Monocyte-derived dendritic cells display a highly activated phenotype and altered function in patients with familial Mediterranean fever.

Dendritic cells (DCs) are sentinels of the immune system that bridge innate and adaptive immunity. By capturing antigens in peripheral tissue, processing and presenting them with concurrent expression of co-stimulatory molecules and cytokine secretion they control and modulate immune reactions. Through pattern recognition receptors, DCs sense molecules that are associated with infection or tissue damage, frequently resulting in the formation of inflammasomes upon intracellular stimulation. The inherited autoinflammatory familial Mediterranean fever (FMF) is associated with deregulated activity of the pyrin inflammasome leading to acute inflammatory episodes. However, differentiation and function of DCs in this disease are as yet unclear. Therefore, we first determined DC subpopulation frequency in peripheral blood of a cohort of FMF patients. Joint evaluation without classification according to specific patient characteristics, such as mutational status, did not disclose significant differences compared to healthy controls. For the further examination of phenotype and function, we used immature and mature monocyte-derived DCs (imMo-DCs, mMo-DCs) that were generated in vitro from FMF patients. Immunophenotypical analysis of imMo-DCs revealed a significantly elevated expression of CD83, CD86 and human leukocyte antigen D-related (HLA-DR) as well as a significant down-regulation of CD206, CD209 and glycoprotein NMB (GPNMB) in our FMF patient group. Furthermore, FMF imMo-DCs presented a significantly higher capacity to migrate and to stimulate the proliferation of unmatched allogeneic T cells. Finally, the transition towards a more mature, and therefore activated, phenotype was additionally reinforced by the fact that peripheral blood DC populations in FMF patients exhibited significantly increased expression of the co-stimulatory molecule CD86.

Oxytocin receptors and human parturition: a dual role for oxytocin in the initiation of labor.

The concentration of oxytocin receptors increased in the myometrium of pregnant women and reached maximum levels in early labor. Concentrations of oxytocin receptors were also high in the decidua and reached a maximum at parturition. In vitro, prostaglandin production by the decidua, but not by the myometrium, was increased by the addition of oxytocin. Oxytocin may therefore stimulate uterine contractions by acting both directly on the myometrium and indirectly on decidual prostaglandin production. Oxytocin receptors are probably crucial for the onset of human labor, and the stimulus for the increase in uterine prostaglandins may be oxytocin originating from the fetus.

Oxytocin release and uterine activation during parturition iin rabbits.

Plasma oxytocin was measured by a specific RIA in blood of pregnant and parturient rabbits obtained through an indwelling cardiac catheter. Uterine activity was continuously recorded by means of indwelling intrauterine balloons. Plasma oxytocin concentrations were low throughout gestation (mean +/- SE, 16.1 +/- 2.0 pg/ml), with no rise toward term. During parturition, a significant increase in plasma oxytocin was observed in all but 3 of 21 rabbits studied. Plasma oxytocin rose rapidly and reached high levels within minutes of the beginning of labor contractions. The mean concentration was 193 +/- 55 pg/ml (SE) 30--60 sec before the expulsive phase. The highest oxytocin concentrations were usually observed at the delivery of the first fetus (mean, 258 +/- 89 pg/ml); this was followed by a rapid decline. Baseline levels were reached in 20--60 min. Uterine activity during parturition was well correlated with plasma oxytocin; an abrupt increase was observed a few minutes (5.1 +/- 1.2 min) before the expulsion of the young, followed by a gradual disappearance over 30--70 min. Little or no circulating oxytocin was detected during delivery in 3 rabbits. In these, the course of parturition was abnormal and protracted, resulting in a high percentage of stillborn young. The series of strong contractions associated with normal delivery was absent. By contrast, abortion in 2 rabbits was associated with elevated plasma oxytocin levels and increased uterine activity. These findings indicate that a substantial amount of oxytocin is released into the circulation during delivery and suggest that the normal activation of the uterus at parturition depends on oxytocin. The stimulus eliciting the release of oxytocin is not known. Dilatation of the birth canal by the passage of a fetus was not consistently followed by detectable oxytocin release, and during delivery, a second release of oxytocin was often unrelated to any apparent stimulus. Intact spinal cord caudal to T5 does not appear to be essential for the release of oxytocin at parturition, since spinal transsection in 2 rabbits was associated with normal oxytocin release at delivery. Injections of synthetic oxytocin caused a dose-dependent increase in plasma oxytocin and uterine activity. Disappearance of oxytocin from the circulation followed a double exponential curve; the mean half-life of the initial rapid phase was 1.82 min after single injections and the half-life of the low component was 26.5 min. The initial volume of distribution was close to the volume of the vascular compartment, and the total apparent volume of distribution was about twice the size of the extracellular compartment. After constant infusions, a half-life of 3.6 min was obtained for the uncorrected values during the initial phase.

