The role of the bed nucleus of the stria terminalis in stress-induced inhibition of pulsatile luteinising hormone secretion in the female rat

The bed nucleus of the stria terminalis (BNST) occupies a central position in the neural circuitry regulating the hypothalamic-pituitary-adrenocortical axis response to stress. The potential role of the BNST in stress-induced suppression of the gondotrophin-releasing hormone (GnRH) pulse generator, the central regulator of the reproductive system, was assessed by examining the effects of micro-infusion of corticotrophin-releasing factor (CRF) or its antagonist into the BNST on pulsatile luteinising hormone (LH) secretion or stress-induced inhibition of LH pulses, respectively. Ovariectomised oestrogen-treated rats were implanted chronically with bilateral cannulae in the dorsolateral BNST and i.v. catheters. CRF (25, 50 or 100 pmol in 200 nl of artificial cerebrospinal fluid) administered bilaterally into the BNST resulted in a dose-dependent decrease in LH pulse frequency, and induced Fos expression in glutamic acid decarboxylase immunostained neurones in the medial preoptic area. These results suggest that the activation of hypothalamic GABAergic neurones in response to intra-BNST administration of CRF may be involved in the suppression of LH pulses. Furthermore, administration of CRF antagonist (280 pmol astressin-B, three times at 20-min intervals) into the BNST effectively blocked the suppression of pulsatile LH secretion in response to restraint (1 h) but not hypoglycaemic (0.25 U insulin/kg, i.v.) stress. These data suggest that CRF innervation of the dorsolateral BNST plays a key, but differential, role in stress-induced suppression of the GnRH pulse generator.

Corticotrophin-releasing factor alters the timing of puberty in the female rat

Puberty is a developmental process that is dependent upon activation of the hypothalamic gonadotrophin-releasing hormone (GnRH) pulse generator. It is well established that the stress neuropeptide, corticotrophin-releasing factor (CRF), has a profound inhibitory action on GnRH pulse generator frequency. Although stress is known to affect the timing of puberty, the role of CRF is unknown. The present study aimed to test the hypothesis that CRF plays a critical role in the timing of puberty. On postnatal day (pnd) 28, female rat pups were chronically implanted with i.c.v. cannulae and received 14 days of administration of either CRF, CRF receptor antagonist (astressin-B) or artificial cerebrospinal fluid via an osmotic mini-pump. A separate group of rats served as nonsurgical controls. As a marker of puberty, rats were monitored for vaginal opening and first vaginal oestrus. Levels of CRF, CRF receptor types 1 and 2 (CRF-R1, CRF-R2) mRNA expression in micropunches of the medial preoptic area (mPOA), hypothalamic paraventricular nucleus (PVN) and arcuate nucleus (ARC) were determined across pubertal development; brain tissue was collected from a naive group of rats on pnd 14, 32, on the day of vaginal opening, and pnd 77 (Adult). Administration of CRF resulted in a delay in the onset of puberty, whereas astressin-B advanced pubertal onset. Additionally, CRF and CRF-R1 mRNA expression was reduced in the mPOA, but not ARC, at puberty. In the PVN, expression of CRF, but not CRF-R1 mRNA, was reduced at the time of puberty. These data support the hypothesis that CRF signalling may play an important role in modulating the timing of puberty in the rat.

Neonatal lipopolysaccharide exposure delays puberty and alters hypothalamic Kiss1 and Kiss1r mRNA expression in the female rat

