Effect of growth hormone and thyroxin on cardiovascular system of hypophysectomized rats

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Abstract
Growth hormone, thyroxin, or growth hormone and thyroxin were given for a period of 4 weeks to rats hypophysectomized 2–3 months previously. The effect of these treatments on blood pressure, weight and rate of the heart, cardiac output, and work was measured under basal conditions and during acute loading (infusion of polyvinylpyrrolidone into the right side of the heart) as well as during chronic loading (constriction of the aorta). The changes in cardiovascular parameters in the basal state due to hypophysectomy could all be reversed by thyroxin treatment. Thyroxin alone was inadequate in restoring the response of the hearts to either acute or chronic loading. Growth hormone in combination with thyroxin could restore or even exaggerate the normal response to both chronic and acute loading as well as maintain the basal parameters. Growth hormone itself had comparatively little effect; it caused some increase in the weight of the heart and stroke volume. It is concluded that both thyroxin and growth hormone are necessary for the normal function of the cardiovascular system.