Synergistic effect of human relaxin and progesterone on human myometrial contractions

A novel treatment strategy for preterm birth: Intra-vaginal progesterone-loaded fibrous patches

Progesterone-loaded poly(lactic) acid fibrous polymeric patches were produced using electrospinning and pressurized gyration for intra-vaginal application to prevent preterm birth. The patches were intravaginally inserted into rats in the final week of their pregnancy, equivalent to the third trimester of human pregnancy. Maintenance tocolysis with progesterone-loaded patches was elucidated by recording the contractile response of uterine smooth muscle to noradrenaline in pregnant rats. Both progesterone-loaded patches indicated similar results from release and thermal studies, however, patches obtained by electrospinning had smaller average diameters and more uniform dispersion compared to pressurized gyration. Patches obtained by pressurized gyration had better results in production yield and tensile strength than electrospinning; thereby pressurized gyration is better suited for scaled-up production. The patches did not affect cell attachment, viability, and proliferation on Vero cells negatively. Consequently, progesterone-loaded patches are a novel and successful treatment strategy for preventing preterm birth.

The role of inflammation and infection in preterm birth

Much emphasis in recent decades has been devoted to inflammation and infection as a premier causal mechanism of preterm birth. This article explores the epidemiologic, clinical, and animal data that exist to support this conceptual paradigm as well as proposed mechanisms through which to potentially mitigate the adversity of prematurity. Truly successful interventions are not likely to occur until the pathogenesis of preterm birth and the role of inflammation in causing not only parturition but also fetal and neonatal injury is fully elucidated.

Evidence that corticotropin-releasing hormone modulates myometrial contractility during human pregnancy

As human pregnancy advances, CRH increases exponentially and is hypothesized to trigger the transition from myometrial quiescence to active contractions at labor. Paradoxically, CRH stimulates cAMP production, suggesting it should cause relaxation. To evaluate CRH as a mediator of quiescence, the effect of CRH on contractions in preterm and term myometria with concurrent progesterone (P4) was determined. In late gestation, we hypothesized that high concentrations of CRH down-regulate agonist-activated-cAMP relaxatory pathways and that increased phosphodiesterase (PDE) activity induces heterologous down-regulation of agonist-activated-cAMP pathways. CRH caused dose-dependent relaxation of spontaneously contracting myometrial strips of 31 +/- 8% (mean +/- sem; n = 12) and 35 +/- 20% (n = 3) in term and preterm samples, respectively. CRH with P4 pretreatment caused a 40 +/- 13% (n = 4) reduction in contractility, whereas in matched samples, CRH alone exerted a 26 +/- 6% (n = 4) reduction, with a shift of CRH dose-response curves (P < 0.01, ANOVA). Pretreatment of strips with 10(-7) m CRH did not attenuate relaxation induced by subsequent CRH (n = 3) or salbutamol (beta(2)-agonist) treatment (n = 9). PDE inhibition by rolipram showed a 2.2- and 1.5-fold increase in maximal relaxation induced by CRH and salbutamol, respectively, with a shift of both dose-response curves (P < 0.05 and P < 0.01, ANOVA). In conclusion, CRH at physiological concentrations acts synergistically with P4 contributing to myometrial quiescence. P4 withdrawal may reduce CRH-mediated relaxation. Our functional model does not support homologous or heterologous down-regulation of agonist-stimulated-cAMP pathways by high CRH concentrations. PDE inhibition potentiates CRH and salbutamol-induced relaxation. Up-regulation of PDEs, through chronic cAMP elevation by CRH, could provide a mechanism for down-regulation of agonist-stimulated-cAMP pathways at term.

Medroxyprogesterone acetate, but not progesterone, protects against inflammation-induced parturition and intrauterine fetal demise

OBJECTIVE

This study was undertaken to determine whether progestational agents can prevent inflammation-induced preterm parturition and fetal demise.

STUDY DESIGN

The activation of contractile and inflammatory pathways in response to localized intrauterine inflammation was investigated by using quantitative polymerase chain reaction (PCR). Serum progesterone (P4) levels and alterations in progesterone receptor-B (PR-B) were determined with radioimmunoassay and quantitative PCR, respectively. With our in vivo model of intrauterine inflammation, animals were randomly assigned to pretreatment with P4 or medroxyprogesterone acetate (MPA) before intrauterine lipopolysaccharide (LPS). Animals were observed for preterm delivery. The number of live pups 48 hours after intrauterine LPS was recorded for each treatment group. The ability of MPA to alter signal transduction pathways leading to preterm parturition were investigated by quantitative PCR and histochemical studies.

