Sterile Horn Research Articles

Myometrial arginase activity increases with advancing pregnancy in the guinea pig

OBJECTIVES: Arginase has been suggested to play an important role in cellular growth and development, particularly important to the fetus, by supplying L-ornithine for the synthesis of polyamines. The purpose of this investigation was to determine whether pregnancy alters myometrial arginase activity and whether estradiol was responsible for the change. STUDY DESIGN: Myometrium and kidney were obtained from nonpregnant and pregnant guinea pigs of known gestational age. Arginase activity was measured under physiologic conditions by the conversion carbon 14 - labeled guanidino-L-arginine to carbon 14 - labeled urea. The concentrations of the enzyme's substrate, L-arginine, and its principal metabolite, L-ornithine, were measured in myometrium from near-term pregnant animals by use of an amino acid analyzer. Finally, a group of random cycle guinea pigs received 500 μg/kg estradiol for 5 days before the myometrium was removed. RESULTS: Myometrial arginase activity in pregnant animals was more than double that of myometrium from nonpregnant animals by the time the first measurement was made at 0.14 gestation. It continued to rise, peaking at values >25-fold higher than the nonpregnant activity by 0.90 gestation. Arginase activity in the myometrium underlying the placental implantation site was >25 fold higher ( p < 0.05) than myometrium from nonpregnant animals when first studied at 0.63 gestation and 10-fold higher than the contralateral fundal myometrium at the same time of gestation. Myometrial arginase activity in the sterile horn of six pregnant animals was half that of the horn containing one or more pups, but still five times higher than that of nonpregnant animals. Renal arginase activity also rose with advancing pregnancy, but the magnitude of the increase (up to 2-fold) was much smaller than that observed in either the fundal or placental implantation site myometrium. Estradiol had no significant effect on myometrial arginase activity. CONCLUSIONS: These studies demonstrate that pregnancy increases myometrial arginase activity and that the presence of placenta or fetus is necessary for the maximal effect. (A M J O BSTET G YNECOL 1996;174:779-82.)

Spontaneous activity in vitro of the uterine horns of unilaterally pregnant rats. Relations with glycogen and triglycerides levels

Effects of the placental implantation on the in vitro spontaneous contractile activity of uterine strips incubated in a glucose-free KRB medium, and its relationship with the glycogen and triglycerides tissue levels, have been analysed using unilaterally pregnant rats. The spontaneous activity increased with pregnancy duration, both in the implantation zone (Impl) and the interembryonic segment (Inter) of the pregnant horn. It increased in the contralateral sterile horn (SH) also. Activity was significantly greater in SH and Inter than in Impl, at the same stage of pregnancy. Uterine glycogen, but not triglycerides, appeared to be the substrate used to sustain contractile activity, as its concentration was greater in Impl, the relatively quiescent zone.

Refractoriness of the gravid rat uterus to tocolytic and biochemical effects of atrial natriuretic peptide

1. Effects of atrial natriuretic peptide (ANP) on tension development, particulate guanylate cyclase activity and guanosine 3':5'-cyclic monophosphate (cyclic GMP) concentrations of uteri from oestrogen-treated, progesterone-treated, ovariectomized and pregnant rats were determined in vitro. 2. ANP inhibited the tension development by myometrial tissues from oestrogen-treated virgin rats and the sterile horn of 10 to 14 day pregnant rats but not of the uterus from pregnant and progesterone-treated rats. 3. Inhibition of cyclo-oxygenase and lipoxygenase activities did not restore the tocolytic activity of ANP on gravid uterus. ANP exerted a tocolytic effect on nongravid uterus submaximally stimulated by prostaglandin F2 alpha (PGF2 alpha), oxytocin, vasopressin, angiotensin II or 5-hydroxytryptamine (5-HT). 4. Ovariectomy decreased the tocolytic effects of ANP, which could be restored by oestrogen treatment. 5. The refractoriness to the tocolytic effect of ANP in pregnant rats was not accompanied by a decrease in its relaxant effects on isolated aortic strips. 6. Tocolytic effects of isoprenaline, isobutylmethyl xanthine and hydroxylamine were not influenced by pregnancy or progesterone treatment. Up to a concentration of 3 mM, sodium nitroprusside did not affect myometrial tension development. 7. Pregnancy and progesterone treatment markedly inhibited ANP-induced increases in myometrial particulate guanylate cyclase activity and cyclic GMP concentrations but did not influence the effects of ANP on aortic cyclic GMP concentrations. 8. It is concluded that exposure of the myometrium to circulating and placentally-produced progesterone is responsible for the pregnancy-induced decrease in the effects of ANP on myometrial particulate guanylate cyclase activity and cyclic GMP concentrations and in turn on myometrial tension development.

