Androgen-induced relaxation of uterine myocytes is mediated by blockade of both Ca2+ flux and MLC phosphorylation

Abstract

Context: Uterine quiescence must be maintained until pregnancy reaches term. Premature activation of myometrial contractility leads to preterm labor and delivery. Objective: To scrutinize the potential of androgens to relax the myometrium and the mechanism of their action. Samples: A pregnancy-derived myometrial smooth muscle cell line (PHM1-41) and myometrial strips prepared from tissues obtained from pregnantwomen(lean, n=9; obese, n=6) undergoing elective cesarean section at term and from nonpregnant C57BL/6 mice (n=5) were each utilized. Design: The contraction of collagen-embedded PHM1-41s and the stretch-induced contraction of humanandmurine myometrial stripswereassessed after incubation with Testosterone (T), dihydrotestosterone (DHT), and T conjugated to BSA. Intracellular calcium ([Ca2+]) and phosphorylated myosin light chain concentrationswerequantified inPHM1-41s usingaFluo-4Ca2+assayandin-cell Westerns, respectively. Setting: University research institute. Results: DHT and T, but not T conjugated to BSA, impaired the contractile function of PHM1-41s and of human and murine myometrial strips. The response was rapid (observed within minutes), wassustainable forupto 48 hours,andwasnot abolishedonknockdownof the androgen receptor. DHT (100 =M) reduced the amplitude of lean strip contraction to 2-2%of the pretreatment value and T (100 =M) to 3.3-1%. These values for obese strips were 15-6.7% and 11-6.7%, respectively. At the same doses, in murine strips, DHT reduced the amplitude to 4.8-3% and T to 4.9-3%. DHT (50 =M) pretreatment reduced the oxytocin-stimulated increase in [Ca2+] (P.0001; n = 6) and phosphorylated myosin light chain (P 05; n = 5) in PHM1-41s. Conclusion: Lipid-soluble androgens could be developed as tocolytic agents for the treatment of preterm labor.