Testosterone Regulation of Acetylcholinesterase in the Rat Levator Ani Muscle

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The levator ani muscle (LA) is an androgen-dependent structure of the male rat that responds to testosterone plasmatic levels (T). The acetylcholinesterase (AChE) activity in LA is higher than in other rat fast muscles; gonadectomy of the adult male produces marked atrophy of LA and decreases the total muscle AChE activity by 50% (1). The initial T effects on the LA occur by priming of the motoneuron during the rat sexual differentiation. Later on, the influence of androgen on AChE depends on intact motor innervation (2-3). This study investigated the influence of T on the AChE molecular forms of the LA comparatively to the non-target extensor digitorum longus muscle (ELD) from intact and castrated adult male rats. The control LA and ELD weighed 165.8 ± 2.1 mg and 134.9 ± 3.9 mg while the total AChE activity was 6178 ± 50 units and 3613 ± 297 units, respectively. Globular (G) forms accounted for 93% of the total AChE activity in LA (G1 = 37%; G2= 3%, G4=53%) whereas the asymmetric (A) form A12 was only 3% of the total activity. The main AChE molecular forms in ELD of the control group were Gl (44%), G4 (43%) and A12 (13%). After 15 and 30 day gonadectomy, the LA weighed 50% and 42% of the controls, respectively. Total AChE activity was reduced by 52% in part because of the marked decrease of the G1 form to 17% of control. The G4 and A12 activities also decreased after 30 days hormonal withdrawal to 55% and 30% of control, respectively. The relative decrease of Gl, G4 and A12 forms was followed by 163% increase of the G2 form. The proportion of molecular forms in the ELD was not affected by gonadectomy. To evaluate a direct effect of T on the muscle fiber, perineal T-target muscle cells and non-target hindlimb muscles cells from newborn male rats were cultured.