Release of oxytocin and vasopressin by intracerebroventricular vasoactive intestinal polypeptide.

Vasoactive intestinal polypeptide (VIP)ergic nerves innervate both the neurohypophysis and the hypothalamus. To test the hypothesis that VIP is a releasing factor for neurohypophyseal hormones, rats were given intracerebroventricular (icv) infusions of VIP in doses varying from 0.3 pmol/kg.min to 3 nmol/kg.min for 5 min (0.001-10 micrograms/rat). Serial blood samples were drawn from the vena cava for measurement of oxytocin (OT), vasopressin (AVP), and VIP by RIA. After the VIP infusions mean plasma OT and AVP levels rose in a dose-dependent manner; the rise was significant for both hormones at the dose of 300 pmol/kg.min. Peak levels after infusion of 3 nmol/kg.min were greater for OT than AVP [96.1 +/- 14.7 vs. 33.9 +/- 9 microU/ml (mean +/- SE); n = 6]. In addition, the concentration of plasma OT increased more promptly than that of AVP. Plasma OT was significantly raised over control values at 5 min, whereas plasma AVP was not increased until 15 min after the VIP infusion began. The concentration of VIP in peripheral plasma rose somewhat after icv infusions (maximum, 300 pmol/liter 30 min after 10 micrograms/rat), but the rise was only 5% of that observed after systemic infusions of equimolar doses of VIP (maximum, 6000 pmol/liter 5 min after 10 micrograms/rat). Peak plasma OT levels after administration of 3 nmol/kg.min VIP were significantly higher after icv than after systemic infusion of the same dose of VIP reported previously. Intravenous injection of 0.5 ml VIP antiserum with a binding capacity of VIP of 2.3 micrograms/ml before the icv administration of VIP (1 microgram/rat) did not prevent the VIP-induced rise in plasma OT and AVP. These observations suggest a central site of action for VIP in OT and AVP release, probably in the hypothalamus. The results are in harmony with the hypothesis that endogenous VIP is a physiological regulator of OT and AVP release in rats.

Correlation between oxytocin receptor concentration and responsiveness to oxytocin in pregnant rat myometrium: effects of ovarian steroids.

Marked changes in the uterine binding of oxytocin (OT) occur in rats at the time of parturition or after treatment of ovariectomized rats with estrogen or progesterone. To ascertain that these binding sites represent the biological receptors for OT, we measured the uterine response to OT in various groups of rats in which specific OT binding was also determined. Intact pregnant rats and rats ovariectomized on day 20 of gestation and treated thereafter with oil, estradiol benzoate (5 micrograms/24 h), progesterone (5 mg/24 h), or estradiol and progesterone together had indwelling balloons inserted on day 20 for the recording of uterine response to either iv bolus injections or iv infusions of OT. The uterus was removed 24-48 h after balloon insertion, and OT binding to the particulate fraction as well as nuclear estrogen and cytosolic estrogen receptor concentrations were determined. An inverse correlation (r2 = 0.758) was found between the concentration of OT-binding sites and the threshold dose of OT, and a linear correlation was found between the concentration of binding sites and the uterine activity induced by OT infusion (r2 = 0.852). We conclude, therefore, that the high affinity (Kd, 1-2 nM) binding sites for OT represent the physiological receptors. The concentration of these sites increased progressively during estrogen treatment. Progesterone completely inhibited this estrogen-induced rise. After ovariectomy, there was a modest, but significant, increase in OT receptor concentration which also was prevented by progesterone. The increase in OT receptor concentration was correlated with the estrogen receptor concentration in intact pregnant and estrogen-treated ovariectomized animals, but not in the other groups of animals. The apparent affinity of the receptors for OT was not significantly affected by hormone treatment. We conclude that the concentration of receptors is a major factor controlling the uterine responsiveness to OT, and that the receptor concentrations are regulated by ovarian hormones in a manner related to estrogen receptor activation. In addition, estrogen appeared to enhance the coupling of OT receptor occupancy to the tissue response to OT.