Flowers of Hibiscus rosa-sinensis, a potential source of contragestative agent. III: Interceptive effect of benzene extract in mouse

In mouse, oral administration of the benzene extract of Hibiscus rosa-sinensis flowers at a dose level of 1 gm/kg body weight/day 5–8 of gestation led to termination of pregnancy in about 92% of the animals. The effect was associated with a significant fall in peripheral level of progesterone and increase in uterine acid phosphatase activity, as measured on day 10. The ovary exhibited signs of luteolysis, and the corpus luteal Δ 5-3 β-hydroxysteroid dehydrogenase activity decreased markedly. The interceptive effect of the extract was prevented completely by exogenous progesterone (1 mg/mouse/day) or chorionic gonadotropin (1 1.μ./mouse/day) and partially (62.5%) by exogenous prolactin (500 ug/mouse/day). In unilaterally pregnant mouse having traumainduced deciduomata in the sterile horn, the extract caused resorption of the fetuses, and regression of the deciduomata accompanied by reduction in weight of the ovaries. Luteolysis, may be due to interference with the luteotropic influence, and a consequent fall in plasma level of progesterone have been suggested as the plausible cause of termination of pregnancy.

Histochemical demonstration of a concomitant reduction in neural vasoactive intestinal polypeptide, acetylcholinesterase, and noradrenaline of cat uterus during pregnancy

Noradrenaline, acetylcholinesterase, and vasoactive intestinal polypeptide (VIP) were visualized in uterine nerves of cats by histochemical techniques. Alterations were followed in different regions of the organs at various stages of pregnancy and compared with the situation in non-pregnant controls. Positively stained nerve fibres, the adrenergic type being particularly well developed, were found along the muscle bundles and around blood vessels in the smooth muscle layers, as well as in the mucosa, of both uterine horns and cervix. The nerve supply was especially prominent in the upper part of the cervix. The distribution of VIP-immunoreactive and acetylcholinesterase-positive nerve fibres resembled each other, but they were less numerous than the adrenergic fibres. In the course of pregnancy there was a marked reduction in the number of all positively reacting nerves, so that almost no fibres were visible in the uterine horns near term. A small number of positive nerve fibres was found to remain, however, in the wall of the sterile (empty) horn during unilateral pregnancy. The reduction was less prominent in the cervix, particularly its lower part. Distinct changes were encountered already during early and mid pregnancy in those parts of the uterine wall distended by the growing conceptus, where almost no fibres were seen. The nerve supply was more intact in the non-distended portions located between the fetuses, and especially in the empty horn of unilateral pregnancy. No overt reduction in the number of positively stained nerve fibres was found in the cervix at these pregnancy stages. The results show that marked alterations take place in the uterine autonomie innervation during such an entirely physiological event as pregnancy. There is reason to assume that the histochemical observations reflect both structural and functional alterations in the innervation related both to the type of nerves involved and to the localization of the conceptus.

Local secretory response by the mouse uterine epithelium to the presence of a blastocyst or a blastocyst-like bead.

The ultrastructure of the uterine secretion appearing locally at the site of a blastocyst or a blastocyst-like bead was compared to the ultrastructure of the secretion present in a sterile horn of similarly treated mice. The secretion consisted of a homogeneous substance with small vesicles. The secretion was sparse and only slightly electron dense in a sterile horn, while it was more abundant and denser in a horn with a luminal object. Around a blastocyst, the secretion appeared more dense than it did around a bead, while the small vesicles of the secretion were more frequently occurring around a bead than around a blastocyst. It is concluded that a luminal object like a blastocyst is capable of eliciting a local secretory activity in the uterine epithelium, and it is suggested that this secretion is rich in hydrolytic enzymes.

Accessory deciduomata in artificially prolonged pseudopregnancy in the golden hamster

In the golden hamster (Mesocricetus auratus) pseudopregnancy lasts for only 9 or 10 days. If deciduomata are induced during pseudopregnancy they undergo necrosis from Day 8 onwards (Turnbull & Kent, 1963), but if deciduomata are induced in a sterile horn, they are maintained throughout the whole 16 days of the pregnancy (Orsini, 1968). We have shown in an earlier study of hamster pregnancy (Pijnenborg, Robertson & Brosens, 1974) that the spiral arteries of the placental bed and of deciduomata undergo progressive decidualization. The morphological changes can be timed precisely according to the day of gestation; spontaneous necrosis of the decidualized spiral arteries of deciduomata begins on Day 12 and extends to the myometrial segments, but even by term does not involve the medial terminal arteries. At about the time that necrosis begins in the spiral arteries of deciduomata there is a sharp fall in the peripheral plasma progesterone level (Lukaszewska & Greenwald, 1970; Gutknecht, Wyngarden & Pharriss, 1971). It seemed possible that the necrosis could be due to progesterone deprivation, but experiments to test this hypothesis (Pijnenborg et al., 1975) failed to prevent spiral artery necrosis even when the peripheral plasma progesterone level was kept artificially high by daily parenteral injections of progesterone. To investigate the matter further we have compared the deciduomata induced in hamsters in which pseudopregnancy was artificially prolonged and fetal tissue was absent with the deciduomata induced in the sterile horn of unilaterally pregnant hamsters as described earlier (Pijnenborg et al., 1974).

