A Practical Approach, Second Edition=Ronald D. Ho.pdf

TESTING FOR REPRODUCTIVE TOXICITY 4637. Reproductive SenescenceThere is a loss of the regular ovarian cycles and associated normal cyclical changes in the uterineand vaginal epithelium with advancing age in the female rat. Although the mechanisms causingreproductive senescence are not thoroughly understood, there are age-dependent alterations thatoccur within the hypothalamic-pituitary control of ovulation. 150,151 Cumulative estrogen exposuremay play a role in the loss of ovarian function in rats since adulthood estrogen treatment canaccelerate the loss of function. 152 In contrast, depletion of oocytes is the principal cause of the lossof ovarian cycling in humans. 153 Early onset of reproductive senescence in females (e.g., asevidenced by cessation of normal cycling, ovarian pathology, or an endocrine profile that isconsistent with reproductive senescence) should be considered an adverse female reproductiveeffect.8. Developmental and Pubertal AlterationsThe Guidelines for Developmental Toxicity Risk Assessment 11 and the Guidelines for ReproductiveToxicity Risk Assessment 38 are available as more detailed references to determine whether effectsinduced or observed during the pre- or perinatal period should be considered adverse. Significanteffects on sexual development (e.g., malformations of the internal or external genitalia, alteredanogenital distance) or age at puberty, whether early or delayed, should be considered adverse.Other adverse effects for females include alterations in age for various developmental landmarks(nipple development, vaginal opening) or alterations in vaginal cyclicity.G. Vaginal Cytology1. DescriptionEvaluation of the estrous cycle is used to detect alterations in the normal female reproductivesystem. Beginning at puberty (approximately 45 days of age in the rat), distinctive cyclic changesin uterine cytology occur in response to the ovarian hormones, estradiol and progesterone. Femalerats are polyestrous, with normal cycles ranging between 4 and 5 days. Estrous cycles continuethroughout the reproductive lifespan of the female, except during pregnancy and lactation orpseudopregnancy. Vaginal lavage is a simple, noninvasive method of collecting vaginal cells fordetermination of the estrous cycle. Vaginal lavage can also be used to confirm mating (presence ofsperm). Changes in vaginal cytology reflect changes in circulating ovarian hormone levels (estradioland progesterone). Monitoring of the estrous cycle in rats over several weeks provides informationabout the length of the cycle and about alterations in cyclicity, such as the induction of prolongedor persistent estrus or diestrus (pseudopregnancy).The estrous cycle is separated into three or four distinct phases: metestrus (also called DiestrusI), diestrus (also called Diestrus II), proestrus, and estrus. 154 The metestrus or diestrus (Diestrus Iand II) duration is usually 2 to 3 d, the proestrus duration is usually 1 d, and the estrus durationis also 1 d. Metestrus (Diestrus I) vaginal smears contain leukocytes, few polynucleated epithelialcells, and a variable number of cornified epithelial cells (some of these cells are beginning toroll). 140 Diestrus (Diestrus II) vaginal smears contains a mixture of cell types, primarily leukocytes,a variable number of polynucleated epithelial cells, and few to no cornified epithelial cells.During this period, vaginal epithelial cells are proliferating and sloughing off into the vaginallumen. The proestrus vaginal smear contains numerous, round, polynucleated epithelial cells (inclumps or strands), a variable number of leukocytes, and few to no cornified epithelial cells.Serum estradiol falls rapidly on the evening of proestrus as the ovarian follicles leutinize.Ovulation occurs early in the morning of vaginal estrus. Proliferation of the vaginal epitheliumdecreases, and cornified epithelial cells predominate. The estrus vaginal smear contains no© 2006 by Taylor & Francis Group, LLC