SIGNIFICANT CHANGES IN THE ACTIVITY OF GABATRANSAMINASE AND SUCCINATE SEMIALDEHYDE DEHYDROGENASE OF MOUSE HYPOTHALAMUS FOLLOWING PERIPHERAL INJECTION OF CHOLECYSTOKININ-8 AND/OR CAERULEIN

The activities of 4-aminobutyric-2-oxoglutaric acid transaminase (GABA-T) and succinate semialdehyde dehydrogenase (SSADH) were determined in mouse hypothalamus after peripheral injections of cholecystokinin-8 (CCK-X)and/or caerulein (CLN). GABA transaminase activity was measured utilizing endogenous succinate semialdellyde dehydrogenase to convert the product of GAB A-T, succinate semialdehyde, to succinate. The concurrently formed NADH was used as an estimate of GABA-T activity. Similarly, the activity of SSADH was determined in terms of NADH. Injection of CCK-8 and/or CLN inhibited the GABA-T and SSADH activities in dose-dependent responses. The activities of GAB A-Tand SSADH were diminished by 52 and 66 percent respectively, 30 minutes after injection of CCK-8 (50 µg/kg body weight).Similarly, peripheral injection of CLN (50 µg/kg body weight) reduced the activity of GABA-T and SSADH by 56 and 65 percent respectively, in 30 minutes. Using ill vitro models, the full activities of GABA-T and/ or SSADH, after incubation with CCK-8 and/or CLN, were restored following 30 hours of dialysis at 4°C. These results indicate direct and reversible interactions between the catabolizing enzymes of GABA (GABA-T and SSADH) and the peptides CCK-8 and CLN.