Structure-activity in the carrageenans: iota-carrageenan and experimental oedemagenic activity

The oedemagenic activities of several iota-carrageenans from Eucheuma spinosum have been compared using the rat hindpaw model. From the parent iota-carrageenan of weight average molecular weight 541 100 an acid-degraded iota-carrageenan (Mw = 20 300) was obtained which on fractionation yielded five iota-carrageenans Mw ranging from 73 700 to 4 600. The oedemagenic activity of iota-carrageenan resided in the fraction of Mw = 73 700, the parent undegraded high molecular weight iota-carrageenan being no more active and fractions of lower molecular weight being inactive. Fractionation was based on differential solubilities of the barium salts of the fractions in water and aqueous ethanol and was probably determined by aspects of primary structure in addition to molecular weight.