Porcine Luteal Cells Research Articles

The influence of adiponectin on the transcriptomic profile of porcine luteal cells.

Reproductive functions are closely related to nutritional status. Recent studies suggest that adiponectin may be a hormonal link between them. Adiponectin is an adipocytokine, abundantly expressed in adipose tissues. It plays a dominant role in lipid and carbohydrate metabolism by stimulating fatty acid oxidation, decreasing plasma triglycerides, and increasing cells' sensitivity to insulin and has direct antiatherosclerotic effects. The hormone is also postulated to play a modulatory role in the regulation of the reproductive system. The aim of this study was to identify differentially expressed genes (DE-genes) in response to adiponectin treatment of porcine luteal ovarian cells. The global expression of genes in the porcine ovary was investigated using the Porcine (V2) Two-color gene expression microarray, 4 × 44 (Agilent, USA). Analysis of the microarray data showed that 701 genes were differentially expressed and 389 genes showed a fold change greater than 1.2 (p < 0.05). Among this number, 186 genes were up-regulated and 203 were down-regulated. The list of DE-genes was used for gene ontology analyses. The biological process list was generated from up-regulated and down-regulated DE-genes. We found that up-regulated products of DE-genes take part in 30 biological processes and down-regulated products in 9. Analysis of the interaction network among DE-genes showed that adiponectin interacts with genes involved in important processes in luteal cells. These results provide a basis for future work describing the detailed interactions and relationships explaining local regulation of adiponectin actions in the ovary of pigs.

Expression of orexins and their precursor in the porcine ovary and the influence of orexins on ovarian steroidogenesis in pigs

Orexins A and B are hypothalamic neuropeptides associated with homeostasis and the reproductive system. The aim of the study was to compare the expression of the prepro-orexin gene and the intensity of orexins immunoreactivity in the porcine ovary (corpora lutea, granulosa and theca interna cells) during four different stages of the oestrous cycle (days: 2–3, 10–12, 14–16 and 17–19) and to examine the in vitro effect of orexins on the secretion of steroid hormones by porcine luteal, granulosa and theca interna cells. The highest expression of prepro-orexin mRNA was observed in theca interna cells on days 17–19 of the oestrous cycle. The highest content of immunoreactive orexin A was noted in corpora lutea on days 10–12 and the highest level of immunoreactive orexin B on days 14–16 of the cycle. Immunoreactive orexin A concentrations were higher in theca interna cells than in granulosa cells, whereas similar levels of immunoreactive orexin B were observed in both cell types. Under in vitro conditions, at the concentration of 10nM, orexins A and B inhibited FSH-induced oestradiol secretion by granulosa cells. The obtained results suggest that the pattern of orexin peptide expression in the porcine ovary is related to the animals’ hormonal status. Our findings imply that orexins can affect porcine reproductive functions through modulation of ovarian steroidogenesis.

Direct in vitro effect of LH and steroids on leptin secretion by porcine luteal cells during the late-luteal phase of the estrous cycle

Direct in vitro effect of LH and steroids on leptin secretion by porcine luteal cells during the late-luteal phase of the estrous cycle

The influence of IL-1β, TNFα and IL-6 on induction of apoptosis in cultured porcine luteal cells

The influence of IL-1β, TNFα and IL-6 on induction of apoptosis in cultured porcine luteal cells

Direct in vitro effect of LH and steroids on leptin gene expression and leptin secretion by porcine luteal cells during the mid-luteal phase of the estrous cycle

Leptin, the product of the ob gene, is implicated in the control of reproductive functions in different species. Leptin transcript and protein are present in several tissues including adipose tissue and corpus luteum. The regulation of leptin mRNA expression and leptin secretion in porcine luteal cells is not clear. In this study, we determined leptin and OB-Rb mRNA/protein levels in porcine luteal cells during the mid-luteal phase of the estrous cycle (days 10–12) and examined, in vitro, the effects of LH, 17-β estradiol (E2) and progesterone (P4) on leptin gene expression and leptin secretion in those cells. Leptin and long form of leptin receptor (OB-Rb) mRNA expressions as well as leptin and OB-Rb protein were detected in the luteal cells by real-time PCR and fluorescence immunocytochemistry (F-ICC), respectively. Isolated luteal cells, after preliminary culture (48h) were treated with LH (1; 10; 100ng/ml), E2 (0.02; 0.2; 2; 20ng/ml) and P4 (20; 100; 200ng/ml) for 24h. LH did not induce significant changes in leptin mRNA expression in the luteal cells. A higher level of leptin transcript was found in the presence of E2 (0.02ng/ml) or P4 (200ng/ml). Estradiol (0.2ng/ml) and P4 (200ng/ml) increased leptin secretion by luteal cells. Our results indicate that leptin and OB-Rb genes and proteins are expressed in porcine luteal cells and suggest that steroid hormones (E2 and P4) affect leptin mRNA expression and leptin secretion during the mid-luteal phase of the estrous cycle.

