RESUMO
In rats kept at a constant temperature (24 +/- 1.5 degrees C) and on a reversed day/night cycle (light from 11 p.m. to 11 a.m.), the amount of food eaten during the first 2 h of darkness and during 24 h was measured every day. When reserpine or guanethidine were injected 5 min before the beginning of the dark period on four consecutive days, there was no significant change in the 0.5-, 1-, or 24-h food intake on the injection days, but there was a significant increase in the 0.5-, 1- and 2-h food intake during the next five to eight days, without any change in the 24-h intake. A single injection of dichloroisoproterenol produced no change on the day of injection but it induced a significant increase in the 0.5-, 1- and 2-h intake on the following 15 days, without any change in the 24-h intake. The increase in the early night-time feeding without any change in the 24-h intake was interpreted as an increase in meal size (diminished preabsorptive satiation) compensated by a decrease in meal frequency. Both reserpine and guanethidine are catecholamine depleters but the latter does not penetrate into the brain. Dichloroisoproterenol is a beta-blocker acting on the glycogenolytic effects of catecholamines. The results thus agree with the hypothesis that glycogenolysis elicited by the liberation of intrahepatic catecholamines from the sympathetic nerve endings and chromaffin cells plays a role in preabsorptive satiation.
