ArticleBiology of sex differences2023
The mixed legacy of the rat estrous cycle.
Article in Biology of sex differences, 2023. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 5 papers.
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Who cites it
5 citing papers in PubMed.
- Targeting early pulmonary fibrosis with bone marrow mesenchymal stem cells and their derived exosomes: a comparative study of inhalation versus injection delivery in bleomycin-induced rat lung injury.Naunyn-Schmiedeberg's archives of pharmacology · 2026Article
- Sex Differences in Metabolite-Immune Circuits of Neuroinflammation.Immunological reviews · 2026Review
- Sex-dependent effects of psychedelics: review of evidence from rodent models.Frontiers in psychiatry · 2026Review
- Platelets in angiogenesis and pulmonary progenitor cell homing under chronic intermittent hypoxia.Scientific reports · 2025Article
- From smooth brains to rocky mountains: Quentin Pittman in a Quintessentially Canadian career.Brain, behavior, and immunity · 2025Article
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1 author.
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Abstract
backgroundThe rat estrous cycle first characterized by Long and Evans in 1922 profoundly affected the course of endocrine research. Investigators took advantage of sex steroid hormone fluctuations associated with the cycle to assess hormonal influences on anxiety, depression, food intake, stress, brain structure and other traits. Similarities of the rat estrous and human menstrual cycles facilitated understanding of human reproductive physiology. I assessed the impact of awareness of the estrous cycle on the emergence of a sex bias that excluded female rats from biomedical research.
methodsBeginning with the 1918 volume of the American Journal of Physiology and ending in 1976 when the journal subdivided into several separate disciplinary journals, all studies conducted on rats were downloaded; the use of females, males, both sexes and sex left unspecified was tabulated for 485 articles. A second analysis tracked the number of rat estrous cycle studies across all disciplines listed in PubMed from 1950 to 2021.
resultsThe description and awareness of variability associated with the rat estrous cycle was correlated with a precipitous decline in investigations that incorporated both sexes, a marked increase in male-only studies and a striking sex bias that excluded female rats. The number of rat estrous cycles studies increased markedly from earlier decades to a peak in 2021.
conclusionsThe initial description the rat estrous cycle was correlated with a substantial decline in investigations that incorporated both sexes; one result was a marked increase in male-only studies and a striking sex bias that excluded female rats from biomedical research. Recognition of the advantages of studies that incorporate the rat estrous cycle has resulted in recent years in an increase of such investigations. Female rats and females of several other species are not more variable than their male counterparts across traits, arguing for female inclusion without requiring cycle monitoring. There, remain, however, many advantages of incorporating the estrous cycle in contemporary research.
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