Ongoing effects of preterm birth on the dopaminergic and noradrenergic pathways in the frontal cortex and hippocampus of guinea pigs

Children born preterm have an increased likelihood of developing neurobehavioral disorders such as attention-deficit hyperactivity disorder (ADHD) and anxiety. These disorders have a sex bias, with males having a higher incidence of ADHD, whereas anxiety disorder tends to be more prevalent in females. Both disorders are underpinned by imbalances to key neurotransmitter systems, with dopamine and noradrenaline in particular having major roles in attention regulation and stress modulation. Preterm birth disturbances to neurodevelopment may affect this neurotransmission in a sexually dimorphic manner. Time-mated guinea pig dams were allocated to deliver by preterm induction of labor (gestational age 62 [GA62]) or spontaneously at term (GA69). The resultant offspring were randomized to endpoints as neonates (24 h after term-equivalence age) or juveniles (corrected postnatal day 40, childhood equivalence). Relative mRNA expressions of key dopamine and noradrenaline pathway genes were examined in the frontal cortex and hippocampus and quantified with real-time PCR. Myelin basic protein and neuronal nuclei immunostaining were performed to characterize the impact of preterm birth. Within the frontal cortex, there were persisting reductions in the expression of dopaminergic pathway components that occurred in preterm males only. Conversely, preterm-born females had increased expression of key noradrenergic receptors and a reduction of the noradrenergic transporter within the hippocampus. This study demonstrated that preterm birth results in major changes in dopaminergic and noradrenergic receptor, transporter, and synthesis enzyme gene expression in a sex- and region-based manner that may contribute to the sex differences in susceptibility to neurobehavioral disorders. These findings highlight the need for the development of sex-based treatments for improving these conditions.

Progesterone receptor isoform expression in response to in utero growth restriction in the fetal guinea pig brain

Intra-uterine growth restriction (IUGR) is a significant in utero complication that can have profound effects on brain development including reduced myelination and deficits that can continue into adulthood. Progesterone increases oligodendrocyte proliferation and myelin expression, an action that may depend on the expression of progesterone receptor (PR) isoforms A (PRA) and B (PRB). The objective of this study was to determine the effect of IUGR on PR isoform expression in the brain of male and female fetuses and whether effects were associated with a reduction in myelination. We used a guinea pig model that involves selective reduction in maternal perfusion to the placenta at midgestation (35 days, term 70 days). This resulted in a significant reduction in body weight with marked sparing of brain weight. PRA, PRB and myelin basic protein (MBP) expression were measured in the brains of male and female growth-restricted and control fetuses at late gestation. MBP, as a measure of myelination, was found to decrease in association with IUGR in the CA1 hippocampal region with no change observed in the cortical white matter. There was a marked increase in PRA, PRB and total PR expression in the IUGR fetal brain. Control female fetuses demonstrated significantly higher PRA:PRB ratios than males; however, this sex difference was abolished with IUGR. These data suggest the central nervous system effects of clinical use of progesterone augmentation therapy in late pregnancy should be carefully evaluated. The overall upregulation of PR isoforms in association with IUGR suggests increased progesterone action and a possible neuroprotective mechanism.

Molecular characterization of renin-angiotensin system components in human intrauterine tissues and fetal membranes from vaginal delivery and cesarean section

A prorenin-angiotensin system (RAS) could, via the (pro)renin receptor (ATP6AP2), have various effects in human intrauterine tissues, either directly by prorenin/ATP6AP2 cell signaling, or indirectly via angiotensin II and/or angiotensin 1-7. Here we describe RAS components in fetal membranes, decidua and placenta collected at elective cesarean section (non-laboring), after spontaneous delivery (after labor, n = 38), and in myometria (n = 16) from elective (non-laboring) or emergency cesarean (laboring) deliveries. Angiotensinogen (AGT), angiotensin-converting enzyme 1 and 2 (ACE; ACE2), angiotensin receptor 1 and 2 (AGTR1; AGTR2) and angiotensin 1-7 receptor (MAS1) mRNAs were measured by qRT-PCR and proteins were localized by immunohistochemistry. In myometrium, prorenin (REN), ATP6AP2, and downstream signaling proteins zinc finger and BTB domain-containing protein 16 (ZBTB16), transforming growth factor-β1 (TGFβ1) and prostaglandin-endoperoxide synthase 2 (PTGS2) mRNAs were also measured. RAS mRNAs, except AGTR1 and AGTR2, were abundant in decidua and lowest in amnion compared to the other tissues. ACE, AGT and PTGS2 mRNAs were higher in laboring than non-laboring myometrium, suggesting that the myometrial RAS is involved in labor. Angiotensinogen and prorenin staining in amnion, chorion and decidua was pervasive despite their mRNAs being low in amnion and chorion. In placenta, prorenin, angiotensinogen and AGTR2 were present in syncytiotrophoblasts, ACE was in fetal endothelium, while ACE2 distribution was diffuse. AGTR1 and AGTR2 mRNAs and proteins were abundant. No differences were evident in the staining patterns with labor. These results are consistent with the hypothesis that fetal vascular ACE might contribute angiotensin II to the fetus, whilst syncytial ACE2 might hypothetically have a role in converting angiotensin II to angiotensin 1-7 in maternal blood.

The effect of betamethasone treatment on neuroactive steroid synthesis in a foetal Guinea pig model of growth restriction

There are ongoing concerns that antenatal corticosteroids, which are administered to women at high risk of delivering preterm to reduce the incidence of respiratory distress syndrome, have adverse effects on foetal brain development and subsequent effects on behaviour and learning, when administered as repeated courses. The present study aimed to examine whether repeated betamethasone treatment alters the expression of the key-rate limiting enzyme, 5alpha-reductase, in the synthetic pathway of the potent neuroactive steroid allopregnanolone in the brain and placenta and whether this effect is potentiated in growth restricted foetuses. To investigate this, pregnant guinea pigs carrying either control (sham surgery) or growth-restricted foetuses were treated with vehicle or betamethasone (1 mg/kg/day) for 4 days prior to sacrifice (65d). Placental insufficiency was induced by the ablation of uterine artery branches supplying each placenta at mid gestation, resulting in foetal growth restriction characterised by 'brain sparing'. Real-time reverse transcriptase polymerase chain reaction was used to determine relative 5alpha-reductase type 1 and 2 mRNA expression in the placenta and brain. Immunohistochemistry was used to examine the glial fibrillary acidic protein (GFAP) expression in the subcortical white matter, CA1 and dentate regions of the hippocampus. 5alpha-reductase type 2 mRNA expression in the brain was markedly reduced by betamethasone treatment in male foetuses compared to vehicle-treated controls but not in female foetuses. In addition, 5alpha-reductase type 1 expression in the brain was increased by growth restriction and/or betamethasone treatment in female foetuses but expression in males foetuses did not increase. 5alpha-reductase type 2 expression in the placenta was markedly reduced by betamethasone treatment compared to vehicle-treated control. Intrauterine growth restriction and betamethasone treatment reduced GFAP expression in the CA1 region of the hippocampus in the brains of male but not female foetuses. These data indicate that betamethasone treatment suppresses placental expression and has sexually dimorphic effects on expression of neuroactive steroid synthetic enzymes in the brain. These actions may lead to adverse effects on the developing brain, particularly in male foetuses, such as the observed effects on GFAP expression.

