Effect of nitric oxide synthase inhibitors on ovum transport and oviductal smooth muscle activity in the rat oviduct

The effect of the inhibition of nitric oxide synthase (NOS) on ovum transport and oviductal motility in rats was investigated. Three different NOS inhibitors were injected into the ovarian bursa at oestrus or day 3 of pregnancy. Oviducts and uteri were flushed 24 h later and the presence of ova was recorded. In oestrous and pregnant rats, treatment resulted in accelerated egg transport, as shown by a decrease in the number of ova present in the oviducts. In cyclic rats, intrabursal injection of 1 mg kg-1 of either N-monomethyl-L-arginine (L-NMMA) or N omega nitro-L-arginine methyl ester (L-NAME) elicited a 30% reduction in the number of ova present in the oviducts, whereas in pregnant animals, the same dose of L-NMMA produced a reduction of 40%. Simultaneous administration of the NO donor spermine NONOate (5 mg kg-1) completely reversed the effect of L-NMMA. Tubal motility was assessed by microsphere displacement analysis within the oviduct. Surrogate ova were transferred to the oviductal lumen at oestrus and 24 h later the effect of intraoviductal injection of 1 microgram L-NMMA or vehicle was assessed. The microspheres in the isthmus showed an oscillating motion, and periods in which movement was not detectable. However, L-NMMA treatment produced a 3.6-fold increase in the maximum instant velocities and a significant reduction in the resting periods of the microspheres compared with the control group (P < 0.001). These results provide evidence that NO inhibition increases tubal motility that results in accelerated ovum transport, and indicate that NO could act as a paracrine signal between different layers of the oviductal wall, providing a role for endogenous NO in regulation of tubal function.     

Oviductal and uterine influence on the development of Day-2 equine embryos in vivo and in vitro

The objective of this experiment was to contrast the influence of the oviductal and uterine environments on development of Day-2 embryos. Embryos were transferred to oviducts or uteri of synchronous recipient mares, or were incubated in oviductal co-culture, in uterine co-culture or in defined culture medium. Significantly more (P < 0.02) embryos transferred to the oviduct versus the uterus survived until Day 11 after ovulation (5 7 vs 0 7 , respectively). Significantly more (P < 0.001) embryos developed to expanded and hatched blastocysts in uterine co-culture than in culture medium (6 7 vs 0 7 , respectively). The rate of embryo development to expanded blastocysts was not significantly different (P > 0.1) in oviductal co-culture versus uterine co-culture (3 7 vs 6 7 , respectively), or in oviductal co-culture versus culture in medium (3 7 vs 0 7 , respectively). Three of 7 and 6 of 7 embryos developed to hatched blastocysts greater than 2000 mum in diameter during oviductal and uterine co-culture, respectively, while 0 of 7 embryos cultured in medium expanded to greater than 500 mum in diameter. Proportions of embryos that developed for at least 9 days.     

Embryo-initiated oviductal transport in mares.

The hypothesis that equine embryos initiate oviductal transport in mares was tested by placing day 6 uterine embryos in the oviducts of day 2 (n = 10) or day 5 (n = 10) recipient mares and attempting to collect the embryos from the uterus 48 h later. To determine whether the surgical transfer procedure initiated oviductal transport, medium alone was placed in the oviducts of day 2 (n = 10) inseminated mares (sham transfer), and uterine embryo collections were attempted 48 h later. Embryos were transported through the oviduct of day 2 recipients by day 4 (instead of day 5 to 6) in six of ten mares, which was not significantly less (P greater than 0.1) than in day 5 recipients (9 of 10). Oviductal transport was not primarily initiated by the surgical transfer procedure, since oviductal transport occurred in only one sham transfer. There was no significant difference (P greater than 0.1) in the diameter of embryos placed in the oviducts of day 2 and day 5 recipient mares (180 +/- 13.8 versus 187 +/- 11.3 microns, respectively). However, embryos collected from the uterus were significantly smaller (P less than 0.05) in day 2 than in day 5 recipients (375 +/- 85.4 versus 659 +/- 43.6 microns, respectively). One uterine embryo had shed its zona pellucida before being placed in, and transported through, the oviduct of the recipient mare.     

