Primordial follicles

Menstrual cycling is dependent upon the hormones secreted by the Graafian follicles. Once the primordial follicles are depleted, the secretion of oestrogen and progesterone progressively fails and menstrual cycle activity gradually decreases, a period which is characterised by irregular cycles. The differences in steroid hormone production or plasma levels between pre- and post-meno-pausal women are as follows ... 

Isoprene [7.34 mmol/kg bw by intraperitoneal injection] affected ovarian follicles in 21-day-old B6( 3F. mice. Small (primordial) follicle counts were reduced by 76 5% while growing (primary to pre-antral) follicle counts were reduced by 46% 8% when compared with the respective sesame seed oil controls (Doerr et al., 1995). 

The postlactational ovary should contain primordial and growing follicles as well as the large corpora lutea of lactation. In the two-generation study, the histopathological examination includes assessment of qualitative depletion of the primordial follicle population in the parental animals. A quantitative evaluation of primordial follicles should be conducted for FI females the number of animals, ovarian section selection, and section sample size should be statistically appropriate for the evaluation procedure used. Examination should include enumeration of the number of primordial follicles, which can be combined with small growing follicles, for comparison of treated and control ovaries. 

Hirshfield AN (1994) Relationship between the supply of primordial follicles and the onset of follicular growth in rats. Biol Reprod, 50 421-428. 

Shirota M, Soda S, Katoh C, Asai S, Sato M, Ohta R, Watanabe G, Taya K, Shirota K (2003) Effects of reduction of the number of primordial follicles on follicular development to achieve puberty in female rats. Reproduction, 125 85-94. 

The frequency of the menstrual/estrous cycle varies among species. For example, monoestrous species (e.g., dogs, cats) exhibit 1-2 cycles per year, whereas polyes-trous species (e.g., rodents, primates) exhibit more frequent cycles of shorter duration. Primordial follicles, each consisting of an oocyte surrounded by a single layer of flattened somatic cells known as granulosa cells, are recruited to become primary follicles, a transition marked by increased oocyte size, formation of a glycoprotein matrix (zona pellucida) around the oocyte, and transformation to cuboidal-shaped... 

Female reproductive toxicity includes adverse effects on reproductive organs and related endocrine systems. Endpoints that reflect toxicity include sexual behavior (receptivity to the male at appropriate times in the cycle), age at onset of puberty, fertility (the ability to produce offspring in normal number), gestation length, parturition, lactation, loss of primordial follicles, and age at reproductive senescence. 

Q1 The primordial follicles in which ova develop, form in the embryo and the maximal number 1-2 million, is present at birth. Follicles are located in the cortex of the ovary and each contains a primary oocyte. Following sexual maturation at puberty about 200 000 follicles remain, some of these will develop into primary follicles. During reproductive life a number of the primary follicles develop further, leading to ovulation, the remainder decline (a process known as atresia). 

Clinically, menopause is defined as the last physiologic menstrual cycle in which pituitary gonadotropins (e.g., LH, FSH) have stimulated the maturation of a primordial follicle and caused ovulation. The transition from full reproductive potential to final ovarian failure is known as the climacteric, a period that begins about age 40. As estradiol levels in the blood gradually fall below normal, the early symptoms of the climacteric occur, s including anxiety, mood swings, irritability, and in some instances,... 

Another rare cause of amenorrhea is the so-called resistant ovary syndrome. This primary hypogonadal condition is associated with increased concentrations of plasma FSH and LH, and ovaries that contain predominantly primordial follicles. It is thought to arise from a defect in FSH receptors. This disorder can be diagnosed only by examination of an ovarian biopsy specimen, which will exhibit functioning ovarian follicles despite the presence of amenorrhea. Ovulation can sometimes be induced in these patients with administration of high doses of gonadotropins. 

Characteristics of the human menstrual cycle throughout reproductive life have been well described. A woman is born with approximately two million primordial follicles in her ovaries. During a normal reproductive life span, she ovulates less than 500 times. The vast majority of follicles undergo atresia. 

FOX03a is involved in the apoptosis of naked oocytes and oocytes of primordial follicles from neonatal rat ovaries. Biochem Biophys Res Commim 381(4) 722-727. 

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