LACTASE PERSISTENCE VERSUS DECLINE IN HUMAN ADULTS - MULTIFACTORIAL EVENTS ARE INVOLVED IN DOWN-REGULATION AFTER WEANING

Background & Aims: In nonhuman mammals, lactase activity declines duri ng or after weaning. In contrast, about one half of the human species maintains high lactase activity even in adulthood. To clarify this dif ference, this study examined some parameters for which contrasting obs ervations have been reported in connection with lactase decline. Metho ds: Lactase activity, lactase messenger RNA (mRNA) levels, and in vitr o lactase biosynthesis were determined in normal jejunal samples from a large group of white adults, all born in or near Naples. Results: Of 44 individuals, 10 were lactase persistent and 34 were hypolactasic. Biosynthesis of prolactase correlated well with lactase mRNA levels, i ndicating transcriptional control; it did less so with steady-state la ctase activity. Examination of lactase mRNA levels and lactase activit y/lactase mRNA ratios revealed a heterogeneous pattern of lactase mRNA level, lactase synthesis, and activity in both lactase persistent and hypolactasic subjects. Conclusions: Both transcriptional and posttran scriptional factors cause the decline of intestinal lactase. This prob ably explains the multifarious observations that most studies on adult -type hypolactasia have reported. The single overriding factor disting uishing lactase-persistent subjects from hypolactasic subjects is the high rate of lactase biosynthesis.