Lipid metabolism and in vitro production of progesterone and prostaglandin F during induced regression of porcine corpora lutea

Changes in Porcine Corpus Luteum Proteome Associated with Development, Maintenance, Regression, and Rescue during Estrous Cycle and Early Pregnancy

Corpus luteum (CL), a transitory gland, undergoes rapid growth in a limited time to produce progesterone (P4) followed by its regression. A complex molecular signaling is involved in controlling luteal P4 production. In the present study, 2D gel electrophoresis-based proteomics and in silico functional analysis were used to identify changes in key proteins and pathways in CL along the different stages of the estrous cycle as its development progresses from early (Day 3) to mid-luteal phase (Day 9), effective functioning (Day 12) followed by regression (Day 15) or, in the case of pregnancy, rescue of function (Day 15). A total of 273 proteins were identified by MALDI-MS/MS analysis that showed significant changes in abundances at different stages of CL development or regression and rescue. Functional annotation of differentially abundant proteins suggested enrichment of several important pathways and functions during CL development and function maintenance including cell survival, endocytosis, oxidative stress response, estradiol metabolism, and angiogenesis. On the other hand, differentially abundant proteins during CL regression were associated with decreased steroid synthesis and metabolism and increased apoptosis, necrosis, and infiltration of immune cells. Establishment of pregnancy rescues CL from regression by maintaining the expression of proteins that support steroidogenesis as pathways such as the super-pathway of cholesterol biosynthesis, RhoA signaling, and functions such as fatty acid metabolism and sterol transport were enriched in CL of pregnancy. In this study, some novel proteins were identified along CL development that advances our understanding of CL survival and steroidogenesis.

Arachidonic acid inhibits hCG-stimulated progesterone production by corpora lutea of primates: potential mechanism of action

Arachidonic acid (AA) is a precursor of metabolites known to affect the corpus luteum (CL) in many species, including primates. We have shown that some of these products (prostaglandins F2 alpha and E2) inhibit pro-gesterone (P4) production and activate the phosphatidylinositol (PI) pathway in CL of rhesus monkeys. A direct role of AA in luteal function has also been suggested. The current experiments were designed to investigate the effect of AA on P4 synthesis and to examine the ability of AA to activate the PI pathway in CL of rhesus monkeys. Basal and hCG-stimulated P4 production by luteal cells collected during the midluteal phase was measured after treatment with AA (1, 5, and 10 microM) or linoleic acid (1, 5, and 10 microM). Dispersed cells (50,000/tube) were incubated at 37 degrees C for 2 h. AA elicited a dose-dependent decrease in hCG-stimulated, but not in basal, P4 production. hCG-stimulated P4 production was reduced (P < 0.01) at AA doses of 5 microM (12.1 +/- 1.5 ng/mL) and 10 microM (8.6 +/- 1.8 mg/mL) to hCG alone (18 +/- 1.6 ng/mL). There was no significant effect of 1 microM AA (15.2 +/- 1.6). Response to linoleic acid was dissimilar and was not dose-dependent. Viability of cells was not affected by any treatment. Indomethacin, a prostaglandin synthesis inhibitor, and nordihydroguaiaretic acid, an inhibitor of lipoxygenase, did not interfere with the inhibitory effect of AA. Activation of the PI pathway was assessed by monitoring the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PIP2) to inositol phosphates and by monitoring increases in intracellular free calcium concentrations ([Ca2+]i) in individual cells. Moreover, the ability of AA to activate protein kinase C (PKC) in luteal cells was measured using a [3H]phorbol dibutyrate (PDBu) binding assay. AA did not alter PIP2 hydrolysis or [Ca2+]i, however, AA (10 microM) increased specific binding of [3H]PDBu to luteal cells (P < 0.05). We conclude that AA inhibits hCG-stimulated P4 production by primate luteal cells. AA exerts this action without being converted to prostaglandins or leukotrienes. This inhibition may be mediated through the activation of PKC. These results suggest a possible role for AA in the regulation of luteal function in primates, and that PKC-activation by AA may promote its effects.

Effects of Cloprostenol administration on neutral lipid and prostaglandin F metabolism by porcine luteal tissue

The effects of Cloprostenol administration on porcine luteal lipid metabolism, progesterone production, and prostaglandin F production were examined in 32 pigs at day 12 of the estrous cycle. Pigs were killed between 0 and 18 hours after treatment. Recovered luteal tissue was incubated at 0 C and at 37 C in the absence and presence of dibutyryl cyclic AMP and indomethacin. Net in vitro release of progesterone from luteal tissue was depressed within 1 hour after Cloprostenol treatment whereas net in vitro release of prostaglandin F was accelerated 4 hours after Cloprostenol treatment. Inclusion of dibutyryl cyclic AMP in the incubation media did not alter progesterone production but did enhance prostaglandin F production at 0 and 1 hour after Cloprostenol treatment. Inclusion of indomethacin in the incubation media completely inhibited the Cloprostenol-induced acceleration of in vitro luteal PGF production. Cloprostenol treatment increased luteal triglycerides and decreased luteal free cholesterol and cholesterol esters within 1 hr after treatment. Arachidonic acid percentages in free fatty acids and triglycerides were also increased within 1 hr after treatment. When 37 C and 0 C incubations were compared, in vitro luteal accumulation of free fatty acids was maximum at 1 hr after Cloprostenol treatment. In vitro accumulation of triglycerides in luteal tissue was comparatively uniform at all times examined during the first 18 hr after Cloprostenol treatment. Comparison of 37 C and 0 C incubations further revealed that luteal triglycerides were active in accumulation of arachidonic acid. Inclusion of dibutyryl cyclic AMP and/or indomethacin in the incubation media did not alter luteal lipid contents or fatty acid compositions. Blood plasma progesterone was depressed at 4 hours after Cloprostenol whereas 13,14-dihydro-15-keto-prostaglandin F2a was elevated at 18 hours after treatment. Blood plasma free fatty acids increased 330 percent at 4 hours and free fatty acid compositions also changed at this time. In both luteal tissue and blood plasma, changes in steroid and fatty acid metabolism occurred prior to changes in prostaglandin metabolism, suggesting that Cloprostenol induced functional luteal regression prior to altering prostaglandin metabolism.

Factors affecting steroid and prostaglandin secretion by reproductive tissues of cycling and pregnant sows in vitro

The secretion of prostaglandin E2 and prostaglandin F2 alpha by endometrial and corpus luteum tissues of cycling and pregnant sows in vitro has been measured and the effects of arachidonic acid and steroids on prostaglandin secretion studied. In general, both types of tissues in vitro exhibited a gradually increasing capacity to secrete prostaglandin as the cycle progressed, although the most significant increase was in prostaglandin F2 alpha secretion. An inverse relationship between prostaglandin and progesterone secretion was observed, and, while indomethacin inhibited prostaglandin secretion, it was without effect on progesterone. A much lower capacity for prostaglandin secretion was observed with tissues from pregnant sows. Prostaglandin secretion by endometrial and corpus luteum tissues of the cycle were stimulated by exogenous arachidonic acid which also stimulated prostaglandin E2 secretion in pregnant sows. This clearly suggests that phospholipase A2 activity which controls substrate availability is of considerable importance in pig reproductive tissues. The effects of steroid hormones on prostaglandin secretion by pig reproductive tissues was more complex although in general oestradiol appeared to be inhibitory while progesterone was stimulatory.