Biliary excretion of some diquaternary ammonium cations in the rat, guinea pig and rabbit.

1. The extent of the excretion in the bile and urine of the (14)C-labelled dications, diquat, paraquat, morfamquat, decamethonium and dimethyltubocurarine in bile-duct-cannulated rats, guinea pigs and rabbits was examined. 2. These compounds were excreted unchanged in bile and urine, except diquat, which was metabolized to a significant extent (18% of the dose) in the rabbit only. 3. The extent of the biliary excretion of diquat (mol wt. of ion 184), paraquat (186), decamethonium (258) and morfamquat (469) was less than 10% of the dose in the three species, whereas that of dimethlytubocurarine (653) was greater than 10% in the rat and rabbit but not in the guinea pig. 4. These results together with data from the literature suggest that the molecular weight at which the excretion of dications in the bile exceeds 10% of the dose is in the region of 500-600, which differs from the values for monocations (Hughes et al., 1973) and anions (Millburn et al., 1967; Hirom et al., 1972).