Sexual dimorphism in the growth response of entire and
gonadectomized rats to clenbuterol.
Sillence, M. N., M. M Reich, and B. C. Thomson.
CSIRO Division of Tropical Animal Production, Tropical Beef Centre,
Rockhampton, Queensland, 4702, Australia.
APStracts 2:0031E, 1995.
This study compared the anabolic effects of clenbuterol in male and
female rats, and determined the relative contribution of testicular
and ovarian hormones to any observed gender difference. Seventy two
12-wk-old rats were used in a 2 x 2 x 2 factorial design in which
animals were either male or female; entire or gonadectomized at 3 wk
of age; and fed either a control diet, or a diet containing 4 mg
clenbuterol/kg feed for 8 days. Compared with entire male rats,
entire females gained 64% less weight, had lighter carcasses (-36%)
and gastrocnemius muscles (-62%), and had higher plasma
concentrations of the catabolic hormone corticosterone (P<0.05).
Castration had a negative effect on growth in male rats, and
ovariectomy had a positive effect in females, but there was still a
gender difference in body weight between gonadectomized males and
females, which amounted to 34% of the gender difference observed in
intact rats. The density of [beta]2-adrenoceptors in skeletal muscle
was not different between males and females, nor was it affected by
gonadectomy. Clenbuterol increased both weight gain and gastrocnemius
muscle weight, with the latter response in entire and castrated male
rats (+1.31g and +1.17g) being more than double that seen in entire
and ovariectomized females (+0.58g and +0.55g). The downregulation
response of [beta]2-adrenoceptors in this muscle was remarkably
consistent in all treated groups (-50% to -53%). It is concluded that
the size of the muscle growth response to clenbuterol is gender
-related, but that a large proportion of this gender difference
persists in gonadectomized animals, and so cannot be accounted for by
the actions of gonadal hormones beyond 3 wk of age.
Received 1 July 1994; accepted in final form 20 January 1995.
APS Manuscript Number E246-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 1 March 1995.