Establishment of pregnancy in the pig: I. Interrelationships between preimplantation development of the pig blastocyst and uterine endometrial secretions

Effect of exogenous estrone sulfate on embryonic survival during asynchronous transfers in the pig

The effect of exogenous estrone sulfate (5 mg/day for 10 consecutive days starting on Day 10 after mating) on survival of embryos during asynchronous transfers was studied in Large White x Landrace gilts. Superinduction transfers were conducted by placing Day 4 embryos (younger) into mated Day-5 recipients (older) and vice versa. Treatment with estrone sulfate improved embryo survival in the transfer of younger embryos to recipients with a more developed uterine environment, but it did not affect the survival rate of older embryos in pregnant recipients. The results of the study also showed that when older embryos were transferred to a less developed uterine environment with or without estrone sulfate treatment they were better able to survine than younger embryos transferred to a more developed uterine environment.

Developmental potential of day 13 porcine embryonic disk under in vitro culture conditions

Embryonic disks were microsurgically isolated from adjacent trophoblast tissue and cultured for varying periods in vitro. During the first 24 h of culture, vesicles (1 to 4/disk) composed of mesoderm and endoderm formed from the ventral surface. In the subsequent culture period, the vesicles continued to increase in size and by 96 h in vitro, most originally multivesiculated explants possessed a single vesicle formed by delamination and coalescence of smaller vesicles. Scanning electron microscopy revealed the formation of grooves and ridges in abnormal attempts at differentiation by the embryonic ectoderm. Endoderm comprising the outer tissue layer of the vesicle underwent a gradual alteration in surface morphology during in vitro culture. Initially flat, with a paucity of microvilli, these cells became dome-shaped with an abundance of microvilli. In addition, they became highly secretory as revealed by the presence of numerous secretory droplets at their surface. After culture for periods of up to 10 d, several explants displayed areas containing pulsating tissue, with contractions occurring at a rate of 20 to 30/minute, indicative of mesoderm differentiation. Culture of porcine isolated embryonic disk in vitro should enhance investigations into the regulation of germ layer formation and differentiation and assist in determining the tissue source of conceptus secretory products.

Survival of small and large littermate blastocysts in swine after synchronous and asynchronous transfer procedures

Thirty-two crossbred sows were assigned to synchronous and asynchronous embryo transfer procedures to determine if, within a litter, small blastocysts were as viable as large blastocysts. Synchronous embryo transfers were established when donors and recipients displayed the onset of estrus (Day 0) within 6 h of each other. Asynchronous transfers were established when recipients displayed the onset of estrus 18 to 24 h after that of donors. An equal number (four or five) of the smallest and largest diameter blastocysts, from a Day 7 donor, were transferred to separate uterine horns of a Day 7 (synchronous) or a Day 6 (asynchronous) recipient. Each recipient's uterine horns were ligated at the external bifurcation to prevent transuterine embryonic migration. The percentage of blastocysts surviving was determined 300 h (12.5 d) after donors exhibited estrus. Small as well as large Day 7 blastocysts survived following asynchronos transfer to a Day 6 recipient. However, fewer (P<0.01) small blastocysts survived synchronous transfer than large blastocysts. These data suggested that small blastocysts were lost due to asynchrony with the uterine environment; however, when transferred to a less advanced environment, small blastocysts were equally viable as large blastocysts.

Early pregnancy signals in domestic animals

Large early embryonic death losses occur in all domestic animals and these losses are temporally related to early pregnancy recognition signals. Binucleate trophoblastic cells, which migrate to the endometrial endothelium, are a potential vehicle for early (day 15-20) communication between the mother and the embryo in ruminant animals. In cattle, the first pregnancy recognition signal, which results in increased progesterone secretion by the corpus luteum as early as day 10, appears to be a small (less than 10,000 Mr) heat-labile lipid-soluble molecule that can be adsorbed by dextran-coated charcoal. Although this substance has not yet been identified, there is a possibility that it is embryo-derived platelet-activating factor (EDPAF). EDPAF appears to influence progesterone synthesis by causing the release of luteotropic factors (arachidonic acid metabolites and serotonin) from activated platelets. The second pregnancy recognition factor in cattle and sheep appears to be a trophoblastic peptide having a molecular weight of 22,000-24,000 daltons (bTP-1, cattle) or 17,000 daltons (oTP-1, sheep). These compounds do not have direct luteotropic effects, but are thought to exert their antiluteolytic effects by inhibiting the production of luteolytic eicosanoids (PGF2 alpha) by the endometrium. A third early pregnancy signal in cattle is an hCG-like protein that appears in allantoic fluid on day 25, just after the disappearance of bTP-1. There is as yet no clear evidence that steroids produced by the conceptus act as early pregnancy signals in ruminants. However, estrogens appear to provide the essential early signal for corpus luteum maintenance in the pig.

