COMPARISON OF THE EFFECTS OF 2-DEOXYGLUCOSE AND IMMOBILIZATION ON SECRETION AND SYNTHESIS RATE OF CATECHOLAMINES IN THE ADRENAL-GLAND - A MICRODIALYSIS STUDY IN CONSCIOUS RATS

Using microdialysis, extracellular 3,4-dihydroxyphenylalanine (DOPA), noradrenaline (NA) and adrenaline (AD) concentrations in the adrenal g land were monitored in conscious rats during and after 60 min of immob ilization (IMM) as well as after injection of 500 mg kg(-1) 2-deoxyglu cose (2-DG). IMM produced a rapid and transient increase in secretion of AD (20-fold), NA (13-fold) and DOPA (3.6-fold). This was accompanie d by an increase in blood pressure (+18 mmHg) and heart rate (+146 b.p .m.). Repeated exposure to IMM (daily 60 min, for 5 days) had no influ ence on either catecholamine secretion of haemodynamic profiles, indic ating the lack of habituation to stressful conditions. Unlike IMM, the stress of 2-DG-induced central neuroglucopenia stimulated the release of AD without affecting NA secretion. AD levels peaked (5.1-fold incr ease) 40-60 min after 2-DG injection and then slowly declined. 2-DG in duced no changes in blood pressure but reduced the heart rate (-48 b.p .m.). In separate experiments, steady-state dialysate DOPA levels, rea ched during continuous infusion of decarboxylase inhibitor NSD 1015 in to adrenal gland tissue through the dialysis probe, served as an index of adrenomedullary tyrosine hydroxylase (TH) activity. IMM evoked a m arked increase in TH activity (DOPA formation increased 2.7-fold), whi ch remained elevated 60 min after the cessation of stress when AD and NA secretion had already fallen to baseline. After 2-DG, despite signi ficant hormonal response, adrenal TH activity was unchanged. These res ults give clear evidence that IMM and 2-DG-induced neuroglucopenia may be considered as two different types of stressful stimuli.