Luteal regression: a redefinition of the terms

The corpus is a transient endocrine gland that is specialized for production of progesterone and that plays a critical role in establishment and maintenance of pregnancy. The life span of corpus varies between species and, within a species, can be dramatically altered by events such as mating or pregnancy. Regardless of duration of its life span, corpus eventually enters a dynamic process during which it loses capacity to produce progesterone and undergoes involution. The overall process of has been referred to by a variety of terms over last several decades. In Table Table1,1, we show results of a cursory MEDLINE/PubMed search on performed in November of 2002, which reveals that most frequently utilized term for this process is followed by luteal and then, to a lesser extent, by and Other terms, such as luteal involution, or regression lag far behind in usage. The necessity of using several keywords to search for information on is illustrated by fact that in our sample MEDLINE/PubMed search, only 47% of manuscripts retrieved using keyword luteal regression were also retrieved when using keyword luteolysis. This inconsistency in terminology can result in serious under-retrieval and under-citation of papers using less popular keywords. Table 1 Results of a cursory MEDLINE/PubMed search performed on November 2002 using terms as listed. To quote Rossdale and Cox in their communication entitled Terminology: a mark of scientific progress [1]: Scientific terminology must be as exact as is possible within state of knowledge available. As our knowledge of molecular mechanisms participating in process of evolves, some of commonly used terms cited above have been rendered obsolete, inappropriate, and even incorrect. The foremost of these is still one of most common terms used to define process of regression, most probably because it is listed among Medical Subject Headings (MeSH), and, therefore, used most frequently. MeSH is U.S. National Library of Medicine's controlled vocabulary used for indexing articles in PubMed. MeSH terminology provides a consistent way to retrieve information that may use different terminology for same concepts. In MeSH, is defined as degradation of corpus luteum and further described as ...characterized by involution and cessation of its endocrine function. From a biology point of view, means rupture of plasma membrane, leading to release of cytoplasm and death of cell [2]. If interpreted with strict accordance to Latin, lysis refers to disintegration, as recently discussed by Davis and Rueda [3]. Over last decade, it has become clear that involution of corpus is associated with a phenomenon of programmed death or apoptosis [4]. Because apoptosis is an organized process that does not involve a major inflammatory response, and because majority of cells are removed prior to rupture, term when applied to is largely inaccurate. Therefore, while term luteolysis remains very popular – 1251 manuscripts were retrieved using word and only 403 were retrieved using terms luteal regression in MEDLINE/PubMed search (see Table Table1)1) – this term no longer accurately reflects mechanisms involved in regression. In 1999, McCraken et al. [5] stated that the term luteolysis may be something of a misnomer; but also referred to deep entrenchment of this term in literature. However, exponential increase in number of scientific manuscripts published in recent years ensures that a prompt move to replace older term with a more accurate descriptor will rapidly result in an overturn of current ranking displayed in Table Table11 and that only a minority of papers will continue to be retrieved using older term. Despite fact that a strict definition of appears to regard only disintegration of corpus luteum, broader interpretations are rife within literature. Rothchild [6] defined luteolysis as stopping secretion of progesterone by corpus luteum. Two other recent reviews take a middle road. Hoyer [7] refers to fall in progesterone secretion as but considers regression, or death, true regression. Niswender et al. [8], while referring to as demise of corpus luteum, go on to describe loss of progesterone synthesis and secretion – not a event – as part of of corpus luteum. As previous paragraph shows, adjectives structural and functional cannot be overlooked when addressing terminology in field of regression. These words have had a consistent presence in literature concerning of corpus since Malven and Sawyer [9] described process of in rat as having two components: 1) an initial termination of secretory function and 2) a subsequent morphological of nonfunctioning corpora lutea. A few years later Malven et al. [10] used term to describe morphological of persistent, corpora lutea in hypophysectomized rat. The definition of nonfunctional provided in this manuscript expanded upon 1966 description of first component of in rat by explaining that corpora lutea did not secrete enough progesterone to induce deciduoma formation following endometrial traumatization. Thus, corpora lutea were nonfunctional in terms of progesterone production and potential for establishment of pregnancy. Since appearance of these early papers, terms and of corpus (or more popular phrasing and luteolysis) have gained relative acceptance and usage. The cursory MEDLINE/PubMed search shown in Table Table11 turned up 82 references containing phrase luteolysis, of which 5 were 2001 and 2002 publications, and 72 references containing phrase luteolysis, of which 14 were 2001 and 2002 publications. The prevalence of term over in recently published articles may be due in part to a greater disparity in perceived meaning of latter term. This stems largely from studies in rats, in which it was revealed that corpora lutea which no longer secreted significant quantities of progesterone retained many functions, including active steroidogenesis [11-13]. It is our contention that these two frequently described components of process of (i.e. cessation of progesterone secretion and disappearance of structure) merit equal attention. However, timing and inter-relationship of these two types of regressive changes appears to vary by species. As new information on molecular steps triggered during is obtained, these mechanisms will need to be defined as they relate to these facets of overall regressive process. Davis and Rueda [3] advised that terms and used in context of should be adequately defined by authors in context of particular species and reproductive stage being studied, with which we concur. It is not extreme to predict that with advancement of knowledge in process of researchers will find increasing difficulties in establishing limits as to what mechanisms belong to functional facet of regression, and which ones are part of structural facet, as is a process of synchronized events. For example, it now appears that progesterone itself is responsible for preventing onset of apoptosis and disintegration [14-17].

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