Biomedical subjects

A J Peterson

Publications and source records attributed to A J Peterson.

At least 19 recordsLinked to original sources

PubMed2006

Expression of genes associated with allantois emergence in ovine and bovine conceptuses.

In the development of ruminant embryos, the emergence and growth of the allantois is critical for the establishment of the chorioallantoic placenta. The allantoic membrane contributes to all the vasculature that perfuses the placental tissues and the fetal membranes. Using suppressive subtractive hybridization to compare mRNA from Day 13 ovine preimplantation conceptuses (prior to allantoic emergence) with Day 17 allantoic membrane, we identified nine genes whose expression was associated with the emergence of the allantoic sac. Collagen alpha 1 type XII, collagen alpha 2 type I, collagen alpha 2 type V, epsilon 4 beta-globin, osteonectin, and uroplakin were expressed at significantly greater levels in ovine Day 17 allantois compared to Day 13 conceptuses. These genes are associated with the extracellular matrix and most likely are involved in establishing and strengthening the structural integrity of the allantoic sac and in the development of the blood vessels. RalB expression increased with development although at significantly greater levels in the allantois only at Day 19. Hoxa-10 and RhoA showed no differential expression during this period. All these genes showed a similar temporal pattern of expression in bovine conceptuses at equivalent stages of development with significantly greater expression of all these genes, except for Hoxa-10, found in Day 24 allantois compared to Day 14 conceptuses. This suggests that the role they play in allantoic emergence, growth and function is conserved in both ruminant species and that their expression is regulated in a similar manner. The interactions and regulation of this process remains to be fully explained.

Allantois↗

PubMed2005

Expression of TGF-beta1, TGF-beta2, TGF-beta3 and the receptors TGF-betaRI and TGF-betaRII in placentomes of artificially inseminated and nuclear transfer derived bovine pregnancies.

Bovine nuclear transfer pregnancies are characterized by a high incidence of placental abnormalities, notably, increased placentome size and deficiencies in trophoblast cell function and establishment of placental vasculature. Alterations in gene expression during placental growth and development may contribute to the appearance of large placentomes in pregnancies derived from nuclear transfer. The placenta synthesizes a number of cytokines and growth factors, including the transforming growth factor-betas (TGF-betas) that are involved in the establishment, maintenance and/or regulation of pregnancy. All forms of TGF-beta and their receptors are present at the fetal-maternal interface of the bovine placentome, where they are thought to play an important role in regulating growth, differentiation, and function of the placenta. Using real-time RT-PCR, we have examined the expression of TGF-beta1, TGF-beta2, TGF-beta3 and the receptors TGF-betaRI and TGF-betaRII in placentomes of artificially inseminated (AI) and nuclear transfer (NT)-derived bovine pregnancies at days 50, 100 and 150 of gestation. TGF-beta1, TGF-beta2 and TGF-beta3 mRNA expression increased by 2.0-2.8-fold, while TGF-betaRI and TGF-betaRII mRNA expression decreased by 1.7-2.0-fold in NT placentomes compared to AI controls at all gestational ages examined. These findings indicate that NT placentomes may be resistant to the growth suppressive effects of TGF-betas and could contribute to the placental proliferative abnormalities observed in NT-derived placentas. Alternatively, deficiencies in placentation may provide a mechanism whereby TGF-betas are dysregulated in NT pregnancies.

Activin Receptors, Type I↗

PubMed2004

A dynamic model for ovulation rate reveals an effect of the estrogen receptor genotype on ovarian follicular development in the pig.

A mathematical model that describes the recruitment and growth of ovarian follicles was fitted to data on ovulation rate and the measurements of plasma estradiol collected at times during the estrous cycle for individual gilts. The method of least squares was used to obtain estimates of the parameters of the mathematical model. The estimated model parameters were the maximum estradiol production for a follicle, development of each follicle after commitment, and a function describing the initial estradiol production of committed follicles. The estimated parameters for each pig were classified by estrogen receptor (ER) genotype (AA or BB) and analyzed using a multivariate analysis of variance. There were differences between genotypes (P < 0.05) for the parameter that described the initial distribution of individual follicles at recruitment. Gilts with ER genotype BB recruited follicles that varied more in size but had fewer very small follicles, indicating that the ER gene affects the relative estradiol secretion of the follicles at commitment. This analysis is an example of a general approach to genetic studies that uses a mathematical model of the physiology as a statistical basis for estimating gene action.

