Prolonged Estrus Research Articles

Vaginal estrus in unmated belding's ground squirrels

Belding's ground squirrels are seasonally breeding rodents that have a single annual mating season (ca. 3 weeks long) which begins shortly after their vernal emergence from a 7-month period of hibernation. In this study, changes in vaginal estrus were assessed among unmated captive females. Following a 7-month period in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females were in vaginal estrus within 24–48 hr of removal from the coldroom. Rather than exhibiting repeated cycles, adults (⩾ 2 years old) remained in prolonged estrus (typically 3–4 weeks, but 8–10 weeks in some cases), whereas yearlings exhibited similar but shorter and possibly periodic changes in vaginal condition. The difference between the two age classes persisted in a second year of testing, indicating that the preadult status of yearlings (in the first year of testing) did not primarily account for the difference. In another experiment, removal from the coldroom was delayed for 24 days relative to adults removed at a time coincident with emergence from hibernation of free-living females. The “delayed” adults showed persistent vaginal estrus for a shorter total duration, such that both groups reached anestrus at approximately the same time. This implies that the latency to anestrus is not simply a fixed period from the time of removal from the coldroom.

A note on the effect of zeranol administration on oestrous cycle length and hormonal profiles in cows

ABSTRACTZeranol is an anabolic agent with oestrogenic actions commonly used in fattening beef cattle. This experiment was designed to determine the effects of zeranol administration on oestrous cycle lengths, plasma progesterone concentrations and the exhibition of oestrus in mature cows. Administration of 36-mg zeranol implants during the early, middle or later portion of the oestrous cycle did not alter the length or persistence of oestrous cycles, nor were progesterone profiles different from those observed in untreated cows. Some cows that received zeranol exhibited a prolonged oestrus. The regularity of oestrous cycles in cows treated with zeranol indicates that it may be possible to utilize zeranol as an anabolic and lactopoetic agent in post-partum beef cows.

Abnormes Sexualverhalten Zusammengehaltener, Weiblicher Hemiechinus Auritus Syriacus (Insectivora: Erinaceinae)

Two female Hemiechinus auritus syriacus (litter mates) were kept together for 4 weeks and demonstrated intense homosexual activity and prolonged oestrus during the entire period. This resulted also in an unwillingness to mate for one and a half, and two and a half years, respectively.

Effect of suppression of the surge of follicle-stimulating hormone with porcine follicular fluid on follicular development in the rat.

To examine the manner in which the FSH surge of one oestrous cycle recruits follicles for ovulation in the subsequent cycle, porcine follicular fluid (PFF) was used to alter the pattern of endogenous FSH secretion during the periovulatory period. OVaries of animals killed at oestrus or metoestrus were examined histologically for the presence of large follicles (greater than 400 micrometers in diameter) after treatment. Large follicles were absent in ovaries of PFF-treated animals at oestrus, while control rats had an average of 2.7 large follicles per ovary. By metoestrus, however, ovaries of rats treated with PFF contained several large, healthy follicles. Only when PFF treatment was continued throughout the evening of oestrus was the appearance of large follicles prevented at metoestrus. Our results suggest that the prolonged oestrus portion of the FSH surge, rather than the pro-oestrous portion, is responsible for follicular recruitment during the normal oestrous cycle in the rat. They also indicate that compensatory follicular development occurs in response to the FSH rebound which has been shown to follow FSH suppression.

Effects of gamma-oryzanol on the maintenance of estrous cycles in aged rats.

Gamma-oryzanol was orally administered daily 10 mg for 10 days to 9-11 months old female rats showing regular estrous cycles, and vaginal smears were observed for 60-100 days. As compared with untreated controls which gradually became to exhibit spontaneous prolonged estrus or diestrus during a 60-100 day observation period, gamma-oryzanol treated rats maintained high incidence of regular cyclicity.

The prolonged storage and survival of spermatozoa in Chiroptera

The prolonged storage of spermatozoa by bats was first reported by Pagenstecher in 1859, and subsequently attracted the attention of several early comparative anatomists and histologists whose work has been thoroughly reviewed by Hartman (1933). Hartman was initially sceptical about the fertilizing capacity of the stored spermatozoa (Hartman & Cuyler, 1927) and it was left to Wimsatt (1942, 1944) to undertake the first critical experiments of isolating inseminated females from males and observing the developing embryo in the reproductive tract after arousal from hibernation in spring. Further work, reviewed by Wimsatt (1969), has shown that sperm storage is one facet of the complex reproductive adaptations of bats living in temperate latitudes where a period of hibernation occurs during prolonged oestrus.

