Influence of progressive starvation upon brain and adrenal monoaminergic activity in developing rats of two different ages.

Experiments show the influence of progressive starvation upon the synthetic and metabolic activity of monoaminergic function in the brain and the adrenal gland of young rats of two different ages. Brain and adrenal monoamine oxidase (MAO) showed a tendency to decline with the prolongation of the starvation interval. After 60 h of starvation, MAO activity was irreversibly decreased, even with 24 h of feeding, in the two age groups. Cerebral catechol-O-methyltransferase (COMT) activity was very slightly affected in response to the starvation in the older group, but the younger group showed an increased level of enzyme activity, and refeeding after 60 h of starvation of the young rats produced further increases. 60 h of starvation produced an increase in COMT activity of the adrenal gland of the older rats whereas the younger group did not show any marked change. Adrenal phenylethanolamine-N-methyltransferase (PNMT) declined after 24 and 48 h of starvation in the older rats, but the younger rats showed progressive increases after similar intervals of starvation. After 60 h of starvation, PNMT in the adrenal gland of the old rats increased significantly when compared to the control value, but the younger rats did not show any important change. Adrenal stores of adrenaline rose progressively up to 60 h of starvation in the old rats whereas the younger group responded in a contrary manner. Adrenal noradrenaline followed a similar pattern of evolution in both groups up to 60 h of starvation (when the results are expressed per milligram of adrenal protein), and refeeding had very little influence on the effects of starvation. The effects of starvation upon adrenal and cerebral MAO activity were verified with two different substrates. The results provide evidence that the metabolism of monoamines by oxidative deamination can be markedly affected by starvation, and this can be irreversible even after 24 h of feeding of starved rats. COMT activity augments when MAO activity declines.