Frog Vena Cava Bioscene 17 INNOVATIONS Use of the Frog Heart Preparation to Teach Students about the Spontaneous Mechanical Activity of the Vena Cava

Abstract: Most undergraduate physiology texts describe veins simply as reservoirs for blood and conduits for return of blood to the heart. This article describes a laboratory exercise that can be performed by students to demonstrate that veins are much more than reservoirs and conduits for blood flow: they possess a dynamic rhythmic contraction. In this exercise, we recorded the simultaneous beating of the frog postcaval vein (PCV; in mammals this is the inferior vena cava) and atrium by connecting them to separate force displacement transducers. In vivo, the PCV and atrium both contract ~ 35 beats/min; however, the contractions are not synchronous with each other. We developed a simple scoring method (comparative temporal analysis) to illustrate that the atrium contractions do not drive the contractions of the PCV. Instead the atrium and PCV contract independently of each other. To support our hypothesis that the atrium and PCV contractions were independent we removed the PCV from the frog and suspended it in an organ bath. The PCV rhythmically contracted as in vivo. The autonomic neurotransmitter, norepinephrine, did not affect the force of contraction and heart rate. In contrast, acetylcholine abolished the contractile activity. This investigation has encouraged discussions about the source and physiological significance of the rhythmic PCV contractions. This article provides some hypotheses about its significance, as well as possible evolutionary origins of the veins ’ mechanical activity. Overall, the implementation of this exercise into the classic frog heart preparation will deepen the students ’ understanding about the venous side of the cardiovascular system and give them insight into the integrative nature of physiology. Key words: contraction, veins, physiolog