Effects of vasopressin on the human non-pregnant uterus: studies with analogues of different vasopressor potencies

Oxytocin mRNA content in the endometrium of non-pregnant women

OBJECTIVE

To study oxytocin mRNA in the human endometrium at different phases of the menstrual cycle.

DESIGN

An exploratory study in non-pregnant women.

SETTING

The Department of Obstetrics and Gynecology, Lund University Hospital, Sweden.

PARTICIPANTS

Thirty-three women of fertile age undergoing hysterectomy or endometrial curettage on routine benign gynaecologic indications.

METHODS

Endometrial tissue was obtained throughout the menstrual cycle. The presence of oxytocin mRNA was investigated by in situ hybridisation and by real time PCR.

MAIN OUTCOME MEASURES

Oxytocin mRNA signalling intensity found by in situ hybridisation of tissue obtained at different times of the menstrual cycle. Relative amounts of oxytocin mRNA measured by real time PCR.

RESULTS

The signal for oxytocin mRNA obtained by in situ hybridisation was more pronounced in glandular epithelial cells than in stromal cells. Furthermore, it was most marked around mid-cycle. The expression of oxytocin mRNA was confirmed by real time PCR.

CONCLUSIONS

The results indicate that oxytocin may be synthesised in the endometrium of non-pregnant women, particularly in the glandular epithelial cells. Hormone released from these sources may have a paracrine action on the uterus. Oxytocin mRNA expression seems to be ovarian hormone dependent with the highest concentration around mid-cycle.

Cu(II) complexation potentiates arginine vasopressin action on nonpregnant human myometrium in vitro

Copper may influence in vivo and in vitro uterine activity. Recent evidence has shown that cupric ions can easily form complexes with oligopeptides like arginine vasopressin (AVP). The high complex stability in vitro suggests a possibility of complex formation in vivo, in the uterus of intrauterine device users. In vitro isometric contractions were recorded in uterine tissues from nonpregnant premenopausal women undergoing hysterectomy and the effect of Cu-AVP complex on isolated human nonpregnant myometrium was investigated. The addition of the Cu(II)-AVP complex to the bath medium led to a concentration-dependent increase of the contractile activity. The activity was somewhat lower for the complex (-log EC(50) of 8.5 +/- 0.2, n = 7) than for AVP, but the difference was not statistically significant (p = 0.11). The maximal responses (E(max)) of the myometrium strips treated with AVP and the Cu (II)-AVP complex did not differ significantly. To assess the effect of presence of Cu (II) in the medium on tissue response to AVP, myometrium strips were preincubated for 20 min in the medium containing 10(-6) mol/L Cu(II) prior to the administration of AVP. The chosen Cu (II) concentration was below the threshold of effect on the spontaneous contractile activity in our experiments. The presence of cupric ions in the bath caused a significant leftward shift in the concentration-response curve to AVP.

Operational correlates of prostanoid TP receptor expression in human non-pregnant myometrium are unaffected by excision site or menstrual cycle status of the donor

1. Cumulative concentration-effect curves for the selective prostanoid TP receptor agonist, U46619, were constructed in strips of human non-pregnant myometrium grouped according to tissue excision site (top, lateral wall, lower uterine segment, sub-serosal or sub-endometrial), tissue orientation (strips cut either parallel or perpendicular to the serosa) and donor menstrual status (proliferative or secretory phase). 2. U46619 was excitatory in all tissues. There was no significant difference in either pEC50 or maximum response between groups (P<0.05). The range of pEC50 values was 6.8+/-0.1 (lateral wall, proliferative phase, n=5) to 7.1+/-0.3 (lateral wall, secretory phase, n=5). The range of maximum response values was 0.9+/-0.8 N cm-2 (lateral wall, proliferative phase, n=5) to 3.1+/-1.0 N cm-2 (lateral wall, secretory phase, n=5). 3. Saturation binding analyses were conducted using the radiolabelled TP receptor agonist, [125I]-BOP. Binding parameters were estimated for membranes prepared from human non-pregnant myometrium excised from the lateral wall and grouped according to donor menstrual status. 4. There were no significant differences in the mean pKd and [R]tot values for [125I]-BOP binding between the two groups (proliferative phase: pKd=8.3+/-0.3, [R]tot=412+/-319 fmol mg protein-1, n=5; secretory phase: pKd=8.5+/-0.4, [R]tot=369+/-192 fmol mg protein-1, n=6; P<0.05). 5. These data indicate that U46619-mediated responses in human non-pregnant myometrium are not influenced by tissue excision site, tissue orientation or donor menstrual status and that [125I]-BOP binding is not influenced by donor menstrual status. This suggests that the TP receptor population is homogeneous throughout the human non-pregnant myometrium, and not subject to hormonal regulation.

