HOAGLAND, T.M.*; ROESER, M.; OLSON, K.R.: Venous Function in Trout

The venous system is an important effector of cardiovascular homeostasis in mammals, whereas this vasculature’s function in fish, remains nebulous. Fish live in a gravity-free environment and their veins appear poorly endowed with smooth muscle, therefore it has been suggested that fish veins serve primarily as passive conduits for the return of blood to the heart. In the present study, venous function was examined in unanesthetized rainbow trout in vivo, through the construction of vascular capacitance curves. Vascular compliance and unstressed blood volume can be determined from these curves and they are key indexes for describing venous function. Through the use of pharmacological probing via autonomic nervous system blockers in both fresh and salt water adapted fish, it appears clear that venous regulation takes place. Furthermore, this active regulation of venous capacitance lends evidence to support a role in cardiovascular homeostatic control by the venous vasculature, in trout.