Immunological challenge experienced in early life can have long-term programming effects on the hypothalamic-pituitary-adrenal axis that permanently influence the stress response. Similarly, neonatal exposure to immunological stress enhances stress-induced suppression of the hypothalamic-pituitary gonadal (HPG) axis in adulthood, but may also affect earlier development, including the timing of puberty. To investigate the timing of the critical window for this programming of the HPG axis, neonatal female rats were injected with lipopolysaccharide (LPS; 50 microg/kg i.p.) or saline on postnatal days 3 + 5, 7 + 9, or 14 + 16 and monitored for vaginal opening and first vaginal oestrus as markers of puberty. We also investigated the effects of neonatal programming on the development of the expression patterns of kisspeptin (Kiss1) and its receptor (Kiss1r) in hypothalamic sites known to contain kisspeptin-expressing neuronal populations critical to reproductive function: the medial preoptic area (mPOA) and the arcuate nucleus in neonatally-stressed animals. We determined that the critical period for a significant delay in puberty as a result of neonatal LPS exposure is before 7 days of age in the female rat, and demonstrated that Kiss1, but not Kiss1r mRNA, expression in the mPOA is down-regulated in pre-pubertal females. These data suggest that the mPOA population of kisspeptin neurones play a pivotal role in controlling the onset of puberty, and that their function can be affected by neonatal stress.

Down-regulation of hypothalamic kisspeptin and its receptor, Kiss1r, mRNA expression is associated with stress-induced suppression of luteinising hormone secretion in the female rat

Identification of kisspeptin (Kiss1) and its G protein-coupled receptor 54 (Kiss1r) as an essential component of the hypothalamic-pituitary-gonadal (HPG) axis controlling gonadotrophin secretion raises the possibility that kisspeptin-Kiss1r signalling may play a critical role in the transduction of stress-induced suppression of reproduction. We examined the effects of: (i) three different stressors, known to suppress pulsatile luteinising hormone (LH) secretion; (ii) corticotrophin-releasing factor (CRF); and (iii) corticosterone on Kiss1 and Kiss1r expression in key hypothalamic sites regulating gonadotrophin secretion: the medial preoptic area (mPOA) and arcuate nucleus (ARC). Ovariectomised oestrogen-replaced rats were implanted with i.v., subcutaneous or i.c.v. cannulae. Blood samples were collected at 5-min intervals for 5-6 h for detection of LH. Quantitative reverse transcriptase-polymerase chain reaction was used to determine Kiss1 and Kiss1r mRNA levels in brain punches of the mPOA and ARC collected 6 h after restraint, insulin-induced hypoglycaemia or lipopolysaccharide stress, or after i.c.v. administration of CRF, or acute or chronic subcutaneous administration of corticosterone. We observed down-regulation of at least one component of the kisspeptin-Kiss1r signalling system by each of the stress paradigms within the mPOA and ARC. CRF decreased Kiss1 and Kiss1r expression in both the mPOA and ARC. Both acute and chronic stress levels of corticosterone resulted in a concomitant decrease in Kiss1 and an increase in kiss1r mRNA expression in the mPOA and ARC. This differential regulation of Kiss1 and Kiss1r might account for the lack of effect corticosterone has on pulsatile LH secretion. Considering the pivotal role for kisspeptin-Kiss1r signalling in the control of the HPG axis, these results suggest that the reduced Kiss1-Kiss1r expression may be a contributing factor in stress-related suppression of LH secretion.

The hormonal control of uterine luminal fluid secretion and absorption

The secretion of uterine luminal fluid initially provides a transport and support medium for spermatozoa and unimplanted embryos, while the absorption of uterine luminal fluid in early pregnancy results in the closure of the lumen and allows blastocysts to establish intimate contact with the uterine epithelium. We have established an in vivo perfusion technique of the lumen to study the hormonal control of the events in the peri-implantation period. Fluorescein-labelled dextran was included in the perfusion medium to monitor fluid movements and the concentrations of Na(+) and CI(-) ions in the effluent were monitored. Using an established regimen of steroid treatment of ovariectomized rats mimicking early pregnancy, oestradiol caused fluid secretion, while progesterone resulted in an amiloride-sensitive fluid absorption. Fluid absorption peaked at about the expected time of implantation. The effect of progesterone could be inhibited by treatment with a high dose of oestradiol, by the anti-progestin RU486, and by the presence of an intra-uterine contraceptive device. Studies of expression of Na(+) and CI(-) channels (ENaC, CFTR) indicated that these channels were subject to tissue-specific regulation within the uterus, but more work is required to determine their role and the factors controlling their abundance and localization in early pregnancy.

