Time course changes in in vivo muscle mechanical function and Ca²⁺ regulation of force following experimentally induced gradual ovarian failure in mice

Abstract

The abrupt cessation of ovarian hormone release is associated with declines in muscle contractile function, yet the impact of gradual ovarian failure on muscle contractility across peri‐, early‐ and late‐stage menopause remains unclear. In this study, a 4‐vinylcyclohexene diepoxide (VCD)‐induced ovarian failure mouse model was used to examine time course changes in muscle mechanical function. Plantar flexors of female mice (VCD: n = 10; CON: n = 8) were assessed at 40 (early perimenopause), 80 (late perimenopause), 120 (menopause onset) and 176 (late menopause) days post‐initial VCD injection. A torque–frequency relationship was established across a range of frequencies (10–200 Hz). Isotonic dynamic contractions were elicited against relative loads (10–80% maximal isometric torque) to determine the torque–velocity–power relationship. Mice then performed a fatigue task using intermittent 100 Hz isometric contractions until torque dropped by 60%. Recovery of twitch, 10 Hz and 100 Hz torque were tracked for 10 min post‐task failure. Additionally, intact muscle fibres from the flexor digitorum brevis underwent a fatigue task (50 repetitions at 70 Hz), and 10 and 100 Hz tetanic [Ca2+] were monitored for 10 min afterward. VCD mice exhibited 16% lower twitch torque than controls across all time points. Apart from twitch torque, 10 Hz torque and 10 Hz tetanic [Ca2+], where VCD showed greater values relative to pre‐fatigue during recovery, no significant differences were observed between control and VCD mice during recovery. These results indicate that gradual ovarian failure has minimal detriments to in vivo muscle mechanical function, with minor alterations observed primarily for low‐frequency stimulation during recovery from fatigue.

Investigating the temporal effects of ovarian failure on single muscle fibre contractility using a chemically-induced ovarian failure model in mice

“…Mice were weighed and given daily intraperitoneal injections (160mg/kg) of VCD (MilliporeSigma, Oakville, ON) for 15 consecutive days (Hinks et al, 2024;Hubbard et al, 2023;Mashouri et al, 2024;Perez et al, 2013). VCD accelerates follicular atresia by inducing the selective loss of primary and primordial follicles in the ovary but leaves intact the rest of the ovary for residual hormone production.…”

“…Some groups have even reported absolute force values ~20% higher for the EDL muscle at the joint level for 10-week-old rodents 7 weeks post-OVX compared to age-matched controls (Suzuki & Yamamuro, 1985). Using a VCD-induced model of ovarian failure, the absolute and specific force of the SOL whole muscle and plantar flexors in young mice was not different (Greising, Carey, et al, 2011;Hinks et al, 2024).…”

“…Using an OVX model of ovarian failure in adult rodents, reductions in absolute and specific force at the whole muscle and single fibre level by ~10-30% for the soleus (SOL) and extensor digitorum longus (EDL) have been reported ~1-3 months post-OVX (Greising, Baltgalvis, et al, 2011;Hubbard et al, 2023;Moran et al, 2007;Moran et al, 2006;Wattanapermpool & Reiser, 1999). However, others using similar models reported no difference in absolute or specific force for SOL and EDL whole muscles in ~2 (Fillion et al, 2019) and ~5-6-month-old rodents 2 weeks (Fillion et al, 2019;Greising, Baltgalvis, et al, 2011) or 2 months post-OVX (Cabelka et al, 2019;Cabelka et al, 2021;Hinks et al, 2024). Some groups have even reported absolute force values ~20% higher for the EDL muscle at the joint level for 10-week-old rodents 7 weeks post-OVX compared to age-matched controls (Suzuki & Yamamuro, 1985).…”

“…Most studies investigating the effects of reduced estrogens on muscle contractile function use the ovariectomized (OVX) model, whereby ovaries are surgically removed, leading to a sudden halt in ovarian hormone production which does not mimic the prolonged transitional phase of naturally occurring menopause (Hoyer et al, 2001;Mayer et al, 2004). Thus, in the present study, we induced gradual ovarian failure in mice to allow for the investigation of the perimenopausal transition on muscle contractile function (Brooks et al, 2016;Fernandes et al, 2019;Hubbard et al, 2023;Mashouri et al, 2024) into late-stage menopause (Hinks et al, 2024).…”

“…17β-estradiol-deficiency is generally associated with reductions in both absolute and specific (absolute force normalized to muscle size) force production in skeletal muscle (Collins et al, 2019;Lowe et al, 2010;Tiidus, 2011;Tiidus et al, 2013), but not always (Fillion et al, 2019;Greising, Baltgalvis, et al, 2011;Hinks et al, 2024;Mashouri et al, 2024). Using an OVX model of ovarian failure in adult rodents, reductions in absolute and specific force at the whole muscle and single fibre level by ~10-30% for the soleus (SOL) and extensor digitorum longus (EDL) have been reported ~1-3 months post-OVX (Greising, Baltgalvis, et al, 2011;Hubbard et al, 2023;Moran et al, 2007;Moran et al, 2006;Wattanapermpool & Reiser, 1999).…”