The activities of maltase, lactase, alkaline phosphatase and enterokinase were followed in the small intestine of rats during prenatal development. These enzymes were detectable only after the 17th day of gestation. Furthermore, each enzyme exhibited a different pattern of prenatal presence. Maltase activity appeared first (day 18), followed by lactase and alkaline phosphatase (day 19) and then enterokinase (day 20). Except for enterokinase, all of the enzymes attained a level of activity close to the newborn levels at the final day of gestation. Induced intrauterine growth retardation during the 3rd trimester led to a decrease in intestinal weight proportional to the reduction of body weight. The decrease in size of the small intestine was caused by a reduction in cell number rather than cell size. Induced intrauterine growth retardation also resulted in a selective reduction in the specific activities of lactase and alkaline phosphatase, but not of enterokinase and maltase. These results suggest that reduction in maternofetal blood flow in the 3rd trimester of gestation will cause a selective decrease in some brush border enzymes (lactase and alkaline phosphatase) but does not affect others (maltase and enterokinase).

In both protein energy malnutrition and vitamin D deficiency, defects in some immunological functions have been noted, but the effects on complement and immunoglobulin concentrations have not been evaluated. We assessed the effects of malnutrition and vitamin D deficiency on immunoglobulins and C3 in rats in early postnatal life during weaning and early adulthood using the rocket immunoelectrophoresis technique. In well-nourished rats, the serum levels of IgG increased from 88.5 ± 10.2 mg/dl in the newborn period to 883.4 ± 104.8 mg/dl at weaning (day 19). The adult levels, 1,325.9 ± 60.8 mg/dl, were attained by 35 days of age. Serum IgA was not detectable by our method until 20 days of age (1.1 ± 0.2 mg/dl) and reached adult levels (13.4 ± 3.2 mg/dl) by day 35. IgM was detectable in the serum of pups at 5 days of age (0.4 ± 0.07 mg/dl), increased to 27.5 ± 6.9 mg/dl at weaning and approached adult levels (93.7 ± 9.9 mg/dl) at day 35. C3 levels at birth were only 36% of adult levels and did not change during the suckling period. They then increased to levels comparable to those of adults at the age of 35 days. Serum immunoglobulins and C3 in malnourished rats were not significantly different from age-matched control pups. In pups born to dams fed a vitamin-D-deficient diet from 3 weeks of age, only the serum IgG and C3 levels were significantly lower than those of normal pups at day 1 (IgG level: 65.2 ± 6.1 vs. 88.5 ± 10.2 mg/dl; C3 level: 20.3 ± 6.9 vs. 36.2 ± 3.1% of an adult level; p < 0.005). Thus the increased susceptibility of malnourished young animals to infection does not appear to be related to a lowering of serum immunoglobulin and complement concentrations.