Differential damage and repair responses of pubococcygeus and bulbospongiosus muscles in multiparous rabbits

Abstract

Damage and regeneration of the pubococcygeus and bulbospongiosus muscles are differently influenced by multiparity in rabbits. This could rely on the anatomical location, metabolism, myofiber composition, and muscle exertion during pregnancy and/or the delivery of each muscle.

Fiber type composition of pubococcygeus and bulbospongiosus striated muscles is modified by multiparity in the rabbit

“…During the two phases of the micturition process of female rabbits, the Pc muscle is activated during the continence and the Bs muscle during the voiding phase . As it can be inferred from data of nulliparous rabbits (present study), fatigue resistence of the Pc muscle during the continence is higher than that of the Bs muscle, which instead requires a high contractile force to expel urine from the bladder. We found a significant reduction in the percentage of fast type fibers in the Pc muscle accompanied with an increase in the percentage of intermediate fibers.…”

“…Changes affecting the fiber types and morphometry of the Pc and Bs muscles are possibly related to injuries due to the four consecutive and successive deliveries, as well as to the hormonal status underlying multiparity . Regarding the fiber sensibility to damage, several authors report an increase of cross sectional areas in slow fibers but not in fast or intermediate fibers after hind limb suspension, anesthetics infiltration, or injury during contractions .…”

“…Our results further show that slow fibers in Pc and Bs muscles of multiparous rabbits, conforms groups of fibers with middle cross sectional area, in a similar manner as the slow fibers located in the pubocaudal muscle of multiparous beagles, and as the fast fibers in smallest bins of cross sectional areas after multiparity. Those histological changes are probably related to the degeneration‐regeneration process after multiparity and the consequent loss of contractile protein in fast fibers. The fusion of myoblasts during the recovery process after muscle damage results in an increase of the cross sectional area of the new myofibers, and the traslation of the nuclei to the muscular fiber periphery .…”

“…Females were pregnant and lactating for 20 days when pups were weaned, as it occurs in normal, natural conditions. On the day of the fourth delivery, neonate pups were decapitated in order to prevent lactation and to give female rabbits the opportunity to reach a hormonal condition similar to nulliparous rabbits that were not exposed to any reproductive stimulus . Multiparous rabbits were killed at postpartum day 20 (M20, n = 5) with an overdose of sodium pentobarbital (60 mg/kg, ip; Pisa).…”

“…Besides plausible neurological alterations, it is clear that multiparity affects the morphometry of these muscles and reduces their contractile force . Some of such effects are indeed coincident with biochemical and molecular markers indicating the occurrence of ongoing particular damage‐repair processes in the Pc and Bs muscles in multiparous rabbits . Most of the observed effects could be explained, among other factors, by changes in the proportion of fiber type phenotypes in each muscle.…”