In vitro development of day-2 equine embryos co-cultured with oviductal explants or trophoblastic vesicles

This study compared the in vitro development of Day-2 equine embryos co-cultured with either trophoblastic vesicles or oviductal explants. Embryos were collected surgically from the oviducts of pony mares 2 d after ovulation and assessed for stage of development. Culture medium was Ham's F12 and Dulbecco's Modified Eagle's Medium (50:50 v/v) in a humidified atmosphere of 5% CO(2) in air at 38.5 degrees C with either trophoblastic vesicles or oviductal explants. The quality score of embryos was assessed daily. After 4 d in culture, embryos were stained (Hoechst 33342) and evaluated with epifluorescence to determine the number of nuclei present. Six of seven embryos co-cultured with oviductal exmplants developed to the morula/blastocyst stage, while four of seven embryos co-cultured with trophoblastic vesicles developed to the morula stage. More (P = 0.1) embryos co-cultured with oviductal explants reached the blastocyst stage than embryos co-cultured with trophoblastic vesicles (3 7 vs 0 7 , respectively). The number of cells was higher (P = 0.1) for embryos co-cultured with oviductal explants than for embryos co-cultured with trophoblastic vesicles (162.6 +/- 32 vs 87.3 +/- 28, respectively). The number of cells for embryos co-cultured with either oviductal explants or trophoblastic vesicles appeared to be lower than for embryos matured in vivo that were recovered from the uterus at Day 6 (378, 399, >1000). The co-culture of early equine embryos in a completely defined medium with either trophoblastic vesicles or oviductal explants can support development to at least the morula stage. The co-culture of embryos with oviductal explants resulted in superior development of four-to eight-cell embryos, as indicated by the proportion that reached the blastocyst stage and by the number of cells.     

Time of embryo transport through the mare oviduct

The objectives of this study were 1) to determine the time of embryo transport through the mare oviduct, 2) to determine whether equine embryos increase in diameter prior to the time of oviductal transport, and 3) to assess the stage of equine embryonic development at the time of oviductal transport. The time of oviductal transport (interval from ovulation to uterine entry) was estimated by collecting embryos from the mare oviduct or uterus at 2-hour intervals from 120 to 168 h postovulation. The time of oviductal transport was 130 to 142 h, since 9 9 embryos were located in the oviduct from 120 to 128 h; 7 14 embryos were in the oviduct and 7 14 embryos were in the uterus from 130 to 142 h; and 13 14 embryos were in the uterus from 144 to 168 h postovulation. Embryos collected during the period of oviductal transport (130 h to 142 h) were not significantly larger (P>0.1) in diameter than embryos collected prior to the period of oviductal transport (162.5+/-3.7 vs 156.7+/-3.1 mum, respectively). During the period of oviductal transport, embryos collected from the uterus were not significantly larger (P>0.1) in diameter than embryos collected from the oviduct (160.7+/-3.2 vs 164.3+/-7.0 mum, respectively). During this same period 12 14 embryos were compact morulae, and 2 14 embryos were blastocysts.     

