Previous studies on the contractile properties of human myofibrils reported increase, decrease, or no change with aging, perhaps due to the differences in physical activity, diet, and other factors. This study examined physical performance and contractile characteristics of myofibrils of vastus lateralis (VL) muscle in young adult and old African green vervet monkeys. Animals were offered the same diet and lived in the same enclosures during development, so we were able to examine skeletal muscle function in vivo and in vitro with fewer potential confounding factors than are typical in human research studies. Fiber atrophy alone did not account for the age-related differences in specific force and maximal power output. Regression modeling used to identify factors contributing to lower fiber force revealed that age is the strongest predictor. Our results support a detrimental effect of aging on the intrinsic force and power generation of myofilament lattice and physical performance in vervet monkeys.
[Show abstract][Hide abstract] ABSTRACT: The muscle mass-specific mean power output (P MMS,mean) during push-off in jumping in marmosets (Callithrix jacchus) is more than twice that in humans. In the present study it was tested whether this is attributable to differences in muscle contractile properties. In biopsies of marmoset m. vastus lateralis (VL) and m. gastrocnemius medialis (GM) (N=4), fibre-type distribution was assessed using fluorescent immunohistochemistry. In single fibres from four marmoset and nine human VL biopsies, the force–velocity characteristics were determined. Marmoset VL contained almost exclusively fast muscle fibres (>99.0%), of which 63% were type IIB and 37% were hybrid fibres, fibres containing multiple myosin heavy chains. GM contained 9% type I fibres, 44% type IIB and 47% hybrid muscle fibres. The proportions of fast muscle fibres in marmoset VL and GM were substantially larger than those reported in the corresponding human muscles. The curvature of the force–velocity relationships of marmoset type IIB and hybrid fibres was substantially flatter than that of human type I, IIA, IIX and hybrid fibres, resulting in substantially higher muscle fibre mass-specific peak power (P FMS,peak). Muscle mass-specific peak power output (P MMS,peak) values of marmoset whole VL and GM, estimated from their fibre-type distributions and force– velocity characteristics, were more than twice the estimates for the corresponding human muscles. As the relative difference in estimated P MMS,peak between marmosets and humans is similar to that of P MMS, mean during push-off in jumping, it is likely that the difference in in vivo mechanical output between humans and marmosets is attributable to differences in muscle contractile properties.
"Unlike the miR-1 family which is organized as bicistronic genes (Kusakabe et al., 2013), miR-208b and miR-499 are encoded within the slow myosin heavy chain (MHC) genes (van Rooij et al., 2009) and thereby are restricted to type I fibers and modulate fiber type (Endo et al., 2013; McCarthy et al., 2009; van Rooij et al., 2009). A transition from fast-to slow-twitch fibers has been reported in aging rodents and humans (Andersen, 2003; Lexell, 1995), and type-I fibers largely outnumber type-II fibers in our samples from monkey and human vastus lateralis muscles (Choi et al., 2013; Zhang et al., 2014). Thus, changes in miR-208b and miR-499 are intriguing and particularly relevant for muscle fiber function. "
[Show abstract][Hide abstract] ABSTRACT: Specific alterations in the pulsatility of luteinizing hormone (LH) are linked to obesity-related subfertility in ovulatory women. Vervet monkeys (Chlorocebus aethiops sabaeus) are an Old World nonhuman primate that develops obesity and has a menstrual cycle similar to humans. We evaluated follicular-phase LH pulses in 12 adult normal-weight female vervets. Serum was collected every 10 min for 4 h by using a tether device in conscious, freely moving monkeys on menstrual cycle days 2 through 5. Serum estradiol was collected daily during the follicular phase to identify the luteal-follicular transition. For comparison, we used data from 12 ovulatory normal-weight women who had undergone frequent blood sampling of early-follicular LH. LH pulse frequency was similar, with 2.8 ± 0.7 LH pulses during 4 h in vervets compared with 2.3 ± 0.7 LH pulses during 4 h in women. The LH pulse mass (percentage change in the pulse peak over the preceding nadir) was 123.2% ± 27.4% in vervets and 60.9% ± 14.9% in humans. The first day of low serum estradiol after the follicular-phase peak was denoted as the day of the luteal-follicular transition. Luteectomy was performed on luteal days 7 through 9, and corpora lutea were confirmed by histology. We demonstrate that follicular LH patterns in vervets are similar to those in humans and that the luteal phase is easily identified by monitoring daily serum estradiol. These findings demonstrate that vervet monkeys are a suitable animal model for evaluating LH pulse dynamics longitudinally in studies of diet-induced obesity.
Comparative medicine 10/2013; 63(5):432-8. · 0.74 Impact Factor
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