Anna Kostrzewska

Receptor binding of oxytocin and vasopressin antagonists and inhibitory effects on isolated myometrium from preterm and term pregnant women

Objective To test binding affinities for, and inhibitory effects on, myometrium of some oxytocin and vasopressin antagonists with respect to their therapeutic potential.

Effect of ovarian steroids and diethylstilbestrol on the contractile responses of the human myometrium and intramyometrial arteries

Estriol, estradiol, progesterone and diethylstilbestrol in the concentration range of 0.2-40 microM inhibited the spontaneous contractions of the myometrium in a dose-dependent manner but the differences in IC50 values obtained with different hormones were not statistically significant. All these hormones caused a concentration-dependent inhibition of the K(+)-induced contraction. The IC50 values were lowest for diethylstilbestrol and highest for estriol. Vasopressin at concentrations of 1.5 x 10(-6) - 1.8 x 10(-3) U/ml stimulated myometrial contractions. These responses were also inhibited by ovarian steroids and diethylstilbestrol. The IC50 values for estriol and progesterone were significantly higher than for estradiol or diethylstilbestrol. The values for estriol and progesterone did not differ significantly. In the uterine arteries, which lacked spontaneous activity, ovarian steroids and diethylstilbestrol inhibited contractions induced by K+ depolarization. As with myometrium, the lowest effect was observed with estriol and the highest with diethylstilbestrol. A dose-dependent inhibition by all four hormones (0.2-40 microM) of vasopressin-induced contractile responses of the uterine arteries was observed. With the lowest concentration of progesterone, however, the arterial response to vasopressin was enhanced. The increases by progesterone (0.02 and 0.2 microM) of responses induced by vasopressin were statistically significant (P < 0.05). The present data strongly suggest that, in human myometrium and uterine arteries, ovarian steroids and diethylstilbestrol cause a more pronounced inhibition of receptor-mediated than of voltage-dependent Ca2+ channels. The increase by a very low (physiological) concentration of progesterone of vasopressin-induced responses in both myometrium and arteries may be of significance in the pathophysiology of dysmenorrhea.

Potent inhibition by tamoxifen of spontaneous and agonist-induced contractions of the human myometrium and intramyometrial arteries

OBJECTIVE Our purpose was to elucidate the mechanism of direct (nongenomic) action of antiestrogens on spontaneous and agonist-induced contractions of the human myometrium and uterine arteries. STUDY DESIGN Myometrial strips and pieces of uterine arteries were obtained from nonpregnant premenopausal women undergoing hysterectomy. Spontaneous activity of myometrium and responses of myometrium and artery to K(+)-depolarization and vasopressin were recorded under isometric conditions. Quantification of the responses was done by planimetry. RESULTS The 50% inhibitory concentration values for tamoxifen, clomiphene, and cyclofenil in the case of myometrial spontaneous activity were 2.8, 43, and 331 nmol/L, respectively. Vasopressin-induced contractions in both the myometrium and arteries were potently inhibited by tamoxifen, and the 50% inhibitory concentration for the myometrium (1.4 nmol/L) was significantly lower (p < 0.05) than that for the arteries (11 nmol/L). Although tamoxifen caused no inhibition of responses induced by high potassium chloride (80 mmol/L), responses induced by low potassium chloride (20 mmol/L) were inhibited by 40% to 50% in both the myometrium and arteries. Glibenclamide reversed the inhibition by tamoxifen of spontaneous myometrial activity. CONCLUSIONS Tamoxifen is a highly potent inhibitor of the contractile activity of the human nonpregnant myometrium and uterine arteries. It is suggested that tamoxifen could have strong potential in the treatment of dysmenorrhea.