Analysis of Variance↗

PubMed2003

Improving successful pregnancies after embryo transfer.

Over the past 20 years the rate of blastocyst development in vitro has improved through the development of sequential defined media, refining the oxygen concentrations during culture and providing substrates to ameliorate free radical accumulation. Despite these advances there has been little progress in improving calving rates after the transfer of in vitro produced embryos. This suggests that the culture conditions have been very effective in enabling those fertilised oocytes to reach the blastocyst stage that otherwise would not occur in vivo. We suggest that the next advance by which the embryo transfer technology gains more acceptance in cattle production will be identifying those cows which are intrinsically superior recipients. This must be coupled to the development of non-invasive assessments of the developmental competence of both the oocyte and the blastocyst. Until these two goals are achieved the ET industry will remain static and unable to overcome the economic loss caused by embryo mortality occurring 7-10 days after transfer.

Abortion, Veterinary↗

PubMed2002

Effects of follicular size of cytoplast donor on the efficiency of cloning in cattle.

In cattle, oocytes obtained from follicles smaller than 3 mm in diameter can undergo maturation in vitro, progressing to MII and undergoing fertilization, but are developmentally incompetent. Cytoplasts were prepared from in vitro matured oocytes aspirated from small (1-3 mm) or large (6-12 mm) follicles and fused to serum starved mural granulosa cells. Following activation, reconstructed embryos were cultured for 7 days and classified G1 to G4, before being processed for nuclei counting or transferred to synchronized recipients. Oocytes from small follicles had lower rates of polar body extrusion (59.6 vs. 69%; 731/1230 vs. 608/857) and fusion (71.4 vs. 78.8%; 360/497 vs. 364/465; P < 0.06). There were no differences in total rate of blastocysts development (60 vs. 59.8%; small vs. large), or any grade classification. A significant interaction was detected between follicle size and embryo grade with G3 embryos from small follicles having a greater cell number. Developmental competence of G1 and G2 embryos did not differ at day 27 (48 vs. 46%; 16/33 vs. 17/37; small vs. large). Although there were no differences in fetal size between the two groups, differences in allantois length (53 vs. 86 mm; small vs. large; P < 0.002) and allantois width (9.5 vs. 13 mm; small vs. large; P < 0.06) were seen. No differences in survival to term (2/13 in each group) were observed. These results indicate that cytoplasts from follicles of 1-3 and 6-12 mm in diameter are equally developmentally competent when used in a nuclear transfer procedure.

Animals↗

PubMed2001

Conversion and temperature profiles during the photoinitiated polymerization of thick orthopaedic biomaterials.

Polymerization of a tetrafunctional monomer was investigated under a variety of photoinitiation conditions to assess the ability to form thick materials in situ for orthopaedic applications. The major biological concerns include local cell and tissue necrosis due to the polymerization exotherm and low conversions at greater depths due to light attenuation through thick samples. Experimental results indicate that depth of cure and temperature rises are controllable by altering the photoinitiator concentration, initiating light intensity, and type of photoinitiator. For example, no measurable conversion was detected at a 1.0 cm depth when polymerization was initiated with 1.0 wt% DMPA and 100 mW/cm2 ultraviolet light, whereas approximately 40% conversion was obtained when the initiator concentration was lowered to 0.1 wt%. This conversion was further increased to approximately 55% when a photobleaching initiator system was employed. At the highest rate of initiation studied (i.e., 1.0 wt% DMPA irradiated with 100 mW/cm2 ultraviolet light), a maximum temperature of approximately 49 degrees C was reached at the sample surface; however, this temperature dramatically decreased to approximately 33 degrees C when the light intensity was decreased to 25 mW/cm2. Finally, dual initiating systems that synergistically combine the advantages of photoinitiation and thermal initiation were investigated.

Biocompatible Materials↗

PubMed2001

Reversible immunoneutralization of human follitropin receptor.

