Sexual activity increases plasma concentrations of cholecystokinin octapeptide and offsets hunger in male rats.

ABSTRACT

Male rats deprived of food for 48 h ignored food pellets immediately after ejaculating with a sexually receptive female rat as did males tested 5 min after i.p. injection of 5 micrograms cholecystokinin octapeptide (CCK-8) or males which had consumed food pellets for 1 h. The concentration of CCK-8 in plasma was increased to comparable levels (10.1 +/- 3.8 (S.E.M.); 11.3 +/- 3.7 and 7.2 +/- 0.5 pmol/l respectively, compared with 1.2 +/- 0.3 pmol/l for NaCl-injected controls) under each of these conditions, whereas the concentration of gastrin increased only after food consumption (18.4 +/- 3.8; 17.7 +/- 5.4 and 54.3 +/- 7.0 pmol/l respectively, compared with 21.5 +/- 2.1 pmol/l for NaCl-injected controls). The effect of ejaculation on the latency to starting to eat was partially reversed by i.p. injection of 50 mg of the CCK-8 antagonist proglumide, but neither treatment with proglumide or CCK-8 nor consumption of food affected the display of sexual behaviour. The results support the suggestion that CCK-8 is a 'satiety peptide' in the rat.