CENTRAL AND PERIPHERAL NOREPINEPHRINE TURNOVER AFTER HINDLIMB SUSPENSION IN THE RAT

After a 9-d hindlimb suspension, the turnover rate of norepinephrine ( NE) in rats was determined in A1, A2 (rostral and caudal), AS and A6 c ell groups, as well as in peripheral target organs (heart and kidneys) . The NE turnover rate decreased after hindlimb suspension respectivel y in caudal A2 (67.5%, p 0.001), rostral A2 (63%, p < 0.001) and in A5 cell groups (62.5%, p < 0.001), but remained unchanged in Al and A6 r egions. The peripheral sympathetic outflow response was selectively mo dified: in suspended rats, the NE turnover was mainly decreased in atr ia (79%, p < 0.001) and in ventricles (44%, p < 0.001); there were no biochemical changes in kidneys. It was concluded that a 9-d hindlimb s uspension: 1) impaired the noradrenergic neuron activity of A2 and A5 cell groups, which are involved in the central cardiovascular regulati on, and particularly in the baroreceptor reflex mechanism; and 2) main ly altered the cardiac NE turnover and induced a selective response of peripheral target organs.