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Endothelin-1 is thought to play a role in the regulation of gastrointestinal function including its secretory role. This study investigated the localisation of endothelin-1 in the mucosa of the large intestine of normoxic and chronically hypoxic rats. Chronic hypoxia was produced by maintaining the animals in a hypoxic chamber. After animal perfusion/fixation, colonic segments from normoxic and hypoxic rats were investigated by the postembedding immunogold labelling procedure. In the microvasculature from normoxic (control) animals immunolabelling visualised as single particles was low and confined to the cytoplasm of endothelial cells. In the epithelium, immunolabelling was found mainly at the basal and apical regions of the cells. Chronic hypoxia for 10 d greatly enhanced the level of immunolabelling both in endothelial and epithelial cells of the mucosa. In endothelial cells clusters of gold particles were found in the cytoplasmic matrix and the subendothelium. Epithelial cells showed intense labelling, located mainly in the luminal/apical region within vacuole-like spaces and in the brush-border. In conclusion, hypoxia induces increase in immunoreactivity to endothelin-1 in gut endothelial and especially epithelial cells in the colonic mucosa.

The localisation and colocalisation of neuronal isoform (type I) nitric oxide synthase, endothelin-1, arginine-vasopressin and substance P in endothelial cells of rat coronary and femoral arteries was investigated by pre-embedding and postembedding immunocytochemistry. Nitric oxide synthase appeared in a high proportion of endothelial cells of both arteries (about 89% in the femoral artery, examined with the preembedding avidin-biotin-peroxidase method, and in almost all cells of the coronary artery, examined with the postembedding immunogold technique). Double immunogold labelling in single cells demonstrated the colocalisation of nitric oxide synthase with endothelin-1, arginine-vasopressin and substance P. The immunolabelling was mostly confined to the cytoplasmic matrix. It is suggested that nitric oxide synthase/nitric oxide and the peptides examined may be involved in local control of blood flow in coronary and femoral arteries.