17beta-Estradiol and environmental estrogens significantly affect mammalian sperm function

BACKGROUND

Compounds with estrogenic activity can affect reproductive function in mammals. This study investigated possible effects of 17beta-estradiol (E(2)) and three weakly estrogenic environmental estrogens on mammalian sperm capacitation and fertilizing ability in vitro.

METHODS

Uncapacitated and capacitated mouse sperm suspensions were incubated for 30 min in the presence of E(2), genistein (Gen), 8-prenylnaringenin (8-PN) and nonylphenol (NP), and then assessed using chlortetracycline (CTC) fluorescence analysis. In addition, treated uncapacitated sperm suspensions were tested for changes in fertilizing ability.

RESULTS

In uncapacitated cells, E(2) at >or=1 micromol/l and Gen, 8-PN and NP at >or=0.001 micromol/l, significantly stimulated capacitation and acrosome reactions. Hydroxytamoxifen (an estrogen antagonist) did not inhibit responses to any of these compounds. In capacitated cells, E(2) had no effect, but the other three compounds significantly stimulated acrosome reactions. Added to uncapacitated suspensions, 10 micromol/l E(2), 0.1 micromol/l Gen and 0.1 micromol/l 8-PN all significantly stimulated sperm fertilizing ability ( approximately 76% oocytes fertilized) compared with untreated control sperm ( approximately 36%).

CONCLUSIONS

This study provides the first evidence that E(2) and environmental estrogens can significantly stimulate mammalian sperm capacitation, acrosome reactions and fertilizing ability, with the environmental estrogens being much more potent than E(2). The inability of hydroxytamoxifen to block these responses suggests that classical estrogen receptors may not be involved. Whether these responses have effects on fertility in vivo remains to be determined, along with the mechanisms of action involved.

Assessment of estrogenic activity in some common essential oil constituents

Estrogenic responses have not only been associated with endocrine function, but also with cognitive function. Several studies have indicated that estrogen replacement therapy has favourable effects on cognition, and may have potential in the prevention and treatment of Alzheimer's disease. Thus, ligands for the estrogen receptor, that have a better efficacy and adverse-effect profile than drugs currently available, require investigation. This study was undertaken to investigate the potential estrogenic activity of a number of essential oil constituents. Initially, estrogenic activity was determined by a sensitive and specific bioassay using recombinant yeast cells expressing the human estrogen receptor. At high concentrations, estrogenic activity was detected for citral (geranial and neral), geraniol, nerol and trans-anethole, while eugenol showed anti-estrogenic activity. Molecular graphics studies were undertaken to identify the possible mechanisms for the interaction of geranial, neral, geraniol, nerol and eugenol with the ligand-binding domain of the estrogen alpha-receptor, using the computer program HyperChem. Citral, geraniol, nerol and eugenol were also able to displace [(3)H]17beta-estradiol from isolated alpha- and beta-human estrogen receptors, but none of these compounds showed estrogenic or anti-estrogenic activity in the estrogen-responsive human cell line Ishikawa Var I at levels below their cytotoxic concentrations, and none showed activity in a yeast screen for androgenic and anti-androgenic activity. The potential in-vivo estrogenic effects of citral and geraniol were examined in ovariectomized mice, but neither compound showed any ability to stimulate the characteristic estrogenic responses of uterine hypertrophy or acute increase in uterine vascular permeability. These results show that very high concentrations of some commonly used essential oil constituents appear to have the potential to interact with estrogen receptors, although the biological significance of this is uncertain.

Progesterone stimulation of fluid absorption by the rat uterine gland

The purpose of this study was to test the hypothesis that the steroid environment affects fluid absorption by the uterine glands. Laser scanning confocal microscopy of the distribution of an extracellular marker (fluorescein isothiocyanate-labelled dextran) within rat uterine glands showed that the endometrial glands change their fluid handling characteristics under different hormonal conditions. Under progesterone dominance, the glands showed an amiloride-sensitive dextran accumulation indicating sodium-dependent fluid absorption; however, this was absent in the oestrogen-dominated state. The rate of fluid uptake in the progesterone-stimulated gland opening was estimated to be approximately 1 x 10(-4) cm s(-1), requiring a suction pressure of between 10 and 20 mm Hg at the mucosal surface. This study provides the first direct evidence of fluid absorption by the uterine glands. Such absorption may provide the mechanism for closure of the uterine lumen and immobilization of the blastocyst necessary for implantation.