Effects of SR 49059, an orally active V1a vasopressin receptor antagonist, on vasopressin-induced uterine contractions

OBJECTIVE

To test the effect of SR 49059, an orally active, nonpeptide, selective and specific antagonist of the vasopressin V1a receptors in humans.

DESIGN

A placebo-controlled, double-blind, cross-over trial.

SETTING

The Department of Obstetrics and Gynaecology, Lund University Hospital, Sweden.

PARTICIPANTS

Twelve healthy women, who had previously been sterilised by tubal ligation.

INTERVENTIONS

The women participated on days 1, 2 or 3 of two menstrual cycles, with intrauterine pressure recordings and intravenous bolus injections of 10 pmol/kg body weight of lysine vasopressin given 1 h before and at 1, 2 and 3 h after oral administration of 300 mg of the study drug or of placebo.

MAIN OUTCOME MEASURE

The area between the recording curve and zero level of pressure. Vital signs, safety parameters and drug plasma concentrations were also measured.

RESULTS

The spontaneous uterine activity as well as the response to lysine vasopressin injections before administration of the test drugs were almost identical at the two experiments. Following intake of SR 49059 the area under the recording curve (0-10 min) after the second, third, and fourth injection of lysine vasopressin were reduced by 57, 42, and 66%, respectively, compared with placebo. Trough plasma concentrations of lysine vasopressin were markedly higher and systolic blood pressure slightly lower after antagonist administration than after placebo, whereas no significant difference between treatments was observed in diastolic pressure, heart rate or plasma osmolality.

CONCLUSIONS

This study demonstrates for the first time a biological effect of an orally active vasopressin V1a antagonist in humans in vivo and the results support the importance of vasopressin in uterine activation. The differences between study drug and placebo treatments in lysine vasopressin levels and systolic blood pressure, but lack of difference in osmolality indicate that SR 49059 antagonises the effect of lysine vasopressin on the vasopressin V1a receptor, but not that on the vasopressin V2 one. It is suggested that SR 49059 be explored therapeutically in dysmenorrhoea.

Receptor-mediated uterine effects of vasopressin and oxytocin in nonpregnant women

OBJECTIVE

To study in nonpregnant women myometrial actions of vasopressin and oxytocin and the involvement in these effects of specific uterine receptors.

SUBJECTS

Twenty-eight women undergoing hysterectomy for benign gynaecological disorders.

INTERVENTIONS

Intrauterine pressure recordings. Intravenous bolus injections of 10 pmol/kg body weight of vasopressin and oxytocin. Repeated blood sampling for measurement of vasopressin and oxytocin concentrations in plasma. Recording of effects of vasopressin and oxytocin on isolated myometrium. Estimation of myometrial concentrations of vasopressin V1a and oxytocin receptors. Measurement of plasma oestradiol and progesterone.

MAIN OUTCOME MEASURES

Vasopressin- and oxytocin-induced increases of the area under the in vivo recording curve over 10 minutes and EC50 concentrations of dose-responses in vitro. Concentrations of vasopressin V1a and oxytocin receptors.