Role of neurosteroids in regulating cell death and proliferation in the late gestation fetal brain

The neurosteroid allopregnanolone (AP) is a GABAergic agonist that suppresses central nervous system (CNS) activity in the adult brain, and by reducing excitotoxicity is considered to be neuroprotective. A role for neurosteroids in the developing brain, particularly in late gestation, is still debated. The aim of this study was to investigate effects on proliferation and cell death in the brain of late gestation fetal sheep after inhibition of AP synthesis using finasteride, a 5alpha-reductase type 2 (5alpha-R2) inhibitor. Catheters were implanted in fetal sheep at approximately 125 days of gestation. At 3-4 days postsurgery, fetuses received infusions of either finasteride (20 mg/kg/h; n=5), the AP analogue alfaxalone (5 mg/kg/h; n=5), or finasteride and alfaxalone together (n=5). Brains were obtained at 24 h after infusion to determine cell death (apoptotic or necrotic) and cell proliferation in the hippocampus and cerebellum, areas known to be susceptible to excitotoxic damage. Finasteride treatment significantly increased apoptosis (activated caspase-3 expression) in hippocampal CA3 and CA1, and cerebellar molecular and granular layers, an effect abolished by co-infusion of alfaxalone and finasteride. Double-label immunohistochemistry showed that both neurons and astrocytes were caspase-3 positive. Finasteride treatment also increased the number of dead (pyknotic) cells in the hippocampus and cerebellum (Purkinje cells), but not when finasteride+alfaxalone was infused. Cell proliferation (Ki-67-immunoreactivity) increased after finasteride treatment; double-labeling showed the majority of Ki-67-positive cells were astrocytes. Thus, steroids such as AP appear to influence the constitutive rate of apoptosis and proliferation in the hippocampus and cerebellum of the fetal brain, and suggest an important role for neurosteroids in the development of the brain.

Inhibition of neurosteroid synthesis increases asphyxia-induced brain injury in the late gestation fetal sheep

Allopregnanolone (AP) is a potent GABAergic agonist that suppresses CNS activity, seizure threshold, and excitotoxicity in the adult brain. AP is present in the fetal sheep brain and increases rapidly after asphyxial insult due to increased 5alpha-reductase type-2 (5alphaR-2) expression. The aim of this study was to use finasteride to suppress fetal neurosteroid synthesis, and then determine the effect on brain injury, particularly in the hippocampus, of asphyxia induced in utero by brief occlusion of the umbilical cord. Catheters and an inflatable umbilical cord cuff were implanted in fetal sheep at approximately 125 days gestation. Five days later the fetuses received either finasteride (20 mg/kg/h) or vehicle (40% hydroxypropyl-beta-cyclodextrin) for 2 h. The umbilical cord was occluded (UCO) for 5 min at 30 min after starting the infusion. The fetal brain was obtained 24 h later for examination of activated caspase-3 expression as an index of apoptosis, and to measure AP content. Finasteride treatment alone significantly reduced AP content and increased the number of caspase-3 positive cells in the hippocampus, cerebellum, and the subcallosal bundle, indicating that AP modulates the normal rate of apoptosis in the developing brain. UCO in vehicle and finasteride-treated fetuses produced a similar, marked decrease in O2 saturation (5.8+/-0.6%), but after finasteride treatment UCO caused a significantly greater increase in the number of caspase-3 positive cells in the hippocampal cornu ammonis 3 (CA3) (57.3+/-1.6%) compared with the vehicle-treated fetuses. Thus, 5alpha-reduced steroids such as AP may be protective in reducing cell death following acute fetal asphyxia. Perturbation of normal fetal neurosteroid levels in late gestation (e.g. due to preterm birth, or maternal synthetic steroid treatment to induce fetal lung maturation) could adversely affect brain development and increase its vulnerability to injury.

Changes in the expression of prostaglandin E and F synthases at induced and spontaneous labour onset in the sheep

The differential production of prostaglandin (PG) F(2 alpha) and PGE(2) within the uterine compartment may play a role in controlling myometrial contraction. We hypothesized that the enzymes downstream of PG endoperoxide synthase-2 (PGHS-2) determine the ratio of PGF(2 alpha) and PGE(2) in the utero-ovarian vein plasma and the time of normal and preterm labour onset. The aim of this study was to simultaneously determine the expression of PGF and PGE synthases (PGFS and PGES) in gestational tissues at spontaneous and induced-preterm labour in sheep. Myometrial, endometrial and placental tissue were obtained from ewes in dexamethasone-induced preterm labour, age-matched control ewes, and ewes in spontaneous term labour for analysis of mRNA expression by real-time PCR. PGFS mRNA expression was significantly increased following dexamethasone-induced and spontaneous labour onset in placentome (P<0.01) but was unchanged in the myometrium and endometrium. In contrast, PGES mRNA expression remained unchanged or decreased. PGHS-2 mRNA expression was increased in all tissues examined in both dexamethasone-induced and spontaneous labour (P<0.001). Plasma PGE(2) and PGF(2 alpha) concentrations rose in both dexamethasone-induced and spontaneous labour with the ratio of PGF(2 alpha):PGE(2) increased with labour onset (P<0.05). These results are consistent with the hypothesis that the increased expression, of PGFS is responsible for the increased PGF(2 alpha):PGE(2) ratio and this, together with increased PGHS-2 expression, accounts for myometrial activity at labour onset. The findings point to PGFS expression as a key factor in regulating the uterotonic process in the sheep.

Progesterone receptor localization and isoforms in myometrium, decidua, and fetal membranes from rhesus macaques: evidence for functional progesterone withdrawal at parturition

OBJECTIVE

It is not known whether withdrawal of progesterone (P) action is a prerequisite for parturition in women or in nonhuman primates because concentrations of circulating progesterone or progesterone receptors (PR) in myometrium and decidua do not decrease before delivery. To examine this potentially important regulatory mechanism, we determined PR isoforms, PR localization, and mRNA in myometrium, decidua, and fetal membranes from rhesus monkeys during pregnancy and in spontaneous labor at term.

METHODS

Gestational tissues were obtained midpregnancy (day 80-100), late pregnancy (day 130-145), and during spontaneous labor at term (day 161-167). Samples of rhesus monkey myometrium, decidua, chorion-decidua, and amnion were collected and analyzed for total nuclear and cytosolic PR by competitive binding assay. Progesterone receptor isoforms were identified and quantified by Western blot analysis, and PR mRNA was determined by a specific ribonuclease protection assay. Nuclear PR was localized by immunohistochemistry with monoclonal anti-PR (JZB39) after microwave stabilization.

RESULTS

Myometrium and decidua showed no change in total PR during pregnancy and labor. Nuclear PR was not detected in fetal membranes by binding assay but was localized in amnion epithelial and mesenchymal cells and in chorion laeve cytotrophoblasts by immunohistochemistry. Staining for PR was substantially less by serial antibody dilution in fetal membranes than in decidua. Message for PR was confirmed in all tissues analyzed. A significant (P <.05) shift in the ratio of PR isoforms (from PR-B dominance at midpregnancy to PR-A dominance in labor) was observed in myometrium but not in decidua. Both PR-A and PR-B isoforms and PR nuclear staining were nearly undetectable in amnion obtained during labor.

