| The brain-gut peptides cholecystokinin (CCK) is synthesized by enteroendocrine I cell of the proximal small intestine and by central neurons. The release of CCK from the former is associated with the stimulation of pancreatic enzyme secretion and gallbladder contraction, the inhibition of gastric emptying, the regulation of intestine motion, the acceleration of insulin and somatostation releases from pancreatic islets. Meanwhile, the release of CCK from the latter is a satiety factor, which regulates the feed intake of animal. CCK occurs in various molecular forms in animal, but the cholecystokinin octapeptide (CCK8) has the whole biological function of CCK. To know the nutritional and physiological functions and the underlying mechanisms of active immunization against cholecystokinin in pigs, two experiments were conducted to study the effects of active immunization against cholecystokinin octapeptide on performance, nutrient digestibility, endocrine hormones, pancreatic development, pancreatin activity, pancreatic tissue lesion and the gene expressions of CCK and CCK receptor in pigs.Exp. 1 Effects of Active Immunization against Cholecystokinin octapeptide on Growth Performance and CCK Gene Expression in Pigs.10 DLY pigs with body weight of 27.55 1.71 kg were distributed randomly into 2 treatments with 5 replicates of 1 pig. The treated group was immunized with 370 g CCK8 conjugated to human serum albumin (hSA). Primary inoculation was on day I and booster inoculations were on day 29, 43 and 57. The control group was immunized against hSA by the same protocol. In the whole test, pigs were fed ad libitum. Blood samples were collected on day 71 and assayed for the content of CCKg and antibody titre of CCK. All pigs were slaughtered on day 77. Proximal jejunum and pituitary gland were rapidly removed, freezed in liquid nitrogen and stored under -70 C for the assay of CCKmRNA. The results showed: (1). The average day weight (ADG) was 14.29%(P=0.23) greater and feed intake (FI) was 9.34%(P=0.34) greater for CCK immunization group than the control group. (2). The content of CCK8 in treated group decreasedby 19.77% (P<0.15) and the liter of CCK8 antibody increased by 67.63% (P<0.01) compared with the control group. (3) The levels of CCK gene expressions in jejunum and pituitary of the treated group decreased significantly (P<0.05) compared with the control group. The date indicated that active immunity at the dose of 370 g CCKg had a tendency to increase feed intake and growth rate of pigs, due to the decrease of CCK8 content in serum resulted from the increase of CCK antibody litre in serum and the inhibition of CCK gene expression in proximal jejunum and pituitary gland.Exp.2. Effects of Active Immunization against CCK8 at two Doses on Performance, Pancreatic Functions and Gene Expressions in Pigs.A single factor design was conducted to explore the effects of CCKg active immunization at 2 doses on performance, pancreatic functions and gene expressions in pigs. 15 DLY pigs of 27.66 1.71 kg of body weight were distributed randomly inlo 3 treatments with 5 replicates of 1 pig. The CCK8 level of group 1, 2 and 3 was 0 g, 250 g and 500 g conjugated to hSA respectively. Primary inoculation was done on day 1. Booster inoculations were on day 29, 43 and 59. In the whole test, pigs intook food and drank water at liberty. Blood samples were collected on day 1, 15, 29, 43, 59 and 71 and assayed for antibody litre of CCK in surem, or for the contenl of CCKg, insulin and leptin in serum. All pigs were slaughtered on day 74 and took out the proximal jejunum, pancreas and pituitary gland rapidly. A part of pancreas was fixed with 4% formaldehyde solution for examining pancreatic histomorphology, and the other part of pancreas, jejunum and pituitary gland were frozen in liquid nitrogen, and stored under-70'C for assaying the content of CCK mRNA and CCK-A receptor mRNA. The results showed: (1). It existed the dose response of CCK active immunization on growth performance in pigs. FI was 11.76%(P<0.05) greater and ADG was 14.
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