Plasma cholecystokinin concentrations in 3-day-old lambs: effect of the duration of fasting preceding a sucking bout.

Cholecystokinin (CCK) is a regulatory peptide released into the circulation after the ingestion of food. Our knowledge concerning the factors affecting its pattern of secretion in the mammalian neonate is scanty. Therefore, in this work we studied plasma concentrations of CCK in 3-day-old lambs after a sucking bout that followed either a short (2 h) or a long fasting period (9 h). Plasma concentrations of CCK were measured by radioimmunoassay in blood samples collected from jugular veins 10 min before, immediately after a sucking bout, and then at 10-min intervals during the following hour. In the first experiment a period of fasting of 2 h before allowing the lambs to suck did not lower the levels of CCK. On the other hand, a significant decrease was recorded 10 min after feeding ended. Between 20 and 50 min after the end of sucking, the mean CCK concentration rose back to the pre-feeding level before decreasing again at 60 min. In the second experiment a period of fasting of 9 h, on the other hand, significantly lowered the levels of CCK. Plasma levels also tended to decrease immediately after sucking was ended. This was followed by a substantial rise and levels remained high during the rest of the sampling period. It was concluded that the decrease recorded immediately after a sucking bout could be due to an inhibitory effect of the oral phase while the following rise reflected the stimulatory effect of milk nutrients on intestinal CCK-producing cells.