Search

Es completamente innecesario enfatizar la necesidad de la anticoncepción en un mundo en el que cada año se agrega ochenta millones de individuos. En sólo 25 años la población mundial habrá duplicado su tamaño actual. En muchos lugares del mundo la escasez de alimentos y otros recursos naturales está haciéndose ya evidente, en otras, las consecuencias de las tasas de crecimiento de la población se sienten principalmente en el deterioro del ambiente. En todas partes del mundo las presiones de las poblaciones siempre crecientes y más jóvenes son capaces de crear desorden y violencia social y política.

Plasma oxytocin (OT) concentrations were determined in 14 late-pregnant and parturient Angus-Hereford cows. Jugular and utero-ovarian veins were cannulated for simultaneous withdrawal of blood samples. Samples were collected at 10-min intervals for 6 h once weekly beginning 60‐14 days before the date of expected delivery (group 1), or daily 3‐7 days before the due date (group 2). In a third group, samples were collected at 15min intervals every other day for 12 h beginning 1 wk before calving. Basal levels of OT were low, the overall mean for both veins was 0.46 6 0.03 mU/ml until a week before parturition, and then increased to 0.77 6 0.1 mU/ml (P , 0.02). Spurts of OT occurred intermittently on all days. Interpeak intervals averaged 71.0 6 10.7 min until Day 214, and from Day 214 to Day 21 the intervals were 44.0 6 5.3 min (P , 0.05). From Day 260 to Day 225 the amplitudes of OT peaks were low and similar in both veins (mean 1.37 6 0.1 mU/ml). From Day 214 to Day 21 the peak amplitudes were 3.6 6 0.4 mU/ml on average (P , 0.02). During the last 2 wk the utero-ovarian peak of OT was frequently higher than the peripheral peak. In addition, a number of spurts were observed in the utero-ovarian vein

Cyclooxygenase 1 and 2 (COX-1 and COX-2) mRNA were measured by ribonuclease protection assays in total RNA extracted from intercaruncular and caruncular endometrium, myometrium, cotyledons, and cervical mucosa of pregnant cows. Tissues were obtained at gestational ages of 150 days and 275 days and at term not in labor, at term in labor, and 6-12 h postpartum. Additionally, the effect of oxytocin (OT) on COX-2 expression was determined in intercaruncular endometrium of six third-trimester cows (between 230 and 270 days of pregnancy), three of which were injected with OT (200 IU) and three with saline 2 h before tissues were harvested. Prostaglandin F2alpha (PGF2alpha) metabolite was measured in plasma samples taken at 15-min intervals before and after the injections. Results showed that COX-2 mRNA was expressed in every type of tissue examined, although in different concentrations and beginning at different stages. Other than in seminal vesicular and prostate glands used as positive controls, low concentrations of COX-1 mRNA were detected only in myometrium and caruncles. Cotyledons had the highest concentration of COX-2 transcripts at all stages studied. Caruncles had about half the concentration of COX-2 transcripts that was seen in cotyledons, and on Day 150 even less. COX-2 mRNA expression in both tissues increased with advancing gestation, but there was no difference between samples from term-no-labor and term-in-labor cows. COX-2 mRNA concentrations in endometrium and myometrium were low; they varied randomly during pregnancy with no significant increase until postpartum, when COX-2 transcripts in endometrium had increased severalfold whereas those in myometrium were similar to values before parturition. Cervical mucosa expressed COX-2 mRNA weakly until term but had increased markedly at parturition. Injection of 200 IU of OT induced a substantial increase in endometrial COX-2 mRNA concentration within 2 h; this was associated with linearly increasing plasma concentrations of 13, 14-hydroxy-15-keto-prostaglandin F2alpha, which were still rising at termination of the experiment. The results suggest that endogenous OT is a major factor in induction of COX-2 expression and PGF2alpha release at term and during parturition in cows.

