Intestinal absorption of Mn-mesoporphyrin in a small bowel sac system: Effect of oleic acid

The authors investigated the effect of oleic acid ( cis-9-octadecenoic acid) (OA), a lipidic carrier, on the intestinal absorption rate and T1 relaxation time of manganese (III) mesoporphyrin (Mn-mesoporphyrin), a prototype hepatobiliary contrast agent for magnetic resonance imaging. Mn-mesoporphyrin was formulated with OA at various concentrations. Small bowel sacs were created in 36 rats and fdled with complexed and free Mn-mesoporphyrin. Intestinal absorption of Mn-mesoporphyrin was measured with spectrophotometry at 364 nm. T1 relaxation times were measured in samples of Mn-mesoporphyrin solutions, bowel wall, liver, and bile. Absorption rates ranged from 4.2%/cm 2/h to 13%/cm 2/h. Absorption was greatest (13%/cm 2/h) when a combination of 1 mmol/L Mnmesoporphyrin and 26.5 mmol/L OA was used. The T1 of bile decreased from 2,480 to 248 msec (maximum decrease) in rats that received Mnmesoporphyrin. Mn-mesoporphyrin is absorbed from the small bowel in both the lipid-associated and free form, resulting in substantial shortening of the T1 in bile.