Persistent infertility in ewes after prolonged exposure to oestradiol-17 beta

Merino ewes were treated with implants which released 300 micrograms oestradiol-17 beta per day or 5 mg progesterone per day, or both, for 9 months (Months 1-9), and after an 11-month intermission were treated again for 6 months (Months 20-26). Ewes were run with rams at Months 16, 28 and 40. Fertility was not affected by the first exposure period, but the second exposure to oestradiol reduced the fertility of ewes at both subsequent mating periods. Affected ewes returned to service more frequently (P less than 0.01) and were less likely to conceive (P less than 0.05). After mating, a normal population of spermatozoa was established in the caudal cervix, but transport through the cervix was impaired in affected ewes and there were fewer spermatozoa (P less than 0.01) in the cranial cervix. In affected ewes, the spinnbarkeit of cervical mucus was reduced (P less than 0.05), and the histological appearance of the cervix changed, looking like that of the uterus. Treatment with progesterone did not affect fertility, cervical mucus or sperm transport, but diminished the histological abnormalities produced by oestradiol (P less than 0.05). These results show that oestradiol-17 beta given after puberty can cause the same kind of permanent sexual transdifferentiation that is produced by the oestrogenic isoflavones in ewes with clover disease. The results suggest that this change may require more than a single exposure to oestrogen.     

Essential role of ZP molecules in tubal transport of embryos in mice

Our understandings of the molecular and cellular mechanisms underlying tubal transport of embryos are poor. This study describes the essential role of the molecules on the zona pellucida (ZP) in the tubal transport of mouse embryos. The bovine and porcine embryos that were interspecifically transferred to the mouse oviduct were selectively retained in the oviduct and rarely transported to the uterus. Antiserum ZP3-9 against synthetic peptides that are specific for mouse ZP3, significantly interfered with tubal transport of the treated embryos. The treatment of mouse embryos with antiserum ZP2-20 against the synthetic peptides, deduced from the sequences that are conserved in the structure of ZP2 from mouse and human, also inhibited their tubal transport. Among various proteolytic and glycosidic enzymes, treatments with trypsin and beta-glucosidase prior to transfer to the oviduct, significantly interfered with the tubal transport of the enzyme-treated mouse embryos. We hypothesize that species-specific epitopes on the ZP may be recognized by the oviductal cilia and/or the epithelial cells of ducts for tubal transport.     

Oviduct response to prostaglandins: Influence of estradiol and progesterone

Oviductal motility was measured in the isthmus of ovariectomized New Zealand rabbits. The effects of estradiol and progesterone on spontaneous motility and on the response of the oviduct to exogenously administered prostaglandin E₁ (PGE₁) and PGF_2α were determined. Estradiol treatment significantly increased both the amplitude (P<0.05) and frequency (P<0.01) of spontaneous contractions. The amplitude of spontaneous activity was less following progesterone treatment than following estradiol treatment (P<0.05). Progesterone treatment increased the duration of oviduct response to PGE₁ (P<0.05). Estradiol treatment had no effect on the response to PGE₁. Increased oviductal activity caused by PGF_2α lasted significantly (P<0.01) longer in ovariectomized, untreated animals than in ovariectomized animals treated with estradiol or progesterone. Progesterone was more effective than estradiol in decreasing the duration of the response to PGF_2α. These effects of steroid hormones on the responsiveness of the oviduct to PGE₁ and PGF_2α could contribute to the physiological control of egg transport. The nadir of ovarian hormone influence, as in the recently ovariectomized animals and as occurs immediately after ovulation, is associated with a high responsiveness of the oviduct to PGF_2α. This could effectively increase isthmic occlusion and prevent the eggs from passing through the oviduct prematurely. The gradual increase in ovarian estradiol and progesterone secretion during the 3 days following coitus could result in decreased responsiveness to PGF_2α and increased responsiveness to PGE₁. These changes might cause relaxation of isthmic tone and allow movement of eggs through the isthmus into the uterus.     

Limitations of oviductal transfers in swine

Eighty-six crossbred gilts were used in a series of experiments 1) to determine if eight-cell embryos enter the uterus before four-cell embryos do, and 2) to investigate the effects of transferring older, more developed embryos, either with or without intact zona pellucidae, to the oviducts of swine. Results of these experiments suggested that both four-and eight-cell embryos randomly enter the uterus on Days 3.5 to 4 (Day 0 = onset of estrus). Though there were no differences in survival rates or subsequent morphology of recovered embryos when transferred to the oviduct or uterus on Day 4, the transfer. of Day-6 embryos to the oviduct resulted in lower (P < 0.01) survival rates, and the recovered embryos were smaller (P < 0.01) than those introduced into the uterus. Survival rates were lower (P < 0.06) for zonae-free embryos transferred to the oviduct than for zonae-intact embryos; however, these differences were not evident when zonae-free embryos were transferred into the uterus. These experiments demonstrate that oviductal transfer procedures in swine are limited to zonae-intact, preblastocyst stage embryos.     