The purpose of this study was to determine the specificity and concentration of oxytocin (OT) and arginine vasopressin (AVP) binding sites in non-pregnant (NP) human and rhesus monkey endometrium, myometrium and fibromyomas, and to determine the cellular localization of OT receptor (OTR). Besides [3H]AVP, [125I]LVA, a specific VP1 receptor subtype antagonist, was used to determine vasopressin receptor (VPR) concentrations. Samples were obtained from 42 pre-menopausal and three pregnant women (5, 13 and 35 weeks gestation), and several NP and pregnant monkeys. Specificity of binding was assessed in competition experiments with unlabelled agonists and antagonists of known pharmacological potency. Cellular localization of OTR was determined by immunohistochemistry. In NP human uterine tissues, [3H]AVP was bound with higher affinity and greater binding capacity than [3H]OT, whereas in pregnant women and in NP and pregnant rhesus monkeys, uterine OT binding capacity was greater. OT and AVP binding sites discriminated very poorly between OT and AVP; [125I]LVA binding sites were more selective than [3H]AVP. Their ligand specificity and binding kinetics indicated the presence of two distinct populations of binding sites for OT and AVP in primate uterus. Endometrium of NP women and monkeys had low OTR and VPR concentrations. Myometrial and endometrial OTR and VPR were down-regulated in midcycle and in early human pregnancy, they were up-regulated in the secretory phase and second half of pregnancy. Immunoreactive OTR in NP uterus was localized in patches of myometrial muscle cells and small numbers of endometrial epithelial cells.

The affinity and specificity of an antagonist of oxytocin, [1-D(CH2)5,Tyr(ME)2,Thr4,Tyr-NH2(9)]ornithine vasotocin (OTA), to oxytocin receptors (OTR) in bovine gestational endometrium was determined in displacement experiments with oxytocin (OT) and vasopressin (AVP) analogues and compared to myometrial OTR. OTA had the highest affinity in both tissues. The effect of OTA on OT-induced increase in plasma concentration of 13,14-dihydro-15-keto-prostaglandin F2alpha metabolite (PGFM) was studied in 24 late-pregnant cows. Treatments consisted of i.v. saline; OT (50 IU); OTA (1200 microg); and OTA (400, 1200, or 4000 microg) injected i.v. 5 min before OT (50 IU) (n = 4 each). Samples were collected from jugular vein at 15-min intervals for 30 min before and 3 h after the injection of OT. Progesterone was measured in once-daily samples taken for 7 days after the experiment. OT caused a twofold increase in plasma PGFM within about 60 min (p < 0.005), with levels returning to baseline at 150-180 min; OTA (1200 microg) caused a gradual lowering of basal plasma PGFM over 180 min (p < 0.05). The 400-microg or 1200-microg dose of OTA did not alter OT-induced PGFM response, whereas the 4000-microg dose inhibited it almost completely (p < 0.005). Plasma progesterone declined after the experiment in all cows, with no differences among groups. Because OTA inhibits OT-induced release of endometrial prostaglandin F2alpha it may be a good tocolytic agent.

Oxytocin (OT) receptor (OTR) concentrations were determined in the cervix of nonpregnant cows on cycle Days 0, 3, 7-8, 17, and 19 (n = 3-4 cows each day); [3H]OT was used as the labeled ligand. Mucosal and muscle layers of the cervix were also analyzed separately for both ligand binding and expression of the OTR gene using a newly developed RNase protection assay (RAP). Cellular localization of OTR protein was determined by immunohistochemistry. All regions of cervix from cows at estrus had high concentrations of OTR; in the luteal phase, all were sharply down-regulated. At estrus the mucosal layer had about 30-fold higher concentrations than the muscle layer. OTR mRNA was readily detected by RAP in the mucosa from estrous cows, while much weaker signals were found in the muscle. On Days 7-17, the OTR mRNA signals in both mucosa and muscle were very faint or nondetectable. Thus, there was a good correlation between ligand binding and mRNA expression, which suggests that OTR concentrations are mainly regulated at the transcriptional level. The epithelial cells at the luminal surface of the mucosa were the principal site of immunoreactive OTR; muscle cells showed significantly weaker signals. Previously, OT was found to stimulate prostaglandin (PG) E2 output in vitro in bovine cervical tissues. Since PGE2 is capable of softening the cervix, our findings suggest that OT may have a novel physiological function to cause softening of the bovine cervix mediated by the release of PGE2.

