Ultrastructure of the Myocardium and Left Ventricular Microvasculature in White Rats Under Short-Term Experimental Exposure to Hemp Seed Oil

Cardiovascular diseases represent one of the most significant medical and social challenges of modern times, underscoring the need to identify new approaches for preventing structural and functional abnormalities in the myocardium and the vascular bed. Objective. To determine the nature and characteristics of ultrastructural changes in cardiomyocytes and components of the myocardial microcirculatory bed in rats following a 4-week course of experimental hemp seed oil administration. Methods. The experimental study was conducted on sexually mature male white laboratory rats. Animals in the experimental group received hemp seed oil orally at a dosage of 0.5 ml/kg/day for 4 weeks. Transmission electron microscopy was used to evaluate the submicroscopic organization of the myocardium and to compare the findings with those from control and intact animals. The ultrastructure of the cardiomyocyte contractile apparatus, mitochondria, sarcoplasmic reticulum, nuclei, sarcolemma, and intercalated discs was analyzed. The state of the microcirculatory bed was also examined, specifically the ultrastructure of capillary endothelial cells, the basement membrane, pericytes, arterioles, and venules. Results. After 4 weeks of experimental hemp seed oil administration, the overall ultrastructural organization of the cardiomyocytes remained preserved. Most cells exhibited an orderly orientation of myofibrils with distinct sarcomere delineation. The Z-lines largely maintained their proper transverse alignment. The observed changes primarily affected the mitochondrial and sarcoplasmic components and were characterized by moderate structural heterogeneity of mitochondria, focal clearing of the matrix, and variability in cristae density. No signs of myofibril destruction, cardiomyocyte edema, or disruption of membrane structures were observed. The integrity of the endothelial lining was preserved within the microcirculatory bed. Capillary endothelial cells exhibited intact intercellular junctions, a moderate number of pinocytotic vesicles, and a continuous basal lamina. In some microvessels, moderate luminal dilation and alterations in the configuration of the endothelial luminal surface were noted. Conclusions. Four-week administration of hemp seed oil is associated with moderate ultrastructural remodeling of cardiomyocytes and myocardial microvessels, without the development of destructive changes. Mitochondria are the most sensitive intracellular structures, whereas the contractile apparatus of cardiomyocytes generally maintains its organized sarcomeric structure. Changes in the microcirculatory bed appear to reflect functional adaptation of the endothelium and optimization of transendothelial exchange.