Tissue distribution and temperature of xenobiotic hydrolysis in the dungeness carb ( Cancer magister)

Abstract

Homogenized samples (10 μg) from the hepatopancreas, gill, muscle, and cardiac stomach or the dungeness crab ( Cancer magister) were exposed in vitro to [1- 14C]methyl palmitate at 8, 13 and 18°C to determine the distribution of xenobiotic hydrolytic activity and its temperature dependence. Methyl palmitate was chosen to provide an ester for hydrolysis and represent the many fatty add esters in commonly used chemical oil spill cleanup agents. Metabolites were identified and quantified by high-pressure liquid chromatography (HPLC), fraction collection, and liquid scintillation counting. Palmitic acid was the only product; no oxidized or conjugated products were detected, and efficient hydrolysis of [1- 14C]methyl palmitate occurred only in the hepatopancreas. Also, variation between individual crabs was significant (all, p < 0.01); during a 5-min incubation period with 0.81 ± 0.09 nmol of [1- 14C]methyl palmitate at 13°C, the mean ambient seawater temperature encountered along the central California coast, hepatopancreatic hydrolytic activity ranged from 12.64 to 3.55 nmol/g/min (21.9–78.1%). Despite individual variation, activity significantly increased at 18°C and decreased at 8°C (both, p < 0.01). In contrast, the other tissues exhibited a much lower activity. Following 40-min incubation with 0.81 ± 0.09 nmol [1- 14C]methyl palmitate at 13°C. hydrolysis averaged 1.33 to 0.13 nmol/g/min (0.8–7.2%) in homogenates from the cardiac stomach. 0.45 to 0.03 nmol/g/min (0.2–2.8%) in those from gill, and 0.52 to 0.14 nmol/g/min (0.9–3.1%) in those from muscle. While differences between crabs were also significant (all, p <0.01), only hydrolysis in the cardiac stomach was significantly correlated to changes in the ambient temperature (both, p < 0.05). In summary, xenobiotic esters are efficiently hydrolyzed by dungeness crabs. The hepatopancreas is the main site of hydrolysis, which is temperature dependent. Therefore, the ambient seawater temperature during which crustaceans are exposed to xenobiotic esters is important in determining their ability to detoxify them, and thus reduce their toxic effects.