Interaction of vasopressin and prostaglandin on myometrial activity in vivo in the first trimester of human pregnancy

Effects of bleeding on uteroplacental, umbilicoplacental and yolk-sac hemodynamics in early pregnancy

OBJECTIVE

To determine the influence of vaginal bleeding with or without a persisting subchorionic hematoma on uteroplacental, umbilicoplacental and yolk-sac hemodynamics in early pregnancy.

DESIGN

Twenty-six consecutive patients with vaginal bleeding entered this longitudinal study 1-3 days after the beginning of vaginal bleeding and were re-examined every 1-2 weeks. In three cases vaginal bleeding occurred at the 5th completed gestational week, in 13 at the 7th week, in nine at the 8th week and in one case at the 10th week. A subchorionic hematoma was identified in one case at the 5th week, in nine cases at the 7th week, in nine cases at the 8th week, and in seven cases at the 10th week. Four pregnancies ended in miscarriage. Blood velocity waveforms of uterine, arcuate, radial, spiral, umbilical, chorionic and yolk-sac arteries were obtained by transvaginal pulsed Doppler ultrasound and peak systolic velocities, time-averaged maximum velocities and pulsatility indices were calculated. The results were compared with our earlier observations in normal pregnancy obtained with a similar study protocol.

RESULTS

At the 7th week, radial artery pulsatility-index values (mean (SD)) were higher in pregnancies with vaginal bleeding (1.84 (0.59); P = 0.04) and in pregnancies with a subchorionic hematoma (1.96 (0.63); P = 0.03) than in normal pregnancies (1.40 (0.46)). The pulsatility-index values of uterine, arcuate, spiral, umbilical and chorionic arteries did not differ between the groups. Vaginal bleeding with or without a subchorionic hematoma at the 8th week did not affect any of the measured parameters. Persistence of the subchorionic hematoma until the 10th week did not affect uterine, arcuate, radial, spiral, umbilical or chorionic artery hemodynamics. Yolk-sac hemodynamic parameters did not differ between the groups.

CONCLUSIONS

Vaginal bleeding with or without a subchorionic hematoma is associated with increased radial artery impedance at the 7th week of pregnancy. Persistence of the subchorionic hematoma does not affect utero- and umbilicoplacental circulation.

Maternal endocrine and fetal metabolic responses to heat stress

Heat-stressed pregnant ewes deliver intrauterine growth-retarded lambs. Selected maternal and fetal changes were investigated during acute heat stress in order to elucidate the mechanism for this growth retardation. Uterine blood flow decreased 20 to 30% in pregnant ewes during 1 degree C increases in core temperature. The decreases were accompanied by 60 and 100% increases in serum oxytocin and antidiuretic hormone, respectively. These effects were mimicked by salt loading or injections of antidiuretic hormone or oxytocin, suggesting a role for either or both hormones in regulating uterine blood flow during pregnancy. Chronically heat-stressed pregnant ewes were delivered by Caesarean section. Their fetuses were approximately 20% smaller than thermoneutral controls. Within each pair of heat-stressed twins, one fetus weighted one-third less than its litter mate. No difference in weights were observed within the control twins. The livers and brains of the heat-stressed fetuses were disproportionate in size. The livers from the small heat-stressed twins contained only one-half the protein of the controls and one-fourth the protein of their litter mates. Muscle protein was decreased in the heat-stressed fetuses, and liver and muscle glycogen were elevated as were liver arginase, glutamate-pyruvate transaminase and muscle creatinine. These results are consistent with the following hypothesis: heat stress stimulates the release of maternal antidiuretic hormone or oxytocin, which reduces uterine blood flow and causes a shift in fetal metabolism from anabolic to catabolic pathways; one fetus of heat-stressed twins is more severely affected than its litter mate.