CONCLUSION

A shift to PR-A dominance in myometrium at term together with a loss of PR in fetal membranes provides evidence for a functional progesterone withdrawal mechanism, which may facilitate the initiation of parturition in primates.

Inhibition of prostaglandin synthesis and its effect on uterine activity during established premature labor in sheep

OBJECTIVE

Continuous infusion of the selective prostaglandin synthase type-2 inhibitor nimesulide, together with the oxytocin receptor antagonist atosiban, inhibits glucocorticoid induction of labor in sheep. We evaluated the effectiveness of this treatment commencing after the onset of premature labor when prostaglandin concentrations are already significantly elevated.

METHODS

Premature labor was induced in chronically cannulated fetuses by constant fetal dexamethasone infusion. After the onset of active labor in each ewe, defined as uterine electromyographic (EMG) activity twice basal levels, ewes received combined nimesulide and atosiban (20.0 and 4.12 mg/kg per day, respectively; n = 6) or vehicle (n-methyl-2-pyrrolidone and saline each 1 mL/hour; n = 4) infusions for 48 hours. Maternal and fetal plasma PGFM (13,14-dihydro-15-keto PGF2alpha, the stable metabolite of prostaglandin (PG) F2alpha) and PGE2 concentrations were measured before, during, and after infusions.

RESULTS

Four nimesulide- and atosiban-treated ewes successfully completed the 48-hour infusion period with no deliveries occurring during inhibitor treatment, or up to 6 hours after inhibitor treatment. Delivery was delayed in two other ewes, compared with control animals. Uterine EMG activity in nimesulide- and atosiban-treated ewes (n = 4) was significantly reduced during the 48-hour inhibitor treatment period. Maternal and fetal prostaglandin concentrations were significantly decreased in inhibitor-treated ewes during and after the infusions.

CONCLUSIONS

The combination of nimesulide and atosiban treatment for 48 hours successfully inhibited the progression of active premature labor to delivery. This study further supports the potential value of this treatment regime for the inhibition of premature labor.

Effect of finasteride on behavioural arousal and somatosensory evoked potentials in fetal sheep

This study examines the effect of inhibiting the synthesis of gamma-aminobutyric acid(A) (GABA(A)) agonist steroids on behavioural activity and somatosensory evoked potentials (SEP) in late gestation fetuses. Pregnane steroid production was suppressed by infusion of the 5alpha-reductase inhibitor, finasteride in chronically catheterised fetal sheep, 130-135 days gestation. Finasteride treatment (160 mg in 10 ml of vehicle over 2 h) significantly increased the incidence of fetal arousal during the period 4-10 h after commencing the infusion (P<0.05, n=6), whereas other behavioural parameters were not effected. In three of four animals, finasteride produced an increase in the amplitude of the N22 peak of the SEP during high voltage electrocortical activity. We conclude that suppression of pregnane steroid synthesis, by inhibition of the 5alpha-reductase enzyme, increases arousal activity in the fetus which is consistent with a reduction in GABA(A) receptor mediated inhibition.

Localization of p450scc and 5alpha-reductase type-2 in the cerebellum of fetal and newborn sheep

Prenatally, neuroactive steroids that modulate GABAergic activity may be synthesized de novo within the fetal brain. We have examined changes in immunoreactivity staining for the steroidogenic enzymes cholesterol P450 side-chain cleavage (P450scc), and 5alpha-reductase type-2 in the cerebellum of late gestation (130-145 days gestation) fetal sheep and newborn lambs (1-4 weeks of age). Both enzymes were predominantly localized in the Purkinje cell body and dendrites of the fetal and newborn cerebellum, with weaker immunoreactivity in a few cells of the inner granular layer. P450scc immunoreactivity was present in Purkinje neurons expressing either of the neuronal microtubule associated proteins MAP1b/5 or MAP2a/b, but was absent from GFAP and HNK-1 positive cells. Soma of Purkinje neurons were also immunopositive for 5alpha-reductase type-2 in the fetuses, but expression decreased to just detectable levels in the 1-2 and 2-4 week old lambs. Both MAP1b/5- and MAP2a/b-positive Purkinje neurons showed 5alpha-reductase type-2 expression in the fetus, whereas the residual 5alpha-reductase staining in the newborn lamb was present only in MAP2a/b-positive Purkinje neurons. Allopregnanolone in the cerebellum decreased from 21.8+/-1.9 ng/g wet weight in fetuses at 140-145 days gestation to 6.7+/-0.5 ng/g in 2-4 week old lambs (P<0. 05). Thus, synthesis of neuroactive steroids from cholesterol is possible in cerebellar neurons in late gestation and persists into neonatal life, 5alpha-reductase type-2 expression is greater in the fetus compared to the neonate, and allopregnanolone concentrations in the cerebellum decrease significantly after birth.

Inhibition of premature labor in sheep by a combined treatment of nimesulide, a prostaglandin synthase type 2 inhibitor, and atosiban, an oxytocin receptor antagonist

OBJECTIVE

The aim of this study was to compare the effects of the selective prostaglandin synthase type 2 inhibitor nimesulide, alone or in combination with the oxytocin receptor antagonist atosiban, on the progression of glucocorticoid-induced premature labor in sheep. Effects on circulating maternal and fetal prostaglandin concentrations and on fetal well-being were also examined.

STUDY DESIGN

Premature labor was induced in ewes with long-term catheterized fetuses by infusion of dexamethasone (1 mg/d) starting at 138 +/- 1 days' gestation. Ewes also received an infusion of either nimesulide and atosiban (20.0 and 4.12 mg/kg per day, respectively; n = 5), nimesulide alone (20.0 mg/kg per day; n = 5), or vehicle only (n = 9). Plasma 13,14-dihydro-15-keto-prostaglandin F(2)(alpha) and prostaglandin E(2) concentrations were measured before and during infusions in plasma samples obtained from the maternal and fetal carotid arteries and the utero-ovarian vein.

RESULTS

No fetuses from ewes treated with nimesulide and atosiban were delivered during treatment. These animals were killed electively 98.0 +/- 6.8 hours after the commencement of dexamethasone induction. This was significantly longer than the delivery times for those ewes treated with nimesulide alone (71.2 +/- 3.9 hours; n = 5) and for vehicle-treated ewes (51.4 +/- 1.7 hours; n = 9). Both maternal and fetal plasma 13, 14-dihydro-15-keto-prostaglandin F(2alpha) and prostaglandin E(2) concentrations in nimesulide and atosiban-treated ewes and in nimesulide-treated ewes decreased during treatment. In contrast, vehicle-treated ewes showed a significant increase in maternal and fetal plasma 13,14-dihydro-15-keto-prostaglandin F(2alpha) and prostaglandin E(2) concentrations during dexamethasone induction. Uterine electromyographic activity observed in nimesulide and atosiban-treated ewes was significantly suppressed with respect to activities in both vehicle- and nimesulide-treated ewes during the treatment period. All fetuses were alive at delivery or scheduled death.