Brahman cows with known breeding dates received i.v. injections of either 10 or 100 IU oxytocin (OT) on Days 50, 150, 250, or 280 of gestation (n = 6 for each stage). Concentrations of the prostaglandin (PG) F 20 metabolite, 13,14-dihydro-15-keto-prostaglandin (PGFM), and OT were measured in samples of peripheral plasma collected at 15-min intervals for 1 h before and 1 h after treatment and then at 30-min intervals for 3 h. Plasma progesterone was measured daily for 14 days after OT injections on Days 50 and 250 of gestation. The increase in plasma OT after injection was dose-dependent (p = 0.001) but not affected by stage of gestation. Plasma PGFM increased after OT in a dose- and stage-dependent manner (p = 0.0001). At Day 280, the increase in plasma PGFM after 100 IU OT was sevenfold greater than at Day 50. Plasma progesterone declined significantly during the 7th to 12th days postinjection and returned to normal pregnancy values by the 14th day (4.4 ± 0.3 ng/ml) except in two cows treated on Day 50 of gestation that later aborted. In these, plasma progesterone was significantly lower, 2.6 0.1 ng/ml. In a second experiment, the concentration of OT receptors was determined in endometrium collected from purebred Angus or Hereford cows slaughtered on Days 50, 150, 250, and 280 of gestation (n = 3 or 4 at each stage). Endometrial concentrations of OT receptor changed as a function of gestational age, increasing sixfold from Day 50 to Day 280, which was parallel to the increase by OT of plasma PGFM. Thus, endometrial OT receptors are functionally coupled to PGF2, release during pregnancy, and their concentration determines the magnitude of OT-induced PGF2, release during gestation. Consequently, endogenous OT is a factor in the regulation of PGF2. release from the bovine uterus during pregnancy and parturition.

The peptide hormone oxytocin is produced both in the hypothalamus and in certain peripheral organs. The extent of extra-hypothalamic hormone synthesis in the pregnant cow has not previously been examined. In this study we have analyzed different tissues from the pregnant bovine reproductive tract and corpus luteum for the presence of mRNA encoding the oxytocin peptide as well as the oxytocin receptor. In uterine tissues oxytocin mRNA could only be detected sporadically with the help of a reverse transcription-polymerase chain reaction method, implying only very low levels of expression. The caruncles showed a consistently low level of oxytocin gene expression, which appeared up-regulated at term. However, in the corpus luteum there was a significant level of oxytocin gene expression at term, particularly following the onset of labor. The transcript levels were sufficiently high to be measurable by both RNase protection assay and by Northern hybridization; these levels imply a rescue of the oxytocin gene expression seen in the corpora lutea of cyclic and early pregnant cows. At the peptide level this expression was confirmed by immunohistochemistry. A sensitive RNase protection assay was developed to detect transcripts encoding the oxytocin receptor. Transcripts were detected in most uterine tissues, including the caruncles, with highest levels in the endometrium and myometrium at term. No transcripts could be detected in the corpus luteum at any stage of pregnancy, nor in the amnion. The results suggest the possibility of local, paracrine effects of oxytocin within the uterus of the pregnant cow. The rescue of luteal oxytocin at term could act to supplement the circulating hormone of pituitary origin.

OBJECTIVE: Our purpose was to determine whether RU 486 (mifepristone) has direct estrogenic activity in uterine myocytes. STUDY DESIGN: Ovariectomized adult rats were treated with RU 486, and its effect on uterine oxytocin receptor concentration, as a marker of estrogenic activity, was measured. Results were compared with th induction by RU 486 of an estrogen-responsive reporter gene in a cultured Syrian hamster uterine myocyte cell line. RESULTS: Baseline oxytocin receptor concentration was 58.8 ± 7.2 fmol/mg protein (mean ± SEM) and increased to 227 ± 49 fmol/mg with 17β-estradiol (2.5 μg/kg) and to 145 ± 18 fmol/mg afte RU 486 (5 mg/kg) treatment, an effect that was inhibited by the antiestrogen ICI 182,780 (1.5 mg/kg). In the cultured Syrian hamster uterine myocyte cell line cells RU 486 (10 −6 mol/L) caused a 2.17 ± 0.17-fold increase in the expression of the reporter gene versus 113.0 ± 7.4-fold with 17β-estradiol (10 −8 mol/L). The estrogenic activity of RU 486 was dependent on the presence of both estrogen receptor and the promoter's estrogen response element. CONCLUSION: RU 486 has a weak estrogen-like activity in uterine myocytes. This activity may partly explain the therapeutic effects of RU 488 on this target organ.

