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Journal of Experimental Biology 28,141-164 (1951)
Published by Company of Biologists 1951

The Temperature-Pulse Rate Curve of the Isolated Frog'S Heart (RANA TEMPORARIA)

C. L. SMITH ¹

¹ Zoological Department, University of Liverpool

1. The form of the temperature-pulse rate curve of the isolated frog's heart, when perfused with Ringer solution containing adrenaline, has been determined over the range 7-17° C. for monthly samples of frogs over a whole year. Five different types of curve were obtained during this seasonal survey, namely types A, B, C, D and E. Of these types, A and C respectively correspond to the winter and summer temperature- pulse rate curves described by Barcroft & Izquierdo (1931), while the remaining three have not previously been described. Type E, which is a linear relation with a mean temperature coefficient (Q₁₀) of 2.12, has been interpreted as being the least complex form, in which the action of temperature on the pulse-rate is not complicated by the action of other factors.

2. The addition of various extracts of the anterior pituitary gland to the medium perfusing type E hearts led to a disproportionate increase in pulse rate above 10° C, so that the observed temperature coefficient was increased and curves of type B or D were produced. The variation in the response obtained by various pituitary extracts has been attributed to quantitative differences.

3. The typical action of anterior pituitary extract was only obtained when the heart was perfused with Ringer solution containing adrenaline. This phenomenon has been explained by assuming that there is a synergistic action between adrenaline and an anterior pituitary hormone which is inhibited at temperatures below about 10°C.

4. Thyroxine was found to have no action on the type E heart perfused with Ringer containing adrenaline, but if an extract of anterior pituitary were also present, then the type E curve was changed into type C. This is in agreement with the work of Carter (1933). Experiments were also made which showed that previous injection of thyroxine into frogs kept in the cold changed type A (winter) into type C (summer) curves.

5. It was found that adrenaline could either increase, decrease, or have no effect on, the temperature coefficient of the isolated heart. A decrease in the temperature coefficient was only observed in cases where the hearts had been isolated from frogs with active thyroids and has been attributed to the experimental technique employed. The fact that an increase in temperature coefficient may or may not be caused by adrenaline, as well as the fact that type A or C curves have been obtained when hearts were perfused with adrenaline-free Ringer has been attributed to the persistence, in varying degree, of an active sympathetico-mimetic substance in the heart for at least several hours after isolation.

6. It has been shown that the type C temperature-pulse rate curve is the only one which can definitely be attributed to the presence of the thyroid hormone. The seasonal occurrence of this type of curve closely parallels the cycle of thyroid activity described by Sklower (1925) and Meisenheimer (1936).