CONCLUSIONS

These results indicate that the combination of an inhibitor of prostaglandin endoperoxidase H synthase type 2 with an oxytocin receptor antagonist is more effective in inhibition of preterm labor than is treatment with a prostaglandin endoperoxidase H synthase type 2 inhibitor alone. The clinical use of atosiban to prevent the oxytocin-stimulated increase in uterine activity associated with labor in combination with nimesulide may permit reduction of the dose of nimesulide used to a level that has minimal impact on fetal well-being.

Characterisation of GABA(A) receptors in fetal, neonatal and adult ovine brain: region and age related changes and the effects of allopregnanolone

Progesterone metabolites acting via GABA(A) receptors suppress central nervous system (CNS) activity. The aim of the present study was to examine binding characteristics of GABA(A) receptors in fetal, newborn and adult sheep brains using [(35)S]TBPS, and to determine the effects of allopregnanolone on this binding. Receptor affinity (K(D)) and density (B(MAX)) in the brainstem were not different in fetal, newborn (1-2 days old) and adult brains. In the hypothalamus K(D) and B(MAX) increased significantly in the fetus between 85 and 128 days gestation, and were then similar to postnatal and adult values. In the frontal cortex K(D) and B(MAX) increased progressively between 85 days and term ( approximately 147 days gestation), and were then not different from postnatal and adult values. The K(i) values for the GABA(A) receptor antagonist picrotoxin was similar at all ages. Allopregnanolone inhibited [(35)S]TBPS binding in the presence of 5 microM GABA, but enhanced binding in the absence of GABA. These results show that (i), functional GABA(A) receptors are present in the fetal brain from at least 85 days gestation; (ii), 3alpha-pregnane steroids modify receptor affinity in the late gestation fetal brain; and (iii) there are region-specific changes in GABA(A) receptor binding parameters. Steroid modulation of the GABA(A) receptor in the fetal brain is likely to influence fetal CNS activity in late gestation.

Effect of a neuroactive steroid infused into the cerebral ventricles of fetal sheep in utero using small infusion volumes

Placental progesterone metabolites may influence fetal behaviour during late gestation. We have investigated the effect of the neuroactive metabolite, pregnanolone, on the sleep/awake behaviour of fetal sheep. These studies can only be effectively performed in unanesthetized animals with chronically implanted leads and catheters. The relatively large internal volumes of these catheters raises problems for cerebroventriclear infusions. Therefore, we developed a device with negligible deadspace ( approximately 10 microl) consisting of a ventricular cannula attached to a small cap which allowed the instillation of microl volumes of neuroactive steroids into a cerebral ventricle of fetal sheep in utero. Two catheters attached to the cap allow it to be filled in a push-pull configuration. The smaller internal diameter of the ventricular cannular prevents the solution entering the ventricle until the outflow catheter is occluded and solution is forced through the probe. Using this device, the infusion of 5beta-pregnane-3alpha-ol-20-one (pregnanolone, 1 mg), in 35% hydroxypropyl-beta-cyclodextrin, resulted in a marked suppression of fetal behaviour parameters indicative of arousal, while vehicle alone did not affect these parameters. We conclude that neuroactive steroids can be infused into the cerebroventricular system of chronically catheterised fetal sheep in small volumes and that pregnanolone may act directly to influence fetal behaviour.

Efficacy of the selective prostaglandin synthase type 2 inhibitor nimesulide in blocking basal prostaglandin production and delaying glucocorticoid-induced premature labor in sheep

OBJECTIVE

The purpose of the study was to determine the effects of selective prostaglandin synthase type 2 inhibitors on basal prostaglandin concentrations in the fetal and maternal circulations and on the labor-associated increase in prostaglandin production in sheep.

STUDY DESIGN

The effects of maternal nimesulide (0.01, 0.1, and 1 mg/kg) and 6-methoxy-2-naphthylacetic acid (1, 5, and 10 mg/kg) administration were examined (n = 5) at 134 +/- 1 days' gestation. At 138 days' gestation premature labor was induced by fetal dexamethasone infusion (1 mg/d). Ewes were treated with either vehicle or nimesulide infusion (20 mg. d-1. kg-1, n = 5 per group).

RESULTS

Nimesulide and 6-methoxy-2-naphthylacetic acid decreased basal prostaglandin production in a concentration-dependent manner. Delivery of nimesulide-treated ewes was delayed by >/=17 hours with respect to that of control ewes (53.9 +/- 2.6 hours). In 2 nimesulide-treated ewes labor did not progress to delivery despite membrane rupture. The increase in prostaglandin concentrations usually seen during dexamethasone-induced labor was abolished in nimesulide-treated ewes and also in their fetuses.

CONCLUSIONS

Highly selective inhibitors of prostaglandin endoperoxidase H synthase 2 may be required to spare fetal prostaglandin production and limit potential side effects during the suppression of preterm labor.

Effects of pregnanolone on behavioural parameters and the responses to GABA(A) receptor antagonists in the late gestation fetal sheep

Placental progesterone metabolites may suppress fetal behaviour by interacting with GABA(A) receptors. In an initial study, the effect of 5beta-pregnan-3alpha-ol-20-one (pregnanolone) given as a bolus (2.5 and 5.0 mg) or infused at a rate of 25 mg/h was investigated in unanaesthetized, catheterized fetal sheep, 127-135 days gestation. The incidence of fetal breathing movements (FBM) and behavioural arousal activity, defined as nuchal muscle electromyographic (EMG) activity during low voltage electrocortical (LV ECoG) activity were suppressed by pregnanolone administered as a bolus, while the pregnanolone infusion produced a significant decrease in arousal and EOG activity, and an increase in the presence of HV ECoG. The effect of pregnanolone on fetal behaviour and arousal induced by the GABA(A) antagonist picrotoxin was also investigated. Picrotoxin was given as a bolus (approximately 300 microg/kg) and pregnanolone was subsequently administered as a bolus (5.0 mg), and behavioural parameters were recorded and analysed. The incidence of arousal and FBM were 1.1 +/- 1.6 min/10 min and 2.5 +/- 2.3 min/10 min, respectively, before picrotoxin treatment and increased during the 10-20 and 20-30 min epochs after picrotoxin treatment (arousal: 5.0 +/- 2.2 and 6.5 +/- 3.6 min/10 min, respectively, n = 6, P < 0.05; FBM: 7.3 +/- 3.2 and 9.3 +/- 1.2 min/10 min, respectively, n = 6, P < 0.05). The picrotoxin-induced increases in arousal and FBM were significantly suppressed (n = 6, P < 0.05) by pregnanolone treatment to 1.6 +/- 1.5 min/10 min and 4.6 +/- 2.3 min/10 min, respectively. We conclude that; (i) the GABA(A) active steroid pregnanolone suppresses basal and picrotoxin-induced fetal arousal and FBM; and (ii) steroid sensitive GABA(A) receptors may regulate fetal behaviour and breathing.