RESULTS

Intrauterine inflammation is associated with decreased serum progesterone levels and decreased transcription of PR-B. Preterm delivery rates were 100% for LPS alone, 63% for LPS+P4, and 0% for LPS+MPA. No live pups remained at 48 hours in the LPS or LPS+P4 groups. Pretreatment with MPA significantly preserved fetal viability. MPA suppressed activation of contraction-associated genes and inflammatory mediators and prevented cervical ripening in response to intrauterine inflammation.

CONCLUSION

MPA, with its progestational and anti-inflammatory properties, prevented inflammation-induced preterm parturition and significantly preserved fetal viability.

No effects of human relaxin on the active and passive biomechanical properties of isolated cervical specimens from nonpregnant women

OBJECTIVE

To evaluate the effect of human relaxin (hRLX-2) on the active and passive biomechanical properties of cervical tissue in vitro.

MATERIAL

Cervical samples were obtained from the middle part of the cervix in 22 nonpregnant women undergoing hysterectomy.

METHODS

The effect of hRLX-2 (10(-7) M) on the active biomechanical properties was studied on vasopressin (10(-8) M) induced smooth muscle contractions in an organ bath model. The effect on the passive biomechanical properties were studied after incubation of the strips for 48 h with hRLX-2 (10(-8) M and 10(-9) M). Subsequently, the specimens were stretched in a material testing machine until they broke. The load applied and the elongation were simultaneously recorded and the results translated into stress-strain curves.

RESULTS

hRLX-2 did not influence the vasopressin-induced contractility of cervical strips from nonpregnant women in this study. No synergistic effect of progesterone could be demonstrated. The passive biomechanical properties (tensile strength, extensibility, stiffness of failure energy) did not change significantly after relaxin incubation. The results obtained in vitro do not suggest an important physiological effect of relaxin on the human nonpregnant cervix.

Effect of leuprolide acetate in patients with functional bowel disease. Long-term follow-up after double-blind, placebo-controlled study

We initially investigated the effects of a gonadotropin-releasing hormone analog, leuprolide acetate, in 28 patients with moderate to severe functional bowel disease in a phase-II, randomized, double-blind, and placebo-controlled study using Lupron Depot 3.75 mg (which delivers a continuous low dose of drug for one month) or placebo given intramuscularly. After completing that 12-week study period during which their symptoms had improved significantly (P < 0.01-0.5), the 28 patients were allowed to continue receiving leuprolide acetate; they were monitored for an additional 40 weeks. Of those 28, 25 (89%) finished the 52-week treatment. Drug administration was changed from the monthly low-dose form of leuprolide acetate to a daily subcutaneous dose that was gradually increased from 0.5 mg daily to an effective therapeutic dose (1.0-1.5 mg). All subjects received estrogen replacement during this period. Continued use of leuprolide acetate at maximum therapeutic dosage and over longer periods of time produced even more striking and significant changes in the disabling and debilitating symptoms of functional bowel disease. Nausea, abdominal pain, early satiety, anorexia, and abdominal distension decreased markedly (P < 0.0001) and vomiting was also reduced (P < 0.01) more than in the short-term, low-dosage, double-blind study. Combined total symptom scores and overall assessment also changed significantly in the long-term phase (both P < 0.0001).

Synergistic effect of relaxin and progesterone on cyclic adenosine 3',5'-monophosphate levels in the rat uterus