Investigations of the human Follitropin receptor (hFSHR) have failed to identify the tertiary structure that forms the active hormone-receptor interaction site which is essential to develop an immunocontraceptive based upon the receptor. To identify such a domain of hFSHR, an immunoneutralizing monoclonal antibody (mAb) 106-105 (IgG2b) was generated. Flow cytometry tested whether mAb 106-105 recognized native hFSHR. The epitope of mAb 106-105 was mapped by Western blot and by peptide ELISA. Inhibition of hFSH binding and bioactivity was determined by radioreceptor assay and by cAMP production, respectively. MAb 106-105 bound native hFSHR through an epitope including residues 300-315. MAb 106-105 completely blocked hormone binding to receptor and cAMP production by Y1-R cells expressing hFSHR. These effects were completely reversible by increasing the concentration of hFSH. Coincubation of this antibody with peptide D300-F315 blocked antibody activity. These data demonstrate that a discrete linear hFSHR epitope is a target for interference with hormone activity. These results further demonstrate that antibody binding to the extracellular domain (ECD) of hFSHR and subsequent bioactivation can be modulated through a domain specific hindrance, offering a reversible immunoneutralizing target.

Animals↗

PubMed2001

Gonadotrophin responsiveness, aromatase activity and insulin-like growth factor binding protein content of bovine ovarian follicles during the first follicular wave.

The aim of this study was to examine the function of granulosa cells and hormone concentrations in follicular fluid in bovine ovarian follicles during selection of the first dominant follicle. Ovaries were obtained from beef heifers on days 1-5 after ovulation: follicles > 4 mm in diameter were dissected and follicular fluid and granulosa cells were collected from individual follicles. Oestradiol production by granulosa cells after culture with testosterone was used to determine aromatase activity and responsiveness to gonadotrophins was determined by cAMP production after culture with FSH or LH. Concentrations of oestradiol, progesterone and insulin-like growth factor binding proteins (IGFBPs)-4 and -5 were measured in follicular fluid. Follicles were classified as largest or smaller (days 1 and 2), or dominant or subordinate (days 3-5). Aromatase activity was greater in granulosa cells from the largest follicle than in granulosa cells from smaller follicles on days 1, 3, 4 and 5 (P < 0.05). Responsiveness to LH was not detected in granulosa cells on day 1, but from day 2 to day 5 cells from the largest follicle were significantly more responsive than cells from smaller follicles (P < 0.05). Responsiveness to FSH was detected in granulosa cells from all follicles from day 1 onwards and did not differ between cells from the largest follicle or smaller follicles on any day. Follicular fluid concentrations of oestradiol and the ratio of oestradiol:progesterone were greater and concentrations of IGFBP-4 and -5 were lower in the largest follicle than in smaller follicles from day 2 to day 5 (P < 0.05). In conclusion, selection of the dominant follicle is associated with increased granulosa cell aromatase activity followed by increased cAMP response to LH and follicular fluid oestradiol concentrations, and decreased follicular fluid concentrations of IGFBP-4 and -5 within 2 days after ovulation.

Animals↗

PubMed2000

A model of follicular development and ovulation in sheep and cattle.

A dynamic model to describe ovarian follicular development following commitment has been developed. It identifies follicular growth with oestradiol production and assumes that this growth is the result of intra-ovarian stimulation, gonadotrophin stimulation, and inhibitory interactions among the follicles, where larger follicles suppress the growth of the smaller follicles. The variables of the model are the levels of oestradiol in each follicle at commitment, the rate of change of oestradiol production by individual follicles during follicular development, and the level of oestradiol that will induce luteinizing hormone (LH) surge. Changes in the variables of the model could be associated with both genetic and environmental effects. The behaviour of the model is consistent with experimental observations. The model can be expanded to include exogenous follicle-stimulating hormone (FSH) administration assuming that FSH is associated with advancing the maturation of gonadotrophin-dependent follicles without affecting the number of committed follicles. The use of the model to explore FSH administration strategies is demonstrated. The model confirms that the response to FSH administration depends on both the amount of FSH and the time of administration. The largest number of double ovulations occurred when FSH was given at the time of the deviation of the dominant and subordinate follicles.

Animals↗

PubMed2000

Human follicle stimulating hormone receptor variants lacking transmembrane domains display altered post-translational conformations.

