BIOSYNTHETIC GROWTH-HORMONE INCREASES THE COLLAGEN DEPOSITION RATE IN RAT AORTA AND HEART

Disorders of the cardiovascular system often are associated with alterations in the metabolism of the collagens of these tissues. A method for in vivo determination of collagen deposition rate in small tissue samples is delineated and used for assessment of the effect of biosynthetic growth hormone (GH) injections on the collagen deposition rate in rat aorta and cardiac musculature. Rats were injected with GH, and the controls with saline, twice daily for 7 days. The in vivo collagen deposition rate was measured by injecting iv a large dose of [H-3]-proline with a flooding dose of ''cold'' proline, followed by determination of the production of [H-3]-hydroxyproline during a 4-h labelling period. Extractable collagens that were not bound in the tissue and therefore do not contribute mechanical strength to it were removed from the samples. H-3-Labelled- and ''cold'' amino acids were assessed by reversed-phase HPLC combined with simultaneous now scintillation detection on the same sample. In the control group the deposition per hour was 0.13 +/- 0.02% (mean +/- SEM) in aortic intima media and 0.72 +/- 0.09% in cardiac left ventricular musculature. Growth hormone induced a threefold increase (p < 0.001 and p < 0.01, respectively) in the collagen deposition rate: 0.45 +/- 0.06% in aortic intima media and 2.43 +/- 0.45% in cardiac left ventricular musculature. The method described enables a rapid and sensitive determination of collagen deposition per hour in small tissue samples from experimental animals. The collagen deposition rate of cardiac musculature is fivefold higher compared with that of aortic intima media. Biosynthetic GH induces a threefold increase in the collagen deposition rate of these tissues.