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Published in Asim Kurjak, Ultrasound and Infertility, 2020
Joseph G. Schenker, Aby Lewin, Menashe Ben-David
Further follicular development takes place in the leading follicle when LH receptors on the granulosa cell membranes are being synthesized. Presence of both FSH and estradiol is essential for the synthesis of LH receptors in the granulosa cells. Such conditions exist only in the leading follicle, which has the capacity to bind even the declined peripheral FSH concentration (due to high receptor levels) and thus to induce a microenvironment rich with estradiol. Increasing amount of peripheral estradiol can act directly on the pituitary gonadotropes to trigger positive feedback on LH. Concentrations higher than 200 pg /ml of estradiol are needed to achieve the positive feedback on pituitary LH. Moreover, estrogen feedback on LH secretion enhances not only the quantity of LH release, but also its quality by modulation of the LH molecule to one with a higher biological activity. During the late follicular phase, estrogens rise rapidly, reaching a maximum 24 to 36 h before the ovulation. Concomitantly, there is a decline in the circulating FSH to this nadir while FSH increases steadily and then rapidly in a surge-like burst at midcycle, accompanied by a lesser surge of FSH. In the presence of high estradiol concentration and adequate amount of FSH, activation of the granulosa cell LH receptors by the abundant LH will lead to a process of luteinization and an increase in progesterone production. If, however, there is no adequate amounts of either estradiol or FSH in the microenvironment of the follicles, the follicles react to LH bolus with atresia rather than luteinization.
Concordance between sites of tumor development in humans and in experimental animals for 111 agents that are carcinogenic to humans
Published in Journal of Toxicology and Environmental Health, Part B, 2019
Daniel Krewski, Jerry M. Rice, Michael Bird, Brittany Milton, Brian Collins, Pascale Lajoie, Mélissa Billard, Yann Grosse, Vincent J. Cogliano, Jane C. Caldwell, Ivan I. Rusyn, Christopher J. Portier, Ronald L. Melnick, Robert A. Baan, Julian Little, Jan M. Zielinski
Several agents, notably radiation and tobacco smoke, induce malignant lesions at multiple sites or in multiple organ and tissue systems. Volume 100F (IARC 2012c) summarizes the evidence that 1,3-butadiene induces hemangiosarcomas of the heart, malignant lymphomas, bronchiol-alveolar neoplasms, and squamous cell neoplasms of the forestomach in male and female B6C3F1 mice, and acinar cell carcinomas of the mammary gland, granulosa cell neoplasms of the ovary, and hepatocellular neoplasms in female mice. Assessing species concordance with multisite carcinogens is inherently more difficult than with carcinogens that affect a single organ or tissue. Understanding the MOA and other attributes of such multisite carcinogens will be useful in translating results in experimental animals to humans.