Oxytocin receptors were measured in myometrium and intercaruncular endometrium of cows during pregnancy and partu. rition. Concentrations of estradiol-17�l, estrone, and progesterone in peripheral blood were also measured. Receptor concentrations in the endometrium rose almost 200-fold from Day 20 to term (p < 0.0001, ANOVA), from 40 ± 11 to 7300 ± 1430 finol/mg protein. Myometrial receptor concentrations increased 10-fold from 180 ± 36 flMol/mg on Day 20 to 1850 ± 360 ftnol/mg protein at term (p

Human ovarian tissue and bovine ovarian stroma and follicles bound tritiated oxytocin and tritiated arginine vasopressin with similar affinity, whereas bovine corpora lutea bound tritiated oxytocin only. Competition for the binding of tritiated oxytocin by various agonists and antagonists was suggestive of receptor function. The number of oxytocin binding sites varied cyclically in all tissues. In bovine ovarian stroma and corpora lutea the concentrations were lowest on day 14 and highest on days 17, 19, and 21 after ovulation, with a striking peak in the luteal concentration on day 19. In human ovarian tissues the concentrations also were highest in samples obtained in late luteal phase. In large follicles the concentration of oxytocin binding sites was highest on the day of estrus and lowest on day 7. In bovine ovary the number of arginine vasopressin binding sites was approximately 50% lower than oxytocin binding sites and the cyclic variations were not significant. Human ovarian tissue had similar numbers of oxytocin and arginine vasopressin binding sites. Because bovine ovaries produce oxytocin and arginine vasopressin the results suggest a paracrine or autocrine role for these neuropeptides in luteolysis and ovulation. Although their synthesis in human ovaries is still controversial the presence of binding sites suggests a physiologic role in the regulation of human ovarian function as well.

The oxytocin receptor (OTR) is part of an ancient hormone system expressed in diverse phyla in relation to acute reproductive smooth muscle responses, such as egg-laying, birth, or milk letdown. The regulation of the OTR gene, while correlating with steroid levels in vivo, remains elusive. There appear to be both inhibitory and stimulatory influences acting upon a constitutive pattern of basal expression. We have found no evidence, however, for an effect of the sex steroids either directly on gene transcription, or on the receptor itself at the protein level. In the prostatic carcinoma cell line Du145, we have shown that up-regulation of the OTR gene transcription can be effected by cAMP. In an attempt to characterize the expression of the OTR protein in vivo, we have shown, using ligand-blotting, that the OTR can be expressed at different sizes in transfected cells and in myometrium. Also, in the myometrium at term, immunohistochemistry suggests that there is both an increase in OTR protein per cell, as well as in the number of smooth muscle cells expressing OTR, emphasizing that perinatal changes are the results of both individual gene activation events and gross cellular differentiation. The OTR is a valuable model system reflecting molecular changes in the perinatal period. When we understand how this important molecule is regulated, we will also be a long way towards understanding the mechanisms controlling myometrial contractility at birth. Experimental Physiology (2001) 86.2, 289-296.

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 has multiple actions in bovine reproductive tract and it was our purpose to determine the nature of these actions and their significance for the physiology of bovine reproduction. The bovine oxytocin receptors (OTR) gene was cloned and its expression studied during the cycle and pregnancy. OTR mRNA changed in parallel with OTR with control occurring mainly at the transcriptional level. However, the endocrine regulation of OTR were found in endometrium and cervical mucosa at estrus and at parturition. In both tissues OTR were suppressed in the luteal phase and early pregnancy. Whereas cervical OTR remained suppressed throughout pregnancy, endometrial OTR began to increase soon after implantation and reached higher concentrations in midpregnancy than at estrus. OTR in caruncles did not increase until third trimester, and OTR in cervical mucosa, cotyledons and fetal membranes increased only at term. Myometrial OTR showed less variation and OTR were present throughout the cycle and pregnancy but increased significantly during mid- and late pregnancy. OTR were localized in endometrial epithelial cells and lumina epithelial cells of cervical mucosa as determined by immunohistochemistry. Endometrial OTR were functional throughout pregnancy and mediated PGF release from day 50 onwards in a receptor density related manner. OTR in cervical mucosa mediated PGE release both in vivo and in vitro, as shown in cyclic cows. The ontogeny of uterine OTR was studied from third trimester fetal stage until puberty. OTR were present in endometrium and cervical mucosa in high concentrations throughout this period; myometrial OTR began to increase somewhat later but also reached adult values by 6-mo of age. In the prepuberal heifers OT injections failed to initiate PGF2a, release. The influence of steroids on the effect of OT was examined. Ovariectomy and E2 were without effect, but P4 with or without E2 induced a massive PGF2a release in response to OT in spite of reduced OTR. Bovine cyclooxygenases (COX-1 and COX-2) were cloned and their expression studied in the endometrium of prepuberal heifers and pregnant cows. Untreated and E2 treated prepuberal heifers did not express COX-2 but P4 treated heifers did express the mRNA for COX-2, albeit weakly. During the second half of pregnancy COX-2 mRNA was strongly expressed in cotyledons and somewhat less in caruncles, whereas endometrium, myometrium and cervical mucosa showed only weak, if any, COX-2 mRNA under basal conditions. However, 2 h after OT injection significant increases in COX-2 mRNA were found in endometrial RNA. Thus OT is capable of inducing the expression of the inducible COX-2 gene, and hence the conversion of arachidonic acid to prostanoids. The results indicate that the functions of OT are numerous and probably essential for successful pregnancy and parturition.

