EFFECTS OF NANDROLONE DECANOATE ON RESPIRATORY AND PERIPHERAL MUSCLESIN MALE AND FEMALE RATS

Thirty male and 18 female adult rats received weekly an intramuscular injection of either saline (control; C), 1.5 mg/kg (low-dose; LD) nand rolone decanoate or 7.5 mg/kg (high-dose; HD) nandrolone decanoate dur ing 5 wk. Compared with respective C, growth rate was stunted in male HD rats from 2 wk of treatment on, whereas it was enhanced in female L D and HD rats after 1 wk. Mass of all muscles studied varied proportio nally to body weight, except for the gastrocnemius (males: 0.49 +/- 0. 04 vs. C: 0.52 +/- 0.03%, not significant; females: 0.17 +/- 0.01 vs. C: 0.15 +/- 0.01%, P < 0.05). In vitro contractile and fatigue propert ies of the diaphragm remained unchanged, except for a decrease in twit ch kinetics (time to peak tension: C, 21 +/- 2; LD, 19 +/- 1; HD, 19 /- 2 ms, P < 0.05; half-relaxation time: C, 26 +/- 5, LD, 25 +/- 5, HD , 23 +/- 3 ms, P < 0.01). Histochemistry of the diaphragm and the gast rocnemius revealed a significant increase in type IIx/b dimensions. In the gastrocnemius, type I fiber dimensions also increased. A pair-fed study, including another 24 female rats, showed that the changes in o ral food intake only partly accounted for the observed anabolic effect s.