Seasonal Changes in Luteal Progesterone Concentration and mRNA Expressions of Progesterone Synthesis-related Proteins in the Corpus Luteum of Mares

Abstract

Abstract. Although circulating progesterone (P 4 ) levels tend to change with the season, little is known about the seasonal changes of P 4 synthesis-related proteins in the corpus luteum (CL) of mares. To examine these changes, seventy-four ovaries containing a CL were collected from Anglo-Norman mares at a local abattoir in Kumamoto, Japan (~N32°), five times during one year. The stages of the CLs were classified as early, mid and regressed by macroscopic observation of the CL and follicles. The mid CL, which had the highest P 4 concentration, was used to evaluate the seasonal changes in P 4 synthesis. The luteal P 4 concentration and mRNA expression of luteinizing hormone receptor (LHCGR) were lowest during early winter and highest during late winter. The mRNA expressions of steroidogenic acute regulatory protein (StAR), P450 cholesterol side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) were lowest during early winter and increased during late winter. These results suggest that P 4 synthesis in the CL is affected by the seasonal changes in the mRNA expressions of P 4 synthesis-related proteins in mares. Key words: Corpus luteum, Mares, Progesterone, Reproductive seasonality, Steroidogenesis (J. Reprod. Dev. 58: [393][394][395][396][397] 2012) M ares are seasonal breeders in which day length (DL) is one of the main environmental factors controlling reproductive seasonality [1][2][3]. The reproductive activity of mares reaches a peak during summer, then decreases during autumn and eventually stops through winter as DL decreases. January 1 in the Northern Hemisphere and August 1 in the Southern Hemisphere are used as the official birth dates for many breeds, especially for racing breeds [4]; therefore, the exposure of mares to artificial light has been used to hasten the reproductive season. Thus, studying reproductive seasonality in mares is relevant for the equine industry.In mammals, the corpus luteum (CL) is an endocrine organ producing progesterone (P 4 ), which is essential for the establishment and maintenance of pregnancy. Although several studies have examined seasonal changes in circulating P 4 concentration in mares, the reported results are not consistent, i.e., the circulating P 4 concentration has been reported to decrease [5][6][7], increase [8] or remain unchanged [9] from the breeding to non-breeding season. Therefore, the effects of season on P 4 synthesis in the CL of mares remain unclear.Luteal P 4 production is regulated by several P 4 synthesis-related proteins [10]. Luteinizing hormone (LH) secreted by the anterior pituitary is the main regulator of luteal function. LH acts through its specific cell surface receptor (LHCGR) and stimulates P 4 production by the CL in ewes [11], rats, sows [12], cows [13] and mares [14]. Steroidogenic acute regulatory protein (StAR) transfers cholesterol from the outer to inner mitochondrial membrane, allowing enzymatic cleavage of the side chain of cholesterol to pregnenolone by P450 cholesterol side-chain ...

Revisión: El Ciclo Reproductivo de la Yegua

“…Pregnenolone leaves the mitochondria and goes to the smooth endoplasmic reticulum, where the enzyme 3β-dehydrogenase hydroxysteroid transforms it into progesterone (Slough et al, 2011). It has been suggested that LH simultaneously increases the expression of the coding genes for StAR protein and the cleavage enzymes of the side chain P450 and 3β-hydroxysteroid dehydrogenase (Beg et al, 2005;Slough et al, 2011;Kozai et al ., 2012).…”