Masuo K, Mikami H, Ogihara T
Changes in sympathetic activity and insulin sensitivity
during body weight reduction in obese subjects
12th Annual ASH Meeting
Am J Hypertens
(Apr) 10:18A 1997
This study addresses the issue of the relationship between obesity, SNS
activity and
hyperinsulinemia. The investigators compare responses of glucose, insulin
and
norepinephrine (NE) during an oral GTT in groups of hypertensive and
normotensive obese
subjects. Assessments were carried out at baseline and following one and
three months of
weight loss.
The main findings are that weight loss improves insulin resistance and
decreases NE levels
during glucose tolerance testing in both normotensives and hypertensives.
However, while
both insulin resistance and NE levels improve simultaneously at one month in
normotensives, NE levels improve at one month in hypertensives but insulin
resistance does
not improve until three months in hypertensives. The authors conclude that
since weight
loss decreases sympathetic overactivity before reductions in insulin
resistance and blood
pressure were evident in hypertensives, the mechanisms mediating the effects
of weight
loss in hypertensives appear to be different from those in normotensives.
Comment: Longitudinal, moderately long-term assessment of changes in
body weight,
insulin resistance and sympathetic activity is an interesting and potentially
fruitful way
of disentangling the highly integrated relationships of these factors and
determining how
each contributes to blood pressure control. The authors suggest that the
schema proposed
by Landsberg, Reaven and others, that hyperinsulinemia drives increased SNS
activity which
in turn contributes to hypertension, may not be valid. However, it should be
noted that
the measures used by the authors for the key assessments (SNS activity and
insulin
resistance) are rather indirect and may easily have missed subtle changes. A
similar
study using state-of-the-art techniques, such as euglycemic clamping and 3H-
NE turnover,
would be very interesting.
(Alan Weder, M.D., University of Michigan)
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12th Annual ASH Meeting
H: Special problems :
Obesity, Insulin Resistance
H: Pathophysiology :
Sympathetic nervous system