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WORK PERFORMANCE OF A RAT HEART-LUNG PREPARATION: STANDARDIZATION AND INFLUENCE OF CORTICOSTEROIDS^1,,2

Department of Physiology, Western Reserve University School of Medicine Cleveland, Ohio

Abstract

Experimental conditions have been established for the operation of a rat heart-lung preparation which result in a high degree of uniformity of work performance as measured by left ventricular work index (LVWI) (proportional to the product of cardiac output and mean arterial blood pressure). At a pcrfusion blood temperature of 37° C heart rate was higher and left ventricular work index lower than at 32° C. Peripheral resistance was adjusted to give an analysis of the work performance of the heart-lung at three different levels of mean arterial blood pressure: 80, 110, and 130 mm. Hg. The lower the pressure, the greater LVWI. Heart rate was not influenced by alterations in peripheral resistance.

LVWI was less in heart-lung preparations perfused with blood from adrenalectomized rats than in preparations perfused with blood from intact rats. Corticosterone, cortisol or aldosterone was added to perfusion blood from adrcnalectomized rats to yield a concentration of 10µg., 10 µg. and 3.2x10^–2 µg. per 100 ml., respectively. These corticosteroids increased LVWI. On the other hand, neither Substance S nor tetrahydrocortisol at 10 µg. per 100 ml. had an effect on LVWI.

A wide range of concentrations (2, 10, 50, and 500 µg. per 100 ml.) of corticosterone and of tetrahydrocortisol was tested in the rat heart-lung at a perfusion blood temperature of 32° C and of 37° C. Tetrahydrocortisol did not increase LVWI at any concentration tested. At high concentrations, this steroid decreased LVWI; the inhibitory concentration at 32° C was less than the inhibitory concentration at 37° C. Corticosterone was effective in increasing LVWI at a concentration of 2 µg. per 100 ml. at 32° C, but was ineffective at this concentration at 37° C. At the higher temperature, corticosterone exerted a stimulatory action in a concentration of 10 µg. per 100 ml. High concentrations of corticostcrone were inhibitory, and as in the case of tetrahydrocortisol, the inhibitory concentration was less for the heart-lung operating at 32° C than at 37° C. These observations indicate that the stimulatory and inhibitory concentrations of corticosterone in the rat heart-lung are temperature dependent.

Footnotes

^1, Aided by a research grant (A-331-C4) from the United States Public Health Service and by a research grant (DA-49-007-MD-990) from the Department of the Army, Office of the Surgeon General, Research and Development Division.

² The authors are indebted to Peter Sindell and to Bill Sayers, High School Junior Research Assistants, for their excellent technical assistance.

³ Arthritis and Rheumatism Foundation Fellow, 1956-present.

Received October 21, 1959.