ACETYL-L-CARNITINE EFFECT ON PITUITARY AND PLASMA BETA-ENDORPHIN RESPONSIVENESS TO DIFFERENT CHRONIC INTERMITTENT STRESSORS

The aims of the present study were: 1) to compare the effect of two di fferent chronic intermittent stressors i.e. cold-swimming versus ether , on the pituitary opioidergic system; 2) to evaluate the response of pituitary and plasma beta-endorphin (beta-EP) to an acute stress in ch ronically stressed rats; and 3) to evaluate the effect of acetyl-l-car nitine treatment (10 mg/day/rat per os at night) on pituitary and plas ma beta-EP changes induced by two different types of chronic stress. T he stressors were applied twice a day for 10 days. Rats were killed ei ther before, during or after the last swimming or ether stress session . Beta-EP was measured by radioimmunoassay in anterior pituitary and i n neurointermediate lobe extracts and in plasma. The following observa tions were made: 1) Chronic intermittent cold-swimming stress increase d anterior pituitary contents and plasma beta-EP levels; 2) both chron ic intermittent cold-swimming stress and ether stress caused an increa se of neurointermediate lobe beta-EP contents; 3) as in control animal s, rats exposed to chronic intermittent swimming stress reduced pituit ary beta-EP contents and raised plasma beta-EP levels in response to t he last acute swimming stress; 4) in contrast to control animals, rats exposed to chronic intermittent ether stress did not show any signifi cant response of the pituitary-plasma opioidergic system to the last a cute ether session; 5) the acetyl-l-carnitine treatment counteracted t he changes evoked by chronic intermittent cold-swimming stress on the pituitary and plasma beta-EP levels. The present data show that chroni c intermittent ether stress impairs the capacity to respond to the acu te stress and that acetyl-l-carnitine may modulate the changes of beta -EP levels following chronic cold-swimming stress exposure.