Vasoactive intestinal peptide (VIP) stimulates oxytocin and vasopressin release from the neurohypophyis.

The concentration of vasoactive intestinal peptide (VIP) was measured by RIA in pituitary extracts of female cats; it was significantly higher in the posterior than in the anterior lobe, 47.3 +/- 3.9 pmol/g wet wt vs. 7.7 +/- 2.0 pmol/g wet wt (mean +/- SE, n = 5 in both instances). To investigate the effect of VIP on the release of posterior pituitary hormones, the concentration of arginine vasopressin and oxytocin was measured by RIA in jugular vein plasma during intracarotid infusion of VIP. The levels of both hormones rose during the 5-min infusion of VIP. Oxytocin levels increased from a mean of 7.9 microU/ml to a maximum of 34.9 microU/ml at 1 min and arginine vasopressin levels from from 27.4 microU/ml to a maximum of 157 microU/ml at 1 min. The levels of both hormones returned to baseline values in about 20 min. Since VIP has been localized to the nerve terminals of the neurohypophysis, these data suggest that endogenous VIP may play a role as a neurotransmitter in the magnocellular hypothalmo-neurosecretory system.

Release of oxytocin and prolactin by suckling in rabbits throughout lactation.

Plasma oxytocin and PRL were measured in serial samples of blood collected from lactating rabbits nursing five to seven (mean, six) young on a once-daily suckling regimen. Each suckling episode lasted 4.0 +/- 1.1 (+/- SD) min on the average. Samples were obtained by means of an indwelling cardiac catheter before and 1, 3, 5, 10, 20, 30, and 60 min after suckling began. Measurements were performed at several stages of early, mid-, and late lactation. Oxytocin levels rose to peak values during suckling and declined rapidly after suckling stopped. PRL levels, on the other hand, did not reach peak values until 1-5 min after suckling had stopped, at which time plasma PRL concentrations plateaued and, in early and midlactation, were sustained at peak levels for 2-3 h; in late lactation, PRL secretion was not sustained after suckling had ceased. Peak PRL levels were relatively constant throughout most of lactation, with no significant differences between groups until late in lactation, when peak levels fell rather abruptly from a mean of 74 +/- 33.5 to 10.5 +/- 13.3 (+/- SD) ng/ml around day 25 in spite of a constant number of young and constant suckling frequency. Suckling failed to elicit any PRL release on day 30, but the administration of fluphenazine, a dopamine antagonist, did cause a rise in plasma PRL. Oxytocin release increased with advancing lactation, rising, on the average, 40 pg/ml on day 2 and to 250 and 490 pg/ml in mid- and late lactation, respectively. Dopaminergic agonist and antagonist drugs given to the doe before the nursing episode did not influence oxytocin release in response to suckling. Without a rise in plasma oxytocin, the young obtained no milk, but above a threshold level, there was no significant correlation between peak oxytocin levels and milk yield. When suckling failed to induce PRL secretion, milk secretion ceased rapidly in spite of copious oxytocin secretion. The failure of suckling to induce PRL release in late lactation, therefore, appears to be an important factor in the cessation of lactation.

Ontogeny of oxytocin receptors and oxytocin-induced stimulation of prostaglandin synthesis in prepubertal heifers.

