Monoamine oxidase (
MAO) activity was studied in whole brain, hypothalamus, adrenals and liver of developing rats subjected to disturbed feeding patterns or
undernutrition for 3 weeks. The rats were divided into six groups: (1) normally fed controls; (2) rats starved for 24 h, fed for the following 8 h and killed after the last
starvation period (PAS); (3) same treatment as in (2) but killed after the last feeding period (PAF); (4) rats starved for 16 h, fed for the following 8 h at a constant schedule, and killed after the last
starvation period (
PS); (5) same treatment as in (4) but killed after the last feeding period (PF), and (6) undernourished (U). Alteration of the feeding time resulted in significant decreases of
MAO activity in the brain and the adrenal gland whereas the hypothalamus and the liver showed a slight increase in activity in the PAS group. In PS rats,
MAO activity increased in the brain, adrenals and hypothalamus; in PF rats, the effects of the treatment were inverse. Both in the PS and PF rats, hepatic
MAO activity was strongly decreased when assayed with
kynuramine. In U rats, hepatic
MAO activity was highly increased when assayed with
kynuramine but the other tissues responded differently. The
adrenaline and
noradrenaline stocks of the adrenal gland were markedly increased in all the treated groups; the maximum increase in
noradrenaline was observed in the PS rats. The results suggest that any disturbance in the feeding pattern affects the
MAO activity in the central and peripheral regions of the young rat during postnatal development. The developing rat seems to get accustomed to new alimentary rhythms, and normal monoaminergic function is rapidly restored when the rat is given a compensatory diet. Increased adrenal
catecholamines after a disturbance in the feeding patterns seem to be a response to stress.