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.

We have measured oxytocin release during lactation in the ewe in response to normal tactile sucking stimuli as well as exteroceptive stimuli emanating from the lamb. Four puerperal ewes that had indwelling catheter inserted in the femoral artery while still pregnant were used. Each nursed a single lamb. Each was studied 2 or 3 times between Days 1 and 15 of lactation during a 2.5-h experimental period that was preceded by a 2-h separation from the lamb in the early morning. Samples were taken before and after the lamb was brought within sight and sound of the ewe but without contact, and then 0.5, 1, 5, 10, 15, 30, and 60 min after suckling began. When another suckling episode intervened, the same sampling schedule was immediately restarted. Suckling occurred in an intermittent fashion; 3 to 4 episodes of 2.9 +/- 2.0 (SD)-min duration took place with variable intervals during the 2.5-h experimental period. Exteroceptive stimuli emanating from the lamb caused plasma oxytocin to rise significantly from basal levels of 10.0 +/- 4.5 to 21.8 +/- 5.7 pg/ml (mean +/- SE, n 10, p less than 0.05). This rise was not seen on Day 1 and in only half of the ewes on Day 2, but thereafter the rise occurred in every instance. A further rise in plasma oxytocin was observed in almost all instances (86%) at suckling. Peak levels were usually observed within 1 min. They were quite variable, ranging from 15 pg/ml to 287 pg/ml, and not related to the milk yield, but were significantly greater than spontaneous pulses observed in nonlactating puerperal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

SUMMARY: The utilization of several inorganic and organic sulphur compounds by three strains of Clostridium perfringens and the production of hydrogen sulphide from these compounds was investigated. Sulphate, sulphite, thiosulphate and sulphide cannot supply sulphur to the organism, neither do they have any effect, when added in non-toxic concentrations, on the growth in media containing utilizable organic sulphur. Cystine or eysteine, which can be replaced by glutathione, were required by the three strains tested; no additional sulphur source was needed by two of the strains, the third requiring also methionine, which can be replaced by homocyst(e)ine. Hydrogen sulphide is produced by growing cultures from sulphite, thiosulphate, cystine, eysteine and glutathione, but not from methionine. Different enzyme systems are concerned with hydrogen sulphide production from cystine and sulphite, respectively. The sulphite-reducing capacity of some cultures was often decreased after several passages in laboratory media, the presence of nieotinamide being then required for this reduction. Sulphite was reduced to sulphide by suspensions of resting organisms. The presence of a hydrogenase system is suggested by preliminary experiments, the organisms being able to activate molecular hydrogen for reduction of methylene blue and sulphite. Other hydrogen donors are utilized by the organisms, in particular glucose. The addition of sulphites does not induce growth on substrates which do not support growth in sulphite-free media.

IT is known from the work of van Dyke and Ames1 that previously administered ethanol blocks the release of antidiuretic hormone (ADH) in response to acetylcholine. Furthermore, during ethanol anaesthesia antidiuretic activity can be detected neither in the blood from the head nor in the urine, and injection of hypertonic saline into the carotid artery does not produce any significant antidiuretic response2. It was found of interest to investigate the effect of ethanol also on the pituitary release of oxytocin. Since assay methods for oxytocin in blood are difficult and rather insensitive, it was found best to study the effect on the puerperal uterus of oxytocin released by suckling in the milk let-down reflex. The post-partum uterus of the rabbit is extremely sensitive to oxytocin, the threshold dose on the first post-partum day, being about 0.03 mu. oxytocin intravenously per kg body-weight3. As is the case in the human, suckling of the young produces a strong oxytocic response on the uterus during the first days after delivery in the rabbit.

