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Intraluteal regulation of prostaglandin F2-induced prostaglandin biosynthesis in pseudopregnant rabbits

¹ Dipartimento di Biologia Molecolare, Cellulare e Animale, Università di Camerino, via F. Camerini 1, I-62032 Camerino, Italy, Dipartimento di Scienze biopatologiche ed Igiene delle produzioni animali e alimentari, ² Sezione di Anatomia veterinaria and ³ Laboratorio di Biotecnologie fisiologiche, Sezione di Fisiologia veterinaria, Università degli Studi di Perugia, via S. Costanzo 4, I-06100 Perugia, Italy

Correspondence should be addressed to C Boiti; Email: cristiano.boiti{at}unipg.it

The objective of the present study was to investigate in rabbit corpora lutea (CL), at both the cellular and molecular level, intraluteal cyclooxygenase (COX)-1, COX-2 and prostaglandin (PG) E2-9-ketoreductase (PGE2-9-K) enzymatic activities as well as in vitro PGE2 and PGF2 synthesis following PGF2 treatment at either early- (day-4) or mid-luteal (day-9) stage of pseudopregnancy. By immunohistochemistry, positive staining for COX-2 was localized in luteal and endothelial cells of stromal arteries at both the stages. In CL of both stages, basal COX-2 mRNA levels were poorly expressed, but rose (P < 0.01) 4- to 10-fold 1.5–6 h after treatment and then gradually decreased within 24 h. Compared to mid-stage, day-4 CL had lower (P < 0.01) COX-2 and PGE2-9-K basal activities, and PGF2 synthesis rate, but higher (P < 0.01) PGE2 production. Independent of luteal stage, PGF2 treatment did not affect COX-1 activity. In day-4 CL, PGF2 induced an increase (P < 0.01) in both COX-2 activity and PGF2 synthesis, whereas that of PGE2 remained unchanged. In day-9 CL, PGF2 up-regulated (P < 0.01) both COX-2 and PGE-9-K activities, and PGF2 production, but decreased (P < 0.01) PGE2 synthesis. All changes in gene expression and enzymatic activities occurred within 1.5 h after PGF2 challenge and were more marked in day-9 CL. Our data suggest that PGF2 directs intraluteal PG biosynthesis in mature CL, by affecting the CL biosynthetic machinery to increase the PGF2 synthesis in an auto-amplifying manner, with the activation of COX-2 and PGE-9-K; this may partly explain their differentially, age-dependent, luteolytic capacity to exogenous PGF2 in rabbits.