Cardiac actions of bovine parthhyroid hormone fragment (1–34) in some lower vertebrates

Abstract

Only recently have the cardiac actions of parathyroid hormone and its N-terminal (1–34) fragment (bPTH(1–34)) been examined. Parathyroid hormone was found to exert a positive chronotropic effect on the heart tissue of several mammals and one amphibian in vivo and/or in vitr. The purpose of the present study was to examine in vitro the heart tissue of several lower vertebrates, particularly aquatic vertebrates, for responsiveness to bPTH(1–34) and, for comparative purposes, isoproterenol. Heart tissue (atrium or the entire heart) from all the animals studied (trout, mudpuppy, bullfrog tadpole, and adult bullfrog) responded to isoproterenol in a dose-dependent fashion with increased heart rate and contractile force. Only the atria from the adult bullfrog, however, responded in a similar manner to the administration of bPTH(1–34). In all cases propranalol (10 −6 M) was able to block both chronotropic and inotropic effects of isoproterenol but had no effect on the cardiac stimulation induced by bPTH(1–34) in the adult bullfrog atrium. The data suggests that cardiac responsiveness to bPTH(1–34) is associated with a terrestrial as opposed to an aquatic existence.