Processing of synthetic somatostatin-28 and a related endogenous rat hypothalamic somatostatin-like molecule by hypothalamic enzymes.
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 radioimmunoassay for tetradecapeptide somatostatin (S-14) in which S-28 crossreacted either 100% (RIA R149) or less than 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 (t 1/2  = 14 min). 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 (t 1/2 = 17 min) 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.
D000818:Animals; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D007031:Hypothalamus / Q000201:enzymology* / Q000276:immunology / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D013004:Somatostatin / Q000378:metabolism*; D053561:Somatostatin-28
D013004:Somatostatin; D053561:Somatostatin-28