Growth hormone administration and exercise effects on muscle fiber type and diameter in moderately frail older people.
OBJECTIVE
Reduced muscle mass and strength are characteristic findings of growth hormone deficiency (GHD) and aging. We evaluated measures of muscle strength, muscle fiber type, and cross sectional area in response to treatment with recombinant human growth hormone (rhGH) with or without a structured resistance exercise program in frail older subjects.


METHODS
Placebo-controlled, randomized, double blind trial.


METHODS
Outpatient clinical research center at an urban university-affiliated teaching hospital.


METHODS
Thirty-one consenting older subjects (mean age 71.3 +/- 4.5 years) recruited as a subset of a larger project evaluating rhGH and exercise in older people, who underwent 62 quadricep-muscle biopsies.


METHODS
Random assignment to a 6-month course of one of four protocols: rhGH administered subcutaneously daily at bedtime, rhGH and a structured resistance exercise program, structured resistance exercise with placebo injections, or placebo injections only.


METHODS
Muscle biopsy specimens were obtained from the vastus lateralis muscle. Isokinetic dynamometry strength tests were used to monitor individual progress and to adjust the weights used in the exercise program. Serum insulin-like growth factor-I (IGF-I) was measured and body composition was measured using a Hologic QDR 1000W dual X-ray densitometer.


RESULTS
The administration of rhGH resulted in significant increase in circulating IGF-I levels in the individuals receiving rhGH treatment. Muscle strength increased significantly in both the rhGH/exercise (+55.6%, P =.0004) as well as the exercise alone (+47.8%, P =.0005) groups. There was a significant increase in the proportion of type 2 fibers between baseline and six months in the combined rhGH treated subjects versus those not receiving rhGH (P =.027).


CONCLUSIONS
Our results are encouraging in that they suggest an effect of growth hormone on a specific aging-correlated deficit. IGF-I was increased by administrating rhGH and muscle strength was increased by exercise. The administration of rhGH to frail older individuals in this study resulted in significant changes in the proportions of fiber types. Whether changes in fiber cross-sectional area or absolute number occur with long-term growth hormone administration requires further study.
Hennessey
J V
JV
Division of Endocrinology, Department of Medicine, Brown University School of Medicine, Rhode Island Hospital, Providence, Rhode Island 02903, USA.
Chromiak
J A
JA
DellaVentura
S
S
Reinert
S E
SE
Puhl
J
J
Kiel
D P
DP
Rosen
C J
CJ
Vandenburgh
H
H
MacLean
D B
DB
D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D001706:Biopsy; D001823:Body Composition; D003131:Combined Modality Therapy; D004311:Double-Blind Method; D005081:Exercise Therapy / Q000379:methods*; D005260:Female; D016330:Frail Elderly; D015577:Geriatric Assessment; D013006:Growth Hormone / Q000172:deficiency* / Q000627:therapeutic use*; D006801:Humans; D007279:Injections, Subcutaneous; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000502:physiology* / Q000648:ultrastructure; D018908:Muscle Weakness / Q000097:blood / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology / Q000534:rehabilitation*; D016896:Treatment Outcome; D014891:Weight Lifting
D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone