NEURAL REGULATION OF ARTERIAL BLOOD-PRESSURE IN SNAKES

Systemic arterial pressures of snakes vary interspecifically in relati on to gravitational demands imposed by environment and behavior. Terre strial scansorial and arboreal species are characterized by comparativ ely high pressures thought to reflect generally greater levels of tota l peripheral resistance. Pulmonary arterial pressures exhibit less int erspecific variation and are generally lower than systemic pressures, such differences being greater in arboreal species. Both systemic and pulmonary arterial pressures are regulated by neurogenic reflexes with arboreal species demonstrating superior capability for regulating blo od pressure during posture change. Baroreceptors have been identified in the truncus arteriosus and central arteries of snakes, and other me chanoreceptive sites are also likely. Efferent mechanisms affecting va scular muscle tone are correlated with dense adrenergic innervation of vessels that varies interspecifically as well as regionally within sp ecies. The evolution of dense but variable adrenergic and peptidergic innervation of the heart and vasculature of snakes emphasizes the impo rtance of autonomic reflexes in mediating regulation of hemodynamics.