The different influence of predominantly antiadrenergic and antidopaminergic neuroleptics on the estrous cycle in rats.

In experiments performed on rats, single subcutaneous doses of predominantly antidopaminergic neuroleptics (fluspirilene, pimozide, and thioproperazine in large doses) elicited persistent diestrus, i.e. pseudopregnancy. Neuroleptics with predominantly antiadrenergic action (levomepromazine, thioridazine, chlorpromazine) as well as phenoxybenzamine injected intraventricularly induced mainly prolonged estrus, i.e. blocking of ovulation. Since pseudopregnancy implies a rise of prolactin secretion, our results indirectly indicate that PIF secretion is stimulated by dopamine. The antiovulatory effect of the antiadrenergic agents, which involves an inhibition of the proestral LH surge, suggests that the discharge of LRF is mediated by an adrenergic mechanism.

Behavior of Ovaries Subcutaneously Transplanted to Ovariectomized Hosts from Normal and Neonatally Estrogenized Donors

An ovary from one-year-old normal or neonatally estrogenized rats were transplanted under the abdominal skin of ovariectomized rats. Vaginal smear records in the two kinds of recipients were characterized by prolonged estrus. All the ovarian grafts consisted mainly of corpora lutea and small follicles after residence for 50 days in the hosts. These findings indicate that the neonatal estrogen injections did not produce any permanent change in ovarian reactivity to gonadotropins.

Effects of dopamine implanted in the median eminence on the estrous cycle of the rat.

A mixture (DA-C) of dopamine hydrochloride and cholesterol in a ratio of 2 to 1 or 5 to 1 by weight was implanted into different hypothalamic regions of the rat and allowed to persist for more than two weeks. The estrous cycles and ovarian histology were examined to determine effects of the treatment. When the tip of the cannula containing DA-C (2 to 1) hit the posterior median eminence (ME) and a small part of the arcuate nucleus (AN), the rats showed prolonged estrus. The ovaries of these rats showed big follicles and no corpora lutea. When the tip of the cannula of DA-C (5 to 1) hit the posterior ME and a small part of the AN, the rats showed prolonged diestrus. The follicles and corpora lutea were small in the ovaries of these rats. Under our experimental conditions, DA seems to inhibit LH and FSH release at the level of the ME. When the tips of the cannulae containing DA-C were placed in AN, n. ventromedialis, n. premamillaris ventralis, n. premamillaris dorsalis, n. dorsomedialis pars ventralis or adenohypophysis, the rats showed cycles with or without minor irregularities.

Infertility of mice induced by antibodies specific for human chorionic gonadotrophin.

ABSTRACT Injections of rabbit antisera to cross-linked human chorionic gonadotrophin (HCG) into female STu mice made tolerant to rabbit γ-globulin, induced prolonged oestrus lasting for 18–60 days and phases of sterility of 37–130 days duration. When immune-competent mice were treated in a similar manner these effects were very markedly decreased due to the interference of antibodies developed against rabbit serum proteins. The results are discussed on the basis of cross-reactions with endogenous gonadotrophins.

The oestrous cycle of rats at high altitude.

Summary. Rats were exposed to an altitude of 14,000 ft for up to 90 days, either in natural cold or at 23° C. An initial tendency to anoestrus was probably due to the sudden change of environment. After about 30 days there was prolonged oestrus, probably as a result of low oxygen pressure. Oestrus was not as prolonged among the cold-exposed animals as among those at 23° C, evidently owing to the anoestrous effect of cold. Recovery usually occurred on descent to sea level.

