gi route & brain: mri of fructose v glucose

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Fascinating finding re: glucose & gi route:

Oral glucose intake inhibits hypothalamic neuronal activity more

effectively than glucose infusion.

<http://www.ncbi.nlm.nih.gov/pubmed/17566114>

Smeets PA, Vidarsdottir S, de Graaf C, Stafleu A, van Osch MJ, Viergever

MA, Pijl H, van der Grond J.

Am J Physiol Endocrinol Metab. 2007 Sep;293(3):E754-8.

We previously showed that hypothalamic neuronal activity, as measured by

the blood oxygen level-dependent (BOLD) functional MRI signal, declines

in response to oral glucose intake. To further explore the mechanism

driving changes in hypothalamic neuronal activity in response to an oral

glucose load, we here compare hypothalamic BOLD signal changes

subsequent to an oral vs. an intravenous (iv) glucose challenge in

healthy humans. Seven healthy, normal-weight men received four

interventions in random order after an overnight fast: 1) ingestion of

glucose solution (75 g in 300 ml) or 2) water (300 ml), and 3) iv

infusion of 40% glucose solution (0.5 g/kg body wt, maximum 35 g) or 4)

infusion of saline (0.9% NaCl, equal volume). The BOLD signal was

recorded as of 8 min prior to intervention (baseline) until 30 min

after. Glucose infusion was associated with a modest and transient

signal decline in the hypothalamus. In contrast, glucose ingestion was

followed by a profound and persistent signal decrease despite the fact

that plasma glucose levels were almost threefold lower than in response

to iv administration. Accordingly, glucose ingestion tended to suppress

hunger more than iv infusion (P < 0.1). */We infer that neural and

endocrine signals emanating from the gastrointestinal tract are critical

for the hypothalamic response to nutrient ingestion./*

Brain functional magnetic resonance imaging response to glucose and

fructose infusions in humans. <http://www.ncbi.nlm.nih.gov/pubmed/21205113>

Purnell JQ, Klopfenstein BA, s AA, Havel PJ, SH, Dunn TN,

Krisky C, Rooney WD.

Diabetes Obes Metab. 2011 Mar;13(3):229-234. doi:

10.1111/j.1463-1326.2010.01340.x.

Aims: In animals, intracerebroventricular glucose and fructose have

opposing effects on appetite and weight regulation. In humans,

functional brain magnetic resonance imaging (fMRI) studies during

glucose ingestion or infusion have demonstrated suppression of

hypothalamic signalling, but no studies have compared the effects of

glucose and fructose. We therefore sought to determine if the brain

response differed to glucose vs. fructose in humans independently of the

ingestive process. Methods: Nine healthy, normal weight subjects

underwent blood oxygenation level dependent (BOLD) fMRI measurements

during either intravenous (IV) glucose (0.3 mg/kg), fructose (0.3 mg/kg)

or saline, administered over 2 min in a randomized, double-blind,

crossover study. Blood was sampled every 5 min during a baseline period

and following infusion for 60 min in total for glucose, fructose,

lactate and insulin levels. Results: No significant brain BOLD signal

changes were detected in response to IV saline. BOLD signal in the

cortical control areas increased during glucose infusion (p = 0.002),

corresponding with increased plasma glucose and insulin levels. In

contrast, BOLD signal decreased in the cortical control areas during

fructose infusion (p = 0.006), corresponding with increases of plasma

fructose and lactate. Neither glucose nor fructose infusions

significantly altered BOLD signal in the hypothalamus. Conclusion: In

normal weight humans, cortical responses as assessed by BOLD fMRI to

infused glucose are opposite to those of fructose. Differential brain

responses to these sugars and their metabolites may provide insight into

the neurologic basis for dysregulation of food intake during high

dietary fructose intake.