Relationship between testosterone supplementation and insulin-like growth factor-I levels and cognition in healthy older men.
BACKGROUND
Our laboratory has previously reported that testosterone (T) administration to older men significantly improves cognitive function. This study examined potential changes in insulin-like growth factor (IGF) IGF-I, IGF-II and IGF-related binding proteins in response to T administration in older men and their relationship to cognitive functioning.


METHODS
Twenty-five healthy community dwelling volunteers, ranging in age from 50-80 years were randomized to receive weekly intra-muscular (i.m.) injections of either 100 mg T enanthate or placebo (saline) for 6 weeks. Serum hormone levels and cognitive functioning was assessed at baseline and twice during treatment.


RESULTS
Significant positive associations between IGF-I and IGF-II and spatial memory, spatial reasoning, and verbal fluency were observed after 6 weeks of T administration. Increased serum T levels from treatment were positively associated with improvement in spatial reasoning performance, whereas estradiol was associated with a decline in divided attention performance. Serum IGF-I, IGF-II and IGFBPs did not change in response to T treatment.


CONCLUSIONS
Our results suggest that T, estradiol and IGF-I may have independent and selective effects on cognitive functioning. Positive associations between T levels and cognition are consistent with an effect of androgen treatment, whereas positive associations between IGF-I levels and cognition are reflective of a relationship between endogenous IGF-I levels and cognition.
Cherrier
M M
MM
Department of Psychiatry and Behavioral Sciences, University of Washington Medical School, 1959 NE Pacific, Box 356560, Seattle, WA 98195, USA. cherrier@u.washington.edu
Plymate
S
S
Mohan
S
S
Asthana
S
S
Matsumoto
A M
AM
Bremner
W
W
Peskind
E
E
Raskind
M
M
Latendresse
S
S
Haley
A P
AP
Craft
S
S
D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology; D003071:Cognition / Q000502:physiology*; D004958:Estradiol / Q000097:blood; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D013037:Spatial Behavior / Q000502:physiology; D013739:Testosterone / Q000008:administration & dosage* / Q000502:physiology*; D014706:Verbal Learning / Q000502:physiology
D018969:Insulin-Like Growth Factor Binding Proteins; D013739:Testosterone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II