Spontaneous Malformations of the New Zealand White Rabbit: The Background to Safety Evaluation Tests

The present interest in malformations of the rabbit stems almost entirely from a chain of events that originated in the thalidomide disaster and expanded through a multiplicity of animal studies which, among other things, demonstrated that thalidomide consistently causes malformations in the rabbit embryo. Culmination of the chain was the acceptance of the rabbit as a suitable species for teratogenicity screening tests in the safety evaluation of new drugs (Table 1). It is now evident that, for drug evaluation studies, susceptibility of the test species to thalidomide is a somewhat doubtful recommendation. Thalidomide is unique and atypical so that a positive result obtained with it is not necessarily indicative that a species will be susceptible to teratogens that depend on quite different modes of action. Fortunately the rabbit (especiaIly the New Zealand White) possesses a number of basic characteristics that are an asset in teratology studies. Some of these characteristics, and the advantages that spring from them, are: domesticated and of moderate size (foetus 40 g, adult 3-4 kg)~easily visible defects, moderate drug need, ease of handling and maintenance, short gestation (32 days); prolonged oestrus and induced ovulation~pregnancy easily and accurately timed, artificial insemination possible;

Concentration of luteinizing hormone in the hypophysis of rats with prolonged estrus

Luteinizing hormone (LH) content was studied in the hypophysis of female rats with permanent estrus occurring both spontaneously or caused by electrolytic hypothalamic injury. To determine the LH content, suspensions of hypophyses, examined individually, were administered to infantile female rats to which folliculostimulating hormone prepared of the blood serum of a pregnant mare (PMS) had been administered.

Effects of Pinealectomy, a Pineal Extract and Pineal Grafts on Light-Induced Prolonged Estrus in Rats

Effects of Pinealectomy, a Pineal Extract and Pineal Grafts on Light-Induced Prolonged Estrus in Rats

Influence of the anticholineric drug pathilon on the reproductive cycle of the female rat.

A new anticholinergic drug, 3-diethylamino-l-cyclohexyl-l-phenyl-l-ethi-odide (Pathilon, Lederle), was tested for its capacity to block ovulation in rats. Thirty adult females were injected with the drug (25, 50 or 75 mg.⁄kg. body wt., s.c.) before the “critical period” on the day of proestrus. The higher doses blocked ovulation in 70% and 95% of the cases, repsectively. Five of 6 animals injected after the critical period with 75 mg.⁄kg. ovulated normally. In 16 rats kept for later observation there was prolongation of diestrus (12-16 days) after postponed or normal ovulation; 11 were pseudopregnant, as proven by decid-uoma formation. Effects of administration during diestrus were examined in 40 rats by injecting a single dose (50 mg.⁄kg.) on diestrus days 1, 2 or 3. There was often an effect on the immediate cycle, either prolongation of the current diestrus (21 rats, 10 pseudopregnant)or prolonged estrus with delayed ovulation (6 rats). In 10 rats prolongation of diestrus followed normal or delayed ovu...

Monomethyl Ether of Stilbestrol and Menopausal Syndrome

Many natural and synthetic Compounds are estrogenic, but until recently only the natural compounds have been used clinically. Diethyl stilbestrol represents the first synthetic compound of acceptable clinical value. Since it is a well-known fact that the derivatives of a compound may possess properties enhancing its clinical uses over that of the original, many derivatives of stilbestrol have been studied by Geschickter and Byrnes (1), and by Dodds, Lawson and Noble (2). It has been found that increasing the length of the side chain of stilbestrol decreases the potency, and esterification with aliphatic acids decreases potency but gives a more prolonged estrus. Sondern, Sealey and Kartsonis (3) and Geschickter and Byrnes (1) have studied the estrogenic effects of dimethyl, diethyl, and dipropyl ethers of stilbestrol giving the ratio of activity as 1:5:10:33. Geschickter and Byrnes (1) have found that the monomethyl ether was as potent as diethylstilbestrol and more potent than estrone.