Suppression of arousal by progesterone in fetal sheep

The high rate of progesterone synthesis by the placenta in late gestation exposes the ovine fetus to high concentrations of progesterone and its metabolites that may affect activity of the fetal brain. The aim of this study was to determine the effect of inhibiting maternal progesterone synthesis on sleep-wake activity in fetal sheep. Fetal and maternal vascular catheters, a fetal tracheal catheter, and electrodes for recording fetal electrocortical (ECoG), electro-ocular (EOG) and nuchal muscle electromyographic (EMG) activity were implanted. At 128-131 days gestation, progesterone production was inhibited by an injection of trilostane (50 mg), a 3beta-hydroxysteroid dehydrogenase inhibitor. Vehicle solution or progesterone (3 mg h(-1)) was then infused into the ewe between 6 and 12 h after the trilostane treatment. Maternal progesterone concentrations were significantly reduced from 1-24 h after trilostane treatment (P < 0.05) when followed by vehicle infusion. Fetal breathing movements (FBM), EOG, nuchal muscle EMG, and behavioural arousal increased 12 h after trilostane treatment (P < 0.05). In contrast, there was no change in fetal arousal, EOG, EMG or FBM activities when progesterone was infused after the trilostane treatment. These findings show that progesterone can influence fetal behaviour, and indicates that normal progesterone production tonically suppresses arousal, or wakefulness in the fetus.

Effect of pregnane steroids on electrocortical activity and somatosensory evoked potentials in fetal sheep

The effect of infusing the neuroactive steroids pregnanolone and iso-pregnanolone on somatosensory evoked potentials (SEP) and electrocortical (ECoG) activity was studied in unanaesthetised fetal sheep, 130-135 days gestation. Intravenous infusion of pregnanolone (6 mg/kg per h) significantly increased the proportion of high voltage ECoG (56.1+/-4.8% vs. control 43.5+/-3.2%, P < 0.05), and decreased low voltage ECoG (43.9+/-4.8% vs. control 56.6+/-3.2%, P < 0.05). Pregnanolone treatment decreased the amplitude of the N25 peak of the SEP (89.9+/-2.8% of control, P < 0.05) evoked following stimulation of the skin of the upper lip. In contrast, iso-pregnanolone treatment had no effect on ECoG activities, or on the amplitude and latency of peaks in the SEP. We conclude that 3alpha-hydroxy pregnane steroids are active at GABA(A) receptors in fetal sheep and can modulate sleep/wake activity before birth.

Prostaglandin endoperoxide H synthase-1 and -2 mRNA levels and enzyme activity in human decidua at term labor

OBJECTIVE

To determine the labor-related changes of prostaglandin endoperoxide H synthase (PGHS) activity and PGHS-1 and -2 abundance in term decidua and to assess the contribution of the PGHS isoforms to the total PGHS activity present in the tissue.

METHODS

Decidua was collected after elective cesarean delivery (CD) or spontaneous labor (SL) at term. Prostaglandin endoperoxide H synthase activity was determined in microsomal fractions, and PGHS-1 and -2 mRNA levels were measured by ribonuclease protection assays. Prostaglandin endoperoxide H synthase-1 and -2 mRNAs were localized in tissue sections by in situ hybridization.

RESULTS

Prostaglandin endoperoxide H synthase specific activity in decidua microsomes at CD was 111 +/- 3 pg prostaglandin-E2/minute/microgram protein (mean +/- standard error, N = 10 patients), not different from enzyme activity measured after SL (110 +/- 27 N = 10 patients, P = .97, Wilcoxon's rank sum test). Prostaglandin endoperoxide H synthase-1 mRNA abundance in CD tissues was 0.283 +/- 0.047 relative densitometric units (mean +/- standard error, n = 26 patients), which did not change with labor (SL: 0.329 +/- 0.073, n = 20 patients, P = .68). Prostaglandin endoperoxide H synthase-2 mRNA abundance was also unaffected by labor (CD: 0.933 +/- 0.255, n = 27 patients; SL: 0.714 +/- 0.179, n = 23 patients, mean +/- standard error, P = .66). Prostaglandin endoperoxide H synthase specific activity was positively and significantly (P < .05) correlated with both PGHS-1 and -2 mRNA levels. In situ hybridization showed the pervasive presence of both PGHS mRNAs in decidua cells with no detectable changes associated with labor.

CONCLUSION

Both isoforms of PGHS are present in term decidua and contribute to enzyme activity and prostaglandin production. Mechanisms regulating decidual prostanoid biosynthesis at labor do not involve changing the levels of expression of the two PGHS isoforms.

Effect of alteration of maternal plasma progesterone concentrations on fetal behavioural state during late gestation

Placental progesterone synthesis exposes the fetus to high levels of progesterone and progesterone metabolites during late gestation which may influence fetal behaviour. To determine the role of maternal progesterone synthesis in the control of fetal arousal state and fetal breathing movements (FBM), the effect of raising and lowering maternal progesterone concentrations was examined in chronically catheterised fetal sheep. Fetal and maternal vascular catheters, fetal tracheal and amniotic fluid catheters as well as electrodes for recording fetal electrocortical (ECoG), electro-ocular (EOG) and nuchal muscle electromyographic (EMG) activity were implanted between 118 and 122 days gestational age (GA). Progesterone, 100 mg, administered twice daily i.m. for 3 days (130-133 days GA) resulted in a marked elevation in maternal plasma progesterone concentrations (370 +/- 121%, n = 5, P < 0.05), but had no effect on fetal plasma concentrations. Fetal EOG episodes and the duration of fetal behavioural arousal were significantly suppressed throughout the progesterone treatment period (74.4-81.1% and 58-65% respectively, P < 0.05, n = 5). Four ewes received Trilostane (25 mg i.v.), a 3 beta-hydroxysteroid dehydrogenase inhibitor, between 136 and 140 days GA. Maternal and fetal progesterone concentrations were significantly lowered by 60 min after treatment (19.8 +/- 8.0% and 39.5 +/- 24.3% respectively, P < 0.05). The incidence of fetal EOG activity increased from a pretreatment level of 26.8 +/- 1.5 min/h to 30.3 +/- 2.8 min/h at 1-6 h and to 35.0 +/- 1.7 min/h (P < 0.05) during the 7-12 h after Trilostane treatment. The duration of FBM episodes was significantly higher at 1-6 h and 7-12 h after Trilostane treatment (19.5 +/- 3.0 and 23.6 +/- 5.5 min/h respectively, P < 0.05) compared with pretreatment levels (11.2 +/- 1.2 min/h). We conclude that increasing maternal progesterone levels suppresses fetal EOG activity and behavioural arousal, whereas reducing maternal progesterone synthesis leads to an elevation of EOG activity and FBM.

Regulation of prostaglandin endoperoxide H2 synthase in term human gestational tissues

Increased production of prostaglandins by the gestational tissues is pivotal for the initiation and maintenance of human labour. A major source of prostaglandins in the pregnant human uterus is the amnion membrane, which synthesizes increased amounts of prostaglandin E2 (PGE2) at parturition. We have found that the activity of prostaglandin endoperoxide H2 synthase (PGHS), the enzyme catalyzing the committing step of prostanoid biosynthesis, increases significantly in the amnion at term and preterm labour, and also prior to the onset of clinical labour at term. Furthermore, the abundance of the mRNA encoding the inducible PGHS-2 isoenzyme was higher in the amnion after spontaneous delivery that before labour. The level of the constitutive PGHS-1 mRNA remained unchanged. In addition, we found a significant positive correlation between PGHS activity and the level of PGHS-2 mRNA, but not of PGHS-1 mRNA, in the individual tissue samples, also indicating that PGHS-2 was selectively induced in the amnion membrane at labour. The regulation of PGHS expression by agonists was studied using primary cultures of amnion cells. Glucocorticoid treatment enhanced the activity of PGHS and the level of PGHS-2 mRNA in the cultured cells, without affecting PGHS-1 mRNA abundance. The stimulation was glucocorticoid specific and was blocked by the glucocorticoid receptor antagonist RU486, suggesting that it was mediated by the glucocorticoid receptor. Inhibition of protein synthesis did not block the accumulation of PGHS-2 mRNA showing that the steroid acted directly, without inducing an intervening protein. Protein kinase C activator and protein phosphatase inhibitor compounds and epidermal growth factor also promoted PGHS-2 mRNA expression, demonstrating the involvement of protein kinase dependent mechanisms in PGHS-2 regulation. However, the role of these effectors in the in vivo control of PGHS-2 expression remains to be determined.