The Effect of Prolactin on Estradiol-17ß and Testosterone Plus 5α-Dihydrotestosterone Secretion by Porcine Luteal Cells in Vitro

Prolactin (1, 5, 10 micrograms/ml) inhibited 5 alpha-dihydrotestosterone (DHT), testosterone (T) and estradiol-17 beta (E2) secretion by luteal cells isolated from porcine corpus luteum on the 13th day of the estrous cycle. The effect of prolactin upon luteal cells on the 5th and 17th day of the cycle was different. Inhibition of DHT, T and E2 secretion in luteal cells on the 5th day of the cycle occurred only after 6 hours of incubation, at prolactin doses of 5 and 10 micrograms/ml of the medium. Luteal cells obtained from corpora lutea with considerable physiological luteolysis (17th day of the cycle) did not react to the presence of prolactin in the incubation medium. The results showed that the effect of prolactin upon luteal cells depended on the intensity of steroidogenesis. Luteal cells on the 5th day of the estrous cycle produced progesterone in the amounts 34 +/- 9.1 ng/ml, on the 13th day: 62 +/- 11.5, and on the 17th day: 7.9 +/- 1.9. The effect of prolactin was most pronounced in case of cells on the 13th day of the cycle. These cells were characterized by the highest production of progesterone. The in vitro observations suggest the role of prolactin in inhibiting synthesis or release of DHT, T and E2 from luteal cells.

The effect of oxytocin and vasotocin upon progesterone, testosterone and estradiol 17 beta-secretion by the luteal cells from cyclic pigs.

Porcine luteal cells were obtained from the corpora lutea on the 13th day of the estrous cycle. The cells were digested with 0.25% trypsin and suspended in the Medium 199 with an addition of 10% calf serum, at a concentration of 5 X 10(4) cells/ml. The cells were incubated with or without 4 and 40 mi.u./ml of oxytocin, 10 and 100 ng/ml of arginine-vasotocin, 1 microgram LH and 50 U/ml hCG. Levels of progesterone, testosterone and estradiol 17 beta were determined with the radioimmunological method, following 6 h incubation. It was found that progesterone secretion under the influence of oxytocine (4 mi.u./ml) was less than in the control group and in the group with LH. Similarly, arginine-vasotocin at a dose of 10 ng/ml inhibited progesterone secretion (P less than 0.05). Higher doses of these peptides had no suppressive effect on the luteal cells. Oxytocin and arginine-vasotocin had no influence on testosterone secretion by luteal cells. However, these cells produced less (P less than 0.05) estradiol 17 beta under the influence of oxytocine than of hCG. The results point to a direct effect of oxytocin and arginine-vasotocin on steroidogenesis in the corpora lutea of cyclic pigs.

Effect of FSH on progesterone secretion by porcine large and small luteal cells isolated from early-developing corpora lutea.

Isolated porcine luteal cells from d 0-3 of the estrous cycle (estrus-d 0) were incubated with or without addition of 0, 10, 10(2) or 10(3) ng FSH/ml. Progesterone (P4) content was determined after 24 hrs of incubation. In nonstimulated conditions the basal P4 production of large cells (LCs) was 65 fold higher than that of small cells (SCs). The LCs but not SCs were stimulated by doses of 10 and 10(2) ng FSH. FSH in doses of 10 and 10(2) ng did not influence P4 production by SCs, but higher doses (10(3) ng) significantly decreased their P4 secretion The results indicated that FSH can have a distinct cellular luteotropic effect during the early development luteal phase of the pig. FSH influenced P4 secretion by LCs whereas, with SCs it had no effect (10 and 10(2) ng) or P4 secretion decreased (10(3) ng).

Large and small cells of the porcine corpus luteum: differential capacity to secrete estradiol and aromatize exogenous androgen during mid- and late luteal phase.

