Sidor, C. and D.G. Blackburn (1997). Effects of testosterone administration and castration on the
forelimb musculature of male leopard frogs, Rana pipiens. Journal of Experimental Zoology 280: 28-37.
Abstract: In Rana pipiens, forelimb muscles that
are used by males to clasp females during amplexus are sexually dimorphic in
mass, protein content, and fiber composition.
This experiment examined the effects of castration and exogenous testosterone
on wet mass, dry mass, and protein content of the 22 major forelimb muscles of
male leopard frogs, to determine whether established patterns of sexual
dimorphism of the muscles are reflected in differential androgen sensitivity. Muscles ranged from highly- and moderately-
responsive to testosterone treatment (e.g., flexors of the elbow and of the
carpus; adductors of the shoulder and of the first digit) to non-responsive to
testosterone (antagonists to these muscles).
The mean dry mass of the testosterone-responsive muscles ranged broadly
from 28% to 164% over control values.
Castration had little or no effect on the response to testosterone, nor
did it affect muscle mass in frogs not treated with hormone, as compared to
sham-operated animals. Experimental
treatment did not alter water content or protein concentration of muscles. The degree of testosterone sensitivity
exhibited among the muscles of males closely correlated with their degree of
sexual dimorphism. We postulate that
androgens influence the functional attributes of male forelimb muscles through
both organizational and activational effects.
Reprints: daniel.blackburn@mail.trincoll.edu