Variant splicing of gonadotropin receptor mRNA commonly occurs, however expression of receptor protein variants and their trafficking has yet to be studied in detail. To determine receptor variant trafficking and intracellular processing in mammalian cells, the intracellular fate of intentionally truncated variants of human follicle stimulating hormone receptor (hFSH-R) expressed in CHO cells was examined. Monoclonal antibodies (mAbs) were made against the hFSH-R's extracellular domain (ECD) expressed in insect cells. Four mAbs 106.156, 106.290, 106.318, and 106.263 were chosen as probes. Epitope mapping using synthetic peptides, and truncated hFSH-R variants revealed that mAb 106.156 bound to ECD residues 183-220, while mAbs 106.318, 106.290, 106.263 bound ECD residues 300-331. Immunofluorescence microscopy showed that mAbs 106.318 and 106.156 stained the surface of fixed, intact CHO cells expressing wild type hFSH-R. However, following cell permeabilization all four antibodies stained hFSH-R in Golgi and endoplasmic reticulum. Permeabilized cells expressing truncated variants ECD213 and ECD254 showed staining accumulated in the endoplasmic reticulum/nuclear envelope continuum. ECD335/His was found to accumulate in extended endoplasmic reticulum (ER). The ER location of ECD335/His was confirmed by double labeling experiments with concanavalin A and ECD mAb. Glycosidase digestion followed by Western blot analysis show ECD213 and ECD335/His to be glycosylated, but not ECD254. Both glycosylated truncated hFSH-R variants were sensitive to peptide-N-glycanase F and endoglycosidase H but insensitive to neuraminidase indicating that these variants possess high mannose type oligosaccharides. Thus truncated hFSH-R variants do not reach the medial or trans Golgi where high mannose oligosaccharides are trimmed and sialic acid is added. These data suggest that the conformation the ECD of the wild type receptor is different from the ECD alone expressed in the endoplasmic reticulum. This information suggests that the ECD serves two distinct roles; the first is to bind FSH and the other is likely to contact the endodomain of the receptor, which presumably leads to activation of the endodomain for signal transduction.

Amino Acid Sequence↗

PubMed2000

Functional analysis of repressor binding sites in the iab-2 regulatory region of the abdominal-A homeotic gene.

Spatial boundaries of homeotic gene expression are initiated and maintained by two sets of transcriptional repressors: the gap gene products and the Polycomb group proteins. Previously, the Hunchback (HB) protein has been implicated in setting the anterior expression limit of the UBX homeotic protein in parasegment 6. Here we investigate DNA elements and trans-acting repressors that control spatial expression of the Abdominal-A (ABD-A) homeotic protein. Analysis of a 1.7-kb enhancer element [iab-2(1.7)] from the iab-2 regulatory region shows that in contrast to Ubx enhancer elements, both HB and Krüppel (KR) are required to set the ABD-A anterior boundary in parasegment 7. DNase I footprinting and site-directed mutagenesis show that HB and KR are direct regulators of this iab-2 enhancer. The single KR site can be moved to a new location 100 bp away and still maintain repressive activity, whereas relocation by 300 bp abolishes activity. These results suggest that KR repression occurs through a local quenching mechanism. We also show that the gap repressor Giant (GT) initially establishes a posterior expression limit at PS9, which shifts posteriorly after the blastoderm stage. Finally, we show that this iab-2 enhancer contains multiple binding sites for the Polycomb group protein Pleiohomeotic (PHO). These iab-2 PHO sites are required in vivo for chromosome pairing-dependent repression of a mini-white reporter. However, the PHO sites are not sufficient to maintain repression of a homeotic reporter gene anterior to PS7. Full maintenance at late embryonic stages requires additional sequences adjacent to the iab-2(1.7) enhancer.

Animals↗

PubMed2000

Bovine embryo culture in vitro: new developments and post-transfer consequences.

The past decade has seen a significant shift away from co-culture systems for cattle blastocyst production. In particular, recent adoption of sequential media systems has increased performance. However, wholly defined systems, such as the replacement of albumin with nonbiological macromolecules, fail to reproduce the nutritive role that this molecule has during development. Cattle blastocysts developed in protein-free medium are metabolically compromised. A further new concept is the use of metabolic inhibitors to stimulate embryo development in vitro. Non-toxic levels of NaN3, 2,4-dinitrophenol or very low oxygen atmospheres (approximately 2%) significantly increase both the yield (by approximately 10-20%) and the quality of blastocysts when these treatments are applied during the peri-compaction period in vitro. Nevertheless, there are also negative consequences of cattle embryo culture, such as fetal oversize and/or significant post-day 35 fetal loss. We have recently found that much of this loss is due to failure of normal allantoic development within the conceptus. Early fetal development is supported by vascularization within the yolk sac, but from day 35 to day 110, loss occurs through poor nutrient supply and an inability to remove nitrogenous wastes, leading to fetal death around day 35. The cause of disrupted allantois development has not been identified as yet, but may share a common 'cause-effect' mechanism with the fetal oversize syndrome.

