Progesterone in ovarian venous plasma and corpora lutea of the pig

Expression Profiles of Fatty Acid Transporters and the Role of n-3 and n-6 Polyunsaturated Fatty Acids in the Porcine Endometrium

Fatty acids (FAs) are important for cell membrane composition, eicosanoid synthesis, and metabolic processes. Membrane proteins that facilitate FA transport into cells include FA translocase (also known as CD36) and FA transporter proteins (encoded by SLC27A genes). The present study aimed to examine expression profiles of FA transporters in the endometrium of cyclic and early pregnant gilts on days 3 to 20 after estrus and the possible regulation by conceptus signals and polyunsaturated FAs (PUFAs). The effect of PUFAs on prostaglandin (PG) synthesis and transcript abundance of genes related to FA action and metabolism, angiogenesis, and immune response was also determined. Day after estrus and reproductive status of animals affected FA transporter expression, with greater levels of CD36, SLC27A1, and SLC27A4 observed in pregnant than in cyclic gilts. Conceptus-conditioned medium and/or estradiol-17β stimulated SLC27A1 and CD36 expression. Among PUFAs, linoleic acid decreased SLC27A1 and SLC27A6 mRNA expression, while arachidonic, docosahexaenoic, and eicosapentaenoic acids increased SLC27A4 transcript abundance. Moreover, arachidonic acid stimulated ACOX1, CPT1A, and IL1B expression and increased PGE2 and PGI2 secretion. In turn, α-linolenic acid up-regulated VEGFA, FGF2, FABP4, and PPARG mRNA expression. These results indicate the presence of an active transport of FAs in the porcine endometrium and the role of PUFAs as modulators of the uterine activity during conceptus implantation.

In vitro release of ovarian progesterone is decreased during the oestrous cycle and pregnancy of swine with obesity/leptin resistance

Previous studies indicate that reproductive prolificacy of obese swine breeds is markedly influenced by embryo losses in early pregnancy. In such period, adequate secretion of progesterone (P4) by the ovary is essential for pregnancy success. This study analyses the luteal functionality during the oestrous cycle and early pregnancy of Iberian sows and Large White x Landrace females, in terms of P4 secretion after in vitro culture of luteal tissue stimulated or not with luteinizing hormone (LH). The secretion of progesterone (expressed in ng/mg of luteal tissue or ng/mgLT) of the corpora lutea of obese Iberian swine was always hampered when compared to lean genotypes, either during early oestrous cycle (110.7 ± 37.8 vs 259.7 ± 10.2 ng/mgLT; p < 0.0001), late oestrous cycle (49.0 ± 3.5 vs 75.92 ± 7.14 ng/mgLT; p < 0.0001) or early pregnancy (38.4 ± 2.1 vs 70.7 ± 5.3 ng/mgLT; p < 0.0001). The differences in basal P4 secretion remained after stimulation with LH. Finally, P4 secretion during early pregnancy of Iberian sows decreased with age and, hence, with obesity features (46.6 ± 4.2 vs 65.5 ± 4.8 ng/mgLT; p < 0.001). In conclusion, the results of the present study provide convincing evidence of a reduced luteal function during oestrous cycle and early pregnancy of sows with obesity/leptin resistance like Iberian sows, which may contribute to the low reproductive efficiency reported in this breed.

Evidence for uterine metabolism of progesterone during early pregnancy in the pig

Two experiments were conducted to examine whether the 40 or 50% decrease in systemic progesterone (P(4)) concentrations between Days 13 and 21 postmating in the pig results from decreased ovarian P(4) secretion or increased uptake of P(4) by the uterus. In Experiment I, five nonpregnant (NP) and four pregnant (P) gilts were sham-operated, and five NP gilts were hysterectomized (HYST) on Days 7 to 9 postestrus or postmating (first day of estrus or mating = Day 0). Femoral arterial blood was obtained once daily from Day 10 until the subsequent estrus (NP gilts) or Day 21 (P and HYST gilts). In Experiment II, blood was collected daily from both utero-ovarian veins of two NP and three P gilts from Days 11 to 18. Femoral arterial P(4) concentrations were similar for all gilts in Experiment I from Days 10 to 14. For NP gilts, femoral arterial P(4) declined (P < 0.01) after Day 14 to reach basal levels by Day 17. Progesterone in femoral arterial blood of P gilts declined (P < 0.01) from Days 13 to 16 and then remained constant through Day 21. Concentrations of P(4) in femoral arterial blood of HYST gilts remained constant from Days 13 to 21 and were greater (P < 0.01) than for P gilts from Days 15 to 21. In Experiment II, P(4) concentrations in utero-ovarian venous blood were similar until Day 14 between NP and P gilts. Utero-ovarian P(4) of NP gilts then declined (P < 0.01) to reach basal levels by Day 16. P(4) concentrations in utero-ovarian venous blood of P gilts increased (P < 0.05) for Days 14 to 18. These results demonstrate that ovarian P(4) secretion increases during early pregnancy in the pig. Further, the absence of a decline in P(4) concentrations in femoral arterial blood of HYST gilts suggests that the declining systemic P(4) levels observed during early pregnancy are a result of uterine uptake and(or) metabolism.

