Processing of synthetic somatostatin-28 and a related endogenous rat hypothalamic somatostatin-like molecule by hypothalamic enzymes |
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Authors: | Hans H. Zingg Yogesh C. Patel |
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Affiliation: | Fraser Laboratories, McGill University Departments of Medicine, Neurology and Neurosurgery, Royal Victoria Hospital and Montreal Neurological Institute, Montreal, Quebec H3A 1A1, Canada |
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Abstract: | Synthetic somatostatin-28 (S-28) as well as a related endogenous rat hypothalamic somatostatin-like compound (3K SLI) were incubated with hypothalamic extracts from which endogenous somatostatin-like immunoreactivity (SLI) had been removed by immunoabsorption. The reaction products were analyzed by gel chromatography, HPLC as well as two different radioimmunoassays for tetradecapeptide somatostatin (S-14) in which S-28 crossreacted either 100% (RIA R149) or < 0.001% (RIA S39). The results indicate that incubation of S-28 with SLI free hypothalamic extracts results in a rapid decrease of total immunoreactivity measured with RIA R149 (). By contrast, with RIA S39 a rise from zero to a peak value at 8 min was measured suggesting the formation of S-14. This was confirmed by subsequent analysis by gel chromatography and HPLC. Using endogenous 3K SLI a decrease of total R149-immunoreactivity with a similar time course () was observed simultaneously with the emergence of material that corresponded to S-14. This converting activity seems to be specific for SLI-containing tissues since similar rates of conversion were observed with extracts from cerebral cortex and cerebellum but not with lung and liver extracts.It is concluded that (1) S-28 is converted to S-14 by hypothalamic enzymes; (2) the processing of 3K SLI is similar, suggesting the two molecules are closely related, if not identical, and (3) the regulation of S-28 to S-14 conversion could represent an important mechanism for controlling the functional activity of somatostatinergic cells. |
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Keywords: | To whom all correspondence should be addressed. |
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