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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

-Lactalbumin Hydrolysate Stimulates Glucagon-Like Peptide-2 Secretion and Small Intestinal Growth in Suckling Rats^1,2

³ Nutritional Science Laboratory, Morinaga Milk Industry Co., Ltd., Zama, Kanagawa 228-8583, Japan and ⁴ Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo, Hokkaido 060-8589, Japan

We investigated whether bovine milk constituents influenced glucagon-like peptide (GLP)-2 secretion and intestinal growth in suckling rats. Male Sprague-Dawley rats (14 d old) received i.g. infusions of a milk protein fraction, a lactose solution, or the cream fraction of milk. The serum concentration of GLP-2, but not GLP-1, markedly increased in rats administered milk protein compared with those given the lactose solution or the cream fraction from 60 to 120 min after administration. In another experiment, both casein (CN) and whey protein isolate stimulated GLP-2 secretion at 120 min after administration, but soy protein and ovalbumin did not. Stimulation of GLP-2 secretion by several milk proteins was similar, including -CN, -lactalbumin (-La), and β-lactoglobulin, in a separate experiment. A hydrolysate of -La obtained by incubation with protease A extracted from Aspergillus oryzae (LaHPA) caused almost twice the GLP-2 release due to intact -La and other -La hydrolysates. Free amino acid concentrations and molecular size distributions did not differ among -La hydrolysates, including LaHPA. In rat pups reared with milk formulae containing -La or LaHPA, LaHPA significantly promoted small intestinal elongation and increased the number of crypt epithelial cells compared with a formula containing intact -La. LaHPA administration also increased the maltase:lactase activity ratio, a marker of maturation of the intestinal mucosa. In conclusion, milk proteins stimulate GLP-2 secretion and contribute to growth and maturation of the small intestine in suckling rats.

^* To whom correspondence should be addressed. E-mail: h-izumi{at}morinagamilk.co.jp.

Manuscript received 26 February 2009. Initial review completed 23 March 2009. Revision accepted 15 May 2009.

Published online 3 June 2009.