Feeding motivation in swine: Relation with insulin, glucose and free fatty acids in portal and jugular blood, and involvement of cholecystokinin

Abstract

The control of feeding motivation was studied in eight castrated male pigs (92.9 ± 1.5 kg) surgically fitted with jugular and portal vein catheters. The first part of the experiment was set up as a cross-over design. Two weeks after surgery, four pigs were fasted for 24 h (FAST) while the remaining four were fed ad libitum (CTL). Three days later, the same procedure was repeated with the treatments reversed. Blood samples were collected every 4 h during the first 16 h of these two 24-h periods. After each 24-h period, pigs were subjected to a feed motivation test during which blood samples were obtained every 5 min for 60 min for CTL pigs and until 30 min after cessation of eating in FAST pigs. Three days later, the second part of the experiment was conducted. Five of the eight pigs were fasted for another 24 h, injected i.v. with 70 μg kg–1 BW of a cholecystokinin (CCK) receptor antagonist (MK-329), and subsequently subjected to a feed motivation test. Insulin, glucose and FFA concentrations were greater (P < 0.001) in portal than jugular blood. Fasting decreased insulin concentrations in both portal and jugular blood, decreased glucose in portal blood only, and increased FFA in jugular blood only. The number of pushes (P < 0.05), duration of eating (P < 0.001) and amount of feed eaten during the feed motivation test (P < 0.01) were all increased by fasting, and were further increased with MK-329 injection. Results indicate that CCK is involved in the control of satiety in pigs and that concentrations of insulin, glucose and FFA in the jugular vein may not always be representative of concentrations in the portal vein. Key words: Swine, insulin, glucose, cholecystokinin, feeding motivation, fast