SHORT-TERM AND LONG-TERM EFFECTS OF TESTOSTERONE ON DIAPHRAGM IN CASTRATED AND NORMAL-MALE RATS

The effects of short- and long-term testosterone absence or treatment on the diaphragm were studied in castrated and sexually normal male ra ts. Compared with control rats (untreated normal males), testosterone absence or treatment did not significantly affect costal weight. In un treated castrated males. there were significant decreases in specific forces, type II fiber cross-sectional area, and myosin heavy chain (MH C) isoform 2B after 2.5 wk. In castrated males that received testoster one, there were significant increases in specific forces, type II tota l fiber proper tional area, and relative expression of all adult diaph ragm fast MHC isoforms (MHC-2(all)) after 2.5 wk. In normal males that received testosterone: the only significant finding was an increase i n MHC-BB after 2.5 wk. Across all groups, there was close correlation between increases in maximum tetanic forces and MHC-2(all). Changes in diaphragm function and composition were closely related to changes in serum testosterone levels at 2.5 wk. The lack of significant change i n diaphragm function at 10 wk. occurred despite changes in serum testo sterone levels and diaphragm composition similar to those at 2.5 wk. T hese findings support our hypothesis that the effects of testosterone are dependent on basal circulating androgen levels and study duration.