To assess the characteristics of sucrose as a pain-reducing substance,
crying in 72 newborn humans during and after blood collection via hee
l prick was determined. In the first study infants drank 2 ml of water
or 2 ml of a 0.770.34- or 0.51-M sucrose solution 1 min prior to bloo
d collection. In the second experiment, a delay of 30, 60, 90, 120 or
240 s was imposed between sucrose intake and the initiation of blood c
ollection. The dose-response function for concentration was flat. The
most effective time delay was 120 s. The effectiveness of the 2-min in
terval accords with previous findings of endogenous opioid release cau
sed by sucrose taste. The flat dose-response function extends findings
in rats and humans that the calming and pain-reducing effects of sucr
ose are not influenced by either concentration or volume, suggesting t
hat the transduction from gustatory afferent to opioid-mediated effere
nt is of an on-off nature and not graded.