Abstract
The satiating potencies of exogenous cholecystokinin-8 (CCK-8) and cholecystokinin-33 (CCK-33) depend on route of administration: the peptides are equipotent after ip administration, but CCK-33 is significantly more potent than CCK-8 after infusion into the hepatic portal vein (hpv). This suggests that CCK-33 has a hormonal and paracrine mode of action, while CCK-8 has only a paracrine mode of action. This hypothesis was confirmed in rats with abdominal vagotomies that spared the hepatic proper nerves: CCK-33 ip decreased 30-min intake of 10% sucrose significantly, but CCK-8 did not (Eisen et al., 2005). To test the hypothesis further, we prepared 7 male rats with chronic hpv catheters and abdominal vagotomies that spared the hepatic proper and gastroduodenal nerves. HPV infusions of CCK-33, CCK-8, or saline began 5 min before and continued for the first 7.8 min of 30-min access to sweetened condensed milk. The largest dose of CCK-33 (26.4 μg/kg) decreased intake >80%, but an equimolar dose of CCK-8 (8 μg/kg) did not (
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