It has been demonstrated previously that aromatization capacity of luteal cells increased as the luteal phase progresses, suggesting that estradiol secretion by regressing corpora lutea could play an active role in regulation of the estrus cycle. To determine whether a specific luteal subpopulation is responsible for this process, luteal cells collected from mature (8-10 days after ovulation) corpora lutea were separated at unit gravity into small (14-26 microns) and large (26-38 microns) cell types. Aliquots of separated cells were incubated overnight in M199 medium alone (= control) or in medium containing: 10 M-5 T, 10(-6) M or 10(-7) M T or 0.1 x 10(-3) M, 0.5 x 10(-3) M or 1 x 10(-3) M aromatase inhibitor CGS 16949A. Both cell types were capable of estradiol production without the addition of substrates. The endogenous content of estradiol was always higher in large granulosa-derived luteal cells (LC) than in small theca-derived luteal cells (SC), and was higher in the late (LLP) than in the mid-luteal (MLP) phase. Both types of cells responded to testosterone by increasing estradiol secretion. Adding aromatase inhibitor to LC isolated from MLP and LLP decreased testosterone-stimulated estradiol secretion. On the other hand, aromatase inhibitor had no effect on testosterone-stimulated estradiol secretion by SC isolated during MLP, and inhibited testosterone-stimulated estradiol secretion by SC isolated during LLP. These data are the first to show the ability of both populations of porcine luteal cells to aromatize exogenous testosterone. The observed lack of aromatase inhibitor influence upon basal secretion of estradiol by SC separated from mature corpora lutea, and the decrease of testosterone-stimulated estradiol secretion by SC isolated from regressing corpora lutea, indicate that cytodifferentiation during luteinization could cause expression of P450arom in theca-derived luteal cells.

Tumor Necrosis Factor (TNF)-Alpha Induces Luteolytic Sensitivity in Porcine Luteal Cells by Activating the Intra-Luteal Prostaglandin (PG) Pathway.

Tumor Necrosis Factor (TNF)-Alpha Induces Luteolytic Sensitivity in Porcine Luteal Cells by Activating the Intra-Luteal Prostaglandin (PG) Pathway.

The effect of oxytocin on progesterone secretion, phosphoinositide hydrolysis and intracellular mobilisation of Ca 2+ in porcine luteal cells

Oxytocin (OT) is involved in the regulation of steroid secretion by the corpus luteum (CL) in pigs, but OT signal transduction in the porcine CL has not been identified. In this study, the effects of OT on in vitro progesterone (P4) secretion, phosphoinositide (PI) hydrolysis and intracellular mobilisation of Ca2+ ([Ca2+]i) were investigated in porcine luteal cells during the early (days 3-5), mid(days 8-10) and late luteal phases (days 12-14) of the oestrous cycle. Basal concentrations of P4 and accumulation of inositol phosphates (IPs) were higher (P < 0.05) on days 3-5 and 8-10 of the oestrous cycle than on days 12-14. Basal [Ca2+]i mobilisation did not differ among studied periods of the oestrous cycle. Oxytocin (10(-7) M) enhanced P4 secretion and PI hydrolysis (P < 0.05) by luteal cells harvested on days 8-10 of the oestrous cycle. Moreover, OT started to increase mobilisation of [Ca2+]i at the 15th (days 3-5 and 8-10) or 30th second (days 12-14) in porcine luteal cells. It was concluded that in pigs OT acts as a regulator of steroidogenesis, stimulating P4 secretion in mature CL. This OT action may be mediated by changes in PI hydrolysis and [Ca2+]i mobilisation.

Effect of prostaglandin E2 and tumor necrosis factor α on the VEGF‐Receptor system expression in cultured porcine luteal cells

