Environmental modulation of the inhibitory action of D-mannoheptulose upon D-glucose metabolism in isolated rat pancreatic islets.
In pancreatic islets prepared from fed rats and incubated at a low concentration (1.7 mM) of D-glucose, D-mannoheptulose (10.0 mM) virtually fails to affect the metabolism of the hexose. Likewise, in islets from starved rats, the relative extent of the inhibitory action of D-mannoheptulose upon D-glucose metabolism is much more marked at high (16.7 mM) than low (1.7 mM) hexose concentration. Nevertheless, despite decreasing the metabolism of D-glucose, starvation augments the sensitivity to D-mannoheptulose in the islets incubated at a low concentration of the hexose, D-galactose, but not D-fructose, also augments the inhibitory action of D-mannoheptulose upon D-glucose metabolism in islets prepared from fed rats and exposed to the low concentration of D-glucose. A comparable situation prevails in islets exposed to 2-ketoisocaproate. Forskolin, however, which decreases D-glucose catabolism in the islets from fed rats exposed to 1.7 mM D-glucose, fails to affect significantly the inhibitory action of D-mannoheptulose on D-glucose metabolism. It is proposed that hexoses transported by the same carrier as D-glucose and non-glucidic nutrient secretagogues somehow increase D-mannoheptulose uptake by the islet cells. The latter two conditions may be operative in islets exposed to a high concentration of D-glucose, this accounting for the exquisite sensitivity to D-mannoheptulose of glucose-stimulated islets.
Picton
S
S
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
Malaisse
W J
WJ
D000818:Animals; D002208:Caproates / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D004435:Eating / Q000502:physiology; D005260:Female; D005632:Fructose / Q000378:metabolism / Q000494:pharmacology; D005690:Galactose / Q000378:metabolism / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D007651:Keto Acids / Q000494:pharmacology; D008356:Mannoheptulose / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013217:Starvation / Q000503:physiopathology
D002208:Caproates; D007651:Keto Acids; D005576:Colforsin; D005632:Fructose; D008356:Mannoheptulose; C013082:alpha-ketoisocaproic acid; D005947:Glucose; D005690:Galactose