Cyclic adenosine 3',5'-monophosphate is known to modulate smooth muscle contractility. Because both relaxin and progesterone have been demonstrated to affect myometrial cyclic adenosine monophosphate activity, we questioned whether the previously observed synergism of these two hormones in inhibiting uterine contractility is mediated via cyclic adenosine monophosphate. Immature rats were treated with estradiol benzoate (n = 7) or a combination of estradiol benzoate and progesterone (n = 7). Uterine horns were isolated, each horn was divided into two segments, and these horn segments were incubated in Ringer-Locke solution, either alone (control) or with 3-isobutyl-1-methylxanthine (MIX) 0.5 mM, MIX 0.5 mM + relaxin 10 ng/ml, or MIX 0.5 mM + relaxin 50 ng/ml. When compared with uterine segments incubated in MIX alone, treatment with MIX + relaxin 50 ng/ml significantly increased cyclic adenosine monophosphate levels in animals treated with estradiol benzoate alone or in combination with progesterone. Relaxin 10 ng/ml was sufficient to significantly elevate mean (+/- SEM) uterine cyclic adenosine monophosphate levels above that of control MIX-treated uteri in animals receiving both estradiol benzoate and progesterone (2.49 +/- 0.39 pm/micrograms deoxyribonucleic acid [DNA] versus 1.08 +/- 0.16 pm/microgram DNA, p less than 0.05) but not in animals receiving estradiol benzoate alone (2.08 +/- 0.32 pm/micrograms DNA versus 1.28 +/- 0.16 pm/micrograms DNA, NS). Compared with treatment with MIX only, MIX + relaxin 10 ng/ml and MIX + relaxin 50 ng/ml produced greater increases in uterine cyclic adenosine monophosphate in the steroid combination group than in the estradiol benzoate controls (144.8% and 233.7% versus 71.7% and 156.6%, respectively). These results suggest that the synergism of relaxin and progesterone in inhibiting uterine contractility may be mediated by intracellular cyclic adenosine monophosphate.

The effect of relaxin on calcium fluxes in the rat uterus

Relaxin is a polypeptide hormone that inhibits rat uterine contractions. To test the hypothesis that the mechanism of action of this effect may involve shifts in calcium ions, the biologic action of relaxin on isolated rat uterine horns was directly correlated with measurements of 45Ca2+ efflux from and uptake into the tissues. Kinetic analysis demonstrated that the efflux of 45Ca2+ from rat uterine horns was significantly faster when tissue was incubated with 25 ng/ml relaxin as compared with control tissues incubated with no relaxin. In addition, at the end of the efflux experiments, control uteri contained 3.9% of the starting 45Ca2+, whereas the relaxin-treated uteri contained only 2.55%, indicating greater total Ca2+ efflux from the relaxin-treated horns (p less than 0.05). The effect of relaxin on 45Ca2+ uptake by uterine tissue was also studied. Analysis of uptake curves by linear regression demonstrated that relaxin treatment leads to less total uptake of 45Ca2+ in the uterine tissue, although the differences are not statistically significant. These experiments demonstrate that relaxin inhibition of rat uterine contractions in vitro is associated with a decrease in intracellular free Ca2+, caused, at least in part, by the promotion of Ca2+ efflux. These results represent the first step in defining the mechanism of action of this hormone.

The effect of in vivo progesterone administration on relaxin-inhibited rat uterine contractions

Progesterone pretreatment in vitro was previously shown to sensitize myometrium to the inhibiting effect of relaxin. The following experiments were performed to control for possible artifacts of the in vitro system and to place these studies on a more physiologic basis. Immature rats were treated with estrogen and either progesterone or vehicle only. Uterine horn segments were isolated and mounted in a muscle bath. After a baseline contraction pattern was established by means of electrical stimulation, porcine relaxin was added to the bath. At all dose levels of relaxin, greater inhibition of contraction amplitude occurred in uterine segments of progesterone-treated animals. Since both progesterone and relaxin are present in the circulation from the time of the missed menses in human pregnancy, this interaction suggests a physiologic synergism in the maintenance of early human pregnancy.

The effect of relaxin and progesterone on rat uterine contractions

The effect of porcine relaxin on electrically stimulated in vitro contractions of isolated uterine horn segments from estrogen-pretreated immature rats was studied. Relaxin decreased the amplitude of contractions. A mean of 8.3 ng/ml of relaxin produced a 90% decrease in contraction amplitude. There was a minimal effect of 1.0 microgram/ml of progesterone on contraction amplitude. In vitro pretreatment of the isolated uterine segment with this dose of progesterone for 15 minutes did not significantly affect the dose of relaxin needed to decrease the amplitude of contractions. In contrast, pretreatment with progesterone for 45 minutes significantly decreased the concentration of relaxin needed to decrease contraction amplitude. Only 4.7 ng/ml of relaxin was needed to produce a 90% decrease in amplitude after progesterone pretreatment for 45 minutes (p less than 0.005). Relaxin and progesterone synergize in decreasing the amplitude of uterine contractions in vitro. A similar effect may occur in vivo.