Developmental aspects of oxytocin (OT) receptors (OTR) in uterine tissues before puberty are not known. Bovine ovaries secrete some estradiol, but no progesterone, before puberty; the circulating levels of estradiol are between 1 and 3 pg/ml until puberty. Cross-bred Angus-Brahman heifers, in which puberty occurs around 12 months of age, were used to determine the concentrations of OTR from the late fetal stage to adulthood. PGF2alpha release in response to OT was determined in 3-, 6-, and 9-month-old heifers (n = 4 each). Myometrium, endometrium, and cervical mucosa were obtained from 3-week-old, 3-month-old, 6-month-old, and 9-month-old heifers and from adult cows at estrus. Whole uterus and cervix were taken from third trimester fetuses and at birth. [3H]OT binding and specificity, localization of immunoreactive (ir) OTR, OTR messenger RNA, and OT-induced release of PGF2alpha were determined. The uterus from fetuses and the neonate expressed OTR messenger RNA and bound [3H]OT. At 3 weeks of age, OTR concentrations per mg protein were very low, but at 3 months of age they had increased markedly in all three tissues. At 6 and 9 months of age, levels of OTR had risen further and were similar to those in adult cows at estrus. Prepubertal uterus also possessed separate vasopressin VP1 subtype receptors. The ir-OTR was localized in luminal epithelial cells of endometrium and cervical mucosa, most of which were ir positive, whereas in myometrium, clusters of ir-OTR-positive cells were found among large numbers of ir-OTR-negative cells. The PGF2alpha response to OT was insignificant in heifers of all age groups, in contrast to that in cows at estrus. Endometrial cells from 4- to 5-month-old heifers did not respond to OT with PG release in the absence or presence of added arachidonic acid. Tumor promoters, lipopolysaccharide, and interleukin-2 also failed to elicit PG release in vitro, although they induced PG release in similar cell cultures from cyclic cows. In summary, uterine tissues of prepubertal heifers have high levels of OTR, which appear to be developmentally regulated. These receptors are not coupled to PG synthase, or alternatively, the PG synthase gene is not expressed before puberty, possibly because the tissues have had no previous exposure to progesterone.

Oxytocin and vasopressin receptors in bovine endometrium and myometrium during the estrous cycle and early pregnancy.

The binding of [3H]oxytocin ([3H]-OT) and [3H]arginine vasopressin ([ 3H]-AVP) by bovine endometrial and myometrial membrane preparations obtained on days 0, 7, 14, 17, and 21 after estrus or mating was investigated. [3H]OT was bound with higher affinity than [3H]AVP by both tissues; the mean dissociation constants (KdS) were 0.95 x 10(-9) M and 1.56 x 10(-9) M for OT and AVP, respectively, P less than 0.0001, with no significant variations in the KdS during the cycle. The concentration of [3H]OT binding sites was on the average 50% higher than [3H]AVP across the cycle in both tissues. Endometrial receptor levels varied significantly during the cycle; it was lowest on days 7 and 14, rose significantly on day 17, and peaked on day 21. Myometrial receptor levels decreased from levels at estrus on days 7 and 14, but the changes were not significant. The ratio between endometrial and myometrial receptor concentrations changed from about 10 at estrus to less than 1 in the luteal phase. In early pregnancy, the receptor levels did not differ from nonpregnant levels on days 7 and 14, but on day 17 the endometrial receptor concentrations were significantly lower, and on day 21 those in both tissues were significantly lower. The endometrial OT and AVP receptor concentrations were inversely correlated with plasma progesterone levels (P = 0.005) with no correlation to plasma estradiol, whereas the myometrial receptor concentrations showed no correlation to plasma progesterone but an inverse correlation with plasma estradiol (P = 0.004). We conclude that the endometrial OT and AVP receptor concentrations are more tightly controlled by progesterone than myometrium, and that the bovine conceptus suppresses endometrial OT and AVP receptor concentrations in the preattachment stage either by a local action on the endometrium or indirectly via an antiluteolytic effect.

Oxytocin receptors in nonpregnant human uterus.

