Characterization and distribution of cholinesterase activity in mouse uterine horns: changes in estrous cycle

1. Both butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are present in the mouse uterus, BChE being more abundant. 2. Their molecular forms were sequentially solubilized by different extraction media obtaining three ChE fractions whose specific activity was different, depending on the stage of the estrous cycle: hydrosoluble (estrous: 75.5 +/- 6.6 and diestrous: 47.9 +/- 8.7 mU/mg prot); detergent-soluble or amphiphilic (estrous 26.6 +/- 2.4 and diestrous 14.7 +/- 3.3 mU/mg prot.), and high ionic strength-soluble (estrous: 18.7 +/- 4.2 and diestrous 12.8 +/- 1.2 mU/mg prot.). 3. Histochemical procedures demonstrated a different distribution for both ChE activities. AChE was found in nerves next to smooth muscle cells of the circular layer and blood vessels, while BChE was concentrated in the longitudinal stratum surrounding the smooth muscle cells. Under the predominance of progesterone, BChE was also found in the endometrial glands. 4. Maximal contractions evoked by the addition of ACh to the isolated organ bath were concentration dependent and greater in estrous than in diestrous. Nevertheless the difference at the two stages of the estrous cycle disappeared when contractions were normalized to smooth muscle cross-sectional area. 5. BChE but not AChE inhibition augmented maximal contractions elicited by ACh in longitudinal but not in circular smooth muscle. 6. The effect of BChE inhibition on the contractile force developed was greater at lower concentrations of ACh and did not depend on the stage of the estrous cycle.