The effect of hypophysectomy on experimental endothelial cell regrowth and intimal thickening in the rat

We studied the influence of hypophysectomy on endothelial cell regrowth and intimal thickening following aortic endothelial removal. Modification of this influence by replacement doses of glucocorticoids, mineralocorticoids, thyroxin, and growth hormone also was investigated. Young adult male rats were used, and endothelial removal was achieved by the balloon catheter method. Percent endothelial regrowth and percent intimal thickening were quantified 1 or 2 weeks after injury (3 or 5 weeks after hypophysectomy). One week after injury, endothelial regrowth was 64% in hypophysectomized rats and only 54% in controls. At 2 weeks, values were 80% and 79% respectively. Intimal thickening (percent of wall thickness due to intima) at 1 week was 11% in hypophysectomized and 14% in control rats. At 2 weeks, values were 13% and 22%, respectively. All differences between hypophysectomized and control rats at 2 weeks were statistically significant. Neither endothelial regrowth nor intimal thickening in hypophysectomized rats was altered by hormone replacement. Comparison of areas in which endothelium had not regrown suggested that hypophysectomy had a direct effect on intimal smooth muscle cell proliferation. Thus, hypophysectomy suppresses intimal thickening and accelerates endothelial regrowth after wall injury. Neither effect depends on certain known hormones, and these effects are to some extent independent of one another. These findings are relevant to recent work on growth factors and atherogenesis.