Changes from birth to maturity in the pattern of distribution of lactase and sucrase activity in the mucosa of the small intestine of pigs

I .Measurements were made of changes in lactase and sucrase activity of homogenates of small intestine mucosa of sixty-one pigs varying in age from newborn to mature animals. 2.From each pig, samples for enzyme determination were taken from siu sites along the small intestine.These sites were at 5,20,40,60, 80 and 95 yo of the length of the small intestine, measured from the pylorus. 3.Lactase activity was present at high levels in the newborn pig, the maximum being found at the 20 % site.Between birth and 8 weeks of age there was a fall in the amount of activity in the mucosa of the small intestine.In older pigs the levels of mucosai lactase activity were not greatly different from those found in 8-week-old pigs, although the distribution along the small intestinc tended to change with advancing age.4. Sucrase activity was found only once in thirty-six samples from the small intestine of six newborn pigs, but was present in all six pigs sampled at I week of age.Levcls of activity continued to rise until maturity.Maximum activity was found at the 20 or 40 % site in the younger pigs (1-8 weeks of age).In the older pigs, high activity was found at a wider range of sites, the peak of activity generally being at the 40 and 60 y/o sites.The hydrolytic activities of the intestinal mucosa towards sucrose and lactose have been studied intensively.'The hydrolytic activity towards sucrose is due to one of the a-D-glucoside glucohydrolases (a-glucosidase, EC 3 .2 .I .20)which Dahlqvist (1962) called 'maltase I b'.The hydrolytic activity of small intestine mucosa towards lactose is due to two types of enzyme (Asp, Dahlqvist & Koldovsky, 1969).One of these, with P-galactosidase (EC 3 .2 .I . 2 3 ) and &lucosidase (EC 3.2.I .21) activity, is attached to the brush border and is a true digestive enzyme with a pH optimum of 5-5-60.Within the mucosal cell, and readily released into solution on disruption of the cell, there are one or more soluble or acid P-galactosidases with an uptimuin pH around 3.5.Most measurements of mucosal 'p-galactosidase' or 'lactase' arc the sum of the activities of these two enzymes.For some years it has been known that, during the early postnatal development of the pig, there are drastic and complementary changes in the levels of lactase and sucrase activity in the rnucosa of the small intcstine.I n the newborn pig, lactase activity is higher than in the adult, whereas the a-glucosidascs are absent, or present at low levels (Dabiqvist, 1961 0).Lactasc activity falls during the first z months of life, but the activity of other disaccharidases rises (Bailey, Kitts gi Wood, 1956; Walker, 19590; Hartman, Hays, Baker, Neagle & Catron, 1961).At birth, sucrase activity has generally been found to be absent from the inucosa of the small intestine or present at very