DIESTRUS AND CORPUS LUTEUM FORMATION IN PERSISTENT ESTROUS RATS BY LUTEINIZING HORMONE AND ANTIGONADOTROPIC SERUM1

THE SPONTANEOUS OCCURRENCE of prolonged estrus in the rat was reported in 1921 by Evans and Long (1). Since that time reports of naturally occurring ‘persistent estrus’ have been made by Bryan, et al. (2), Wolfe, et al. (3),and Everett (4). Experimentally produced ‘constant estrus’ has been reported by DuShane, et al. (5),Selye and Collip (6),Pfeiffer (7),and Hill (8,9). Everett (10)hasshown that persistent estrous rats can be made cyclic by the administration of appropriate amounts of progesterone. Eight rats were treated with antigonadotropic serum and 7 rats received LH. The animals were obtained from our colony, which originated from the Sprague-Dawley stock. The vaginal changes were followed by daily smears; laparotomies were performed at appropriate intervals and the ovaries removed for histological study when such a procedure was thought advisable. Since the manipulation of the ovary at the time of laparotomy frequently resulted in adhesions, only one ovary was examined at a given laparotomy.

Molecular structure in relation to oestrogenic activity. Compounds without a phenanthrene nucleus

In earlier publications the oestrogenic activity of a number of synthetic substances has been discussed. The first compounds to be tested contained the phenanthrene ring system, and it was shown (Cook, Dodds and Hewett 1933; Cook and Dodds 1933; Cook, Dodds, Hewett and Lawson 1934; Cook, Dodds and Greenwood 1934) that a high degree of activity is possessed by 9 : 10-dihydroxy-9 : 10-di-n-propyl-9 : 10-dihydro-1 : 2 : 5 : 6-dibenzanthracene. Potency was also observed in the highly unsaturated aliphatic acid, clupanodonic acid, whilst a feeble but definite oestrogenic action was found to be possessed by calciferol. Since neither of these compounds contains the phenanthrene ring system, it was considered that this was not essential for oestrogenic properties. A further interesting observation was made in the partial activity of 1-keto-1: 2: 3: 4: 5: 6: 7: 8-octahydroanthracene. This substance produced an advanced pro-oestrus, but full cornification could not be produced no matter how much of the material was administered. A series of derivatives of acenaphthene was studied because these compounds contain a three-ring system arranged in a manner different from that in phenanthrene. These were tested on ovariectomized rats in the manner described in the above-mentioned publications. Table I shows the results obtained with this group of substances. It will be observed that the most potent member of the series is 1 : 2-dihydroxy-1 : 2-di-α-naphthyl acenaphthene. In doses of 10 mg. this compound produces prolonged oestrus. This new substance confirmed our assumption that the phenanthrene ring system was unnecessary for oestrogenic activity and led to experiments with a number of aromatic carbinols (Table II). This series of compounds showed surprising differences in behaviour. Thus, whilst diphenyl-α-naphthyl carbinol possesses full activity in doses of 100 mg. the corresponding diphenyl-β-naphthyl carbinol and triphenyl carbinol were both without action. The effect of hydroxy groups in the aromatic nucleus was then studied and several phenolic diphenyl methane derivatives were investigated with results as shown in Table III. 3 : 3′- and 4 : 4′- dihydroxydiphenyl methane both showed activity, the latter much greater than the former, but the corresponding dicarboxylic acids were without effect. Many potent substances were found in derivatives of 4 : 4′ dihydroxy-diphenyl methane. From this series it appears that the alkyl substituents on the central carbon atom have no influence on the efficacy of the substance. A single phenyl nucleus has a distinct depressing action, and the diphenyl derivative is completely inert. The introduction of methyl groups in the 3 : 3′ positions appears to diminish the potency in some cases.

The Hormones of the Sexual Glands1

THE influence of the ovaries on other tissues is an established fact; less is known of the effect of other glands upon the ovaries, but evidence is accumulating that the maturity and periodicity of function of the female sexual glands depend on influences from other tissues or glands of the body. Grafting experiments have shown that an ovary from an immature animal inserted into the tissues of an ovariectomised adult reaches maturity sooner than it would have done in its original environment: a mature organ grafted into an immature produces no observable effects and becomes functionless. A. Lipschütz has obtained similar results when an ovary is grafted into a castrated male: if the animal—guinea-pigs were used-is an adult, hormonic effects, as shown by hypertrophy of the mammary glands, set in after 1J-3 weeks, but if the animal engrafted is not fully grown there is a latent period of about six weeks: ovaries from the same female may show these different latencies if grafted into males of different ages (Jour. Biol. et Med. Exper., No. 6, p. 1; 1926). The grafted ovaries, however, do not usually show their normal periodicity, but enter into a state resembling prolonged oestrus.