Biological clearance of HEMA in guinea pigs

No toxicokinetic data are available about the dental composite component 2-hydroxyethylmethacrylate (HEMA) in vivo in the literature. Therefore, the excretion of HEMA in feces and urine in vivo and, using the pendular perfusion technique with segments of jejunum and colon, in the biliary and enteric excretion in situ were investigated in anesthetized guinea pigs. In the in situ experiments, guinea pigs (n=4) received HEMA (0.02 mmol/kg bw labelled with a tracer dose 14C-HEMA 0.3 kBq/g bw) injected into the jugular vein. In the in vivo experiments, guinea pigs (n=4) received HEMA (+14C-HEMA, same dose as above) via gastric tube. Urine and feces were collected for 24 h. In the in situ experiments, organs from guinea pigs were removed 60 min after the beginning of the experiment, and then the 14C-radioactivity was measured. During the 60 min perfusion period the calculated amount of 14C-activity excreted into the total jejunum and colon was 6.0±1.0% and 2.7±0.7% of the dose administered, respectively (mean±sem). Of the 14C-HEMA dose, 5.3±0.3% was found in the bile. Significantly (p<0.05) higher bile/blood concentration ratios were found at 10–40 min after the injection of HEMA, as compared to the ratio at 60 min. The total 14C-recovery in all organs tested was 20.0±2.6%. During 24 h the amounts of 14C-activity excreted in the feces and urine were 1.1±0.1% or 17.1±1.5% of the dose administered, respectively (mean±sem). The total 14C-recovery in all organs tested was 11.6±0.6%. In a second series of in vivo experiments, exhaled air from the animals was captured during the 24 h experimental period. 14C was exhaled to 63.6±2.1% of the administered 14C-HEMA dose (mean±sem; n=4) as 14C-carbondioxide. The results indicate a rapid clearance of 14C-HEMA and/or 14C-HEMA metabolite(s) from the organism, exhalation being the major route of elimination.