Comparison of the oestrogenic effects of infant milk formulae, oestradiol and the phytoestrogen coumestrol delivered continuously in the drinking water to ovariectomised mice

The potential oestrogenic effects of infant milk formulae, coumestrol and oestradiol delivered in the drinking water were investigated in ovariectomised mice. None of the infant formulae tested (three soya, two cow's milk) produced any uterotrophic or mitotic responses in the reproductive tract, although the soya milks displayed weak oestrogenic activity in vitro. Studies of the interactions between coumestrol and oestradiol were undertaken to investigate claims that phytoestrogens may act as oestrogen antagonists. The responses to coumestrol (100 g/ml drinking water) and 17-oestradiol (100 ng/ml) given separately were similar. Combined administration begun simultaneously produced only additive effects on uterine weight and cell proliferation in the vagina and uterus. While pretreatment with coumestrol for 24 h reduced the mitotic response of the uterus 48 h after placement of an oestradiol implant, the uterine weight increase was unaffected and the apparent reduction in mitoses reflected the natural fluctuations in the underlying cycle of cell proliferation. These studies indicate that coumestrol acts as a typical oestrogen and shows only additive effects with oestradiol. The results also indicate that infant soya milk formulae do not constitute a large enough source of oestrogenic compounds to invoke oestrogenic effects in the reproductive tract of mature mice.

Phytoestrogens and gonadotropin-releasing hormone pulse generator activity and pituitary luteinizing hormone release in the rat

Phytoestrogens can produce inhibitory effects on gonadotropin secretion in both animals and humans. The aims of this study were 2-fold: 1) to determine in vivo whether genistein and coumestrol act on the GnRH pulse generator to suppress hypothalamic multiunit electrical activity volleys and associated LH pulses and/or on the pituitary to suppress the LH response to GnRH; and 2) to examine the effect of these phytoestrogens on GnRH-induced pituitary LH release in vitro and to determine whether estrogen receptors are involved. Wistar rats were ovariectomized and chronically implanted with recording electrodes and/or indwelling cardiac catheters, and blood samples were taken every 5 min for 7--11 h. Intravenous infusion of coumestrol (1.6-mg bolus followed by 2.4 mg/h for 8.5 h) resulted in a profound inhibition of pulsatile LH secretion, a 50% reduction in the frequency of hypothalamic multiunit electrical activity volleys, and a complete suppression of the LH response to exogenous GnRH. In contrast, both genistein (1.6-mg bolus followed by 2.4 mg/h for 8.5 h) and vehicle were without effect on pulsatile LH secretion. Coumestrol (10(-5) M; over 2 or 4 h) suppressed GnRH-induced pituitary LH release in vitro, an effect blocked by the antiestrogen ICI 182,780. It is concluded that coumestrol acts centrally to reduce the frequency of the hypothalamic GnRH pulse generator. In addition, the inhibitory effects of coumestrol on LH pulses occur at the level of the pituitary by reducing responsiveness to GnRH via an estrogen receptor-mediated process.

The endocrine activities of 8-prenylnaringenin and related hop (Humulus lupulus L.) flavonoids

The female flowers of the hop plant have long been used as a preservative and a flavoring agent in beer, but they are now being included in some herbal preparations for women for "breast enhancement." This study investigated the relative estrogenic, androgenic and progestogenic activities of the known phytoestrogen, 8-prenylnaringenin, and structurally related hop flavonoids. 6-Prenylnaringenin, 6,8-diprenylnaringenin and 8-geranylnaringenin exhibited some estrogenicity, but their potency was less than 1% of that of 8-prenylnaringenin. 8-Prenylnaringenin alone competed strongly with 17ss-estradiol for binding to both the alpha- and ss-estrogen receptors. None of the compounds (xanthohumol, isoxanthohumol, 8-prenyl-naringenin, 6-prenylnaringenin, 3'-geranylchalconaringenin, 6-geranylnaringenin, 8-geranylnaringenin, 4'-O:-methyl-3'-prenylchalconaringenin and 6,8-diprenylnaringenin) nor polyphenolic hop extracts showed progestogenic or androgenic bioactivity. These results indicate that the endocrine properties of hops and hop products are due to the very high estrogenic activity of 8-prenylnaringenin and concern must be expressed about the unrestricted use of hops in herbal preparations for women.

