Two types of cholinesterase, namely electric eel AChE and horse serum BChE, were used whereas ATCI and BTCI
were employed as substrates for the two enzymes, respectively.
BTCI was extracted from dry seeds and purified according to procedures described in previous papers (Ventura and Xavier-Filho, 1966).
In the other group after 30 minutes of perfusion with BTCI (1.0 [micro]M), guanylin (0.2 [micro]M) was added to perfusate and experimental observations were made for the next 90 minutes.
In order to avoid the influence of individual variations between animals used in this study and to differentiate the effects of BTCI and guanylin, comparisons between various experimental groups were made based in the variation (DELTA) of each group at 30 minutes intervals.
Dose-response experiments suggested that BTCI was capable of inducing changes in renal function.
BTCI pretreatment promoted a significant increment in the variation of fractional [Na.sup.+] excretion induced by guanylin at subthreshold concentrations that was independent of its intrinsic effects ([DELTA]%E[Na.sup.+] of 18.20 [+ or -] 2.17%, [DELTA] t3, P < 0.05, compared with all other groups; Figure 1).
Since BTCI is a medium size protein, it must be filtered by the glomerulus.
The fact that guanylin undergoes renal metabolism and that BTCI enhanced guanylin-induced natriuresis may explain the observation made by Fonteles et al.
Both amino acid sequencing and 3-D spatial modeling have demonstrated that BTCI share strong structural homology with other members of the Bowman-Birk family of protease inhibitors.