GENDER DIFFERENCES IN DIAPHRAGMATIC METABOLIC PROPERTIES OF THE ADULTSPRAGUE-DAWLEY RAT

Adult male Sprague-Dawley rats (greater than or equal to 180 days old) develop an obesity-exacerbated insulin resistance in contrast with fe male animals of the same strain. Given the fact the maintenance of mus cle mass requires an adequate supply of insulin and active insulin rec eptors, we postulated that gender differences might exist in both prot ein content and metabolic properties of skeletal and cardiac muscle in adult Sprague-Dawley rats. Therefore, to test this hypothesis, we exa mined activities of bioenergetic enzymes and total protein content in the diaphragm, the heart and the plantaris muscle in 12-month-old male and female animals. Mean (+/-SD) body weights of male animals were si gnificantly (P<0.05) greater than female animals (598 +/- 8 vs. 362 +/ - 19 g) and the diaphragm weight/body weight ratio was significantly l ower in males compared to females (2.36 +/- 0.05 vs. 3.02 +/- 0.13 mg/ g). The activities of isocitrate dehydrogenase (NADP-specific) and suc cinate dehydrogenase were significantly lower (P<0.05) in male animals compared to females in both the crural and costal regions of the diap hragm, the heart, and the plantaris muscle. In contrast, no gender dif ferences (P>0.05) existed in lactate dehydrogenase activity in any of the muscles studied. Finally, muscle protein concentration was signifi cantly higher in female animals when compared to males (P<0.05) in all muscles studied except the heart. These data support the hypothesis t hat gender differences exist for adult Sprague-Dawley rats in general and specific protein content of the diaphragm, locomotor muscles, and the heart.