Immunohistochemical Detection of Morphofunctional Features of Pulmonary Veins in Rats

Introduction. The histological structure of the small terminal venous vessels in the cranial and caudal segments of the left lung and their innervation remain poorly studied. The aim of this study was to investigate the histological and immunohistochemical structure of the pulmonary vein wall in rats. Materials and Methods. The object of the study was the left lung (LL) of Wistar rats weighing 200–250 g (n=10). The pulmonary vein (PV) of Wistar rats was examined, from its distal sections to its entry into the left atrium. The material was fixed in zinc-ethanol-formaldehyde solution and embedded in paraffin. Paraffin sections (5 μm) were made using a rotary microtome. After deparaffinization, immunohistochemical (IHC) reactions were performed on the sections to detect neural markers: synaptophysin, tyrosine hydroxylase, and PGP 9.5 protein. An IHC reaction for sarcomeric actin was used to identify muscle cells. Results. The rat PV media was shown to contain two types of muscle tissue: cardiac muscle and a thinned subendothelial layer of smooth muscle cells (SMCs). In the caudal part of the LL, most lateral branches of the PV have a muscular wall consisting of an uneven thin layer of smooth muscle fibers. This work describes the cytoarchitecture of venous capillaries located in the parenchyma of the respiratory region. The structure and topography of smooth muscle sphincters characteristic of branches of thin-walled pulmonary veins with a lumen diameter from 25 to 50 μm were studied. A predominance of parasympathetic innervation in the cranial segment of the cardiac muscle of the vessel wall was noted. Sympathetic innervation of the PV is carried out by a thin plexus of catecholaminergic postganglionic terminal varicose axons localized between the myocardial “sheath” and the thinned smooth muscle layer of the vascular intima. The caudal extent of this layer is limited by the boundaries of the sheath itself. A lack of neural structures was noted around thinwalled venous capillaries equipped with smooth muscle sphincters, as well as in septa and acini. Conclusion. IHC reaction for sarcomeric actin allows the study of both cardiomyocytes and smooth muscle cells in the lung. Structural features of the venous wall in the cranial and caudal regions of the rat left lung and differences in their innervation are described. The results are summarized in a diagram and may be of interest to physiologists, surgeons, and clinicians studying cardiopulmonary pathology.

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