Naphthalene treatment alters liver intermediary metabolism and levels of steroid hormones in plasma of rainbow trout ( Oncorhynchus mykiss)

Abstract

To assess the effects of naphthalene on liver intermediary metabolism and plasma steroid hormones, immature female rainbow trout ( Oncorhynchus mykiss), in a first experiment, were intraperitoneally injected (2 μL g −1) with vegetable oil alone (control) or containing naphthalene (10 and 50 mg kg −1) and returned to their tanks. At 1, 3, and 6 h after injection, eight fish were sampled from each group. A second experiment was similarly designed but used fish intraperitoneally implanted (10 μL g −1) with slow-release coconut oil implants alone (control) or containing naphthalene at doses of 10 and 50 mg kg −1 body weight that were sampled 1, 3, and 5 days after injection. At each sampling time, plasma hormone levels (cortisol and 17 β-estradiol) and metabolic parameters in plasma (glucose and lactate) and liver (glucose, lactate, and glycogen levels and HK, GK, GPase, GDH, FBPase, and PK activities) were assessed. Changes described for both hormonal systems resulted in a decrease in plasma levels of cortisol and 17 β-estradiol. Changes observed in intermediary metabolism described effects in several pathways of liver energy metabolism due to naphthalene. These changes can be summarized as increased glycogenolysis, use of exogenous glucose, and glycolysis and decreased gluconeogenesis. The increased energy production in liver suggested by these changes can be related to the increased detoxification activity known to occcur in liver after PAH exposure, and can be also related directly or indirectly to the changes observed in the levels of plasma steroids.