Induction and synchronization of ovulations of nulliparous and multiparous sows with an injection of gonadotropin-releasing hormone agonist (Receptal)

The objective of this study was to determine if administration of a set dose (10 microg) of a gonadotropin-releasing hormone agonist, buserelin (Receptal; Rc), at set times after altrenogest (Regumate; RU) treatment or after weaning was able to induce and synchronize ovulation in female swine (gilts and sows). The pubertal (n=187) gilts were allocated to four groups, all synchronized with RU. Group 1 (RU) was inseminated twice at detected estrus, Group 2 (RU+Rc120) and Group 4 (RU+Rc104) received 10 microg Rc at 120 or 104 h after the end of RU treatment, respectively, and Group 3 (RU+eCG+Rc104) was treated with 800 IU equine chorionic gonadotropin (eCG) at 24h and Rc 104 h after the end of RU treatment, respectively. Gilts were inseminated twice at predetermined times, namely 144 and 168 h (Group 2), 128 and 144 h (Group 3), and 144 and 152 h (Group 4) after the end of RU treatment, respectively. Pregnant gilts were slaughtered at 30 d. Administration of Rc 104 h after the end of RU feeding synchronized ovulation over a 24-h time window in 97.9% and 100% of the gilts of Groups 3 and 4, respectively, whereas Rc administration at 120 h (Group 2) only successfully synchronized 88.9% of the gilts over 24h. Ovulation rates of gilts of Groups 2 and 4 were similar to that of the control group. Pregnancy rates were numerically higher in Groups 2 and 3 (92% and 96%, respectively) compared with those of Groups 1 and 4 (84% and 81%, respectively). Combination of eCG with Rc administration at 104 h (Group 3) increased ovulation rate (+4 CL) but decreased embryo survival to 62% at Day 30. The weaned sow experiment involved 61 sows of a range of parities (2.7+/-0.9), allocated to two control groups (Control 104 group and Control 94 group) and two treated groups (Rc104 group and Rc94 group), which received 10 microg Rc at 104 and 94 h after weaning, respectively. The females were inseminated at detected estrus. All pregnant sows farrowed. After treatment with Rc 94 h after weaning, 100% of sows ovulated over a 24-h time window versus only 68.7% of controls. Farrowing rate and litter size of the sows treated with Rc at that time were unaffected compared with that of control sows. In contrast, Rc administration at 104 h after weaning may have been too late; only 66.7% of the treated sows ovulated during a 24-h period. This proportion was numerically lower but not significantly different than that for control sows. Farrowing rate and litter size of treated sows were not significantly different than that of controls. Administration of Rc at the dose and times selected in this study tightened synchrony of ovulation in gilts and in sows after weaning. It remains to be established if such a synchrony is suitable to obtain good fertility after a single artificial insemination at a predetermined time.

Differential effects of dexamethasone and RU 486, an antigestagen and antiglucocorticoid, on progesterone and relaxin secretion in hysterectomized pigs with aging corpora lutea