The concentration and distribution of specific [3H]oxytocin-binding sites in the nonpregnant human uterus were studied. Oxytocin was bound with an apparent Kd of about 1 nM in the crude membrane fractions of the fundus and corpus. A second class of sites with lower affinity and higher capacity for oxytocin also was found. Consistent with its high uterotonic potency in nonpregnant uteri, arginine vasopressin was as effective as oxytocin in inhibiting [3H]oxytocin binding to corpus and fundus membrane preparations. The concentrations of high affinity binding sites in fundus and corpus were similar and were significantly higher than those of membrane fractions from isthmus or Fallopian tubes. The lowest concentration of sites was found in the cervix. Endometrial membrane preparations contained oxytocin-binding sites in about the same concentration as that in the myometrium. The concentrations of oxytocin receptors in all parts of the nonpregnant uterus were somewhat higher in the luteal phase than in the follicular phase. Concentrations were lowest in postmenopausal uteri. The concentrations of oxytocin receptors in nonpregnant uteri were 50-100 times lower than those in uteri near the end of gestation. These differences correspond to the differences in sensitivity to oxytocin between luteal phase and follicular phase and between the nonpregnant and late term uterus. These findings add support to the evidence that the binding sites for oxytocin represent true oxytocin receptors.

Effects of mating on levels of oxytocin and prolactin in the plasma of male and female rabbits.

The effects of mating on plasma levels of oxytocin and prolactin in male and females rabbits have been investigated. Blood was collected through indwelling cardiac catheters at intervals of 1, 2, 4, 6, 12, 24, 36 and 60 min after mating. In female rabbits additional samples were taken 5h after mating, as well as daily during the ensuing pregnancy or pseudopregnancy. They were also fitted with intrauterine balloons for recording uterine activity. Copulation induced a rapid, transient rise in plasma oxytocin in female rabbits at the same time as a fall in plasma prolactin. Mating or sexual excitement had no significant effect on plasma concentrations of oxytocin or prolactin in bucks. Relatively large fluctuations of plasma oxytocin were seen in male rabbits under normal conditions and after mating, suggesting episodic release of oxytocin in a random fashion. The uterine recordings indicated that, in spite of the modest release of oxytocin, a strong sympathetic adrenal activation occurred in response to mating and this provided the overriding influence on uterine activity. During pregnancy plasma levels of prolactin rose significantly on day 4, and remained raised throughout most of gestation. Plasma prolactin fluctuated widely during the first half of pregnancy but the mean levels were higher than those found during the second half of gestation. When pseudopregnancy was induced with injection of an ovulating dose of LH, plasma prolactin rose in a similar manner as during early gestation or mating-induced pseudopregnancy. Thus, in contrast to rats, stimuli associated with mating have no direct influence on the subsequent release of prolactin in rabbits. The secretion of prolactin during gestation seems to be controlled entirely by ovarian steroids, probably progesterone.

Plasma oxytocin but not prostaglandin F2 alpha metabolite levels at cerclage may predict preterm delivery.

Plasma oxytocin and prostaglandin F2 alpha metabolite (PGFM) concentrations were measured in 45 patients admitted for cerclage during the second trimester. Samples were collected before, 3 hours after, and 3 days after the Shirodkar procedure. Uterine activity was recorded by external tocography twice daily for 30 minutes. Twenty-eight women with uncomplicated pregnancy and commensurate gestational age served as controls. Cervical length, measured by ultrasonography, was significantly shorter before cerclage (36 +/- 2 mm) than after cerclage (43 +/- 2 mm) or compared with controls (48 +/- 1 mm). Bishop scores ranged from 3-6 (median 4) in the cerclage group and 0-1 (median 0) in controls. Fifteen cerclage patients and one control delivered preterm 5-22 weeks after the procedure. Initial plasma PGFM levels were significantly higher in cerclage patients than in controls. The cerclage procedure caused an immediate rise in plasma PGFM and a subsequent fall below initial levels to control values. Neither the initial levels of PGFM nor the increments 3 hours after cerclage correlated with the outcome of pregnancy. By contrast, plasma oxytocin levels before cerclage were significantly higher in patients who subsequently delivered preterm than in those who delivered at term. Cerclage resulted in a significant fall in plasma oxytocin at 3 hours in patients with preterm delivery, but after 3 days the oxytocin levels had returned to the precerclage values. Patients who had increased uterine contractions had significantly higher plasma oxytocin levels but lower PGFM levels than those without contractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of beta-mimetic tocolysis on cervical ripening and plasma prostaglandin F2 alpha metabolite after endocervical application of prostaglandin E2.