Adenosine Triphosphate↗

PubMed2000

Selected contribution: measuring the response time of pulmonary capillary recruitment to sudden flow changes.

To determine how rapidly pulmonary capillaries recruit after sudden changes in blood flow, we used an isolated canine lung lobe perfused by two pumps running in parallel. When one pump was turned off, flow was rapidly halved; when it was turned on again, flow immediately doubled. We recorded pulmonary capillary recruitment in subpleural alveoli using videomicroscopy to measure how rapidly the capillaries reached a new steady state after these step changes in blood flow. When flow was doubled, capillary recruitment reached steady state in <4 s. When flow was halved, steady state was reached in approximately 8 s. We conclude that the pulmonary microcirculation responds rapidly to step changes in flow, even in the capillaries that are most distant from the hilum.

Animals↗

PubMed1999

Development during single IVP of bovine oocytes from dissected follicles: interactive effects of estrous cycle stage, follicle size and atresia.

Previous work suggests that a number of factors such as follicle size, day of estrous cycle, and level of atresia influence the developmental potential of bovine oocytes in vitro. To understand better the interactions of these factors, 1299 follicles > or =3 mm in diameter were dissected from ovaries of synchronized dairy cows on four days (d2, d7, d10, or d15) during the estrous cycle. The oocyte from each follicle was collected and matured, fertilized, and cultured singly to d8 (d0 of culture = IVF). Control follicles (302) were similarly dissected and processed from an ovary pair randomly collected from the abattoir on each slaughter day. Results showed that development to blastocyst was greater in oocytes collected during phases of follicular growth (d2 and d10) than those collected during phases of follicular dominance (d7 and d15; 44.8% vs. 36.0%, respectively: P < 0.001) over all follicle size categories (3-5 mm, 6-8 mm, 9-12 mm and > or =13 mm). Oocyte competence tended to increase with increasing follicle size (P < 0.1). Follicular cells from follicles containing an oocyte that developed to morula or greater by d8 (484 samples) were analyzed by flow cytometry to measure the level of apoptosis. Results showed an increase in mean percent apoptotic cells in subordinate follicles (18.65 +/- 0.86 over all size categories), particularly those of medium size (25.55 +/- 2.2 for 6-8 mm size follicles; P < 0.001), during the dominance phase compared to growth phase (9.25 +/- 0.95 over all sizes; P < 0.05). These results show a significant affect of the stage of estrous cycle on both oocyte competence and levels of follicular atresia.

Animals↗

PubMed1999

Transuterine embryo migration in recipient cattle.

Transuterine migration of bovine embryos following fertilization in vivo is apparently rare, but little is known about migration following embryo transfer. We studied heifers receiving either 1 or 2 in vitro produced embryos to determine 1) the incidence of transuterine migration, 2) the timing of migration and 3) the random or systematic occurrence of the event. In 4 experiments, 436 heifers received embryos and 218 of these were pregnant at necroscopy on either Day 14, Day 18, Day 26 or Day 60 of pregnancy. Overall, 43/218 (20%) of the heifers had embryos that had migrated. The frequency of migration was higher in twin (30/68) than in single (13/150) embryo transfers of pregnant recipients (44 vs 9%; P<0.001), and in contralateral (9/15) than in ipsilateral (33/170) transfers (60 vs 19%; P<0.001). Among the heifers that received embryos by ipsilateral transfer, the migration rate was similar to that in heifers pregnant with a singleton after the transfer of either 1 (2/48) or 2 (4/60) embryos (4 vs 7%, NS). The migration rate was highest at Day 26 (12/37) in heifers receiving twin embryos by ipsilateral transfer but was similar at all other stages of pregnancy (15/111, 32 vs 14%; P<0.01). Migration was first observed by Day 14, and it appears that either further migration occurred over the next 12 d or that migration was associated with a higher survival rate from Day 14 to Day 26. The low migration rate evident at Day 60 suggests that migration by Day 26 was associated with increased embryo or fetal death by Day 60. The data suggest that embryo migration is probably independent for each of a pair of surviving embryos. We conclude that in cattle embryo migration is embryo-dependent, but this capability is dormant unless more than 1 embryo is present in a uterine horn or the embryos are transferred to the contralateral uterine horn. The relationship between migration and embryo survival remains unclear.

