Plasma cholecystokinin concentrations after breast feeding in healthy 4 day old infants.

The aim of the present study was to characterise plasma concentrations of cholecystokinin (CCK) after breast feeding in newborn infants. Fifty eight healthy full term exclusively breast fed infants were investigated at 4 (1) (2-6) days of age. Each infant contributed one blood sample collected just before, immediately after, or 10, 30, and 60 minutes after breast feeding. Plasma concentrations of CCK were measured with a technique consisting of high pressure liquid chromatography separation of gastrins and CCKs and consequent analysis with radioimmunoassay. Mean (SD) preprandial plasma concentrations of CCK (CCK8+CCK-33,39) were 68 (17) pmol/l. A significant increase was seen immediately after breast feeding, which was followed by a decline at 10 minutes and a secondary rise was seen at 30 and 60 minutes. The first peak is likely to be due to a suckling related activation of the vagal nerve and the second to a stimulatory effect of food on CCK-producing cells. An inverse relationship between basal concentrations of CCK and age of the infant was found. In rats peripheral injections of CCK reduce food intake and cause postprandial sedation and sleepiness via activation of an afferent vagal mechanism. CCK release in response to breast feeding may therefore in addition to exerting stimulatory effects on digestion and metabolism contribute to relaxation and sleepiness seen after breast feeding. The high CCK concentrations seen in younger infants may help the infant to remain satiated and calm despite receiving very little food during the first days of life.