The purpose of the present study was to investigate the effects of prostaglandin (PG) E(2) and tumor necrosis factor (TNF) alpha on expression of vascular endothelial growth factor (VEGF) and its receptors, fms-like tyrosine kinase (Flt-1) and fetal liver kinase-1/kinase insert domain-containing receptor (Flk-1/KDR), in cultured porcine luteal cells. Real-time PCR was used for quantification of VEGF and its receptors mRNA, whereas VEGF release by luteal cells was determined by radioimmunoassay (RIA). Only the highest dose of PGE(2) (1 microM) after 6 hr of incubation stimulated VEGF release by luteal cells collected in the mid-luteal phase (P < 0.05). Moreover, PGE(2) (100 nM, 1 microM) significantly stimulated VEGF secretion by luteal cells in the late phase and during pregnancy on Days 10-12 (P < 0.05). Elevated mRNA expression of both VEGF 120 and VEGF 164 isoforms was found in luteal cells cultured with PGE(2). The lack of an effect of PGE(2) on VEGF receptors mRNA expression was observed. TNFalpha was able to significantly stimulate VEGF release from cells obtained in the mid- and late luteal phase or during early pregnancy. All tested doses enhanced mRNA levels of VEGF 120 isoform, but not VEGF 164. Additionally, TNFalpha was able to decrease Flk-1/KDR mRNA expression, whereas Flt-1 mRNA levels were not affected. These results indicated that PGE(2) and TNFalpha influenced VEGF ligand-receptor system expression in porcine luteal cells and may therefore play an important role in regulation of luteal functions during the estrous cycle and pregnancy in pigs.

Expression of proopiomelanocortin, proenkephalin and prodynorphin genes in porcine luteal cells

The objective of the study was to examine the expression of the genes coding for proopiomelanocortin (POMC), proenkephalin (PENK) and prodynorphin (PDYN) in porcine luteal cells isolated from corpora lutea (CL) collected on days 3-6, 8-10 and 13-16 of the oestrous cycle. Total RNA was purified from non-incubated cells and from cells incubated for 48 h in the absence or presence of luteinising hormone (LH). The semi-quantitative RT-PCR technique, involving coamplification of the target and control cDNA (beta-actin or 18S rRNA), was used to examine gene expression. It was found that the genes coding for opioid precursors are expressed in both non-incubated and incubated porcine luteal cells representing the early, mid- and late luteal phase. In non-incubated cells, only POMC mRNA content changed during CL development, whereas the expression of PENK and PDYN genes remained relatively constant. Additionally, the treatment of cells with LH markedly affected the expression of POMC and PENK, but no influence on PDYN expression was observed. The present study indicates that porcine luteal cells may produce opioid peptides and that gene expression of their precursors (except for PDYN) may be modulated in these cells by LH. Moreover, the present results support the involvement of opioid peptides in local regulation within the CL of the pig.

Tumor Necrosis Factor-.ALPHA. Induces Apoptosis in Cultured Porcine Luteal Cells

Some studies in mammalian species recently demonstrated that tumor necrosis factor (TNF)-alpha plays an important role for corpus luteum (CL) function by way of apoptosis during the estrous cycle. The objectives of this study were to clarify the induction of apoptosis in cultured porcine luteal cells by TNF-alpha treatment. Luteal cells prepared from porcine ovaries collected from crossbred mature gilts on Days 10-14 of the estrous cycle were isolated and examined as follows: 1) Flow cytometric analysis was carried out to determine apoptosis in cultured luteal cells. 2) Single-cell gel electrophoresis (comet assay) was performed to investigate apoptotic DNA fragmentation in luteal cells. The results of the flow cytometric analysis and comet assay demonstrated coincidentally that TNF-alpha induces DNA fragmentation in luteal cells causing apoptosis. These results revealed that TNF-alpha is an inducing factor of apoptosis in luteal cells.

Concerted regulation of the porcine steroidogenic acute regulatory protein gene promoter activity by follicle-stimulating hormone and insulin-like growth factor I in granulosa cells involves GATA-4 and CCAAT/enhancer binding protein beta.

We previously demonstrated that FSH alone or in combination with IGF-I activated the porcine steroidogenic acute regulatory protein gene promoter in a concerted manner in primary cultures of granulosa cells. Studies were undertaken to further delineate cis- and trans-acting elements of the porcine promoter and mechanisms mediating FSH stimulation and its augmentation by IGF-I. Mutation of several putative regulatory elements localized hormone-stimulated activity to the highly conserved GATA site and identified novel nucleotides downstream as a functional CCAAT/enhancer binding protein (C/EBP)beta site. In granulosa cell nuclear extracts, GATA-4 and C/EBPbeta formed a high-molecular-weight complex with an oligonucleotide spanning -76 to -32 bp of the porcine promoter. The intensity of this high-molecular-weight complex was increased in granulosa cell nuclear extracts by treatment with FSH alone and was enhanced with the combination of FSH and IGF-I at 2-3 h of treatment. GATA-4 and C/EBPbeta proteins were uniformly expressed with all treatments at time points associated with increased DNA binding. Treatment (2 h) with FSH alone or FSH + IGF-I increased phosphorylation of GATA-4 on a protein kinase A consensus site. The 38-kDa isoform of C/EBPbeta exhibited greater phosphorylation with FSH + IGF-I treatment. Porcine luteal cell nuclear extracts also demonstrated GATA-4 and C/EBPbeta binding to the -76 to -32 bp region of the promoter providing evidence for their cooperation in vivo. These data indicate that GATA-4 and C/EBPbeta are both required for FSH +/- IGF-I stimulation of the porcine steroidogenic acute regulatory protein gene promoter in homologous granulosa cell cultures.