RESULTS

Vasopressin was on average four times more potent than oxytocin in vivo. The effect of vasopressin premenstrually was more pronounced than in women under oestrogen influence only (proliferative phase-hyperproliferation; P = 0.02), and tended to be more marked than in those in the luteal phase (P = 0.07). No significant variation in oxytocin response with the hormonal state was observed. EC50 concentrations of vasopressin were more than 20 times lower than those of oxytocin. The median concentration of the vasopressin V1a receptor was 208 (range 139-343) fmol/mg protein and that of the oxytocin receptor 49 (38-87) fmol/mg protein. Vasopressin receptor concentrations and in vivo effects of this peptide did not correlate, whereas for those of oxytocin a significant correlation was observed (P = 0.02).

CONCLUSION

The high potency of vasopressin in nonpregnant women, particularly premenstrually, firmly supports an aetiological importance of this peptide in the uterine hyperactivity of primary dysmenorrhoea. Oxytocin seems to be less important in this condition in view of its much smaller potency and the absence of increase in effect premenstrually. Vasopressin appears to influence both the oxytocin and the vasopressin V1a receptor sites in the uterus, whereas oxytocin acts specifically on its own receptor.

Oxytocin antagonists in preterm labour and delivery

Evidence has been gained that an oxytocin receptor antagonist given by intravenous infusion effectively stops uterine contractions in threatened as well as in actual preterm labour. The findings suggest that the increase of oxytocin receptors is aetiologically important in uncomplicated preterm labour. Oxytocin antagonists could therefore be an attractive alternative to currently used drugs by virtue of their high specificity and lack of serious side-effects. Their use in prophylactic and maintenance therapy may be greater when modified analogues have been developed that allow non-parenteral therapy.

Radioligand binding studies reveal marked species differences in the vasopressin V1 receptor of rat, rhesus and human tissues

The [3H]arginine-vasopressin ([3H]AVP) binding site in rat, rhesus and human liver and nonpregnant human uterus was characterized and contrasted. [3H]AVP bound with high affinity (Ki values, 0.2-0.6 nM) to preparations of all tissues studied. Competition binding studies using a series of compounds from three structural classes indicate a marked species difference between the rat and primate liver AVP-V1 site. This site in rhesus and human liver however, is essentially identical, indicating that the rhesus liver is an appropriate surrogate for human tissue. These studies also indicate that the AVP-V1 site of nonpregnant human uterus and human liver is equivalent.

Labelling of vasopressin and oxytocin receptors from the human uterus

Four labelled ligands, [3H]arginine vasopressin ([3H]AVP), [3H]oxytocin ([3H]OT), [3H]d(CH2)5[Tyr(Me)2]AVP ([3H]VPA), and [125I]d(CH2)5[Tyr(Me)2-Thr4-Orn8-Tyr(NH2)9]OT([125I]OTA] and nine unlabelled analogues exhibiting enhanced selectivity for rat oxytocin (OT) and vasopressin (VP) receptors were used to characterize OT and VP receptors on myometrial membranes from non-pregnant and pregnant human uteri. On membranes from non-pregnant uteri, [3H]AVP, [3H]VPA, and [125I]OTA labelled with high affinity (Kd values: 3.2, 2 and 0.8 nM, respectively) a major and apparently homogeneous population of sites, the ligand selectivity of which resembled that of rat V1a VP receptors. On membranes from pregnant and non-pregnant uteri, [3H]OT labelled a single population of high-affinity sites that could be distinguished from VP receptors on the basis of ligand selectivity. Several analogues (in particular [125I]OTA) that are highly selective for rat OT receptors exhibited a much less pronounced selectivity for human OT receptors. Experiments with [3H]VPA allowed detection of VP receptors on myometrical membranes from pregnant uteri and confirmed that only OT but not VP receptors increase during pregnancy in humans.