Alkaline sphingomyelinase activity in rat fetus and newborn rat

Abstract

Background: Alkaline sphingomyelinase (SMase) is present in rat and human intestine. The enzyme is potentially interesting because its hydrolysis products might have important signaling effects on cellular functions such as cell proliferation, differentiation and cell death. Alkaline SMase also is needed to digest sphingomyelinase present in a normal diet e.g. milk, meat and seafood. In adult mammalians the highest alkaline SMase activities are found in distal jejunum, while no activity or very low activities are found in stomach and colon. We studied activity and distribution of alkaline SMase in rat fetus and newborn rat to elucidate at what time and where the enzyme activity appears. Methods: Pregnant rats at gestation day 10, 15, 20, 21 and 22 were anesthetized and a cesarean section was performed. Newborn (23 days after conception), 2 day, 1, 3 and 4 week old rats were also anesthetized. The Gl-tract of the fetuses and rats was taken out and alkaline SMase activity was determined and related to protein content. In 10 and 15 day fetuses alkaline SMase activity was determined in the entire animal. Results: No alkaline SMase activity was found at gestation day 10 and 15. Alkaline SMase activity per mg protein was at the detection limit on gestation day 20 (0.40±0.05 nmol/hemg) but increased 10 times at day 22 (4.22±0.53 nmol/hemg). Newborn rats had slightly lower activity compared to 22 day fetuses (2.75±0.09 nmol! hemg), However, activity continued to increase and was 5.98±0.78 nmol! herng at 4 weeks of age. From gestation day 21 distribution of alkaline SMase activity was the same as in the adult animal with the highest level in distal jejunum. One week of weaning had no effect on alkaline SMase activity. Conclusion: Alkaline SMase activity is detected at the last days of the gestation cycle and the activity increase 10 times in 48 hours. The rat thus is born with a high capacity for digestion of sphingomyelinase, most likely needed for digestion of milk sphingomyelinase. A similar increase in activity has been shown for lactase. (MV±SEM)