The auto-regulation of luteal function. GD Niswender
Is intraluteal synthesis of PGF2α required for normal luteolysis? Procedures: • To inhibit intraluteal synthesis of PGF2α we used a biodegradable implant containing indomethacin (0, 1 or 10mg) placed directly into the corpus luteum. • To determine the effects of the treatments we measured concentrations of P4 in daily blood samples, and luteal weights on day 18 of the estrous cycle.
Progesterone (% of time 0) Results * * * * *P<0.05 from 0mg control
Results c 800 c b b 600 a Luteal Weight (mg) 400 a 200 0 0 1 10 Indomethacin (mg) Different letters = P<0.05
Procedures and Results To demonstrate that the effects of indomethacin were local and not systemic ewes with a corpus luteum on each ovary (n=8) were given a control implant into one corpus luteum and 1mg indomethacin into the corpus luteum on the opposite ovary. Indomethacin Luteal weights 0 275±24ng 1 412±83ng* *P<0.05
Summary of Second Experiment Series • Intraluteal administration of indomethacin increased luteal weights (1 or 10mg) and serum concentrations of progesterone (10mg) in ewes. • The effect was local within the corpus luteum and not systemic.
Is PGF2α metabolized during maternal recognition or pregnancy? PGDH mRNA and Enzyme Quantities Day 13 Estrous Cycle Pregnancy *mRNA 177±19 301±47* **enzyme 304±139 631±109** *P<0.001 **P<0.05 *amol/µg PolyA **mg PGFM/ mg protein/min
Does oxytocin cause increased intracellular concentrations of calcium in SLC? Procedure: • Partially purified preparations (±55% steroidogenic-<1%LLC) of SLC were plated overnight. • Cells were loaded with Fura-2AM then calcium concentration was quantified in individual cells using the Incyt2 imaging system. • Oxytocin (0.1-10μM) was added and calcium concentrations were measured for five minutes.
Results 80 500 B A B c c B 400 60 300 % Responding Cells Intracellular Calcium (nM) b 40 A 200 20 100 a A 0 0 0mM 0.1mM 1mM 10mM 0mM 0.1mM 1mM 10mM Oxytocin Different letters = P<0.05
Does intraluteal progesterone concentration influence the responsiveness of luteal cells to oxytocin (SLC) or PGF2α (LLC)? • Purified preparations of SLC and LLC were used for calcium measurements after exposure to progesterone, estradiol, testosterone or cortisol (0,1,10 or 30μg/mL). Procedure:
Results Percentage of SLC responding to oxytocin following steroid treatment. *P<0.05
Results Percentage of LLC responding to PGF2α following steroid treatment.
Results Percentage of LLC responding to PGF2α following steroid treatment. *P<0.05
Summary of Calcium Experiments • Treatment of SLC with oxytocin elicits an increase in intracellular concentrations of calcium. • High concentrations of progesterone prevent the increased concentrations of calcium after treatment of SLC with oxytocin and likely prevent PGF2α induced calcium influx in LLC.
Anti Steroidogenic effects of PGF2α Progesterone secretion Mid Luteal Phase OT Lipoprotein Lipoprotein LH LHR cAMP PKA PKC PKC P4 P4 cPKA P4 OTR COX-2 (CL) (CL) PGF2α PGF2α (UT) PGF2α P Ca+ Ca+ OT Ca+ Ca+ Ca+ OT P4 P4 P4 P4 2 3 1 PGF2αR
Luteolytic effects of PGF2α PKC PKC OTR Ca+ Ca+ OT COX-2 (CL) PGF2α Apoptosis Apoptosis Ca+ Ca+ PKC OT Ca+ Ca+ Ca+ OT P4 IP3 P4 P4 P4 DAG PGF2αR
Definition • Luteolysis: Degeneration or destruction of ovarian luteinized tissue. -Stedman’s Medical Dictionary