Igf-i, growth hormone and/or exercise effects on non-weight bearing
soleus of hypophysectomized rats.
Roy, R. R., C. Tri, E. J. Grossman, R. J. Talmadge, R. E. Grindeland,
V. R. Mukku, and V. R. Edgerton.
Brain Research Institute, University of California, Los Angeles,
LA, CA 90095, Life Sciences Division, NASA-Ames Research Center,
Moffett Field, CA 94035, Department of Physiological Science,
University of California, Los Angeles, LA, CA 90095 and Genentech,
Inc, South San Francisco, CA 94080
APStracts 3:0165A, 1996.
Growth hormone (GH) treatment has a strong interactive effect with
high resistive exercise in maintaining the mass of chronically non
-weight bearing muscles in hypophysectomized (hypox) rats (Grindeland
et al., Am. J. Physiol. 267:R316-R322, 1994). In the present 10-day
study, the effects of another growth factor, i.e. insulin-like growth
factor-I (IGF-I), with and without exercise on the predominantly slow
muscles of hypox, hindlimb-suspended (HS) rats were determined. HS
resulted in a 21, 23 and 30% decrease in the weights of the soleus,
adductor longus and vastus intermedius, respectively, compared to
ambulatory rats. IGF-I treatment alone increased the mass of the
vastus intermedius above HS levels, whereas GH treatment or exercise
alone increased both the soleus and vastus intermedius masses above
HS levels. No interactive effect of IGF-I and exercise on muscle mass
was observed. In contrast, there was a strong interactive effect of
GH and exercise in all three muscles of HS rats, with the soleus
becoming larger than in ambulatory control rats. The fiber type
distribution of the soleus of HS rats was not significantly affected
by any treatment. HS resulted in a 24, 18 (p>0.05), 32 and 20
(p>0.05)% decrease in the cross-sectional areas of soleus fibers
containing type I, IIa, I+IIa and IIa+IIx myosin heavy chains,
respectively, compared to ambulatory hypox rats. Hormone or exercise
alone had no significant effects on fiber cross-sectional areas in HS
rats. However, all fiber cross-sectional areas (except for type
IIa+IIx in IGF-I+Ex rats) were larger in HS rats treated with GH or
IGF-I and exercise than in HS rats, with the effect being somewhat
larger in the GH-treated rats. These data indicate that there is an
interactive effect of both GH and IGF-I with exercise in maintaining
fiber cross-sectional area of chronically non-weight bearing
predominantly slow muscles. Further, the results suggest that the
myosin heavy chain phenotype in rats deficient in all pituitary
factors is unresponsive to short-term administration of either GH or
IGF-I or to exercise or HS.
Received 7 December 1995; accepted in final form 19 February
1996.
APS Manuscript Number A1267-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96