Effect of growth hormone and insulin-like growth factor-I on spontaneous apoptosis in cultured luteal cells collected from early, mature, and regressing porcine corpora lutea

The aim of the present study was to test the hypothesis that growth hormone (GH) and insulin-like growth factor-I (IGF-I) act at a local level to inhibit luteal cell apoptosis. Luteal cells collected from the corpora lutea at different stages of the luteal phase were cultured for 24 h in M 199 medium supplemented with 5% of calf serum to cause attachment cells to the plastic. After 24 h, the media were changed and various concentrations of GH (10, 100 or 200 ng/ml) or IGF-I (30, 50 or 100 ng/ml) were added to the culture medium. Twenty-four hours later, cells were fixed for morphological assessment of apoptotic cells utilising a Hoechst staining technique. To support morphological observations, measurements of caspase-3 activity in cultured porcine luteal cells were performed. Increased incidence of apoptotic bodies and caspase-3 activity accompanied luteal regression and was associated with a decreased progesterone (P4) secretion by luteal cells. GH stimulated P4 secretion by luteal cells collected from developing (ELP) and mature (MLP) corpora lutea but had no effect on its secretion by cells collected from regressing corpora lutea (LLP). Moreover, it had no effect on the incidence of apoptotic bodies in all types of corpora lutea. However, suppression of caspase-3 activity was observed with 100 and 200 ng of GH/ml in all types of corpora lutea. IGF-I had a stimulatory effect on P4 secretion by ELP and MLP, decreased the incidence of apoptotic bodies and suppressed caspase-3 activity in cultures treated with all doses used. In conclusion, our results indicate that both GH and IGF-1 trigger anti-apoptotic effects either indirectly, by increasing progesterone secretion, or directly, through the inhibition of caspase-3 activity and subsequent prevention of apoptotic body formation.

Growth hormone and insulin-like growth factor-I action on progesterone secretion by porcine corpora lutea isolated at various periods of the luteal phase.

This study was conducted to investigate the interactions between growth hormone (GH) and insulin-like growth factor-I (IGF-I) on progesterone (P4) secretion by porcine luteal cells cultured in vitro. Cells isolated from corpora lutea (CL) collected at three different periods of the luteal phase (CL1--early luteal phase; CL2--middle luteal phase and CL3--late luteal phase) were incubated with different doses of GH (10, 100 or 200 ng/ml). After 48 h cultures were terminated and the media were frozen until further P4 concentration analysis. GH (100 ng/ml) increased P4 secretion by CL1 and CL2 and had no effect on CL3. In separate studies these cells were treated for 48 h with IGF-I alone or with GH combined with IGF-I. IGF-I alone increased basal P4 secretion only by cells collected from CL1 while concurrent treatment with GH had no effect on P4 secretion by any type of CL. To investigate the possible mechanism of GH and IGF-I mediated induction of P4 secretion, an inhibitory study was conducted. In this experiment, luteal cells collected from CL1 were cultured in the absence or presence of cycloheximide (an inhibitor of protein synthesis) or actinomycin D (an inhibitor of DNA transcription). Cycloheximide or actinomycin D completely blocked the stimulatory effect of both GH and IGF-I on P4 production but did not reduce basal progesterone secretion suggesting involvement of gene transcription and translation in the GH and IGF-I action on luteal cells. Additionally, the activity of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) under the influence of GH added alone or together with IGF was measured by the conversion of pregnenolone to progesterone. Stimulation of P4 secretion in P5-treated cells in GH-stimulated cultures was not observed, however, high stimulatory effect was noted in IGF-I treated cultures. In conclusion, the present studies indicate that there is direct and cycle stage dependent influence of GH and IGF-I on steroidogenesis in procine luteal cells. It is suggested that both IGF and GH may exert some regulatory action during CL development in the pig.

