Significant changes in the activity of GABA transaminase and succinate semialdehyde dehydrogenase of mouse hypothalamus following peripheral injection of cholecystokinin-8 and/or caerulein

ABSTRACT

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-8] and/or caerulein [CLN]. GABA transaminase activity was measured utilizing endogenous succinate semialdehyde dehydrogenase to convert the product of GABA-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 GABA-T and SSADH were diminished by 52 and 66% respectively. 30 minutes after injection of CCK-8 [50 micro g/kg body weight].Similarly, peripheral injection of CLN [50 micro g/kg body weight] reduced the activity of GABA-T and SSADH by 56 and 65% respectively, in 30 minutes. Using in 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