Interaction of vasopressin and prostaglandins in the nonpregnant human uterus

The interaction of vasopressin (VP) and prostaglandins (PG) on the nonpregnant human uterus was studied in vitro and in vivo. In organ baths arginine (A)- and lysine (L)-VP in concentrations of 0.6 to 100 ng/ml stimulated small human myometrial strips and uterine artery preparations to a similar degree. When these VPs were given in the presence of indomethacin or naproxen in concentrations of 1 microgram/ml and 5 micrograms/ml, respectively, the myometrial and arterial responses were not significantly influenced. PGF2 alpha in concentrations of 0.01-100 ng/ml stimulated the myometrial preparations but caused a slight relaxation of the arteries, with PGE2 the myometrial effects were insignificant and the relaxation of the arteries greater. When AVP was given together with either of the PGs to the bath the result was generally a summation of the individual effects of both types of substances.--In vivo during intrauterine pressure recordings in nonpregnant women 1-2 days before onset of menstruation LVP in single intravenous injection of 1.2 micrograms markedly stimulated uterine contractions. The response remained practically unaltered after pretreatment with 500 micrograms of naproxen given orally. The responses to LVP were also closely similar before, during and after intravenous infusion of PGF2 alpha at a rate of 5 micrograms/min.--It is concluded that the effect of VP on myometrium and uterine arteries is not to any great extent mediated by local synthesis of PG and that PGs do not cause potentiation or inhibition of the VP effects on the nonpregnant uterus.

Involvement of prostaglandins in vasopressin stimulation of the human uterus

The involvement of prostaglandins (PG) in the vasopressin (VP) action on the human uterus was investigated in healthy women during three menstruations. Intrauterine pressure was recorded and total pressure area measured. Repeated plasma samples were taken for estimations of arginine(A)- and lysine(L)-VP, 15-keto-13,14-dihydro-PGF2 alpha and 11-ketotetranor PGF metabolites. During the first menstruation LVP was infused in a dose of 0.08 micrograms/min. During the second menstruation the infusion of LVP was repeated with the same dose, but 70 min before infusion the women received an oral dose of 500 mg of naproxen. During the third menstruation PGF2 alpha was administered intravenously in a dose of 25 micrograms/min. LVP infusion per se caused a significant increase in uterine activity and plasma levels of LVP and PG metabolites. When the women were pretreated with naproxen practically the same uterine activity was induced and closely similar plasma levels of LVP were obtained, but the levels of PG metabolites decreased significantly in comparison with the first series of experiments. Infusion of PGF2 alpha caused an increase in uterine activity but no change in the plasma levels of AVP. The results indicate that uterine stimulation with VP is possible without an obligatory last step of PG synthesis and release. The results also support the concept that an elevated VP level in primary dysmenorrhoea may be of aetiological importance and is not just released as a 'stress'-hormone because of the dysmenorrhoeic pain.

Uterine effects of N-alpha-triglycyl-(8-lysine)-vasopressin and 8-lysine-vasopressin in the first trimester of pregnancy

Myometrial effects of a vasopressin hormonogen (N-alpha-triglycyl-(8-lysine)-vasopressin, TGLVP) and of 8-lysine-vasopressin (LVP) were studied in early pregnancy. Intrauterine pressure was recorded in 28 women, who were to have a therapeutic abortion at 8-12 weeks of gestation, and intravenous injection of TGLVP (0.5 and 1 mg) or LVP (0.1, 0.2 and 0.4 IU) were given, or control recordings without drug injection were obtained. TGLVP generally caused a biphasic increase in uterine activity with a rise in uterine tone as the most conspicuous initial effect followed by an increase in amplitude and duration of contractions. In the higher dose group the uterine activity remained significantly higher than in the controls during the rest of the recording period of 4-7 h. The magnitude of effect with the two doses of TGLVP did not differ significantly. The initial myometrial response to LVP resembled that to TGLVP but the effects disappeared within 10-45 min. In the controls the uterine activity did not change. It is suggested that vasopressin analogues could have a therapeutic value in the induction of abortion, but further basic studies are required to define this.