Malabsorption of carbohydrates.
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Age Factors↗
Biomedical subjects
J Hans Hoekstra
Publications and source records attributed to J Hans Hoekstra.
Adaptation of glucose production and gluconeogenesis to diminishing glucose infusion in preterm infants at varying gestational ages.
In preterm infants low plasma glucose concentrations are frequently observed. We hypothesized that the infants' ability to adapt endogenous glucose production to diminishing exogenous supply is disturbed, but will improve with increasing gestational age. Glucose production rate and gluconeogenesis were measured using stable isotope techniques with [6,6-2H2]glucose and [2-13C]glycerol in 19 preterm infants (10 < or = 30 wk and nine >30 wk gestational age) on d 5.0 +/- 1.4 of life. Exogenous glucose was administered at a rate of 33 micromol x kg-1 x min-1 followed by 22 micromol x kg-1 x min-1. In the first 2 h after the decrease in exogenous supply, plasma glucose concentration declined comparably in both groups: < or =30 wk, from 4.3 +/- 1.2 to 3.2 +/- 0.9 mM; >30 wk, from 3.7 +/- 0.7 to 3.0 +/- 0.6 mM. Thereafter, only in infants >30 wk an increase was observed, to 3.4 +/- 0.8 mM. Glucose production rate increased comparably in both groups: < or =30 wk, from 6.0 +/- 4.1 to 8.8 +/- 3.4 micromol x kg-1 x min-1; >30 wk, from 7.8 +/- 4.6 to 11.6 +/- 5.2 micromol x kg-1 x min-1. This increase was equivalent to approximately 30% of the decline in exogenous glucose. Gluconeogenesis increased comparably in both groups: <30 wk, from 3.2 +/- 1.2 to 4.5 +/- 1.3 micromol x kg-1 x min-1; >30 wk, from 4.3 +/- 1.9 to 6.8 +/- 2.9 micromol x kg-1 x min-1. We conclude that preterm infants can only partly compensate a decline in exogenous glucose supply by increasing endogenous glucose production rate, probably because of limitations in the final common pathway of intracellular glucose metabolism (i.e. glucose-6-phosphatase). The ability to maintain the plasma glucose concentration after a decrease in exogenous supply is better preserved in infants >30 wk owing to more efficient adaptation of peripheral glucose utilization.
Alanine↗
Cloning and functional characterization of the mouse fructose transporter, GLUT5.
Mouse GLUT5 cDNA and a 7.7-kb genomic fragment have been isolated and characterized. The cDNA sequence suggests mouse GLUT5 is composed of 501 amino acids, and has 69-88% amino acid identity with human, rat, and rabbit GLUT5. Expression of mouse GLUT5 cRNA in Xenopus laevis oocytes showed that GLUT5 mediated fructose transport, with a K(t) of 13 mM. Northern blot studies detected GLUT5 mRNA expression in mouse small intestine, kidney, and testis, with transcript sizes of approximately 2.1, 2.1, and 2.8 kb, respectively. 5'Rapid Amplification of cDNA Ends (5'RACE) determined that the differences in transcript sizes occurred because GLUT5 possessed alternative transcriptional initiation sites in somatic and germ cells. In agreement with studies in rats and rabbits, mouse small intestinal GLUT5 mRNA expression levels were increased following exposure to a 65% fructose-enriched diet. In addition, developmental studies showed a significant increase in GLUT5 mRNA expression levels in adult mouse testis when compared to prepubertal mouse testis. To begin to identify the cis-acting domains responsible for GLUT5 expression characteristics, a 7.7-kb GLUT5 genomic fragment was isolated from a mouse lambda fix11 library and sequenced. The clone contained exons 1-4 and 5' flanking regions. Moreover, caudal homeobox gene (CdxA), upstream stimulatory factor (USF), and sex-determining region of Y (SRY) binding sites were identified in the 5' flanking region that may be responsible for GLUT5's expression characteristics: tissue distribution, sensitivity to dietary fructose in the small intestine, and developmental expression in the testis.
Amino Acid Sequence↗