EFFECT OF HYPOPHYSECTOMY AND HORMONE TREATMENT ON THE HEART–LUNG PREPARATION OF RATS

Abstract

Heart–lung preparations (h.l.p.) were made in normal rats, hypophysectomized rats, and in hypophysectomized rats treated with either growth hormone or thyroxine or both. While mean arterial pressure was kept constant at 100 mm Hg, the flow into the heart was increased stepwise until cardiac output did not rise any further (maximum cardiac output (m.c.o.)). Hypophysectomy substantially decreased the m.c.o., even when expressed per kilogram body weight. Thyroxine treatment alone or with growth hormone completely restored the m.c.o. to normal. However, when the m.c.o. was calculated per gram of left ventricle weight, it did not reach the normal level in any of the hypophysectomized rats investigated. Growth hormone, on the other hand, raised the stroke volume (expressed per gram of left ventricle) of hypophysectomized rats without affecting the rate of the heart.