Poissons, grenouilles, femmes et hommes: the appropriation and retention of archetypal systems for reproduction

In contradistinction to other biological systems, the reproductive mechanisms in sexually reproducing species are unique in that their success relies upon a synchronous interaction between two separate individuals. Reproduction has become increasingly more efficient as higher forms have developed internal fertilization and gestation. Although our anthropomorphic perspective has dominated the understanding of reproductive processes, 'recent discoveries' make it clear that this reproductive efficiency has been gained by retention of previously present biological mechanisms whose origins are in the vestigial excretory tracts and ducts which are the precursors of the reproductive tract. We refer to these as 'archetypal systems'. They include the interaction between sex steroid sensitive tissues and sex steroids, the renin-angiotensin system and the macrophage/monokine response to infection. Through these mechanisms the reproductive tracts have maintained control over the microenvironment in which the reproductive processes occur. Thus, gamete development in male and female, and fertilization and early embryonic existence in the female tract prior to implantation still occur in compartments which are extracorporeal, i.e., separated from blood or subendothelial spaces, and are controlled by cellular mechanisms found in ancient excretory tracts. Since the majority of the changes between lower forms and contemporary mammals are anatomical modifications which have favoured the success of these extracorporeal events within the developing, generally land-based mammals, we should take special note of lower animals, understanding the evolutionary appropriation of mechanisms designed to furnish the suitable microenvironment from the surrounding tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Conceptus development, uterine response, blood gases and endocrine function of gilts exposed to increased ambient temperature during early pregnancy

Fifteen crossbred gilts were used to determine the influence of heat stress during Days 8 to 16 after onset of estrus on the development of conceptuses and uterine and endocrine functions. Ten gilts were bred 12 and 24 h after the onset of estrus (Day 0), and five gilts were nonbred controls. On Day 5, catheters were inserted into the uterine-ovarian vein (UV), saphenous artery (SA) and saphenous vein (SV) of each gilt. An electromagnetic blood flow transducer was implanted around the main uterine artery. Pregnant (n=5) and nonbred (n=5) control gilts were exposed to 21 +/- 1 degrees C, and pregnant heat-stressed gilts (n=5) were exposed to 37 +/- 1 degrees C for 12 h and 32 +/- 1 degrees C for 12 h daily during Days 8 through 16 after estrus. Treatment did not influence the partial pressure of oxygen (PO(2)) and of carbon dioxide (PCO(2)) in the UV, SA and SV blood. Uterine blood flow was not altered by heat stress. On Day 16, total wet weight of conceptuses was reduced in the gilts that were heat-stressed compared with conceptuses from control gilts. Incorporation of (3)H-leucine into macromolecules in vitro by conceptuses from the heat-stressed gilts was reduced compared with control gilts. Concentrations of 15-keto-13, 14-dihydro prostaglandin F(2alpha) (PGFM) in peripheral blood were greater than 1 ng/ml between Days 13 to 16 after estrus in 20% of the pregnant control gilts, 60% of the heat-stressed pregnant gilts, and 100% of the nonbred gilts. Concentrations of estradiol in the SA were affected by treatment. These results indicate that heat stress of gilts between Days 8 to 16 after estrus reduced the amount of conceptus tissue and altered concentrations of estradiol in the peripheral circulation, but uterine blood flow and PO(2) and PCO(2) in blood were not affected.

