Reduced injury and scar in acute myocardial infarctions treated with human growth hormone

Repair processes of cells submitted to an injury may exhibit an indirect identifying feature of its activity, based on the amount of connective tissue that could be traced with special stains and morphometry. Hydroxyproline concentration in tissue is also an index with which the presence and amount of repair mechanisms can be assessed. They may be quantitated appropriately in correlation with the end products of collagen, which represent the amount of cicatricial tissue. In order to correlate the size of the scar in myocardial infarcts with the amount of connective tissue, a determination of hydroxyproline levels after 30 days of acute experimental infarctions was performed in 3 groups of rats: 10 received a single dose of 2I U of human growth hormone (HGH) per week for 4 weeks, in a bolus injection immediately after the infarction was surgically induced; 10 received the same dose as above in daily injections during a week. Finally, another group of 10 animals which did not receive an active treatment served as controls. All animals were sacrificed at the end of a month. A morphometric study with Van Gieson stain was performed. Hydroxyproline levels were determined. Hydroxyproline levels were considerably lower in hGH-treated rats (T) compared to control (C) rats: 3.30 ug/mg +/- 0.1 vs. 4.10 +/- 0.29 (p < 0.05). Morphometry: T.: 5.23 +/- 2.45 vs. C.: 4.22 +/- 2.15 of the left ventricular wall. Three aneurysms were found in C group versus 1 in T. Human growth hormone administered to a group of rats with myocardial infarction showed obvious dose--effects consisting of a significant diminution of scar tissue in treated rats with a proportional fall in the hydroxyproline levels.