Studies of growth hormone/insulin-like growth factor-I in polio survivors.
In the later years of life, many polio survivors develop post-polio syndrome manifested by progressive muscular weakness. Previous work by the authors showed low IGF-I level in polio survivors compared to age-matched controls. IGF-I concentration tended to be lower in polio survivors who were older, male, obese, and also in persons experiencing difficulty in the activities of daily living which were independent of other factors. IGF-I levels did not correlate with the subjective report of recent decline in functional status. Further studies of nocturnal GH secretion indicated that low IGF-I level was secondary to impaired growth hormone secretion. Low IGF-I levels in subjects with post-polio syndrome were corrected by physiologic doses of hGH and the response was dose dependent. Lesser dosage was required to normalize IGF-I level compared to standard dosages previously used in younger persons. Inasmuch as low IGF-I level resulting from GH deficiency is known to be associated with weakness, muscle atrophy, and decrease in aerobic work capacity, it is postulated that low IGF-I levels that occur in aging polio survivors may have an adverse effect on their neuromuscular function, and that hGH replacement may improve their functional status. Moreover, the new dose-response data may decrease the frequency of side effects in future hGH treatment of older adults.