Arterial blood gases, muscle fiber diameter and intercapillary distance in cardiac hypertrophy of rats with an old myocardial infarction.

Abstract

In rats with a myocardial infarction due to ligation of the left coronary artery a marked right ventricular hypertrophy developed after 41/2 weeks. At this time no difference against control animals was observed in arterial\(P_{{\text{O}}_2 }\),\(P_{{\text{CO}}_2 }\), pH, ideal alveolar\(P_{{\text{O}}_2 }\), and alveolar-arterial O2 pressure difference, as measured in unanesthetized animals at normoxia. In histological sections of the heart stained by PAS reaction capillaries and muscle fibers were counted, and the mean intercapillary distance and muscle fiber diameter were estimated. In the right ventricle of the rats with myocardial infarction both increased when compared with control animals or with sham-operated rats. Fibercapillary ratio was the same in all three groups. Similar results were obtained in the remaining undamaged tissue of the left ventricle of rats with a myocardial infarction when compared with the left ventricle of control or sham-operated rats. Findings concerning intercapillary distance suggest that also in the myocardium which remains intact during the development of the infarction and later hypertrophies, tissue oxygen transport might be impaired, particularly during a stress situation. Results in the right ventricle of rats with myocardial infarction show an opposite trend against rats exposed chronically to simulated high altitude, where in the hypertrophied right ventricle a shorter intercapillary distance occurs and therefore an improvement of tissue oxygen transport might be expected.