RESUMO
Acting primarily through its specific G protein-coupled receptor termed FPr, prostaglandin (PG) F(2alpha) induces regression of the corpus luteum (CL) at the end of a non-fertile oestrous cycle. This study was aimed at cloning a full-length cDNA for FPr and determining its expression and protein concentrations during different stages of CL development in the water buffalo. Serum progesterone and StAR expression were determined to establish temporal relationships between indices of steroidogenesis and changes in FPr expression at different stages of CL development. In contrast to the dairy cow, the stage IV CL (day 20 of the oestrous cycle) did not appear to be functionally regressed in the buffalo. Molecular cloning of a cDNA encoding the buffalo FPr yielded a full length 2193 bp FPr cDNA containing a single open reading frame encoding a 362 amino acid protein with seven putative membrane-spanning domains. The deduced buffalo FPr amino acid sequence possesses a high degree of identity with the other mammalian homologues. Steady state concentration of buffalo FPr transcript increased (P > 0.05) from stage I to stage II/III, and declined at 18 h post PGF(2alpha) injection. The FPr concentration expressed as fmol/microg of plasma membrane protein showed an increase (P > 0.05) from stage I (1.98 +/- 0.10), through stage II/III (2.42 +/- 0.48) to stage IV (2.77 +/- 0.18). High affinity FPr was observed in stage I (K(d) 4.86 nmol) and stage II/III (K(d) 6.28 nmol) while low affinity FPr (K(d) 19.44 nmol) was observed in stage IV. In conclusion, we have cloned a full length FPr cDNA from buffalo cow CL and observed that FPr mRNA expression, receptor number and affinity did not vary significantly (P > 0.05) within the luteal phase of the oestrous cycle.
