Species and technique differences may partially explain these differences

Species and technique differences may partially explain these differences. then significantly declined in DI and DII (p 0.05). Extent of immunostaining for MMP-14, TIMP-1, and TIMP-2 was significantly more abundant in P, E, and DI than in DII (p 0.05). Localization of the MMPs and TIMPs had subtle differences, but immunostaining was predominant in granulosa and theca cells, with significant differences noted in staining intensity between preantral follicles, antral follicles, corpora lutea, and stroma classifications. No significant changes were observed in MMP and TIMP mRNA or extent of protein immunostaining with exposure to 3, 6, 9, or 12 weeks of SD, however protein was present and was localized to follicular and luteal steroidogenic cells. Conclusions Although MMPs appear to be involved in the normal ovarian estrus cycle at the protein level in hamsters, those examined in the present study are unlikely to be key players in the slow atrophy of tissue as seen in Siberian hamster ovarian regression. Background Normal ovarian function is dependent on a series of tissue remodeling events taking place throughout the reproductive cycle. For a number of species, including Siberian hamsters ( em Phodopus sungorus /em ), a seasonal pattern of reproduction is exhibited in response to changes in photoperiod. Long ( 12 h of light per day) photoperiods correlate with abundant environmental resources for many temporal rodents, and therefore can stimulate reproductive physiology and behavior [1]. Follicle development, ovulation, and corpus luteum formation and degradation all occur during the four-day estrous cycle in Siberian hamsters with long LEFTYB day stimulation. In contrast, exposure to short ( 12 h of light per day) photoperiod can terminate reproductive function [1,2], inducing an anestrous/anovulatory state in regressed ovaries [3]. In Siberian hamsters, exposure to 12-14 weeks of short photoperiod results in reduced or absent ovulation and significant reductions in ovarian mass, the number of antral follicles and the number of corpora lutea (CL) [4-6]. In mammalian ovaries, the extracellular matrix (ECM) regulates cellular processes vital for follicle growth and maturation, including proliferation, differentiation, and survival [7], and its synthesis and degradation are vital to ovulation, CL formation, and luteal regression [8]. The remodeling of the ECM is mediated in part by a family of Zn+-dependent endopeptidases, matrix metalloproteinases (MMPs), and their tissue inhibitors (TIMPs). Signaled by a variety of hormones, growth factors, and cytokines, MMPs and TIMPs contribute to the degradation of the ECM in the ovary by cleaving the various tissue components to clear space for new growth [8,9]. MMP and TIMP protein levels and mRNA expression show distinct differences in expression during follicle development and ovulation, and throughout luteal formation and degradation in rats, mice, pigs, cattle, sheep, and primates, suggesting that the concerted action of MMPs may regulate these ovarian events [10-16]. The MMPs specifically investigated in this study are MMPs -2, -9, and -14 and TIMPs -1 and -2. MMP-2 and MMP-9, of the gelatinase class, Panaxadiol promote follicle growth in both rodents and goats [11,17,18], and have been implicated in the ovulatory process. MMP-2 protein is Panaxadiol localized to the granulosa and theca cells and both protein and mRNA are increased in rats following PMSG [10] or hCG administration [19], while in mice, MMP-9 mRNA expression Panaxadiol is increased with LH stimulation [19]. Both MMP-2 and MMP-9 mRNA expressions increase in primate granulosa cells after hCG administration [20], and MMP-2 increases as the ovary returns to function in.