Identification of a potent phytoestrogen in hops (Humulus lupulus L.) and beer

The female flowers of the hop plant are used as a preservative and as a flavoring agent in beer. However, a recurring suggestion has been that hops have a powerful estrogenic activity and that beer may also be estrogenic. In this study, sensitive and specific in vitro bioassays for estrogens were used for an activity-guided fractionation of hops via selective solvent extraction and appropriate HPLC separation. We have identified a potent phytoestrogen in hops, 8-prenylnaringenin, which has an activity greater than other established plant estrogens. The estrogenic activity of this compound was reflected in its relative binding affinity to estrogen receptors from rat uteri. The presence of 8-prenylnaringenin in hops may provide an explanation for the accounts of menstrual disturbances in female hop workers. This phytoestrogen can also be detected in beer, but the levels are low and should not pose any cause for concern.

Identification of a potent phytoestrogen in hops (Humulus lupulus L.) and beer

The female flowers of the hop plant are used as a preservative and as a flavoring agent in beer. However, a recurring suggestion has been that hops have a powerful estrogenic activity and that beer may also be estrogenic. In this study, sensitive and specific in vitro bioassays for estrogens were used for an activity-guided fractionation of hops via selective solvent extraction and appropriate HPLC separation. We have identified a potent phytoestrogen in hops, 8-prenylnaringenin, which has an activity greater than other established plant estrogens. The estrogenic activity of this compound was reflected in its relative binding affinity to estrogen receptors from rat uteri. The presence of 8-prenylnaringenin in hops may provide an explanation for the accounts of menstrual disturbances in female hop workers. This phytoestrogen can also be detected in beer, but the levels are low and should not pose any cause for concern.

Competitive binding of xenobiotic oestrogens to rat alpha-fetoprotein and to sex steroid binding proteins in human and rainbow trout (Oncorhynchus mykiss) plasma

The ability of a variety of "environmental oestrogens" to compete with radiolabelled steroids to rat alpha-fetoprotein (AFP) and to sex steroid binding proteins was investigated in human and rainbow trout (Oncorhynchus mykiss) plasma. For [3H]oestradiol binding to AFP, diethylstilbestrol and 4-nonylphenoxyacetic acid showed significant competition at concentrations about 100-fold greater than oestradiol (relative binding affinities approximately 1% c.f. oestradiol). All other compounds (phytooestrogens: coumestrol, daidzein, genistein; others: 4-nonylphenol, 4-tert-octylphenol, 4-nonylphenoldiethoxylate, 4-tert-butylphenol, bisphenol-A (Bis-A), bis(2- ethylhexl)phthalate, dioctylphthalate, dibutyl phthalate, 2, 4'DDT (op' enantiomer), 2,4'-DDE (mixed enantiomers), kepone) showed only very weak or no competition (relative binding affinities <<0.1% c.f. oestradiol). The situation for both human and fish plasma was very similar, with only very high concentrations (>>1000 fold more than the natural ligand) of a few of the compounds showing any ability to displace the natural ligand. These results suggest that environmental oestrogenic agents are unlikely to produce biological effects by displacing endogenous steroids from plasma steroid binding proteins unless they are present in very high concentrations.

