Action of Growth Hormone and Thyroxine on Aortas of Hypophysectomized Dogs

Young dogs were surgically hypophysectomized and maintained for eleven weeks postoperatively with age-matched normal controls. For three weeks prior to sacrifice, four hypophysectomized dogs were given daily injections of bovine growth hormone (GH, 0.2 mg./kg.) and another four were given daily injections of thyroxine (T₄, 5 μg./ kg.). Aortas were removed, cleaned of adventitia and divided into three segments: arch, thoracic and abdominal. Each portion was analyzed for collagen, elastin, deoxyribonucleic acid (DNA), calcium, total mucopolysaccharides (MPS), hyaluronic acid (HA), heparan sulfate (HS), dermatan sulfate (DS) and chondroitin sulfate (GS). The arch and thoracic aortas of normal animals were found to contain more DNA, CS and elastin but less collagen than the abdominal aorta. Removal of the hypophysis resulted in an overall increase in elastin and DNA content and caused a decrease in all sulfated MPS. Administration of either CH or T₄ to hypophysectomized dogs had a profound effect on the majority of constituents in all segments of aorta. GH returned the content of elastin, DS and CS toward normal in at least two of the three aortic segments. T₄ returned the content of DNA, DS and CS toward normal in all segments. Moreover, T₄ treatment caused significant reductions in collagen and HA contents of thoracic and abdominal segments. These results indicate that: (1) the composition of normal aorta varies with the segment studied; (2) the composition of the aorta is markedly affected by hypophysectomy, CH and T₄ treatment; and (3) individual aortic segments show differential sensitivity to a given hormone.