Glucocorticoids stimulate the expression of prostaglandin endoperoxide H synthase-2 in amnion cells

Corticosteroids increase the production of prostaglandin E2 (PGE2) and the activity of prostaglandin endoperoxide H synthase (PGHS) in cultured amnion cells, although they inhibit prostanoid biosynthesis in numerous other cell types. This suggests that glucocorticoids control the level of PGHS in amnion cells by a hitherto unexplored, positive regulatory mechanism. We have tested the possibility that corticosteroids act by stimulating the expression of messenger RNAs (mRNAs) encoding one or both isoforms of PGHS. Ribonuclease protection assays were used to determine the levels of PGHS-1 and -2 mRNAs and, for reference, gamma-actin mRNA levels in confluent primary cultures of human amnion cells. In untreated cultures, PGHS-1 and -2 mRNA levels were low, often not reaching the level of detection. Dexamethasone (DEX) treatment for 4 h resulted in a measurable level of PGHS-2 mRNA, which increased further 10-fold and 20-fold after incubation with the glucocorticoid for 8 h and 16 h, respectively. The stimulation was dependent on DEX concentration, and was concomitant with an increase in the capacity of the cells to metabolize arachidonic acid to PGE2. PGHS-1 mRNA levels remained low in DEX-treated cells, while the gamma-actin message level showed no change. Estradiol and progesterone had no influence on PGHS-2 mRNA expression, but cortisol increased the PGHS-2 mRNA abundance. The glucocorticoid antagonist RU486 blocked the effect of DEX. Conditioned media of DEX-treated cells did not contain steroid-induced factor(s) stimulating PGE2 production. Inhibition of protein synthesis by cycloheximide potentiated the effect of DEX, and raised the abundance of PGHS-1, PGHS-2, and gamma-actin mRNAs in untreated cells. DEX did not affect the stability of the PGHS-2 mRNA. These results show that glucocorticoids promote PGE2 synthesis by amnion cells by stimulating the expression of PGHS-2 mRNA in a receptor-dependent, selective, and immediate fashion.

Prostaglandin endoperoxide-H synthase-1 and -2 messenger ribonucleic acid levels in human amnion with spontaneous labor onset

Increased prostaglandin (PG) production within the uterine compartment has a pivotal role in the processes leading to labor onset in women. Two PG endoperoxide-H synthase (PGHS) isoenzymes have been identified in a number of cell types. PGHS-1 is constitutively expressed in most cases, whereas PGHS-2 expression is rapidly induced by several agonists. The aims of this study were to determine the levels of PGHS-1 and PGHS-2 expression before and after spontaneous labor (SL) onset in the amnion and to assess the contribution of PGHS-1 and PGHS-2 to enzyme activity. We established and validated ribonuclease protection assays to quantify PGHS-1 and PGHS-2 messenger ribonucleic acid (mRNA) levels in the amnion. PGHS enzyme activity was measured with an established assay. The antisense RNA probes used in the protection assays were generated using human PGHS-1 and PGHS-2 complementary DNAs. These probes specifically detected the 2.8-kilobase mRNA of PGHS-1 and the 4.8-kilobase mRNA of PGHS-2 in amnion RNA samples on Northern blots. We measured mRNA levels in amnion from patients after SL at term and from patients not in labor undergoing elective cesarean section (CS) at term. PGHS-2 mRNA levels were markedly higher after SL compared to levels in CS amnion [5.18 +/- 1.08 (n = 16) and 2.27 +/- 0.50 (n = 15), densitometric units, respectively; P < 0.02], whereas there was no difference in PGHS-1 mRNA levels after labor compared with CS samples. PGHS-2 mRNA levels were also positively correlated with PGHS enzyme activity in 4 separate assays with a total of 25 patients (r = 0.65-0.88; P < 0.05). There was no correlation between PGHS-1 mRNA levels and enzyme activity. We conclude that PGHS-2 mRNA is present in human amnion; its levels are elevated after SL onset, and they are correlated with enzyme activity. The stimulation of PGHS activity at labor onset probably involves increased expression of PGHS-2. The expression of PGHS-1 does not change in association with labor in human amnion.

Prostaglandin endoperoxide-H synthase (PGHS) activity and immunoreactive PGHS-1 and PGHS-2 levels in human amnion throughout gestation, at term, and during labor

Prostaglandins (PGs) are of primary importance in the initiation and maintenance of labor in women. A major intrauterine source of prostaglandins is the amnion, which synthesizes increased amounts of PGE2 at term labor. Because PG endoperoxide-H synthase (PGHS) catalyzes the rate-limiting step of PG synthesis from arachidonic acid, we investigated the changes in amniotic PGHS specific activity during gestation and at term and preterm labor. Also, we determined the level of immunoreactive PGHS protein in the amnion to evaluate the mechanisms by which PGHS activity may be regulated. PGHS specific activity, measured at the amount of PGE2 produced by amnion microsomes under optimal conditions, was 18.2 +/- 3.7 pg PGE2/micrograms protein.min (mean +/- SE; n = 19) at term (37-42 weeks gestation) before the spontaneous onset of labor. PGHS specific activity was significantly higher after spontaneous term labor (38.9 +/- 6.0 pg PGE2/micrograms protein.min; n = 19; P < 0.05). Amnion samples from preterm (< 36 weeks gestation) nonlaboring patients contained low levels of PGHS specific activity (5.9 +/- 1.8 pg PGE2/micrograms protein.min; n = 9), which increased significantly with spontaneous preterm labor (28.3 +/- 6.8 pg PGE2/micrograms protein.min; n = 10; P < 0.05). Longitudinal analysis of the data showed that PGHS specific activity was low in the first and second trimesters of gestation, but increased dramatically before labor onset at term. We detected PGHS protein in all microsomal samples, with an antiovine PGHS antibody recognizing both PGHS-1 and -2 isoforms of the enzyme. However, there was no correlation between PGHS specific activity and the amount of immunoreactive PGHS protein. Using an antibody specific for PGHS-2, we detected immunoreactive protein in only 9 of the 25 tissues examined and found no correlation between PGHS specific activity and the amount of PGHS-2 protein. These results suggest that 1) PGHS specific activity in the amnion increases sharply before the onset of labor at term; 2) further increases in specific activity occur during term and preterm labor; and 3) the specific activity of PGHS in the amnion is not related directly to the amount of immunoreactive enzyme protein.