Apamin inhibits NO-induced relaxation of the spontaneous contractile activity of the myometrium from non-pregnant women

There is now considerable evidence for the involvement of K+ channels in nitric oxide (NO) induced relaxation of smooth muscles including the myometrium. In order to assess whether apamin-sensitive K+ channels play a role in NO – induced relaxation of the human uterus, we have studied the effect of specific blockers of these channels on the relaxation of myometrium from non-pregnant women. In vitro isometric contractions were recorded in uterine tissues from non-pregnant premenopausal women who had undergone hysterectomy. Apamin (10 nM) and scyllatoxin (10 nM) did not alter spontaneous myometrial contractions. However, 15-min pretreatment of the myometrium strips with apamin completely inhibited relaxation caused by diethylamine-nitric oxide (DEA/NO). The pretreatment with scyllatoxin significantly reduced (about 2.6 times) maximum relaxation of the strips induced by DEA/NO (p < 0.05). These results strongly suggest that, beside Ca2+ and voltage dependent charybdotoxin-sensitive (CTX-sensitive) K+ channels, apamin-sensitive K+ channels are also present in the human non-pregnant myometrium. These channels offer an additional target in the development of new tocolytic agents.

Effects of the vasopressin V1a receptor antagonist, SR 49059, on the response of human uterine arteries to vasopressin and other vasoactive substances

BACKGROUND Arginine vasopressin (AVP) activates the uterus via V1a receptors and is apparently an important factor for the myometrial hyperactivity, uterine ischemia and pain of primary dysmenorrhea. The orally active and selective, non-peptide AVP1a receptor antagonist, SR 49059, has been shown to inhibit the myometrial action of AVP, but the specific influence of this substance on the effects of AVP and other vasoactive agents on human uterine arteries is unknown. METHODS Concentration-responses of AVP on isolated medium-sized human uterine arteries were studied after incubation with only vehicle (DMSO, 0.1%) and with SR 49059 in concentrations of 0.5, 2.5 and 10 nmol/L. Furthermore, the concentration-responses of AVP were investigated without and with SR 49059 (2 and 10 nmol/L) on small and medium-sized arteries. Finally, the influence of 2.5 nmol/L of SR 49059 on concentration-responses of endothelin-1, noradrenaline and prostaglandin F2 alpha was studied. RESULTS The EC50 for AVP on medium-sized arteries was 0.53 +/- 13 nmol/L. SR 49059 caused a competitive, dose-dependent inhibition of AVP-responses, the highest concentration giving an EC50 of 460 nmol/L. The pA2 value was 9.84. The responses of the small artery preparations to AVP, both without and with the antagonist, were more pronounced than those of the medium-sized ones. The vasoconstrictive effects of endothelin-1, noradrenaline and prostaglandin F2 alpha were less pronounced than those of AVP and unaffected by pre-exposure to SR 49059. CONCLUSIONS The high potency of AVP on human uterine arteries, particularly those of small size, supports an involvement of the peptide in the regulation of uterine blood flow in both physiological and pathophysiological condition. SR 49059 is a potent and selective AVP V1a receptor antagonist in the smooth muscle of human uterine arteries.

Inhibition of contractile responses of human myometrium and intramyometrial arteries by potassium channel openers

Objectives. The effects of cromakalim and pinacidil on the contractile activity of the isolated human myometrium and intramyometrial arteries were studied.

Vasopressin effects on isolated non‐pregnant myometrium and uterine arteries and their inhibition by deamino‐ethyl‐lysine‐vasopressin and deamino‐ethyl‐oxytocin

Summary. The contractile effects of lysine‐ (L) and arginine‐ (A) vasopressin (VP) on isolated non‐pregnant myometrium and uterine arteries and the inhibition of these actions by two analogues of posterior pituitary hormones, deamino‐ethyl‐LVP (dE‐LVP) and deamino‐ethyl‐oxytocin (dE‐OXY) were investigated. Both AVP and LVP effectively stimulated the smooth muscle preparations. The threshold dose for both agonists was about 2 ng/ml of bath fluid and a maximal response was obtained with approximately 75 ng/ml. No distinguishable effect was produced by dE‐LVP and dE‐OXY alone, but when given before the agonists in concentrations of 150 or 300 ng/ml, dose‐dependent inhibition of the contractions was seen. The inhibition of the uterine artery responses was always greater than the inhibition of the effects on myometrial activity and dE‐LVP appeared to have stronger antagonistic effects than dE‐OXY on the myometrial responses to the agonists. The inhibition of the myometrial and uterine artery responses to AVP could explain the therapeutic effect of dE‐OXY recently found in primary dysmenorrhoea, where increased VP secretion seems to be of aetiological importance.

