Comparative study on the cardiac actions of bovine parathyroid hormone (1-34)

The cardiac stimulatory effects of bovine parathyroid hormone (1-34) [bPTH-(1-34)] were studied on isolated atria and ventricular strips from cobra snakes (Naja naja), ducklings (Anas platyrhynchos), pigeons (Columba livia), Japanese quails (Coturnix coturnix japonica), laboratory rats (Rattus norvegicus), and dogs (Canis familiaris). In all atrial preparations, bPTH-(1-34) caused positive chronotropism. This suggests that the chronotropic effect of PTH is ubiquitous among the terrestrial vertebrates. Only the atria of cobra snakes and ducklings gave positive inotropic responses to PTH. No ventricular preparations showed significant response to bPTH-(1-34). This suggests the absence of cardiac stimulatory PTH receptors in the ventricles. Dog papillary muscle, however, showed slight but significant responses to bPTH-(1-34). The reason for this discrepancy between the responses of papillary muscles and the ventricular strips to PTH is unknown.