Cremaster muscle is not sexually dimorphic, but that from boys with undescended testis reflects alterations related to autonomic innervation

Background/Purpose: The genitofemoral nerve and its motor neuron are known to be sexually dimorphic. An association has been suggested to exist between antiandrogen-induced undescended testis and the genitofemoral nerve. Therefore, the cremaster muscles (CM) from boys and girls with inguinal hernia and boys with undescended testis were compared to evaluate the failed descent through sexual dimorphism. Methods: Samples of CM were obtained from 10 boys and 10 girls with inguinal hernia and 10 boys with undescended testis. Sections were stained for ATPase reactions after acid and alkaline preincubations, and for the expression of myosine heavy chains. The percentages of type 1 and type 2 fibers, and mean diameters of fibers according to the types were determined for each group. Values were compared through Mann-Whitney U test, and P values less than .05 were considered to be significant. Results: CM have mainly been composed of type 1 fibers. Distributions of type 1 and 2 fibers have not shown a difference among groups. Mean diameters of both type 1 and type 2 fibers from girls (P < .05), and mean diameter of type 2 fibers from boys with undescended testis have been significantly smaller than those encountered in boys with inguinal hernia (P < .05). Conclusions: Although the mean diameter of type 1 fibers from boys with undescended testis has been as large as those encountered in boys with inguinal hernia, mean diameter of type 2 fibers has been as small as those encountered in girls. Among various reasons to selectively diminish the size of type 2 fibers, lack of beta adrenergic effect appears to be the most satisfactory explanation.