Expression of type I GNRH receptor and in vivo and in vitro GNRH-I effects in corpora lutea of pseudopregnant rabbits.
The expression of type I GNRH receptor (GNRHR-I) and the direct role of GNRH-I on corpora lutea (CL) function were studied in the pseudopregnant rabbit model. Immunohistochemistry evidenced GNRHR-I and GNRH-I in luteal cells at early (day 4 pseudopregnancy)-, mid (day 9)-, and late (day 13)-luteal stages. Real-time RT-PCR and western blotting revealed GNRHR-I mRNA and protein at the three luteal stages. Buserelin in vivo treatment at days 9 and 13 decreased plasma progesterone levels for 48 and 24  h respectively. In in vitro cultured CL, buserelin reduced progesterone secretion, increased prostaglandin F(2α) (PGF(2α)) secretion and cyclo-oxygenase-2 (COX-2) and nitric oxide synthase (NOS) activities at days 9 and 13, and decreased PGE₂ at day 13. Co-incubation with antagonists for GNRH-I (antide), inositol 1,4,5-trisphosphate (IP₃, 2-amino-ethoxydiphenylborate), and diacylglycerol (DAG, 1-hexadecyl-2-acetyl glycerol) or inhibitors for phospholipase C (PLC, compound 48/80), and protein kinase C (PKC, staurosporine) counteracted the buserelin effects. Buserelin co-incubated with COX inhibitor (acetylsalicylic acid) increased progesterone and decreased PGF(2α) and NOS activity at days 9 and 13, whereas co-incubation with NOS inhibitor (N-nitro-l-arginine methyl ester) increased progesterone at the same luteal stages. These results suggest that GNRHR-I is constitutively expressed in rabbit CL independently of luteal stage, whereas GNRH-I down-regulates directly CL progesterone production via PGF(2α) at mid- and late-luteal stages of pseudopregnancy, utilizing its cognate type I receptor with a post-receptorial mechanism that involves PLC, IP₃, DAG, PKC, COX-2, and NOS.
Zerani
Massimo
M
Scuola di Scienze mediche veterinarie, Università di Camerino, 62024 Matelica, Italy. massimo.zerani@unicam.it
Parillo
Francesco
F
Brecchia
Gabriele
G
Guelfi
Gabriella
G
Dall'Aglio
Cecilia
C
Lilli
Lorena
L
Maranesi
Margherita
M
Gobbetti
Anna
A
Boiti
Cristiano
C
D000818:Animals; D001241:Aspirin / Q000008:administration & dosage; D002064:Buserelin / Q000008:administration & dosage; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000378:metabolism; D004075:Diglycerides / Q000008:administration & dosage; D015237:Dinoprost / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000008:administration & dosage; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D009842:Oligopeptides / Q000008:administration & dosage; D011374:Progesterone / Q000097:blood / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011555:Pseudopregnancy / Q000378:metabolism*; D011817:Rabbits; D011966:Receptors, LHRH / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019311:Staurosporine / Q000008:administration & dosage; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D003189:p-Methoxy-N-methylphenethylamine / Q000008:administration & dosage
D004075:Diglycerides; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D003189:p-Methoxy-N-methylphenethylamine; D011374:Progesterone; D015544:Inositol 1,4,5-Trisphosphate; C057022:iturelix; D015237:Dinoprost; D019001:Nitric Oxide Synthase; D051546:Cyclooxygenase 2; D011493:Protein Kinase C; D010738:Type C Phospholipases; D019311:Staurosporine; D002064:Buserelin; D001241:Aspirin; D019331:NG-Nitroarginine Methyl Ester