Regulation of prostaglandin endoperoxide H synthase by glucocorticoids and activators of protein kinase C in the human amnion

Since glucocorticoids decrease and protein kinase C (PKC) activators increase amniotic PGE2 production, the possibility that they regulate the activity of prostaglandin endoperoxide H synthase (PGHS), the rate-limiting enzyme of prostaglandin synthesis from arachidonate, was investigated. Glucocorticoids inhibited the production of PGE2 from exogenous arachidonate specifically and in a concentration dependent fashion. Furthermore, cortisol decreased PGHS activity and the amount of PGHS protein in amnion microsomes, and reduced the rate of recovery of PGHS after acetylsalicylic acid (ASA) pretreatment. Actinomycin D blocked the inhibition of PGHS recovery by cortisol, but did not suppress the spontaneous recovery of the enzyme, indicating that the glucocorticoid induced a post-transcriptional inhibitor of PGHS synthesis. PKC-activating phorbol esters, such as 12-tetradecanoyl phorbol 13-acetate (TPA) increased the synthesis of PGE2 from exogenous arachidonate, also in a specific and concentration dependent manner. PGHS recovery after ASA treatment was enhanced by TPA. PGHS activity and protein concentrations were increased by phorbol ester treatment; however, this was apparent only in tissues in which the concentrations of PGHS were initially low. These results show that the synthesis of PGHS is positively and negatively regulated in the human amnion by PKC and glucocorticoids, respectively, and suggest that effectors using these pathways may regulate the enzyme in vivo.

Plasma oxytocin and nocturnal uterine activity: maternal but not fetal concentrations increase progressively during late pregnancy and delivery in rhesus monkeys

OBJECTIVE

The purpose of the study was to determine whether rising maternal or fetal plasma oxytocin concentrations could be responsible for the increasing levels of nocturnal uterine activity on the nights preceding delivery.

STUDY DESIGN

Chronically catheterized pregnant rhesus monkeys were exposed to a 16-hour light, 8-hour dark photoperiod (dark 11 PM to 7 AM). Uterine activity and maternal arterial plasma oxytocin concentrations were measured concurrently at weekly intervals in late gestation, on the night preceding term delivery (158 to 167 days, n = 4), and during delivery (149 to 170 days, n = 6). Fetal carotid arterial plasma oxytocin levels were measured during episodes of nocturnal uterine activity in six animals. The effect of oxytocin infusions into the fetus (30 to 480 ng/kg/hr) on uterine activity and on maternal and fetal plasma oxytocin levels was also determined (n = 3).

RESULTS

Maximal nocturnal oxytocin concentrations in the maternal plasma rose progressively during late gestation from 9.9 +/- 3.5 pg/ml at 130 to 139 days to 28.7 +/- 9.8 pg/ml on the night preceding term delivery (p < 0.005); a significant increase in nocturnal uterine activity accompanied this rise (p < 0.001). Maternal oxytocin concentrations were elevated during labor and increased further at delivery (62.5 +/- 5.5 pg/ml, p < 0.05). There was no increase in fetal plasma oxytocin during nocturnal uterine activity (3.1 +/- 0.2 pg/ml) or during labor. Fetal oxytocin infusions raised fetal plasma oxytocin concentrations sixtyfold but had no effect on maternal plasma oxytocin concentrations or on uterine activity.

CONCLUSIONS

Elevated maternal plasma oxytocin concentrations are responsible, at least in part, for the increasing magnitude of nocturnal uterine activity episodes as term approaches and for the elevated uterine activity before delivery at night. Fetal plasma oxytocin does not contribute to nocturnal uterine activity or to maternal plasma oxytocin concentrations.

Estrogen action in the reproductive tract of rhesus monkeys during antiprogestin treatment

We previously reported that RU486 can reverse progesterone (P)-induced suppression of the estrogen receptor (ER) in the uterus of pregnant rhesus monkeys, but we did not determine whether estrogen (E) could act through its receptor in the presence of P and RU486. To pursue this question, we treated spayed rhesus monkeys with various hormonal regimens and evaluated the effects of E in the oviduct and endometrium, with and without RU486 treatment, on ER and progestin receptor (PR) levels, morphology, apoptosis, and degree of proliferation. The latter was assessed immunocytochemically with a monoclonal antibody (Ki-67) against a nuclear antigen present only in proliferating cells. Animals were treated for 2 weeks with 17 beta-estradiol (E2) and then for 2 weeks with E2 plus P to produce a regressed oviduct and a secretory endometrium. The animals were then treated for 2 more weeks with four different treatments, as follows: I) E2, P, and vehicle; II) E2 and vehicle; III) E2, P, and RU486; and IV) E2 and RU486 (n = 4 each). In group I, menstruation did not occur, and the endometrium exhibited stromal cell enlargement, extensive development of the spiral arteries, few Ki-67-positive cells, and low levels of ER and PR. Oviducts in group I remained regressed, Ki-67-positive epithelial cells were few, and levels of ER and PR were low. In contrast, in groups II, III, and IV, the oviducts had responded to E2 and were fully ciliated and secretory, with elevated levels of ER and nuclear PR. All animals in these three groups menstruated and then regenerated their endometrium. The regenerated endometria expressed elevations in ER, nuclear PR, and epithelial Ki-67 index. However, the endometria of RU486-treated monkeys in groups III and IV had significantly more epithelial cell death by apoptosis, increased stromal cell compaction, and fewer Ki-67-positive stromal cells than in the E2 controls (group II). In group IV, RU486 caused a significant decrease in endometrial weight. Thus, RU486 blocked P action and allowed E2 to act in a normal fashion in the oviduct and endometrium on several end points, but it also had antiproliferative effects that opposed E2 action, especially in the endometrium.

Steroid hormone receptors in the adrenal glands of fetal and adult rhesus monkeys

Sex steroid hormone receptors have been identified in the adrenal glands of rodents and may have a role in adrenal function. The highly estrogenic environment during pregnancy has been proposed to influence steroidogenesis by the fetal zone of the primate fetal adrenal gland. In order to determine whether these effects involve receptor-mediated mechanisms, we have examined the concentration and distribution of estrogen receptor (ER), androgen receptor, and progesterone receptor (PR) in the adrenal glands of fetal, immature, and adult rhesus monkeys. Monoclonal antibodies were used for immunocytochemistry (ICC), and in a gradient shift assay, for determination of receptor distribution and concentrations, respectively. There was no difference between the concentrations of ER in the adrenal glands from male and female adult animals (12.4 +/- 2.2, n = 3 and 13.2 +/- 2.0 fmol/mg DNA, n = 7; respectively); however, the concentration of ER in the fetal adrenal glands was markedly lower than in the adults (combined adult 12.7 +/- 1.6, n = 10, and fetal 0.9 +/- 0.4 fmol/mg DNA, n = 7; P less than 0.01). The concentration of ER in the adrenal glands of immature animals was also lower compared to adult animals (6.1 +/- 1.6, n = 6, P less than 0.05). In the adult, ICC revealed that staining for ER was restricted to the cell nucleus and was most dense in the zone fasciculata, with lesser staining in the zona glomerulosa and zona reticularis, and with no detectable staining in the medulla. ER staining was virtually absent in the fetal zone which comprises the major portion of the fetal gland; however, some staining was observed in the narrow definitive zone. The distribution of androgen receptor was similar to that of ER, whereas there was no detectable staining for PR in the adrenals of either adult or fetal animals. We conclude: 1) that the lower concentration of ER in fetal adrenal glands is due to the absence of ER in the fetal zone; 2) the lack of ER and PR in the fetal zone suggests that estrogens and progestins do not influence the growth or function of the fetal zone by receptor-mediated mechanisms; 3) estrogens and androgens may influence the function of the adult adrenal cortex.

