OBJECTIVES: To determine whether aging is associated with a reduction in th
e opioid modulation of feeding, which may be important in the pathogenesis
of the "anorexia of aging."
DESIGN: Three studies on separate days, in randomized order and double-blin
d fashion.
SETTING: Clinical Human Research Laboratory, Department of Medicine, RAH, A
delaide, Australia.
PARTICIPANTS: Twelve older (5 male/7 female) (age 65-84) and 12 young (5 ma
le/7 female) (age 20-26) healthy subjects.
INTERVENTION: Subjects received in double-blinded random order, intravenous
bolus (10 minutes) and then continuous (140 minutes) infusions of saline (
control), naloxone low dose (LD) (bolus 27 mug/kg continuous 50 mug/kg/hr),
or naloxone high dose (HD) (bolus 54.5 mug/kg; continuous 100 mug/kg/hr).
MEASUREMENTS: After 120 minutes, subjects were offered a buffet meal, and t
heir energy intake was quantified. Hunger, fullness, nausea, and drowsiness
were assessed using visual analogue scales. RESULTS: The naloxone LD and H
D infusions had no significant effect on ratings of hunger, fullness, or na
usea, but increased drowsiness (P < .01) compared with the control infusion
in both age groups. Older subjects ate less (P < .001) at the buffet meal
than young subjects during all three infusions. Naloxone infusions reduced
energy intake compared with control (P < .001), LD by 13.2 +/- 5.0% and HD
by 10.7 +/- 5.0%, with no difference between the doses (P = .71). Overall,
naloxone suppressed energy intake in both young and older subjects (P < .01
). This suppression was slightly, but not significantly, greater in young t
han in older subjects (mean of LD and HD 16.4 +/- 4.9% vs 7.5 +/- 4.9%, P =
.42), because of a trend to reduced suppression in older women.
CONCLUSIONS: We conclude that healthy older adults retain their sensitivity
to the suppressive effects of naloxone on food intake. Possible gender dif
ferences in this sensitivity warrant further investigation. A decline in op
ioid activity is unlikely to contribute substantially to the physiological
anorexia of aging observed in older people.