Influence of the trophoblast upon differentiation of the uterine epithelium during implantation in the mouse.

SUMMARY During the preparation of the uterus for implantation of blastocysts the luminal surface of the epithelial cells undergoes a characteristic differentiation. In non-pregnant animals this can be induced by progesterone and oestrogen, but in pregnant animals the basic hormonal control is augmented by a local effect of the blastocyst. This has been demonstrated by examining the uteri of animals made unilaterally pregnant. The differentiation of the luminal epithelial surface of the fertile horn was in advance of that in the sterile horn. The injection of oil into one horn of the uterus of pseudopregnant animals also accelerated the change in the luminal surface of the injected horn. It is suggested that contact with the cell membrane of the trophoblast influences differentiation of the uterine epithelium and that oil is able to mimic this contact reaction.

Effect of Releases of Sterile Horn Flies1 into a Native Population of Horn Flies23

When low numbers of Haematobia irritans (L.) irradiated with 137Cs were released into a native population in Brazos County, TX, they had no effect despite preliminary treatments with insecticide. However, larger releases caused a downward trend in reproduction and resulted in ca. 90% control during the latter part of the study.

Hormonal requirements for the maintenance of deciduomata and pregnancy in the same rat.

Is less progesterone needed in the rat to maintain deciduomata than early pregnancy? We thought that the question could be resolved by studying both phenomena concurrently in the same animal. The following results indicate that under these circumstances progesterone requirements are approximately the same for both tissues. Holtzman rats were mated at pro-oestrus. On the next morning, if vaginal smears contained sperm (= day 1 of pregnancy), the right uterus was severed at the utero—tubal junction thus creating a sterile cornu. On day 5 (between 14.00 and 15.00 h), the sterile horn was traumatized along its entire antimesometrial border with a barbed needle. The rats were hypophysectomized on day 6, between 09.00 and 10.00 h, by a previously described method (Greenwald & Johnson, 1968) and various hormonal regimens involving subcutaneous injections were initiated (Table 1). Progesterone was given daily on days 6–9 at 10.00 h as a single injection in

The relationship between the uterus and ovaries during early pregnancy in the guinea-pig.

SUMMARY In mated guinea-pigs one uterine horn was rendered sterile by ligation of the oviduct 2 or 3 days after finding spermatozoa in the vaginal smear. Two glass beads were inserted into the sterile horn on each of days 3–12 and on day 14 in experimental animals but not in controls. At autopsy on day 20 large corpora lutea were present in both ovaries of the control animals. The presence of beads that had been introduced on days 3 and 4 and on days 10–14 resulted in marked regression of the corpora lutea in the adjacent ovary, in the absence of a decidual reaction in the uterus, while luteal enlargement typical of pregnancy occurred in the contralateral ovary. Beads inserted on days 5–8 caused decidualization in the sterile horn but did not induce premature luteal regression in the ipsilateral ovary.

Unilateral pregnancy in the rabbit. A comparison of the spontaneous uterine activity and response to neurohypophysial hormones of the nonpregnant and pregnant horns.

In 24 conscious unilaterally pregnant rabbits the spontaneous and oxytocin‐induced uterine activity was recorded by either one or two sponge‐tipped catheters placed in each horn. In the pregnant horn the catheters were placed between the fetal membranes and the uterine wall. The recordings were repeated daily during the last days of pregnancy, for 4 to 8 days post partum, and thereafter at longer intervals for up to several weeks. The pregnant horn was consistently more active and more sensitive to oxytocin than the sterile horn up to about 1 week after delivery, when the difference disappeared. Intravenous vasopressin injections up to 0.05 IU did not increase the activity in either horn.

Quantitative changes in myometrial activity in the guinea-pig during pregnancy.

Summary. Intrauterine pressure recordings were made in non-pregnant guinea-pigs, and in either the gravid horn of bilaterally pregnant, or the sterile horn of unilaterally pregnant animals. The results showed that, rather than a reduction of uterine activity during the luteal phase of the oestrous cycle, there was a significant increase compared with the level at oestrus. Activity during pregnancy was reduced compared with nonpregnant levels and this reduction was accomplished by a lowered frequency of pressure cycles while their amplitude remained unchanged. The activity of the gravid horn was significantly less than that of the sterile horn during the mid-third of pregnancy. Both the sterile and gravid horns responded to oxytocin at all stages of pregnancy. From these results, it is suggested that progesterone may not be a myometrial regulatory agent in the guinea-pig.