Effect of indomethacin on egg transport and pregnancy in the rabbit.

Treatment of rabbits with indomethacin (10 mg/kg/day) 48 hr before mating, and with 20 mg/kg at 12 hr followed by 8 mg/kg at 48, 72 or 96 hr after mating did not affect the rate of egg transport through the oviduct. Indomethacin treatment at the time of implantation interfered with pregnancy and caused degeneration and resorption of embryos. These results suggest that inhibition of prostaglandin synthesis does not directly affect egg transport, but that prostaglandin appears to be required for the retention of implanted embryos.     

Estrogen and progesterone receptors in the oviduct during egg transport in cyclic and pregnant rats

We investigated the temporal relationships between ovum transport and changes in the concentration of nuclear steroid receptors in the oviduct of cyclic and pregnant rats. A lack of parallelism between estrogen and progesterone fluctuations in plasma and their respective nuclear receptor concentrations in the oviduct predominated during egg transport. In pregnant animals, oviductal egg transport took 24 h longer than in nonpregnant animals. In both conditions, transport was initiated while the action of estrogen and progesterone on the oviduct--measured as nuclear receptor accumulation--was decreasing. Three or four days later, depending on whether the animal was pregnant, the eggs entered the uterus shortly after an increase in the nuclear receptor accumulation of both hormones. Treatment with RU486, a progesterone receptor-blocking agent known to cause premature arrival of eggs in the uterus, advanced estrogen receptor accumulation in the oviduct of pregnant rats. These data suggest that the arrival of eggs in the uterus is timed by a transitory increase in nuclear estrogen receptor in the oviduct that does not necessarily reflect a similar change of circulating estradiol. Moreover, in pregnant rats, the onset of this estrogenic action is delayed by a progesterone receptor-mediated effect that hinders nuclear estrogen receptor accumulation.     

Disparate effects of estradiol on egg transport and oviductal protein synthesis in mated and cyclic rats

Previously, we found that the dose of estradiol (E2) required to accelerate egg transport increases 5- to 10-fold, in mated compared to cyclic rats. Here we examined protein synthesis in the oviduct of mated and cyclic rats following a single injection of E2 known to accelerate oviductal egg transport or after concomitant treatment with progesterone (P4) known to block this acceleration. On Day 1 of the cycle or pregnancy, E2, P4, or E2 + P4 were injected s.c., and 4 h later oviducts were removed and incubated for 8 h in medium with 35S-methionine. Tissue proteins were separated by SDS-PAGE, and protein bands were quantitated by fluorography and densitometry. In mated rats, E2 and P4 increased different protein bands and P4 did not affect the fluorographic pattern induced by E2. In contrast with mated rats, none of these treatments changed the fluorographic pattern of the oviductal proteins in cyclic rats. Estradiol-induced egg transport acceleration was then compared under conditions in which oviductal protein synthesis was suppressed. Mated and cyclic rats treated with equipotent doses of E2 for accelerating egg transport also received actinomycin D (Act D) locally. Estradiol-induced oviductal egg loss was partially blocked by Act D in mated but had no effect in cyclic rats. We conclude that the oviduct of mated and cyclic rats differs in that only the former responds with increased protein synthesis to a pulse of exogenous E2 and P4 and requires an intact protein synthesis machinery in order to accelerate egg transport in response to E2.     

