Ultrastructural localization of arginine vasopressin in coronary vessels of newborn rat

Abstract.

We report on the ultrastructural distribution of arginine-vasopressin (AVP) in the heart of newborn rats using pre-embedding peroxidase-antiperoxidase immunocytochemistry with a polyclonal AVP antibody for electron microscopy. Positive labelling for AVP was localized in endothelial cells of main coronary arteries and cardiac vessels of smaller diameter (microvessels). Examination of the right coronary artery showed that approximately 58% of the endothelial cells were positive for AVP. Immunoreactivity to AVP in the cytoplasm of arterial endothelium predominated in association with the membranes of granular endoplasmic reticulum and in subplasmalemmal areas. The endothelium of small vessels exhibits less endoplasmic reticulum, but still shows AVP immunoprecipitate in the cytoplasm. It is suggested that endothelial AVP may contribute to vasomotor control of the coronary circulation in the early stages of postnatal development. AVP antibody also labelled some fibroblast/fibroblast-like cells associated with the coronary arteries and microvessels; thus, these cells as well as the endothelium appear to be a source of AVP in the newborn rat heart. The functional significance of these findings is discussed.