UTERO-OVARIAN RELATIONSHIPS IN THE GOLDEN HAMSTER.

ABSTRACT At least half of one uterine horn is required for normal regression of the corpora lutea in the pseudopregnant hamster. Although removal of any portion of the uterus slightly increased the duration of pseudopregnancy, only unilateral hysterectomy or unilateral hysterectomy and removal of the contralateral ovary did so significantly (P &lt; 0.05). The presence of a sterile horn did not influence foetal development in the contralateral horn. No differences were observed in corpus luteum size between the right and left ovaries of animals unilaterally hysterectomized or unilaterally pregnant. Normal oestrous cycle activity continued following transplantation of the ovaries to the cheek pouches and pseudopregnancies were of normal duration. It is concluded from these observations that the amount of uterine tissue is of greater importance in regulating luteal regression in the hamster than its anatomical relationship to the ovary.

Normal growth and persistence of corpora lutea of both ovaries in the unilaterally pregnant guinea-pig.

Guinea-pigs were from the colony at the Institute. Examination of the animals and operative and histological techniques were the same as in previous work (Deanesly, 1967). In the first group (Table 1, Group 1), one uterine horn was removed from four females; one of these failed to mate and another had no corpora lutea on the side of the sterile horn. Such animals are omitted from Table 1. For Group 2, a small piece of one Fallopian tube was removed without disturbance of the vascularization of the uterus or ovary, and for Group 3 one uterine horn was severed or ligatured near the middle. Ovaries were sectioned serially at 7 μ after fixation in Bouin's fluid, and one in six sections were mounted. Two diameters at right angles were measured ( × 27) across the largest sections of each corpus

Experimental observations on the ferret corpus luteum of pregnancy.

The pioneer work of Klein on unilaterally pregnant rabbits, rats and hamsters (Klein, 1933, 1935, 1938) established the role of the pregnant uterus in maintaining, independently of the foetuses, the histological structure and function of the corpora lutea of pregnancy. If the pregnant horn were removed from unilaterally pregnant animals in mid-pregnancy, degeneration of the corpora lutea followed, the progestational proliferation in the sterile horn broke down and a fresh ovulation took place. From these, and from hypophysectomy experiments on the pregnant rat,

MAINTENANCE OF THE CORPUS LUTEUM AND INHIBITION OF PARTURITION IN THE RABBIT BY INJECTION OF ESTROGENIC HORMONE

WE HAVE previously shown (1) that the injection of estrogenic hormone, beginning on the IIth day of pseudopregnancy.in the rabbit prevents regression of the corpora lutea, and that corpora caused to persist by this means are functional. Such corpora on the 26th day after a sterile mating usually are indistinguishable from those of pregnancy of similar duration, and their functional activity is shown by the observation of the uterus and endometrium. The uterine muscle remains insensitive to pituitrin in vitro, and the endometrium, retaining some proliferation, takes on the appearance of that of the sterile horn of a unilateral pregnancy of the same age. Normally in the absence of the injections, the corpora become nonfunctional on the 16th to 17th day, the uterus promptly becomes sensitive to pituitrin, and the endometrium reverts to the unproliferated estrous condition. The purpose of the present experiments was to determine whether injections of estrogenic hormone would have a similar effect on the corpo...

The functions of the Corpus luteum. V.—Changes in the sterile horn during pregnancy, and their relation to changes in the Corpus luteum

Evidence as to the precise role of the corpus luteum during pregnancy is contradictory, especially when different species are compared. Most observers agree that the presence of the corpus luteum is necessary during the early stages of gestation. During the second half of pregnancy, however, the removal of the corpus luteum in certain animals does not lead to immediate abortion. In the guinea-pig Loeb and Hesselberg (1917), Herrick (1928) and Courrier, Kehl and Raynaud (1929) have found that pregnancy may continue for some weeks after double ovariectomy, and Ash-Upmark (1926) has listed a large number of clinical cases in which ovariectomy in women has not disturbed pregnancy. The evidence for the rabbit (summarised by Hammond, 1925), is slightly contradictory, but tends to show that the corpus luteum is necessary during the whole of pregnancy, although this was not the conclusion of Niskoubina (1909). In the rat it appears that double ovariectomy towards the end of pregnancy does not always result in its premature termination (Marshall and Jolly, 1906). More definite information is available for the mouse (Harris, 1927 ; Parkes, 1928), where the presence of the corpus luteum is essential during the whole of gestation.