Comparative effects of 6-hydroxydopamine and alpha-adrenoceptor antagonists on intrauterine migration and spacing of blastocysts in the rat

Sympathetic nerve terminals were destroyed by administration of 6-hydroxydopamine (2 x 50 mg/kg) at 10:00 h on Days 4 and 5 of pregnancy in the rat. In the myometrium, this treatment markedly decreased noradrenaline concentrations (by 99%, P less than 0.001), demonstrating that myometrial noradrenaline is mainly originated from sympathetic nerves; therefore after 6-hydroxydopamine, the distribution and spacing of blastocysts remain unaffected throughout the uterus. Administration of phenoxybenzamine (2 x 6 mg/kg) in the morning of Days 4 and 5, or prazosin (4 x 3 mg/kg) from 12:00 h on Day 4 until 12:00 h on Day 5 disorganized the even distribution of blastocysts from the tubal end to the cervical end of the uterine horns. These results provide evidence that a noradrenergic transmission via action on myometrial post-synaptic alpha 1-adrenoceptors is involved as a regulatory mechanism of uterine motility for distribution and spacing of blastocysts in the rat uterus.     

Effects of asynchrony on rabbit blastocyst development

The development of synchronously and asynchronously transferred rabbit morulae (recovered at Day 3 p.c.) and blastocysts (recovered at Day 4 p.c.) was investigated before the anticipated time of implantation. The results obtained with various techniques (evaluation of gross morphology, measurement of diameter, thymidine incorporation, light and electron microscopy) led basically to the same conclusions. Embryos being asynchronously transferred to the uterus of recipient rabbits survived, at least in terms of certain cellular functions like cell proliferation, for more than 2 days. Development, however, was clearly retarded and ultrastructural examination revealed substantial cell damage. Some blastocysts showed, even after 3 days, normal growth and cell proliferation indicating considerable differences between individuals in the ability to compensate for suboptimal developmental conditions before implantation. In general, this ability was greater in the transferred Day-3 morulae than in the Day-4 blastocysts. Embryonic growth and the ability to dissolve the zona pellucida, to synthesize crystalloid bodies and to differentiate extraembryonic endoderm indicated the maintenance of some developmental functions under asynchronous conditions. Blastocyst development was influenced by the progestational stage of the recipient. At 1 day after transfer into asynchronous older uteri, blastocyst diameters were larger and cell proliferation was increased compared with all other groups, suggesting an attempt of the blastocyst to adjust to the more advanced maternal milieu. Development in asynchronous younger uteri was delayed. No comparable differences in development were found in cultured embryos for which the media had been supplemented with flushings from the same progestational uterine stages as used for transfer. Thymidine incorporation in cultured embryos did not differ between the various supplements (P greater than 0.05) and was generally lower than in chronologically aged asynchronously transferred embryos (P less than 0.05 for Day-3 and P less than 0.001 or P greater than 0.05 for Day-4 embryos).     

Influence of the endometrium, protease inhibitors and freezing on antiviral activity of proteins secreted by pig conceptuses

In Exp. 1, only medium from cultures containing conceptus tissue had antiviral activity (P less than 0.05). Addition of Day-15 pregnant endometrium or Day-14 cyclic uterine flush proteins to cultures containing 200 mg conceptus tissue decreased antiviral activity (conceptus x endometrial protein interaction, P less than 0.06). Effects of endometrium (-54%) and uterine flush proteins (-40%) on antiviral activity of conceptus cultures did not differ from each other (P greater than 0.10). In Exp. 2, antiviral activity was only detected in cultures containing conceptus tissue (P less than 0.06). The amount of antiviral activity in cultures of Day-15 conceptus tissue was not influenced differently (P greater than 0.10) by culture in medium conditioned by endometrium from Day 10 or Day 12 of pregnancy. However, antiviral activity was undetectable in medium conditioned by endometrium from one of the Day-12 gilts. In Exp. 3, antiviral activity was present in medium from only 1 of 3 cultures from Day-12 gilts when assayed unfrozen. Antiviral activity was lower (P less than 0.01) in cultures of conceptuses from Day 12 than Day 14 of pregnancy; however, antiviral activity increased quadratically (P less than 0.05) when cultures contained 0, 0.01, 0.1 and 1.0 units/ml aprotinin, respectively. Freezing and thawing culture medium did not reduce (P greater than 0.10) antiviral activity compared to medium assayed unfrozen (1438 vs 1354 units/ml, respectively). These results suggest a regulatory influence of the endometrium on secretion of antiviral proteins by pig conceptuses in vitro.     