To suppress uterine contractions during cervical ripening induced by prostaglandin E2 (PGE2) gel, beta-mimetic drugs were given orally 30 minutes before PGE2 application to 17 patients with unripe cervix. This prevented the increase in contraction frequency observed during the first four hours after PGE2 application in 17 controls. Nevertheless, cervical ripening proceeded at a similar rate and the clinical outcome was comparable in both groups. Prostaglandin E2 application caused a transient rise in plasma levels of the PGE2 alpha metabolite (13,14-dihydro-15-keto), which was not prevented by pretreatment with beta-mimetics. Patients with premature rupture of the membranes had higher initial plasma PGF2 alpha metabolite levels than those with intact membranes but cervical ripening proceeded with the same rate, and the effect of beta-mimetics was the same in both groups. Thus, cervical ripening induced by PGE2 does not depend on uterine contractions, and increased production of PGF2 alpha is unrelated to the ripening process. There was no difference between the three beta-mimetic agents in the present study.

Intraovarian pressure changes during ovulation in rabbits.

Contractile elements are found in the ovaries of many species, but it has not been possible to ascertain whether these elements are of importance in the process of ovulation. In this report, we describe changes in intraovarian pressure recorded continuously in vivo in unanesthetized rabbits under normal conditions and under the influence of intravenously injected human chorionic gonadotropin (hCG), as well as following the ovulatory stimulus of normal copulation. The recordings were made by means of small latex balloons (0.02- to 0.04-ml volume) attached to indwelling catheters, inserted into the ovarian stroma, and secured with 6-0 nylon sutures. All 24 rabbits studied showed changes in intraovarian pressure indicative of ovarian contractile activity. The intraovarian pressure changes followed a characteristic pattern which was different from the changes in intratubal pressure, recorded simultaneously from the lumen of the ipsilateral fallopian tube, indicating that the contractions of both organs occurred independently. In normal animals, before an ovulatory stimulus was applied, the ovarian contractility pattern consisted of a series of rapid contractions (average amplitude, 6 mm Hg; average frequency; 8 per minute) occurring with intervals of quiescence lasting from 11 to 36 minutes. The base line tonus was frequently elevated during these series of contractions. Mating or an injection of hCG had no immediate effect on intraovarian pressure but, 6 to 8 hours after the stimulus was applied, ovarian contractile activity increased significantly in all rabbits. This enhanced activity persisted for several hours before returning to initial levels approximately 15 to 18 hours after mating or the hCG injection. This demonstration of increased contractile activity about the time of ovulation suggests that ovarian contractions participate in the process of follicular rupture and the extrusion of ova at ovulation. Prostaglandin F2alpha, norepinephrine, and oxytocin were effective in inducing ovarian contractions.

Oxytocin induces PGE2 release from bovine cervical mucosa in vivo.

Oxytocin receptor (OTR) concentrations in bovine cervical mucosa rise steeply a few days before estrus to high concentrations and fall rapidly after estrus. To study the physiological role of these OTR, the effect of OT on the release of PGE, from the cervical mucosa of periestrous cows in vivo was determined by inserting bags made of dialysis tubing containing isooncotic saline solution in the endocervix for two 2-h periods, a fresh bag for each period. During the first period no treatment was given, during the second period OT (100 IU) or saline was injected i.m. PGE2 content in the second bag was significantly greater in OT-treated cows than in saline-treated cows. In a second experiment cervical resistance to stretch, achieved by distention of a balloon inside the cervical canal, was measured in periestrous cows before and 10 h after i.m. injection of OT, or endocervical application of 2.5mg PGE1 in a jelly, or the inactive jelly. A significant reduction in the resistance was achieved with both OT and PGE1; in the doses given the effect of PGE1 was longer lasting than that of OT.