Polichlorinated biphenyls (PCB126 and PCB 153) action on proliferation and progesterone secretion by cultured in vitro porcine luteal cells.

To characterise PCBs action on luteal cell steroidogenesis and cell viability two PCB congeners were selected as model substances. PCB 126 because of its dioxin-like configuration and high toxicity while 153 because it is one of the most commonly detected congeners in breast milk. Luteal cells collected from mature corpora lutea were cultured in M199 medium at 37 degrees C. Control cultures were maintained in that medium alone, while other cultures were supplemented with either PCB 126 (5, 10, 50 and 100 pg/ml) or PCB 153 (5, 10, 50 and 100 ng/ml). After 24 h, 48 h and 72 h of culture media were collected for P4 content analysis. Cell viability was measured using LDH cytotoxicity test. Exposure of luteal cells to all doses of PCB 126 for 24 h had no effect on progesterone secretion while longer, 48 h and 72 h exposure decreased progesterone secretion in a statistically significant manner. Concentration dependent decrease in progesterone secretion by luteal cells was seen after 24 h and 48 h exposure to PCB153 while concentration dependent increase in progesterone secretion was noted after 72 h exposition to this congener. The toxic effect of both congeners was observed only after 72 h exposition to 50 pg/ml and 100 pg/ml in the case of PCB 126 and 50 ng/ml and 100 ng/ml in the case of PCB 153. In conclusion, these results suggest that there are differences in PCB 153 and 126 action in luteal cells. Since information concerning mechanism of PCBs action on luteal cells is scarce, these preliminary experiments are of pioneering character.

Porcine theca cells produce immunoreactive beta-endorphin and change steroidogenesis in response to opioid agonist.

In earlier in vitro experiments opioids affected steroidogenesis in porcine luteal and granulosa cells. The present studies were undertaken to examine the effects of FK 33-824 (opioid agonist) alone or in combination with LH, PRL or naloxone (NAL, opioid antagonist) on steroidogenesis in cultured porcine theca cells. Moreover, we have tested beta-endorphin-like immunoreactivity (beta-END-LI) concentrations in culture media under control conditions and following treatments of theca cells with LH, PRL, progesterone (P4), oestradiol (E2) or testosterone (T). FK 33-824 and NAL significantly increased P4 release by theca cells and inhibited stimulatory effect of LH on this steroid output. PRL-induced P4 secretion from the cells was blunted only by FK 33-824. Secretion of androstenedione (A4) and T was essentially elevated in the presence of FK 33-824 and this potentiation of both androgen release was completely abolished by PRL. NAL blocked stimulatory effect of the opioid agonist only in case of T. Secretion of oestradiol and oestrone was completely free from the influence of both the opioid agonist and antagonist. Pig theca cells were able to produce beta-END-LI but none of tested hormones (LH, PRL, P4, E2 and T alone or in combination) significantly affected this production. In conclusion, these data indicate that porcine theca cells may produce beta-END-LI and change their steroidogenesis in response to opioid peptides.

EFFECT OF EXOGENOUS OVINE PLACENTAL LACTOGEN ON BASAL AND PROSTAGLANDIN-STIMULATED PROGESTERONE PRODUCTION BY PORCINE LUTEAL CELLS

The ability of ovine placental lactogen (oPL) to stimulate progesterone secretion of porcine luteal cells isolated from ovaries in different stages of the oestrous cycle and to support the luteotropic action of PGE2 or to protect the corpus luteum (CL) against the luteolytic action of PGF2 alpha was investigated. oPL in all doses used had no effect on progesterone production of cells isolated from early developing corpora lutea while in doses of 1 and 10 ng/ml it increased oestradiol secretion by this type of cells. In doses of 1, 10 and 100 ng/ml it also increased progesterone secretion of cells isolated from mature corpora lutea in a dose-dependent manner. No influence on progesterone production of cells isolated from regressing corpora lutea was observed. oPL added to the culture media had no effect on PGE2-stimulated progesterone production by cells isolated from mature corpora lutea. However, it exerted a protective effect against the luteolytic action of PGF2 alpha observed in cultures treated with PGF2 alpha alone or in combination with PGE2 in a ratio of 4:1. These studies provide evidence that oPL is luteotropic and supports progesterone production in swine. The fact that oPL acted directly on ovarian steroidogenesis suggests that it may also play some role under non-pregnant physiological conditions. Future studies of structural and functional proteins secreted by the porcine conceptus will help resolve this uncertainty.