The peptide hormone cholecystokinin modulates the tonus and compliance of the bulbus arteriosus and pre-branchial vessels of the rainbow trout (Oncorhynchus mykiss).

The bulbus arteriosus is a compliant structure between the ventricle and ventral aorta of teleost fish. It serves as a "wind-kessel" that dampens pressure variations during the cardiac cycle allowing a continuous flow of blood into the gills. The bulbus arteriosus receives sympathetic innervation and is affected by several circulating substances, indicating neurohumoral control. We have previously shown that the peptide hormone, cholecystokinin (CCK), affects the hemodynamics of the cardiovascular system in rainbow trout (Oncorhynchus mykiss) by increasing flow pulse amplitude without affecting cardiac output. We hypothesized that this could be explained by an altered tonus or compliance/distensibility of the bulbus arteriosus. Our results show that there is a substantial effect of CCK on the bulbus arteriosus. Concentrations of CCK that altered the cardiac function of in situ perfused hearts also contracted the bulbus arteriosus in vitro. Pressure-volume curves revealed a change in both the tonus and the compliance/distensibility of this structure. Furthermore, the stimulatory (constricting) effect of CCK was also evident in the ventricle and vasculature leading to the gills, but absent in the atrium, efferent branchial arteries and dorsal aorta. In conclusion, CCK alters the mechanical properties of the ventricle, bulbus arteriosus, ventral aorta and afferent gill vasculature, thus maintaining adequate branchial and systemic blood flow and pressure when cardiorespiratory demands change, such as after feeding.