Preferential release of oxytocin in response to vasoactive intestinal polypeptide in rats.

Vasoactive intestinal polypeptide (VIP) was infused into the aorta of pentobarbitone-anesthetized rats (n = 12) in stepwise increasing doses of 0.001 to 10 micrograms/rat at rates varying from 0.3 pmol/min/kg to 3000 pmol/min/kg over 3 min. Blood was withdrawn from the vena cava inferior for the measurement of oxytocin (OT) and vasopressin (AVP) by RIA. The loss of blood was compensated for by infusion of isotonic saline (0.9% NaCl with 0.5% human serum albumin). Control rats received this solution only (n = 11). VIP infusions resulted in a dose-dependent increase in plasma OT which was significantly greater than the slight rise observed in the controls. The difference from controls was significant at infusion rates of 3 pmol/min/kg and more. Plasma AVP, on the other hand, did not rise in response to VIP infusions until the infusion rate was increased to 300 and 3000 pmol/min/kg. At these infusion rates, the increments in AVP were much smaller than those of OT, the levels during the highest infusion rates rising to 8.6 +/- 2.8 and 27.2 +/- 4.8 microU/ml, respectively (log normal means). The preferential release of OT in response to exogenous VIP in rats differs from the response in cats where intracarotid administration of VIP resulted in the release of proportionately more AVP than OT. Immunoreactive VIP is found in the hypothalamo-neurohypophyseal system of rats in close proximity of some of the magnocellular neurons as well as within the nerve terminals. This, together with our data, suggests that endogenous VIP may participate in the release mechanism for OT in rats.

The metabolic effects of oxytocin are mediated by a uterine type of receptor and are inhibited by oxytocin antagonist and by arginine vasopressin in the dog.

Infusion of oxytocin (OT) into normal dogs, in doses which produced plasma levels of OT in the physiological range, has been shown to increase plasma levels of glucose, insulin and glucagon and increase rates of glucose production and uptake. This study sought to determine whether there was a correlation between these metabolic effects and the oxytocic potency of four less potent oxytocic analogues when infused into normal dogs. The rank order of oxytocic potency of all 4 correlated well with the rise in plasma glucose levels, and in 3 of the 4 with the rise in plasma insulin levels. An antagonist of the oxytocic effect of OT suppressed the usual OT-induced rise in plasma glucose, insulin and glucagon as well as the increased glucose production and uptake. Arginine vasopressin (AVP) infusion, which by itself did not produce any metabolic effects, blocked completely the effects of OT infusion to raise plasma glucose and insulin levels and increase glucose production and uptake. The data suggest that the metabolic effects of OT in the dog are mediated by OT receptors that are similar to those producing the oxytocic effects. Whether the inhibition by AVP of the metabolic and hormonal effects of OT occurs at the receptor or post receptor level or via other mechanisms remains to be determined.

Regulation of bovine cervical secretion of prostaglandins and synthesis of cyclooxygenase by oxytocin.

Prostaglandin E2 (PGE2) can cause softening of the bovine cervix at oestrus when receptors for oxytocin (OT) are maximally present, indicating a relationship between OT and PGE2 production. It was therefore determined whether OT can stimulate prostaglandin synthesis or induce cyclooxygenase expression in cervical external os segments obtained from pre-oestrous-oestrous cows. Tissues were minced and incubated (50-100 mg mL[-1] 6 h[-1]) in the presence of OT (10 ng mL[-1]), progesterone (P4) (5 ng mL[-1]) and/or indomethacin (5 microg mL[-1]). It was found that OT stimulated basal PGE2 (7.79+/-1.22 ng 100 mg[-1], mean+/-s.e.m.; n = 6) in external os segments from pre-oestrous-oestrous cows (P < 0.03), whereas P4 and indomethacin inhibited basal and OT-stimulated PGE2 production (P < 0.05). Basal prostaglandin F2alpha (PGF2alpha) production was minimal (<1 ng 100 mg[-1]) and OT had no effect on its production. Expression of cyclooxygenase was measured by Western blot analysis following incubation of the tissue (100 mg 1.5 mL[-1] 3 h[-1]) in the presence of OT (10 ng mL[-1]) and in the presence of P4 (5 ng mL[-1]). It was found that OT stimulated the induction of cyclooxygenase II (79+/-10%; n = 7, P < 0.05). In contrast, P4 inhibited the basal expression of this enzyme (-40+/-5%, n = 7, P < 0.05) in the presence or absence of OT. It is concluded that, in vitro, OT stimulates PGE2 synthesis by the bovine cervix at oestrus and that this effect is mediated by cyclooxygenase.

