SUMMARY The successful deployment in recent years of electronic tag technology on Atlantic bluefin tuna has improved our ability to examine their movements throughout the North Atlantic and Mediterranean Sea. This has rapidly improved the ability to distinguish where the bluefin tuna feed and breed. When biological and physical data from the tags are combined with information about sea surface temperature and ocean color from remote sensing technologies, the relationship between the movements and behaviors of the fish can be linked to oceanographic processes. This paper focuses on the results of electronic tagging of bluefin tuna in the western North Atlantic. RESUME

The insecticides mirex and chlordecone suppress the biliary excretion of a wide variety of non-bile acid organic anions in vivo in the rat, and mirex inhibits the uptake of taurocholate (TC), a common bile acid, in isolated rat hepatocytes. We have therefore investigated the effects of mirex and chlordecone on bile acid secretory function (bile flow, bile acid concentration, bile acid secretory rate) in vivo and in the single-pass isolated perfused liver. Male Sprague-Dawley rats were orally dosed with corn oil, mirex (50 mg/kg), or chlordecone (18.75 mg/kg; in vivo studies only) for 3 consecutive days and experiments performed on Day 6. Mirex significantly increased liver weight from 12.2 +/- 0.8 to 20.8 +/- 1.3 g with no change in body weight whereas chlordecone had no significant effect on liver weight (11.9 +/- 0.7 g) or body weight. Mirex significantly decreased while chlordecone increased bile flow per gram liver in vivo; both compounds, however, increased bile flow when expressed per kilogram of body weight. Mirex and chlordecone significantly decreased the bile acid concentration in bile and the bile acid secretory rate (nmol/min/g liver and mumol/min/kg body weight). Studies in the isolated perfused liver were designed to determine the effect of mirex on the ability of the liver to extract increasing concentrations of [3H]TC from the perfusate and excrete it in the bile. Mirex treatment significantly decreased the TC extraction ratio by 40-89% and the hepatic intrinsic clearance by 85-95%. Mirex also significantly decreased the TC-induced choleresis, the concentration of TC in the bile, and the TC secretory rate. The data indicate that mirex treatment markedly inhibits the ability of the liver to extract TC from the blood/perfusate and concentrate it in the bile.

The insecticides mirex and chlordecone have previously been found to suppress the biliary excretion of a wide variety of compounds. In the present studies, the effects of mirex, chlordecone, and phenobarbital on the uptake of two endogenous organic anions, estradiol-17β(β-d-glucuronide) (E217G), an estrogen metabolite, taurocholate (TC), a common bile acid, and an essential amino acid, l-alanine (l-Ala) (0.5 mm), into isolated rat hepatocytes was investigated. Female Sprague-Dawley rats were orally dosed with mirex (12.5, 25, and 50 mg/kg) or chlordecone (6.25, 12.5, and 18.75 mg/kg) dissolved in corn oil for 3 days and isolated rat hepatocytes were prepared 2 days later. Rats were also dosed orally with phenobarbital (50 mg/kg on the first day and 80 mg/kg for the next 4 days) dissolved in distilled deionized water, and isolated hepatocytes were prepared on the sixth day. Mirex significantly reduced the uptake of both organic anions (0.5, 10, and 50 μm E2 17G; 10 μm TC) into hepatocytes by 40–70%, whereas chlordecone had no effect on their uptake. Mirex at 50 mg/kg significantly reduced the Vmax for the low- and high-affinity E217G uptake sites by 70% and decreased the Km for the low affinity uptake site by 60%. Mirex also significantly decreased the Vmax for TC uptake from 1.11 to 0.82 nmol/min/mg protein but had no effect on its Km (23.2 vs 22.9 μm). Mirex at 50 mg/kg was also found to reduce the uptake of 0.5 mm l-Ala by nearly 40%. Phenobarbital had no effect on the uptake of E217G (0.5 μm), TC (10 μm), or l-Ala (0.5 mm). Mirex treatment had no effect on hepatic plasma membrane Na+,K+- or Mg2+-ATPase activity. Neither mirex nor chlordecone at 50–100 μm had any effect on the uptake of 10 μm TC when added directly to hepatocytes from naive rats. These results indicate that mirex decreases the transport of organic anions and l-Ala across the basolateral domain of the hepatocyte in addition to its inhibitory effects on biliary excretion.