Cu(II) complexation does not affect oxytocin action on pregnant human myometrium in vitro

OBJECTIVE Copper may influence the in vivo and in vitro uterine activity. Recent evidence shows that cupric ions can easily form complexes with oligopeptides like oxytocin (OXT). The high complex stability in vitro suggests a possibility of complex formation in vivo. STUDY DESIGN In vitro isometric contractions were recorded in uterine tissues from pregnant women undergoing caesarean sections and the effect of OXT and the Cu-OXT complex on isolated human pregnant myometrium was investigated. RESULTS In the concentration range from 10(-14) to 10(-6)M of OXT alone, pre-formed Cu-OXT complex, and OXT following sample preincubation with Cu(II) salt, nosignificant differences were observed for the following parameters of pregnant uterine smooth muscle contraction: the area under the curve, frequency and amplitude of contraction. CONCLUSION The binding of Cu(2+) ions does not abolish the ability of OXT to interact with oxytocin receptors and stimulate myometrial contraction in vitro.

Altered uterine contractility in response to β-adrenoceptor agonists in ovarian cancer

We aimed to prospectively examine β-adrenoceptor-mediated uterine contractility in women suffering from gynecological malignancies. Myometrial specimens were obtained from non-pregnant women undergoing hysterectomy for benign gynecological disorders, and ovarian, endometrial, synchronous ovarian–endometrial, and cervical cancer. Contractions of myometrial strips in an organ bath before and after cumulative dosages of β2- and β3-adrenoceptor agonists with preincubation of propranolol, SR 59230A, and butoxamine were studied. All agonists induced a dose-dependent attenuation for uterine contractility in endometrial or cervical cancer, similar to that observed in the reference group. Contradictory effects were observed for ovarian cancer alone or in combination with endometrial cancer. CL 316243 or ritodrine abolished the relaxation, whereas BRL 37344 increased the uterine contractility in ovarian cancer. Moreover, β-adrenoceptor antagonists caused varied effects for β2- or β3-adrenoceptor agonists. Our experiments demonstrate that ovarian cancer, alone or as synchronous ovarian–endometrial cancer, substantially alters uterine contractility in response to β-adrenoceptor agonists.

The Assessment of a Selective Inhibition of Potassium Channels and Guanylate Cyclase in the Relaxation Induced by Exogenous Nitric Oxide in the Human Nonpregnant Myometrium

Abstract To evaluate the involvement K+ channels in the relaxation induced by exogenous nitric oxide, after preincubation with L-arginine analogue L-NA in the human nonpregnant myometrium. The activity of myometrial strips, obtained from 60 premenopausal hysterectomised women, mounted in an organ bath was recorded under isometric conditions using force transducers with digital output. Concentration-response curves to DEA/NO after inhibition of endogenous NO were constructed in the absence and presence of soluble granulate cyclase and K+ channels’ blockers. The responses were quantified by calculating the area under the curve, the amplitude and frequency of the contractions. The inhibition of NOS results in slight but significant attenuation of the myometrium strips response to DEA/NO. Pre-treatment with both sGC inhibitors after preincubation with L-NA did not counteract the DEA-NOinduced relaxation of the spontaneous contractions of the myometrial strips. Application of blockers of different types of K+ channels to the myometrial strips significantly attenuated relaxing effect of cumulative DEA/NO administration in all cases. The present data indicate that even when endogenous production of NO is inhibited, the DEA/NO induced relaxation of human non-pregnant myometrium without involving the cGMP pathway.