Estrus cycle

Estrogenic activity. Ability to mimic the female hormone by promoting the development of female secondary sex characteristics and modulating the estrus cycle. 

Ma W. and Klemm W.R. (1997). Variations in equine urinary volatile compounds during the estrus cycle. Vet Res Comm 21, 437-446. 

Perret M. and Barek S. (1991). Male influence on estrus cycles in female Woolly Opossum (Caluromys philander). J Reprod Fertil 91, 557-566. 

F (irregular estrus cycles) 0.28 F (ovarian cysts persistent vaginal estrus) ... 

Rat (Sprague-Dawley) 14-50 ad lib (W) 502 (decreased testicular weights delayed vaginal opening and disruption of estrus cycling) Ronis etal. 1996 PbAc... 

Reduced food intake and efficiency of food use, altered iron metabolism, clinical signs of copper deficiency. Onset of puberty delayed 10 weeks, decreased conception rate (fertility 12-33% vs. 57-80% in controls), disrupted estrus cycle (67% were anestrus vs. 7% in controls), and other signs consistent with decreased releases of luteinizing hormones associated with altered ovarian secretion (3, 4) Growth and fertilization normal liver copper 10 mg/kg DW only 16% of embryos developed normally (2)... 

Some information (e.g. reproductive state) appears to be contained solely within the chemical matrix of certain marks, particularly within the stable genital secretions. Thus, longer-lasting signals may be broadcast to any animal that comes in contact with labial or scrotal marks. Such a scenario seems particularly applicable to females that scent mark most frequently prior to the onset of estrus cycles, but nonetheless when their sex steroids are on the rise (Drea 2007). Such advertisement may encourage male immigration at a time that would maximize the opportunity of female mate choice, even if the mechanism of, or criteria for, selection remain obscure. 

Urine composition depends on testosterone, as in male mice (Schwende etal, 1986) and the wolf, Canis lupus (Raymer etal., 1986). In the wolf, these volatiles signal both sex and sexual maturity (Raymer eta/., 1986). Similarly, composition of female urine changes with the estrus cycle (Schwende etal., 1986). 

The VNO is extremely important in mediating endocrine responses to primer pheromones. Puberty acceleration in female rats by male urine odors can be prevented by electrolytic damage to the vomeronasal nerve. Also, effects of male urine odor such as shortening of the estrus cycle (see Ch. 8) can be eliminated by section of the vomeronasal nerve, or bilateral electrocoagulation of the accessory olfactory bulb (Sanchez-Criado, 1982). In rats, the odor of males stimulates ovulation in females, an effect that is lost if the VNO is extirpated (Johns etal., 1978). Female prairie voles, M. ochrogaster, respond to odors from males with reproductive activation. Surgical removal of the VNO from adult females impedes this reproductive activation by the stud male. The weights of the uterus and the ovaries of these females were lower than those of normal or sham-operated individuals. However, the females without a VNO were still able to locate food by chemical cues (Lepri and Wysocki, 1987). 

Thresholds can vary between and within individuals, with the estrus cycle, and with the chemical background. Some benchmarks will be given here. In laboratory (Wistar) rats, the olfactory detection threshold for ethyl acetate was measured as 7.3 x 10 vol% in subadults, while adult rats were more sensitive (1.4 X 10 vol%) (Apfelbach etah, 1990). (By comparison, among insects the gypsy moth is 10 times as sensitive. The threshold for bombykol, defined as... 

Flehmen (Fig. 5.12) is a behavior shown by male ungulates to primarily female urine. In the stallion, it serves to monitor the estrus cycle, rather than being a step in the actual courtship sequence (Stahlbaum and Houpt, 1989). Table 7.4 lists some examples of the time in the estrus cycle when flehmen is most frequent. 

Table 7.4 Timing of flehmen during estrus cycle...

Voided or bladder urine from single wild house mice also inhibited estrus cycles in females. These two types of urine reduced the normal rate of 2.4 cycles per female in 18 days to only 1.66 and 2.00, respectively. Urine from spayed females was not effective (Pandey and Pandey, 1986). 

Urine odor of adult males induces and synchronizes estrus cycles in adult female mice (Whitten, 1958). The cycles grow shorter and more regular when a male is nearby. A male shortens cycles of 7-8 days to 4-5 days. Exposure to male urine for 48 hours has the same effect. This phenomenon is known as the Whitten effect. The estrus-inducing activity of male urine is retained even after storage at -4 °C or freeze-drying (Gangrade and Dominic, 1986). This has... 

Rat Rattus F Estrus cycles M urine Shortening of cycles Sanchez-Criado,... 

Ever since McClintock (1971) described synchronized estrus cycles in 135 women who roomed together in a women s college dormitory, the search for possible olfactory cues, as occur in other mammals, has continued. The longer the women in McClintock s study spent time together during the academic year (October through March), the closer the times of onset of their menstrual cycles... 

In a later experiment, two pheromones from axillary odor of young women influenced the estrus cycle of other women (Stern and McClintock, 1998). Armpit secretion that appears odorless to humans was applied daily between the upper lip and nose of healthy young women and had two opposite effects depending on the menstrual phase of the odor donors. Secretion from nine donor women, collected on pads in their armpits during the follicular phase of their cycles... 

Priming pheromones hold great promise as means to accelerate puberty or to synchronize and regularize estrus cycles in livestock. 

A number of medical uses of prostaglandins have been discovered and more will probably be developed. While prostaglandins may be required for conception, small amounts of PGE2 or PGF2a induce abortion. PGF2a is also used to induce labor. Prostaglandins are widely employed to control breeding of farm animals, to synchronize their estrus cycles, and to improve the efficiency of artificial insemination.307... 

Parr, M.B., et al. 1991. Langherans cells phagocytose vaginal epithelial cells undergoing apoptosis during the murine estrus cycle. Biol Reprod 45 252. 

These newer methods call for testing to be done in a single sex to reduce variability in the test population. This reduction in variability in turn minimizes the number of animals needed. Normally females are used. Although there is usually little difference in sensitivity between males and females, in those cases where there are observable differences, females are most commonly the more sensitive sex. Normally animal suppliers have an excess of female rats because many researchers order only male rats to avoid physiological changes associated with estrus cycling in females therefore preferential use of female animals for acute testing should not result in excess male animals. 

Early studies of cyclodienes revealed reproductive effects on mice, rats, and dogs associated with changes in the estrus cycle (ref. 100, p. 154). Ottolenghi et al. (ref. 105) observed teratogenic effects on mice and hamsters at 1/2 LD q doses of aldrin, dieldrin and endrin. In addition to the anomalies observed (cleft palate, webbed feet and open eyes), growth retardation and fetal deaths occurred. Effects on the dams were not reported, but none of the expected overt toxic symptoms associated with chlorinated cycloalkenes was in evidence (ref. 105) ... 

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