Oxytocin and the timing of parturition. Influence of oxytocin receptor gene expression, oxytocin secretion, and oxytocin-induced prostaglandin F2 alpha and E2 release.

Oxytocin receptor (OTR) gene expression was studied in various tissues of the reproductive tract of pregnant cows and compared with ligand binding activity. Myometrium, intercaruncular endometrium, caruncular endometrium, cotyledons and fetal membranes, as well as the uterine cervix of pregnant cows expressed the bovine OTR gene. Receptor concentrations, measured by ligand binding to crude microsomal pellets, were comparable to OTR mRNA signal strength in all instances indicating that the receptor protein formation is probably regulated at the transcriptional level. During bovine pregnancy OTR gene expression was initiated at different times depending on the tissue. The expression of the gene for OT peptide was not found in any of the bovine uterine tissues but was found in the corpora lutea at term and during parturition and then at relatively low levels. Therefore endogenous OT is derived almost exclusively from the pituitary during bovine pregnancy. OT secretion occurred in a pulsatile manner during pregnancy; a significant increase in pulse amplitude was observed during the last days before delivery and a large surge was associated with active labor and delivery. We postulate that the temporal order of OTR gene expression in the uterine and intrauterine tissues is a factor in the synchronization of the events that eventually lead to the onset of parturition. Because OT receptor mediates different actions in different tissues OT has multiple functions in the mechanism of parturition. The peptide initiates and maintains myometrial contractions, it stimulates release of PGF2 alpha from the endometrium and fetal membranes and, as demonstrated in this study, OT induces PGE2 release from cervical tissues in an OTR dependent manner. We conclude that in pregnant cows, OT participates both in the events that prepare the reproductive tract for birth and initiate the birth process.

[Oxytocin- and prostaglandin plasma concentrations before and after spontaneous labor: evidence of involvement of prostaglandins in the mechanism of placental separation]. / Oxytozin- und Prostaglandinplasmakonzentration vor und nach spontaner Geburt: Hinweis für die Beteiligung von Prostaglandinen am Mechanismus der Plazentalösung.

The concentrations of oxytocin and PGE, PGF, and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) in maternal peripheral plasma were measured in serial samples taken at full cervical dilatation and 5, 30 and 120 minutes postpartum. The prostanoid levels were also measured in serial samples of umbilical cord blood taken from the placental end in 4 instances. At full dilatation, plasma PGFM, but not PGE and PGF, was significantly raised over control (no labor) values. Just before or at the time of placental separation (5 minutes postpartum), the concentrations of PGF and PGFM were maximal, about twice the level at full dilatation. The level then decreased but at a slower rate than the metabolic clearance rates, indicating that considerable PGF production occurs in decidua and myometrium in the early postpartum period, after fetus, placenta, and the membranes are expelled. The rapid increase in the prostanoid concentrations in the umbilical cord blood draining the placenta after delivery of the infant suggests that the surge of prostaglandins 5 minutes postpartum originates in the placenta, and probably contributes to uterine contraction and placental separation and expulsion. Plasma OT was significantly raised over prelabor values at full cervical dilatation, and during the third stage, but dropped to control levels 30 minutes postpartum. Exogenous oxytocin infusions begun at delivery of the infant caused a marked increase in plasma OT and maintained the PGFM concentrations at a higher level than in the parturients not receiving oxytocin 2 hours postpartum.