Effects of platelet-derived endothelial cell growth factor/thymidine phosphorylase, substrate, and products in a three-dimensional model of angiogenesis

Platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP) is associated with angiogenesis and the progression of human breast and ovarian cancers. The aim of this study was to obtain information about the possible mechanisms of PD-ECGF/TP activity in an established three-dimensional model of angiogenesis. The plan was to study the effects of the enzyme, substrate, products, and further metabolites on the formation and rate of microvessel growth from cultured segments of rat aorta in serum-free media. The end-points were the number and length of microvessels compared with controls after 4, 7, 11, and 14 days in culture. Thymidine (10 to 1000 mumol/L), thymidine-5'-monophosphate (1000 mumol/L), and 2'-deoxy-D-ribose-1-phosphate (1000 mumol/L) inhibited the number of microvessels produced. Conversely PD-ECGF/TP (50 to 100 ng/ml) and beta-amino-iso-butyric acid (1000 mumol/L--a metabolite of thymine) had a significant stimulatory effect (P < 0.05, P < 0.01, P < 0.001 respectively on culture day 11). PD-ECGF (10 ng/ml), beta-amino-iso-butyric acid (1000 mumol/L), and 2-deoxy-D-ribose (100 to 1000 mumol/L) significantly (P < 0.001, P < 0.01, P < 0.01, respectively) stimulated microvessel elongation by day 11. We conclude that PD-ECGF/TP may affect angiogenesis by changing the relative concentrations of pyrimidine-based compounds and their metabolites in interstitial fluid surrounding endothelial cells. Drugs that inhibit PD-ECGF/TP activity may therefore delay abnormal angiogenesis and the progression of various cancers.

Relative potency of xenobiotic estrogens in an acute in vivo mammalian assay

The in vivo effects of xenoestrogens are of interest in relation to their potential health risks and/or beneficial effects on humans and animals. However, the apparent in vivo potency of the examined response can be confounded by a short half-life, and the metabolism of estrogens is very dependent on the nature of conversion and/or inactivation. To minimize such variables, we examined the estrogenic potency of a range of xenoestrogens in an acute in vivo assay--the stimulation of increased uterine vascular permeability in ovariectomized mice 4 hr after subcutaneous administration. While estradiol (E 2 ) and estriol (E 3 ; a relatively weak natural estrogen) readily induced vascular responses [median effective dose (ED 50 ) <10 -9 mol], much higher amounts of xenoestrogens were required. Bisphenol A was about 10,000-fold less potent than E 2 and E 3 , and octylphenol and nonylphenol were about 100,000-fold less potent; dioctyl phthalate, benzyl butyl phthalate, dibutyl phthalate, and trichlorinated biphenol produced no effect. Coumestrol was the most active phytoestrogen, with an ED 50 between 10 -6 and 10 -7 mol; genistein was about 10-fold less potent than coumestrol, and neither daidzein nor formononetin produced any marked effect, even at doses up to 10 -5 mol. All increases in vascular permeability could be blocked by the pure antiestrogen ICI 182,780. There was no evidence that any of the compounds could act as an antiestrogen in this assay or that they could exert synergistic effects in combination. These results indicate that even short-term exposure to most of the xenobiotic estrogens can induce typical estrogenic effects in vivo , but their estrogenic potency is very weak even when assessed in an acute response.

Minimal progesterone support required for the maintenance of pregnancy in mice

A study of the degree of progesterone support required for the maintenance of various stages of pregnancy was undertaken in mice. Mated females were ovariectomized at various stages of pregnancy and progesterone and oestradiol support provided by s.c. Silastic implants with known release characteristics. In the earliest stages of pregnancy (days 1-5), very low concentrations of progesterone (<25% of normal physiological values) were sufficient to maintain pre-implantation stages and allow implantation. In the immediate post-implantation period (days 5-9), the development of implantation sites and decidualization required considerably higher progesterone support. In mid-pregnancy (days 11-14), progesterone alone could not maintain pregnancy unless present in very high amounts; however, the presence of oestradiol during this period lowered the progesterone requirements to well within the physiological range. This effect of oestradiol started on day 11 but required the level of oestradiol support to be kept within strictly defined limits, with high concentrations inducing abortion. Progesterone alone was able to maintain pregnancy from day 15. These results indicate that the minimal progesterone support required for pregnancy in mice varies considerably at different stages of pregnancy and is at least partly modulated by oestradiol.

