The effect of cholecystokinin-octapeptide on food intake and consummatory behavior in lactating rats

Rats are less sensitive to the satiating effect of CCK-8 during some reproductive states such as estrus and proestrus, and in ovariectomized rats following the administration of estradiol and progesterone. The sensitivity of rats to CCK-8's effect on food intake decreases as lactation progresses. During lactation, prolactin and progesterone levels are elevated. Implantation of ectopic pituitaries increases prolactin levels in males and females as well as progesterone levels in females. To evaluate whether or not prolactin elevation modifies CCK's effect on feeding, we studied the effect of CCK-8 on food intake during the early dark cycle in male and female rats implanted with ectopic pituitaries. As previously demonstrated, prolactin levels were elevated in both male and female pituitary-implanted rats and progesterone levels were elevated in the female rats. CCK-8 inhibited food intake in sham-operated male rats, but did not reliably decrease early dark cycle food intake in sham-operated or pituitary-implanted female rats or pituitary-implanted male rats. Thus an elevation in prolactin levels does not appear to modify the effect of CCK-8 on food intake in female rats. We also evaluated the effect of CCK on consummatory and maternal behavior in lactating rats. CCK-8 altered the meal patterns of lactating rats primarily by decreasing the rate of food consumption and increasing the latency to the first meal. The latency to the first meal of rats receiving CCK was increased during early and mid-lactation and the PW period, but not during late lactation compared to that of the saline-injected rats. CCK-8 did not modulate any of the maternal behaviors studied. CCK-8 increased the amount of time spent resting during early and middle lactation, which may help explain the decrease in food intake observed during these periods of lactation.