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

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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 μg 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. J. Endocr. (1987) 115, 91–95