EFFECTS OF TESTOSTERONE ADMINISTRATION AND CASTRATION ON THE FORELIMBMUSCULATURE OF MALE LEOPARD FROGS, RANA-PIPIENS

In Rana pipiens, forelimb muscles that are used by males to clasp fema les during amplexus are sexually dimorphic in mass, protein content, a nd fiber composition. This experiment examined the effects of castrati on and exogenous testosterone on wet mass, dry mass, and protein conte nt 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 hi ghly and moderately responsive to testosterone treatment (e.g., flexor s of the elbow and of the carpus; adductors of the shoulder and of the first digit) to nonresponsive to testosterone (antagonists to these m uscles). The mean dry mass of the eestosterone-responsive muscles rang ed broadly from 28-164% over control values. Castration had little or no effect on the response to testosterone, nor did it affect muscle ma ss in frogs not treated with hormone, as compared to sham-operated ani mals. Experimental treatment did not alter water content or protein co ncentration of muscles. The degree of testosterone sensitivity exhibit ed among the muscles of males closely correlated with their degree of sexual dimorphism. We postulate that androgens influence the functiona l attributes of male forelimb muscles through both organizational and activational effects. (C) 1998 Wiley-Liss, Inc.