Sympathomimetic Activity in the Isolated Frog’s Heart (Rana Temporaria)

Abstract

ABSTRACT In a previous paper (Smith, 1951) the occurrence of various types of relation between temperature and the pulse rate of the isolated frog’s heart was reported. Five main types of curve were observed and their chief features may be briefly summarized as follows. Type A showed an exponential relation between frequency and temperature, and corresponded to the ‘winter’ curve originally described by Barcroft & Izquierdo (1931). Type B was rather similar to A, but instead of the rates lying along an even curve they lay on two straight lines which intersected at about 10° C. Type C showed a linear relation between frequency and temperature over the range investigated and the value of the observed temperature coefficient (Q10) was about 2·5. This form corresponded to the ‘summer’ curve of Barcroft & Izquierdo (1931). Type D was of infrequent occurrence, and in this case the pulse rates for the upper and lower temperatures lay on straight lines of very similar slope, but which had different origins at 7° C. Type E again showed a linear relation between pulse rate and temperature, but in this case the observed temperature coefficient was significantly lower than that found for type C (2·1). It was further shown that pulse rate curves of type B or type D could be produced by treatment of type E hearts with an extract of anterior pituitary gland in the presence of added adrenaline. Type C curves were obtained from type E hearts when they were perfused with Ringer containing anterior pituitary extract, adrenaline and thyroxine. To explain these results it was suggested that there was a synergistic action between an anterior pituitary principle and adrenaline which was inhibited at temperatures below 10° C. Further, as types A, B and C pulse rate curves could be obtained from normal hearts in the absence of external adrenaline, the hypothesis was advanced that the isolated heart was under the influence of an active sympathomimetic substance even when it was being perfused with unmodified Ringer.