Prostaglandin secretion by perifused porcine endometrium: further evidence for an endocrine versus exocrine secretion of prostaglandins

Bilateral perifusion devices were utilized for measurement of prostaglandin secretion by luminal and myometrial surfaces of porcine endometrium. Tissues were collected from Days 10, 12 and 14 pregnant, Day 14 cyclic and Day 14 estrogen-induced pseudopregnant gilts. Each tissue was placed into duplicate perifusion devices and perifused with Krebs-Ringer Bicarbonate solution at 3 ml/10 min for 2 h, fractions collected every 10 min and oxytocin (1 IU/ml) perifused during fractions 6-10 to the luminal side of one chamber and to the myometrial side of the other chamber. Secretion rates of PGF were higher (P less than 0.05) than PGE2 for each status. Secretion rates of PGF and PGE2 were higher (P less than 0.01) from the luminal side for Day 12 pregnant, Day 14 pregnant and Day 14 pseudo-pregnant gilts, whereas secretion was higher from the myometrial side for Day 10 pregnant and Day 14 cyclic gilts. Oxytocin increased (P less than 0.01) prostaglandin secretion from the luminal side regardless of reproductive status. Pregnancy at Day 12 and Day 14, as well as estrogen treatment, were associated with prostaglandin secretion in a luminal (exocrine) orientation versus a myometrial (endocrine) orientation for Day 14 cyclic and Day 10 pregnant gilts. These data indicate an estrogen associated switch between Days 10 and 12 of pregnancy from an endocrine to an exocrine secretion of prostaglandins.

Implantation associated changes in uterine secreted proteins

Cross sectional segments were removed from the uteri of pregnant and pseudopregnant mice and incubated in vitro with labeled amino acids. Proteins that were synthesized and secreted by these explants were separated by two-dimensional polyacrylamide gel electrophoresis and localized by fluorography. As expected, the overall amount of labeled protein secreted into the medium was greater with tissue removed from implantation sites, or an artificially induced deciduoma, than it was with tissue from non-decidualized areas. It was not possible, by means of visual examination of the gels, to determine whether qualitative changes occurred in the patterns proteins that were released. However, by means of dual label ratios, it was demonstrated that the synthesis and secretion of individual proteins was regulated differentially. Furthermore, it was found that when the stimulus for decidualization was a normal implanting embryo, the pattern of protein enhancement was different than it was with an intrauterine thread. The finding that the uterus can distinguish between these two deciduogenic stimuli implies that unique signal factors, which may be important for the establishment of pregnancy, are released by the mouse embryo before implantation.

Sparing effects of intrauterine treatment with prostaglandin E2 on luteal function in cycling gilts

Twelve crossbred gilts, 8 to 9 months of age, were used to study the effects of prostaglandin E2 (PGE2) on luteal function during the estrous cycle. Intrauterine and jugular vein catheters were surgically placed before day 7 of the treatment estrous cycle and gilts were randomly assigned to 1 of 3 treatment groups. Groups I and II received constant intrauterine infusion of vehicle (6.0 ml/24 hr) or PGE2 (2400 micrograms/day; 6.0 ml/24 hr) respectively; while group III was given intrauterine infusions of 400 micrograms PGE2 every 4 hr. All infusions were initiated on day 7 and continued until estrus or through day 23. Jugular blood samples were collected twice daily from days 7 to 30 for progesterone analysis. Intrauterine infusion of PGE2 at the dose and frequencies given in this study delayed the decline in jugular plasma progesterone and resulted in prolongation of the estrous cycle length. The results of this study have shown that PGE2 at the dosage and frequency of administration used was capable of extending corpus luteum function.