The effect of ovarian steroid deficiency on regeneration of oviductal mucosa following reconstructive surgery

In patients with distal tubal occlusion a microsurgical oviductal reconstruction is, apart from the in vitro fertilization, the only treatment option. Unfortunately, the results of reconstructive surgery are often unsatisfactory. The effects of sex steroids on the regeneration process after reconstructive surgery have not been well investigated. This study was aimed to evaluate the effect of decreased concentrations of ovarian sex steroids (castration) on regeneration of the oviduct mucosa after the reconstructive surgery of distally occluded oviducts. The study was performed on 32 female rabbits that underwent unilateral oviduct ligature and resection of fimbriae. The occlusion lasted six (group I) or twelve weeks (group II). After this time the animals were re-operated, and allocated into 4 groups: castration with reconstructive surgery (IA, IIA), reconstructive surgery only (IB, IIB). After next six or twelve weeks the fallopian tubes were examined under light, scanning and transmission electron microscopes. An immunohistochemical reaction for Ki-67 proliferative antigen was also performed. Ovarian steroid levels were evaluated by radioimmunoassays. The castrated animals had significantly lower levels of estradiol, progesterone and 17-hydroxyprogesterone than the control groups. Long lasting tubal occlusion caused pronounced histological changes of tubal mucous membrane (group II). In the rabbits with preserved ovaries and twelve-week long oviductal occlusion (group IIB), the regeneration of the distal end and restoration of fimbria were not complete twelve weeks after microsurgical reconstruction. In castrated animals with long-lasting occlusion (group IIA) the destructive changes, found in the mucosa of tubal ampullas of occluded oviducts before reconstruction, were still present and even intensified twelve weeks following reconstructive surgery. The castration hampered proliferation of the mucosa cells, thus no fimbriae were restored. Low levels of ovarian steroids were found to have adverse effect on fallopian tube regeneration following reconstructive surgery. The effect was noted even in cases with minor preoperative fallopian tube damage. Therefore, the treatment of concomitant endometriosis or uterine fibroids with GnRH analogues should not be recommended simultaneously with microsurgical tubal reconstruction.     

Survival of equine embryos co-cultured with equine oviductal epithelium from the four- to eight-cell to the blastocyst stage after transfer to synchronous recipient mares

In this study we examined the ability of equine oviductal epithelial cells (OEC) to support the development of four- to eight-cell equine embryos in vitro and investigated the ability of co-cultured embryos to continue normal development after transfer to synchronous recipient mares. Equine embryos obtained at Day 2 after ovulation were cultured with or without OEC for 5 days. Those OEC co-cultured embryos that reached the blastocyst stage and embryos recovered from the uterus at Day 7 were surgically transferred to synchronous recipient mares. Co-culture with OEC improved (P < 0.01) development of four- to eight-cell embryos to blastocysts compared to medium alone (11/15 vs 0/6) during 5 days in vitro. Embryos co-cultured with OEC were smaller (P < 0.05) and more delayed in development than Day-7 uterine blastocysts. There was no difference in the Day-30 survival rate of co-cultured blastocysts (3/8) or Day-7 uterine blastocysts (5/8) after transfer to recipient mares. These results indicate that co-culture with OEC can support development of four- to eight-cell equine embryos in vitro and that co-cultured embryos can continue normal development after transfer to recipient mares.     

