RESUMO
Natural intoxication of livestock by ingestion of Ipomoea asarifolia leaves has been reported to occur widely in Brazil. Previous studies carried out by our research group provided strong evidence that a lectin could be involved with the toxic properties of I. asarifolia. To reinforce this hypothesis, a lectin-enriched fraction (LEF) was isolated from I. asarifolia leaves and its toxic effects were assessed. Leaves of I. asarifolia were excised from plants growing widely in the field, mechanically wounded and maintained in a chamber at 25 ± 3 °C for 72h in the dark, under near 100% relative humidity. The leaf proteins were extracted, ammonium sulfate precipitated, chromatographed on DEAE-cellulose and Phenyl-Sepharose to produce LEF that under SDS-PAGE showed a molecular mass of 44.0 kDa and after N-terminal amino acid analysis a primary sequence composed of AGYTPVLDIGAEVLAAGEPY. The in vivo toxicity of LEF assessed by intraorbital injection in mice showed induced severe uncoordinated movements without death. LEF reduced the muscular contraction in a dose depend way and at 29.8 µg/mL (CE(50)) it produces 50% inhibition of contraction, suggesting that LEF blunts autonomic neurotransmission. Isolated rat kidneys were perfused with LEF and no effects on the perfusion pressure or renal vascular resistance were observed, but urinary flow and glomerular filtration rate increased. Moreover, the percentage of tubular transport of Na(+), K(+) and Cl(-) decreased. Histological examination of the kidneys perfused with LEF exhibited little alterations. These toxic effects observed above were concomitant with the increase of LEF hemagglutination activity, which strongly suggest that one of the toxic principles of I. asarifolia is a lectin present in its leaves.
