EFFECT OF SEROTONIN ON FOOD-INTAKE BY PIGLETS DURING THE EARLY POSTNATAL-PERIOD

The effect of serotonin (5-HT) on the consumption of a liquid diet was investigated in 32 Large White x Landrace piglets from 1 to 24 d after birth in 2 experimental series. The piglets were housed individually in cages and were offered a commercial milk diet, Selasan, for sucking from feeding bottles 9 times a day at 2-h intervals with an 8-h break at night. Serotonin (5-hydroxytryptamine creatinine sulphate, Sigma) was administered to piglets (n = 3 to 6) in 0.01 % and 0.05 % solution invariably 10 minutes before feeding at 1, 2, 3, 5, 7, 9, 14, 18, 21, 22 and 24 d after birth in single i.p. doses of 0.05 to 1.00 mg.kg-1. Control piglets were intact (series I) or treated with saline (series II) in volumes corresponding to those of 0.05 mg.kg-1 5-HT doses. Compared with the amount of diet consumed before and after 5-HT injection, the dose of 0.01 mg.kg-1 5-HT reduced the food intake at 9 and 18 d by 48 % and at 21 d by 82 %. The dose of 0.05 mg.kg-1 5-HT reduced the food intake at 3 d by 58 %, at 5 d by 50 %, at 7 d by 93 %, at 9 d by 82 %, at 18 d by 85 %, at 21 d by 94 % and at 22 d by 55 %. The dose of 0.1 mg.kg-1 reduced the food intake of piglets at 1 d by 86 %, at 3 d by 94 % and at 21 d after birth by 99 %. All above-mentioned reductions in food intake were significant. The higher doses inhibited food consumption completely in piglets aged 2, 5 and 7 d. The results of the experiment using 16 times repeated 5-HT injection provided unequivocal evidence that 5-HT exerts a suppressive effect on diet consumption by piglets from 1 to 24 d after birth and that the extent of this suppression is dose-dependent. Moreover, changes were also recorded in the quality of consumption, i.e. in feeding behaviour, and after injection of the higher doses, hyperaemia of the skin and a stimulatory effect on intestinal peristalsis were observed. It is concluded that the serotoninergic system as part of aminostatic food intake regulation is functional already in newborn piglets.