THE EFFECT OF BETA-ADRENOCEPTOR AGONISTS AND ANTAGONISTS ON FRUCTOSE ABSORPTION IN MAN

To explore the effect of beta-adrenoreceptor stimulation and blockade on the extraction of monosaccharide from the upper gut, we first estab lished the malabsorption threshold in 26 normal volunteers using a ser ies of test meals containing varying proportions of fructose and gluco se. Incomplete small intestinal extraction and consequent arrival of c arbohydrate into the caecum was identified by a rise in exhaled breath hydrogen concentration. The malabsorption threshold varied between in dividuals from 30 to 80 g fructose (median 40 g) but was reproducible within individuals, with 90% agreement of repeat studies. The malabsor ption threshold for an individual was unrelated to body height (tau = 0.007, P > 0.05) or weight (tau = 0.003, P > 0.05) but correlated clos ely with time to onset of the breath hydrogen rise of a standard meal (tau = 0.70, P < 0.001). Administration of the beta-adrenoreceptor ant agonist propranolol (160 mg) reduced the quantity of fructose required to exceed the malabsorption threshold from 45, 30-60 (median and rang e) to 40, 30-50 g (P = 0.03); administration of the beta-adrenorecepto r agonist isoprenaline (0.0 1 5 mug. kg/min) increased the quantity of fructose required to exceed the malabsorption threshold by 10 g (55 ( 50-90) g; P < 0.02). The effect of both drugs correlated closely with their transit effect (tau = 0.79, P < 0.01). A beta-adrenoreceptor med iated pathway thus appears to be capable of influencing the extraction of monosaccharide from the small intestine in normal subjects both un der resting and stimulated conditions, probably acting via an effect o n upper gastrointestinal motility.