Influence of complement depletion on sperm function in the female rabbit

Female rabbits were wholly depleted of complement by treatment with anti-complementary cobra venom factor (CVF) 36 h before mating. Complement depletion did not compromise occurrence of the acrosome reaction, as judged by sperm penetration of eggs collected 12-13 h post coitum. However, in CVF-treated females, significantly more spermatozoa had penetrated the egg vestments, more spermatozoa were present in flushings from the oviducts, and sometimes the uterus, than in control females mated to the same males. The results indicate that, although the acrosome reaction is unlikely to depend on complement activation, complement-dependent factors may exert a restrictive effect on spermatozoa after vaginal insemination of the normal female rabbit.     

A possible explanation for the refractoriness of uterine prostaglandin production

Arachidonic acid increased the outputs of prostaglandin (PG) F-2 alpha, PGE-2 and 6-keto-PGF-1 alpha from the Day-7 and Day-15 guinea-pig uterus superfused in vitro. Similar increases in PG output were observed when the arachidonic acid treatment was repeated after an interval of 1, 3 or 5 h. Phospholipase (PL) A-2 increased the outputs of PGF-2 alpha, PGE-2 and 6-keto-PGF-1 alpha from the Day-7 guinea-pig uterus, but repeating the PLA-2 treatment 1 h later failed to stimulate PG output. The increase in outputs of PGF-2 alpha and PGE-2 caused by PLA-2 were partly restored after 3 h and were fully restored after 5 h, whereas the increase in 6-keto-PGF-1 alpha output produced by PLA-2 was only partly restored after 3 and 5 h. PLA-2 had little or no effect on PGF-2 alpha and PGE-2 outputs from the Day-15 guinea-pig uterus initially, and when repeated after 1, 3 and 5 h. This was probably due to the output of these two PGs, particularly of PGF-2 alpha, being stimulated in vivo before removal of the uterus. PLA-2 increased 6-keto-PGF-1 alpha output from the Day-15 uterus initially, but failed to cause a response when administered again 1 h later. After 3 and 5 h, the increase in 6-keto-PGF-1 alpha output from the Day-15 uterus caused by PLA-2 was partly restored. A23187 and PLC increased the outputs of PGF-2 alpha, PGE-2 and 6-keto-PGF-1 alpha from the Day-7 and Day-15 guinea-pig uterus. These responses to A23187 and PLC were reduced (but not abolished) when the two compounds were administered again 1 h later. After 3 and 5 h, the increases in output of PGF-2 alpha and PGE-2 produced by A23187 and PLC had returned to the initial values. The increases in output of 6-keto-PGF-1 alpha from the Day-7 and Day-15 guinea-pig uterus produced by A23187 and PLC were partly restored after 3 and 5 h, except for the response to PLC on Day 7 which was fully restored after 5 h. The results show that there is no failure with time in the mechanism which converts arachidonic acid into PGF-2 alpha in the guinea-pig uterus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of variation in embryo stage on the establishment of pregnancy, and embryo survival and growth in ewes with two embryos

Embryos at different stages of development were transferred to recipient ewes on Day 6 to investigate the effect of variation in stage of development on embryo survival and growth. Three groups of ewes received 2 embryos that were at the same stage of development, Day 4, Day 6 or Day 8. A fourth group received 1 Day-4 and 1 Day-8 embryo. At autopsy on recipient Day 34 there were no significant differences in embryo survival (Day 4, 34%; Day 6, 50%; Day 8, 46%; and Day 4 and 8, 48%). Fetuses developing from Day-8 embryos were heavier than others (Day 4, 1.10 +/- 0.06 g; Day 6, 1.15 +/- 0.06 g; Day 8, 1.41 +/- 0.08 g; P less than 0.05). In Group 4 neither survival nor growth of embryos was significantly affected by the presence of an embryo at a different stage of development. The ability of the uterus to stimulate development of a relatively retarded embryo is confirmed. Apparently the uterus has less effect in slowing the development of advanced embryos.