BENNETT, M.T.*; RODNICK, K.J.: Use of heparin in cannulation studies of rainbow trout (Oncorhyncus mykiss) affects energy substrates in plasma.

Heparin has been used universally to maintain patency during cannulation of fish in metabolic studies. In mammals heparin is an anticoagulant and releases lipoprotein lipase (LPL) from the capillary endothelium, promoting hydrolysis of plasma triglycerides to free fatty acids (FFA). The resulting increase in FFA inhibits glucose metabolism via the glucose/fatty acid cycle and raises plasma glucose levels. The purpose of the present study was to evaluate whether heparin affects plasma glucose and FFA levels in rainbow trout during cannulation. Anesthetized trout (433 � 53 g; 31.8 � 1.0 cm) were cannulated via the dorsal aorta using polyethylene tubing (PE50) and kept under anesthesia or allowed to recover for 48 hours prior to initiation of the study. All animals were kept at 14� C and infused with either normal saline or heparinized saline (100 U/ml) at a rate of 0.508 ml/h. Blood samples were drawn (200 �l) at fixed time intervals, and mixed with 0.6 mg EGTA. Plasma glucose and FFA levels were measured colorimetrically using commercially available kits. Similar to mammals, our results showed that plasma FFA levels increase with heparin administration in rainbow trout, but is dependent upon the nutritional status of the animal. There was also a change in plasma glucose levels, but this change may be sex-dependent. CONCLUSION: Heparin administration, either purposefully or accidentally, during cannulation can modify the results of metabolic studies in fish. The effects of heparin may also be dependent upon sex and nutritional status.