Tissue-type plasminogen activator in somatostatin cells of rat pancreas and hypothalamus

Plasminogen activators (PAs) proteolytically convert plasminogen to plasmin, which, in turn, can degrade most proteins. This system has been implicated in a variety of biological processes. Using immunocytochemical methods, we here describe the localization of tissue-type PA (t-PA) in rat somatostatin cells. In the pancreatic islets, a low number of strongly t-PA-immunoreactive cells was found. By sequential staining, we found these cells to constitute a subpopulation of the somatostatin cells. Biochemical analysis of extracts from isolated rat islets demonstrated the presence of t-PA, and immunoblotting analysis demonstrated one band with a similar electrophoretic mobility. No urokinase-type PA immunoreactivity was found in the rat endocrine pancreas. A granular t-PA immunoreactivity resembling that found in adjacent sections with somatostatin antiserum was found in the median eminence of the hypothalamus. No t-PA immunoreactivity could be detected in somatostatin cells of the gastric and intestinal mucosa.