Pregnancy lasts about 114 days in pigs. Porcine corpora lutea produce not only progesterone but also relaxin (RLX), a peptide hormone that plays a critical role in suppressing uterine motility during pregnancy and in remodelling connective tissues in preparation for imminent parturition. Progesterone concentrations in peripheral blood remain elevated (approximately equal to 25 ng ml-1) for the major part of pregnancy and decrease just before parturition. The decrease in progesterone coincides with the peak prepartum RLX release. Glucocorticoid or antiglucocorticosteroid steroid, RU 486, administration during late pregnancy can induce parturition in the pig. Peak release of RLX and a coincident decrease of progesterone in the circulating blood can also occur in the complete absence of fetuses and uterus in the pig. The effects of glucocorticoid or antiglucocorticoidsteroid administration to such hysterectomized pigs on the secretion of RLX and progesterone were examined in this experiment. Unmated Yorkshire gilts were hysterectomized on days 6-8 (estrus = day 0) and given dexamethasone (total of 30 mg day-1; 2 times i.m. at 0800 and 1600 h) from days 110-118; control animals received vehicle injection during this period. RU 486 (4 mg kg1 body weight) was orally administered once daily (days 111-115) at 0800 h; placebo-treated controls were given the same amount of feed without the drug at this time. RLX concentrations in blood were markedly suppressed (P < 0.01) during dexamethasone treatment (3 +/- 0.9 ng ml-1; mean +/- S.E.) whereas a peak release of RLX (17 +/- 2.8 ng ml-1) occurred in the control group on day 113. In contrast, progesterone concentrations (14 +/- 2.5 ng ml-1) were unaffected by dexamethasone treatment compared with the controls (15 +/- 2.0 ng ml-1; P > 0.82). Upon withdrawal of dexamethasone on day 118, RLX plasma concentrations began to increase and peaked at 14 +/- 2.1 ng ml-1 (P < 0.01) on day 120. In contrast, the antiglucocorticosteroid given to hysterectomized pigs bearing aging corpora lutea caused a marked elevation in circulating levels of progesterone and delayed RLX release until after the end of drug treatment on day 115. Average weights of corpora lutea collected at day 12 were similar between treated and control groups (427 +/- 7 vs. 433 +/- 6 mg; P > 0.68). Results indicate that a synthetic glucocorticoid, dexamethasone, suppresses RLX secretion without causing luteolysis and such suppression is reversible; progesterone secretion remained unaffected. In contrast, the antiglucocorticoid, RU 486, raised progesterone plasma concentration and delayed RLX peak release but did not suppress it during treatment. This experiment provides further evidence that relaxin and progesterone secretion from aging corpora lutea of pigs are regulated through separate mechanisms, and adrenal glucocorticoids may be involved in such a regulation process.

Progesterone secretion and mitochondrial size of aging porcine corpora lutea

A functional dependency between the nongravid uterus and the ovaries is essential to luteolysis and the return to estrus in the pig. After mating of gilts, the corpora lutea develop, and they are required for the maintenance of pregnancy to a normal duration of about 114 days. Hysterectomy of luteal phase (day 6) nongravid gilts results in persistence of the corpora lutea to 150 days. We report that these corpora secrete greater quantities (P less than 0.025) of progesterone than during the later half of gestation (days 54-108). Although aging corpora lutea remain functional for at least an additional 35 days, an abrupt reduction by half in progesterone secretion (16 ng/ml) occurs about day 114 in hysterectomized gilts that coincides with the prepartum decrease to basal serum levels (less than 0.5 ng/ml) at parturition (day 114) and during lactation. Aging corpora lutea remain large (averaging greater than 450 mg) on days 124 and 136 in hysterectomized gilts, whereas they regress (averaging less than 75 mg) in the lactating dams. Mitochondria continue to increase in size in aging corpora lutea of hysterectomized gilts until day 136; in contrast, they decrease during the postpartum period in lactating dams. A precisely timed signal, possibly of ovarian origin or from the CNS and pituitary gland, entrains in hysterectomized and pregnant pigs at day 113 that results in marked shifts in relaxin and progesterone secretion. Progesterone secretion and mitochondrial features suggest that porcine corpora lutea seem genetically controlled and are preprogrammed at estrus for the duration of pregnancy, regardless of the presence of conceptuses or absence of the uterus.

Adrenal secretion rates and adrenal tissue concentrations of pregnenolone, progesterone, 11 beta OH-androstenedione and some other steroids in young pigs and dogs

1. The rates were measured at which a number of different steroids were secreted by the adrenal gland of the eviscerated and nephrectomized young pig and dog.2. In addition to cortisol and corticosterone the following steroids were consistently found to be present in the adrenal venous blood: pregnenolone, progesterone, 11betaOH-progesterone, androstenedione, 11betaOH-androstenedione and adrenosterone.3. The sum of the latter steroids could amount to as much as 30% of the total steroid secretion.4. A severe deficit in the blood volume increased the secretion of pregnenolone and the 17-oxo steroids in the pig.5. alpha-ethyltryptamine failed to inhibit ACTH release if the animals were eviscerated and nephrectomized, or if they were anaesthetized with chloralose instead of pentobarbitone sodium.6. The same steroids as in the adrenal venous blood were found in extracts from the adrenal glands of a number of species.7. The amount of individual steroids present in the adrenal gland of the stressed pig and dog was compared with the rate at which each had been secreted immediately before the excision of the gland.8. There was a positive correlation between the adrenal concentrations and the secretion rates of cortisol, the major glucocorticoid secreted by the pig and the dog.9. In contrast, the rate at which pregnenolone was secreted did not show a consistent relationship to its concentration in the gland.10. A storage mechanism for pregnenolone in the adrenal cortex is proposed.