Role of prostaglandins in development of porcine blastocysts

Rapid elongation of porcine blastocysts between Days 11 to 12 of pregnancy coincides with an increase in uterine luminal content of prostaglandins. The present study evaluated the effect of two prostaglandin synthesis inhibitors (indomethacin and flunixin meglumine) on elongation of porcine blastocysts from spherical to filamentous forms between Day 11 to 12 of pregnancy. Gilts were hemi-hysterectomized on Day 11 of pregnancy. The excised uterine horn was flushed with 0.9% saline and diameter of blastocysts recovered were measured. Immediately following surgery, pregnant gilts were assigned to receive either: 1) vehicle every 4 h, 2) flunixin meglumine (banamine) every 4 h, or 3) indomethacin every 12 h. The remaining uterine horn was removed and flushed after the time of blastocyst elongation estimated for each gilt on basis of blastocyst development in the first horn. Uterine flushings were analyzed for total calcium, protein, acid phosphatase activity, estrone, estradiol-17 beta and prostaglandin F. Pretreatment blastocyst diameter was similar for all groups and ranged from 1 mm to 20 mm. Treatment of gilts with either banamine or indomethacin effectively inhibited (P less than 0.001) the increase in uterine luminal content of PGF. Total calcium, estrone and estradiol-17 beta were not influenced by treatment. Total uterine luminal protein and acid phosphatase activity were reduced (P less than 0.05) in banamine treated gilts compared to those receiving vehicle or indomethacin treatments. Although total PGF recovered in uterine flushings was reduced during the period of blastocyst elongation, treatment with PGF synthetase inhibitors failed to block rapid elongation of blastocysts from the spherical to filamentous forms.

Electron microscopy of the initial stages of placentation in the pig

To elucidate the morphology of the initial stages of epitheliochorial placentation in the pig, material from 10 sows of the Danish Landrace and from one Göttinger minipig gilt from day 13 to day 26 of gestation was processed for scanning and transmission electron microscopy. The observed foetomaternal interaction from day 19 1/2 minipig placenta corresponded well to the observations on the Danish Landrace placenta. From the results and the discussion it was concluded that the following structures were implicated in the initial phases of placentation in the pig: Protruding epithelial proliferations of the uterine epithelium enclosed by chorionic caps serving to immobilize the blastocyst (days 13 and 14). A thick glycocalyx on the maternal and a thin one on the foetal epithelium before contact. Close apposition between the apical plasma membranes from trophoblastic and uterine epithelium (day 14). Development of interdigitating microvilli (days 15-16). Formation of apical domes on the uterine epithelium closely related to the trophoblast provided with long cytoplasmic extensions into a luminal space between the apical domes, apparently representing a transition from histiotropic to haemotrophic nutrition (days 15-20). Placentation, development of interdigitating microvilli between foetal and maternal epithelium, was extended but not terminated in the peripheral zone at day 26.

Biochemical aspects of conceptus--endometrial interactions

Mammalian conceptuses must provide a chemical signal to the maternal system to insure maintenance of corpus luteum (CL) function and of progesterone production and continuation of uterine endometrial secretory activity. These events insure that the developing conceptus is provided with appropriate nutrients, regulatory enzymes and endocrine state to allow successful establishment and maintenance of pregnancy. Pig blastocysts begin to produce estrogens by Day 11 of pregnancy, which prevents secretion of the uterine luteolytic factor (PGF2 alpha) in an endocrine direction, but allows secretion in an exocrine direction, i.e., into the uterine lumen. Therefore, CL are "protected." Blastocyst estrogens also trigger secretion of a group of proteins, including uteroferrin, an iron transport protein, and a family of protease inhibitors whose biosynthesis within the uterine glandular epithelium is under the control of progesterone. Estrogen also appears to promote accumulation of glucose and fructose within the uterine lumen. A complex in vivo "culture medium" is thereby established to promote conceptus development. Pig blastocysts do not undergo invasive implantation within the uterine lumen although they produce the protease, plasminogen activator. Invasion may be prevented by endometrial secretion of progesterone-induced protease inhibitors which are produced in large amounts. In addition to estrogens of conceptus origin, calcium and prostaglandins PGF2 alpha and E2 may affect the uterine vasculature, water and electrolyte transport, capillary permeability, conceptus steroid production, and related events during pregnancy. The blastocysts of the large domestic animals also secrete proteins which include a large glycoprotein (Mr approximately 600,000) and a small acidic protein (Mr approximately 17,000). The latter has been purified from sheep and named ovine trophoblast protein I. These proteins may play unique roles in early pregnancy with respect to establishment and maintenance of pregnancy in the ewe, sow, mare, and cow.