Relaxin and decidualization in mice: a reappraisal

The nature of the physiological stimulus inducing decidualization in the endometrium is unknown. In this study we attempted to verify a recent report that relaxin can induce decidualization in intact mice primed with a high dose of estradiol valerate (5 micrograms) and a low dose (10 micrograms) of medroxyprogesterone acetate. In our study, neither s.c. nor intrauterine relaxin, nor intraluminal arachis oil, (an established deciduogenic stimulus) were able to induce decidualization. In addition, while oil was able to induce decidualization (increased uterine weight, and positive Pontamine Sky Blue and stromal alkaline phosphatase reactions) in ovariectomized mice treated with a regimen of estradiol and medroxyprogesterone acetate designed to produce optimum uterine sensitivity, no decidualization occurred in response to either s.c. or intraluminal relaxin. This study fails to provide any support for a role for relaxin as a deciduogenic stimulus.

Potent inhibitory effects of steroids in an in vitro model of angiogenesis

The regulation of angiogenesis in the ovarian follicle and corpus luteum is unclear. Steroids are produced at very high concentrations in these tissues and we therefore examined the effect of steroids on angiogenesis in vitro. Explants of rat aorta were embedded in collagen gel and cultured in serum-free medium. Capillary-like microvessels were produced from the explants and microvessel number and length were measured in the presence and absence of steroids. At a concentration of 10 micrograms/ml, cortisol, progesterone, 17 alpha-hydroxyprogesterone and medroxyprogesterone acetate produced degeneration of microvessels after 7 days of steroid treatment (P < 0.01). Androstenedione and tetrahydro-S-(11-deoxytetrahydrocortisol) (tetrahydro S) produced degeneration at a slower rate: androstenedione inhibited microvessel growth after 11 days (P < 0.01) and tetrahydro S after 14 days (P < 0.05). Oestriol had no effect on microvessels; oestrone had a slow degenerative effect with significant inhibition seen after 14 days (P < 0.01). Oestradiol-17 beta at a concentration of 10 micrograms/ml completely inhibited microvessel growth from the explant cultures (P < 0.01) while at 1 microgram/ml it caused degenerative effects on growing microvessels. The effects of oestradiol and cortisol were reversible on removal of steroid-containing medium and replacement with 10% serum. We conclude that oestradiol may modulate angiogenesis in tissues in which the steroid concentration is high.

The minimum requirements for oestradiol to induce uterine sensitivity for implantation and decidualization in mice

Steroid-containing s.c. silastic capsules with known physiological release characteristics were used to study the control of implantation and the induction of uterine sensitivity in ovariectomized mice. In mated, ovariectomized animals maintained on progesterone, the implantation sites were detected after approximately 12 h of oestradiol exposure, and alkaline phosphatase activity at the implantation sites developed within 21 h. Implantation could be induced in > 60% of animals by 4 h exposure to an oestradiol implant, in which time approximately 1.6 ng oestradiol would have been delivered. Continuous delivery of a low dose of oestradiol near the threshold for implantation induced a full complement of implantation sites in the responding animals. The sensitivity of implantation to low amounts of oestradiol suggests that this response is at least as sensitive as either the induction of vaginal cornification or the stimulation of uterine weight. The minimum time for the induction of uterine sensitivity when oestradiol and progesterone treatment were started simultaneously was approximately 36 h. The use of slow-release oestradiol-containing capsules provides a good model to investigate the roles of oestradiol in initiating and defining the 'implantation window'.