Animals↗

PubMed1998

In vitro and early in vivo development of sheep gynogenones and putative androgenones.

Genomic imprinting, where only one of the two parental genes is expressed, occurs in many phyla. In mammals, however, this phenomenon has been primarily studied in mice, and to a lesser extent, in humans. To understand how genomic imprinting may affect development in other species, particularly those with a different mode of placental development from mice and humans, 339 sheep zygotes were micromanipulated to contain either 2 large (presumptive male) or 2 small (presumptive female) pronuclei. One hundred and twenty-seven of these embryos and 86 manipulated and nonmanipulated control embryos were transferred to recipient ewes over 3 breeding seasons. Twenty-one control and 7 experimental conceptuses were recovered on day 21. Four of these conceptuses derived from zygotes with 2 small pronuclei were identified by karyotyping to be gynogenones (maternal-derived genome). While the gross morphology of the embryos appeared no different to those of normal controls, the extra-embryonic tissue from the conceptuses showed some hypertrophy and hypervascularization. Preliminary Northern blots of mRNA from allantoic and trophoblast tissue showed an overexpression of H19 and an underexpression of IGF2. Although the sheep gynogenetic phenotype contrasts with that seen in mice, these two genes appear to be similarly differentially expressed.

Animals↗

PubMed1998

Oestrogen regulation of insulin-like growth factor binding protein-3 (IGFBP-3) and expression of IGFBP-3 messenger RNA in the ovine endometrium.

Transcriptional regulation of insulin-like growth factor binding protein-3 (IGFBP-3) by oestrogen was investigated by Northern blot hybridization of endometrial tissue mRNA from anoestrous ewes treated with oestradiol-17beta at either 0, 40 or 80 microg per day for 7 days. The 2.6 kb IGFBP-3 transcript, seen in control animals, was virtually undetectable in treated animals. This suppressive effect was reflected in Western ligand blots of the uterine luminal fluid (ULF) proteins where the concentration of IGFBP-3 was significantly decreased with increasing oestrogen treatments. IGFBP-2 levels were increased with oestradiol treatment but no significant effect was seen on the other minor IGFBP's present in the ULF. Northern analysis also showed that the IGFBP-3 transcript was present from days 12 to 16 of the oestrous cycle but was either absent or very weak on days 0 (oestrus) and 9 of cycling ewes. In situ hybridization of endometrial tissue sections localized the IGFBP-3 mRNA to the luminal epithelial cell layer, areas of the stromal tissue and in some glandular epithelial cells. Oestradiol treatment of ewes down-regulated expression of IGFBP-3 in the endometrium; therefore, the low levels of IGFBP-3 in ULF during the early part of the oestrous cycle is possibly due to elevated levels of plasma oestradiol around oestrus.

Anestrus↗

PubMed1998

The proteolysis of insulin-like growth factor binding proteins in ovine uterine luminal fluid.

During days 12-15 after oestrus (day 0), the uterine luminal fluid (ULF) of both pregnant and non-pregnant ewes contains only two prominent insulin-like growth factor binding proteins (IGFBPs) of 16-18 kDa and 22-24 kDa which preferentially bind IGF-2. Immunoblotting with an IGFBP-3 antibody revealed these to be proteolytic fragments of IGFBP-3. In contrast, the ULF from anoestrus and ovariectomized ewes contained intact IGFBP-3 (40-44 kDa) and IGFBP-2 (34 kDa). Co-incubation of ULF from an anoestrus ewe with that from a day 12 cycling ewe cleaved the IGFBP-3 present into the two lower molecular weight IGFBPs characteristic of ewes in the late luteal phase of the oestrous cycle. The variation in proteolytic activity both during the year and during the cycle suggested an influence of progesterone. Supplementation of progesterone to long-term ovariectomized ewes via a CIDR-G breeding device for 5, 10 or 15 days induced marked proteolytic activity in all 10-day treated sheep. The ULF from the 15-day treated ewes showed reduced activity and could inhibit the activity present in 10-day ULF, suggesting the induction of an inhibitor after prolonged exposure to progesterone treatment. A possible role of IGFBP-3 proteolysis in the ovine ULF may be to selectively increase the bioavailability of IGF-1 in the uterine microenvironment, which may be crucial for the rapid elongation of trophoblast that begins during days 12-15 after mating.

Animals↗