Comparison of plasma oxytocin and catecholamine concentrations with uterine activity in pregnant rhesus monkeys

Pregnant rhesus monkeys exhibit diurnal changes in uterine activity (UA), with episodes of increased UA during the early hours of darkness. The estrogenic environment during late pregnancy serves a permissive role in the maintenance of nocturnal UA episodes and may involve myometrial interactions with oxytocin (OT) and/or alpha-adrenergic stimuli. In the present study we have used chronically catheterized pregnant rhesus monkeys to measure diurnal changes in maternal plasma OT, epinephrine, norepinephrine, and dopamine. We also determined the effects of infusing an OT antagonist (ORF 22164) and the alpha-adrenergic antagonist phentolamine on nocturnal UA episodes. Animals were exposed to a 16-h light, 8-h dark photo-period, with the hours of darkness between 2300-0700 h. Maternal plasma samples were collected at 3-h intervals for 36 h and analyzed by RIA for OT and by high performance liquid chromatography for catecholamines. Plasma OT was correlated with UA in animals that displayed nocturnal UA episodes (r = 0.76; P less than 0.01). Maximal OT concentrations occurred at 2400 h in these animals; plasma OT was higher during the hours of darkness compared to levels during the light phase (10.4 +/- 1.9 and 3.0 +/- 0.3 pmol/L, respectively; n = 4). Some animals did not display nocturnal episodes of increased UA and showed no increase in OT concentrations during the hours of darkness. Maternal plasma catecholamine concentrations were not correlated with nocturnal UA and were maximal during the light phase. Nocturnal UA was abolished within 30 min of infusion of the OT antagonist, but phentolamine infusions had no effect on nocturnal UA. We conclude that 1) changes in maternal plasma catecholamine concentrations are not involved in the generation of nocturnal UA; 2) the presence of episodes of increased UA at night results from increased maternal plasma OT concentrations; and 3) the absence of nocturnal UA in some animals can be explained by a reduced level of OT secretion.

Regulation of oxytocin secretion by the ovine corpus luteum: effect of activators of protein kinase C

The effect of protein kinase C activation and dibutyryl cyclic AMP on oxytocin secretion by ovine luteal tissue slices was investigated. Several putative regulators of luteal oxytocin secretion were also examined. Oxytocin was secreted by luteal tissue slices at a basal rate of 234.4 +/- 32.8 pmol/g per h (n = 24) during 60-min incubations. Activators of protein kinase C: phorbol 12, 13-dibutyrate (n = 8), phorbol 12-myristate, 13-acetate (n = 4) and 1,2-didecanoylglycerol (n = 5), caused a dose-dependent stimulation of oxytocin secretion in the presence of a calcium ionophore (A23187; 0.2 mumol/l). Phospholipase C (PLC; 50-250 units/l) also caused a dose-dependent stimulation of oxytocin secretion by luteal slices. Phospholipase C-stimulated oxytocin secretion was potentiated by the addition of an inhibitor of diacylglycerol kinase (R59 022; n = 4). These data suggest that the activation of protein kinase C has a role in the stimulation of luteal oxytocin secretion. The results are also consistent with the involvement of protein kinase C in PLC-stimulated oxytocin secretion. The cyclic AMP second messenger system does not appear to be involved in the control of oxytocin secretion by the corpus luteum.

Control of oxytocin secretion by ovine corpora lutea: effects of arachidonic acid, phospholipases, and prostaglandins

The involvement of arachidonic acid and arachidonic acid metabolites in the control of oxytocin secretion by ovine corpus luteum was investigated, using slices of luteal tissue incubated in vitro. Oxytocin was secreted at steady rates by luteal slices, during 60-min incubations (315.0 +/- 45.3 pg/mg.h). The secretion of oxytocin was stimulated by arachidonic acid, phospholipase A2 (PLA2), and phospholipase C (PLC) in a dose-dependent manner. The highest doses of arachidonic acid, PLA2, and PLC used stimulated oxytocin secretion by 145.8 +/- 23.0% (P less than 0.01; n = 6), 331.5 +/- 42.4% (P less than 0.02; n = 4), and 955.5 +/- 278.6% (P less than 0.01; n = 4), respectively. Oxytocin secretion by luteal slices was not affected by either prostaglandin F2 alpha (PGF2 alpha) or PGE2 over a concentration range from 3-3000 nM. Furthermore, inhibitors of the cyclo-oxygenase pathway of arachidonic acid metabolism did not consistently affect arachidonic acid and PLA2-stimulated oxytocin secretion. Nordihydroguaiaretic acid, which inhibits 5-lipoxygenase, however, totally abolished arachidonic acid- and reduced PLA2-stimulated oxytocin secretion. The presence of CoCl2 in the incubation medium also significantly reduced basal and PLA2- and PLC-stimulated oxytocin secretion [P less than 0.05 (n = 5), P less than 0.05 (n = 5), and P less than 0.01 (n = 6), respectively]. We have shown that oxytocin secretion from slices of ovine corpus luteum incubated in vitro is stimulated by exogenous and endogenously released arachidonic acid. The data show that PGF2 alpha and PGE2 do not have a role in luteal oxytocin secretion in vitro and PG formation does not appear to be involved in the stimulation of oxytocin secretion elicited by arachidonic acid or PLA2. Arachidonic acid may have its effect via the lipoxygenase pathway.

Secretion of oxytocin and progesterone by ovine corpora lutea in vitro

The mechanisms involved in the control of oxytocin and progesterone secretion by the ovine corpus luteum have been investigated in vitro using luteal slice incubations. Oxytocin and progesterone were secreted at constant rates from luteal slices for 2 h of incubation (366 +/- 60 pg X mg X h and 18.9 +/- 0.18 ng X mg X h, respectively). Secretion of progesterone, but not of oxytocin, was significantly (p less than 0.02) stimulated in the presence of ovine luteinizing hormone. Incubation of luteal slices in medium containing 100 mM potassium, however, resulted in increased secretion of oxytocin and, to a lesser extent, of progesterone (294 +/- 59% and 142 +/- 15%, respectively, p less than 0.05). Basal oxytocin secretion was reduced during incubation in calcium-free medium, compared to secretion in the presence of calcium (70 +/- 15 and 175 +/- 25 pg X mg X 20 min, respectively, p less than 0.01), whereas progesterone secretion was not altered in the absence of calcium. Secretion of both hormones by luteal slices was stimulated by the addition of the calcium ionophore A23187 (p less than 0.05). Addition of prostaglandin F2 alpha (2.8 microM) had no effect on secretion of either oxytocin or progesterone. We have demonstrated that oxytocin and progesterone can be stimulated, independently, from corpus luteum slices incubated in vitro. The pattern of release is consistent with the proposal that oxytocin, but not progesterone, is associated with and actively released from luteal secretory granules. Our results also indicated that prostaglandin F2 alpha does not directly stimulate release of oxytocin or progesterone from luteal cells in vitro.