The effect of intraduodenal glucose on muscle sympathetic nerve activity in healthy young and older subjects.
OBJECTIVE
The cardiovascular response to a meal is modulated by gastric distension and the interaction of nutrients, particularly carbohydrate, within the small intestine. We tested the hypothesis that the depressor effect of small intestinal glucose is greater in older than in young subjects, because the reflex increase in muscle sympathetic nerve activity (MSNA) is blunted by age.


METHODS
The effects of intraduodenal glucose infusion (IDGI) on blood pressure, heart rate and MSNA were evaluated in eight healthy young subjects (4 women; mean age +/- SEM: 28.8 +/- 3.4 years), eight healthy elderly (4 women; 75.3 +/- 1.6 years) and in two patients with symptomatic postprandial hypotension (PPH), one young (21 years), and one old (90 years).


RESULTS
In both young and elderly healthy subjects, IDGI decreased blood pressure (P < 0.05), but the fall in systolic blood pressure was greater in the older subjects (-17.0 +/- 4.1 vs. -6.5 +/- 1.6 mmHg, P < 0.03). MSNA increased similarly, after infusion in both young (9.0 +/- 3.4 bursts/min) and elderly (7.8 +/- 1.0 bursts/min) subjects. Baroreflex sensitivity for number of sympathetic bursts was attenuated in the elderly (P < 0.03). The increase in burst area in the young patient with PPH was attenuated (18 vs. 63% in the healthy young group).


CONCLUSIONS
The fall in BP induced by IDGI was greater in healthy elderly compared to healthy young subjects. The reason for this is unclear, as they have similar increases in MSNA.
van Orshoven
Narender P
NP
Department of Clinical Neurophysiology, Rudolf Magnus Institute of Neuroscience, Utrecht, The Netherlands.
van Schelven
Leonard J
LJ
Akkermans
Louis M A
LM
Jansen
Paul A F
PA
Horowitz
Michael
M
Feinle-Bisset
Christine
C
van Huffelen
Alexander C
AC
Oey
P Liam
PL
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004386:Duodenum / Q000187:drug effects / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000008:administration & dosage*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007022:Hypotension / Q000139:chemically induced; D007441:Intubation, Gastrointestinal; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D005947:Glucose