Treatment of pregnant rats with 1 mg indomethacin/kg twice daily i.m. beginning on Day 20 delayed the onset of parturition by about 21 hr and prolonged the duration of spontaneous parturition by 4 hr. Plasma progesterone and oestradiol levels were determined in daily samples of peripheral blood, and uterine contractions were recorded before and during parturition by means of small, chronically implanted intrauterine balloons which were connected to pressure transducers via fluid-filled catheters. Indomethacin treatment did not inhibit or suppress spontaneous or oxytocin-induced contractions, which were of the same intensity in indomethacin-treated as in control rats. Parturition was induced with oxytocin in the same proportion of treated and control rats, but its induction was not successful in treated rats until 1 day later than in control rats, but its induction was not successful in treated rats until 1 day later than in controls. The onset of parturition was always related to the plasma progesterone level, which declined at a slower rate in indomethacin-treated than in control rats, reaching baseline values approximately 1 day later in the treated animals. The appearance of 20alpha-hydroxysteroid dehydrogenase in the CL of pregnant rats normally occurs on Day 21 of gestation, but activity was not observed until about 1 (0-3) day later in the indomethacin-treated rats, indicating that luteolysis was retarded. Prostaglandin F-2alpha infusions given on Day 21 reversed the effects of indomethacin treatment on plasma progesterone, luteal 20alpha-hydroxysteroid dehydrogenase activity and the timing and duration of parturition, and reduced the high perinatal mortality associated with indomethacin treatment, suggesting that the effects of indomethacin were related to its inhibitory action on prostaglandin synthetase activity. It is concluded that, in rats, indomethacin exerts its effects on parturition through inhibition of luteal regression which was significantly retarded but not prevented, and that indomethacin does not have a direct effect on myometrial contractility.

Uterine activity was recorded in 17 unanesthetized, unrestrained pregnant rats by means of intrauterine balloons inserted at a previous operation. Recordings of intrauterine pressure changes were obtained from Day 18 of gestation onwards and throughout spontaneous delivery, which occurred on Days 22 or 23 of gestation. Oxytocin was injected intravenously through an indwelling polyethylene catheter at intervals. The uterus of the pregnant rat was never quiescent except for short periods of time and it responded to moderate doses of oxytocin (10 mU) throughout the period studied. However, a changing pattern and character of contractions was consistently observed in late pregnancy and toward term the intensity of the uterine response to oxytocin increased markedly. Parturition occurred at a time when the uterine oxytocin sensitivity was maximal. The expulsion of the litter was preceded by a period of continuous uterine activity lasting 2.5 hr on the average and by a period of 5-30 mm of bearing down efforts before the delivery of the first fetus. The deliver�� of successive littermates was associated with continuous uterine activity and only a few abdominal straining efforts, and lasted 1.5 hr on the average. After the last fetus and placenta were born the uterine activity disappeared quickly and in 10-30 mm the uterus was completely quiescent except for infrequently occurring cycles consisting of 3-4 contractions. Rhythmic regular activity started 8-12 hr postpartum.

SUMMARY: The requirements for growth factors, amino acids and inorganic constituents were determined for three strains of Clostridium perfringens (Veillon & Zuber) Holland. A number of substances were tested as energy sources for this organism, and the influence of pH value and temperature on growth was determined. The minimal medium evolved contained: alanine, arginine, aspartic acid, eystine, glutamic acid, histidine, isoleueine, leueine (methionine), phenylalanine, threonine, tryptophan, tyrosine and valine; ammonium chloride, magnesium chloride, ferrous chloride, sodium-potassium phosphate buffer; glucose; adenine, biotin, calcium pantothenate and pyridoxine. For maximal growth the presence of lysine, glycine and serine was necessary. Maximal growth was affected by the balance of amino acids in the medium; the balance of sodium and potassium ions was also important. Certain strain differences were noticed with respect to amino acid and vitamin requirements. Methionine was needed by one strain only; none of the strains required serine (reported essential for strain BP6K of Boyd, Logan & Tytell, 1948b), whereas aspartic acid was essential for all strains tested but not for BP6K. Riboflavine, an essential growth factor in BP6K, had no effect on growth of the strains tested. One of the strains showed a need for added nicotinamide when transferred to a nicotinamide-free medium after several transfers in peptone water.