assay was used in this regard. Guanylin (0.2 microM) induced no changes in kidney function. However, when pretreated by the black-eyed pea trypsin and chymotrypsin inhibitor (BTCI - 1.0 microM; guanylin - 0.2 microM) it promoted increases in urine flow (DeltaUF of 0.25 +/- 0.09 mL.g(-1)/min, P < 0.05) and Na+ excretion (% Delta ENa+ of 18.20 +/- 2.17, P < 0.05). BTCI (1.0 microM) also increased %ENa+ (from 22.8 +/- 1.30 to 34.4 +/- 3.48, P < 0.05, 90 minutes). Furthermore, BTCI (3.0 microM) induced increases in glomerular filtration rate (GFR; from 0.96 +/- 0.02 to 1.28 0.02 mL.g(-1)/min, P < 0.05, 60 minutes). The present paper strongly suggests that chymotrypsin-like proteases play a role in renal metabolism of guanylin and describes for the first time renal effects induced by a member of the Bowman-Birk family of protease inhibitors.

Highlights

Several heat-stable peptides produced by enteropathogenic bacteria are capable of inducing intestinal secretion via the intracellular second messenger, cyclic GMP (Hughes et al, 1978)
The right kidney was perfused with a modified Krebs-Henseleit solution (MKHS) containing albumin (6 g%) for 120 minutes as control (n = 12), according to experimental procedures described in detail by Fonteles et al (1983)
Both proguanylin and uroguanylin/prouroguanylin levels are markedly increased in chronic renal failure (Nakazato et al, 1996)

Summary

Introduction

Several heat-stable peptides produced by enteropathogenic bacteria are capable of inducing intestinal secretion via the intracellular second messenger, cyclic GMP (Hughes et al, 1978). Coli (Theodor Escherich, 1885) heat-stable enterotoxin (STa). The intestinal receptor for STa has been cloned and shown to belong to the family of particulate guanylyl cyclases (pGCs), and was named guanylate cyclase C (GC-C) (Schulz et al, 1990). STa induces natriuresis and kaliuresis in the isolated perfused rat kidney (Lima et al, 1992). This action is mimicked by 8-Br-cGMP (Lima et al, 1992). Potential receptors bind selectively to I125 – STa in several epithelia of the North American opossum, including the kidney (Forte et al, 1989)

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