Control of uterine stromal mitosis in relation to uterine sensitivity and decidualization in mice

The relationship between mitosis, ovarian hormones, decidual stimuli and decidualization was investigated using progestagen-treated ovariectomized mice. Oestradiol, or the intraluminal instillation of oil or saline, all stimulated stromal mitosis. When oil or saline was instilled following oestradiol, the response depended on the dose of oestradiol, the interval between the oestradiol and the instillation, and the time when the mice were killed. After 20 ng oestradiol, the instillation of oil 7 h later induced large mitotic and decidual responses that were evident within 17 h of instillation and increased with time. Smaller mitotic and decidual responses were obtained when the interval between oestradiol and oil was 24 h; there was no response when the interval was 42 h. When a higher dose (100 ng) of oestradiol was given, oil injected 7 h later initially stimulated mitosis (at 17 h), but this effect was reduced at 24 h and no decidualization occurred. After instilling oil 24 or 42 h after 100 ng oestradiol, the mitotic response was limited, and there was no decidual response. Regardless of the dose of oestradiol, saline induced only a transient mitotic response and no decidualization occurred. It is concluded that there are three stimuli that can cause stromal mitosis in the progestagen-treated mouse uterus: oestrogen, an intraluminal stimulus (blastocyst, oil or saline) and factors associated with decidualization. Oestradiol not only induces mitosis, but also produces a period of heightened sensitivity to the mitotic effects of intraluminal stimuli. In addition, low doses of oestradiol induce a period of sensitivity to decidual stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Silastic implants for delivering physiological concentrations of progesterone to mice

Silastic implants filled with progesterone in arachis oil were designed to provide a convenient and reliable method for the delivery of physiological concentrations of progesterone to mice. Placement of the implants in ovariectomized mice resulted in a rapid increase in circulating progesterone within 6 h; stable levels could be maintained for many days. Removal of the implants resulted in a very rapid fall in progesterone concentrations. The delivery of progesterone from the implants could be controlled by varying both the length of the implants and the concentration of progesterone internally. This allowed plasma progesterone concentrations to be maintained and controlled over the entire physiological range.

Silastic implants for delivery of oestradiol to mice

Silastic implants containing oestradiol were developed for delivering a range of physiological concentrations of oestradiol to mice over long periods. The implants consisted of discrete lengths of Silastic tubing containing oestradiol in arachis oil, with a small reservoir of the oestradiol solution at either end of the implant. Studies showed that the release of oestradiol in vitro was proportional to the concentration of steroid within the implant. Implants containing oestradiol at concentrations from 1 to 100 micrograms ml-1 could induce biological responses in ovariectomized mice, ranging from minimal effects on uterine weight and vaginal smears to supraphysiological increases in uterine weight and rapid vaginal cornification. Studies of uterine vascular permeability indicated that significant effects occurred within a few hours of initial placement of the implant. These results suggest that the design of the Silastic implants described in this study provides a useful method for delivering controlled and easily manipulated physiological doses of oestradiol to mice.

Sound levels in rooms housing laboratory animals: an uncontrolled daily variable

High sound levels are known to have adverse effects on the behaviour and physiology of laboratory animals, yet their acoustic environment is rarely monitored. In particular, high-frequency sounds that are above the limit of human hearing, but are well within the limits of many laboratory species (i.e., ultrasounds), are usually ignored. In this study, the acoustic environment of laboratory animals was investigated in a variety of different animal facilities. Sound pressure levels (dB SPL) were monitored for periods up to 24 h over two frequency ranges: a relatively low range (0.01-12.5 kHz), and a high range (12.5-70 kHz). While background sound levels in undisturbed situations were generally low (i.e., below 50 dB SPL), marked increases in sound levels often occurred during the working day, producing characteristic daily variations in the sound profile. Peak SPLs commonly reached values of 80-95 dB in the low-frequency range and 50-75 dB in the higher range. In most cases, sound levels were low over weekends. The results suggested that human activities were a very important source of sound in most animal facilities. In a few situations (e.g., rabbits, marmosets, dogs), the animals themselves provided a significant contribution to the acoustic environment. It is clear that the acoustic environment of laboratory animals is a daily variable that is usually uncontrolled and that may have important implications for behavioural and physiological experiments and for animal welfare.

Timing of the window of uterine sensitivity to decidual stimuli in mice

The refractory period that follows the period of sensitivity to a decidual stimulus in ovariectomized hormone treated mice was investigated. Medroxyprogesterone acetate provided constant progestin concentrations and silastic implants containing oestradiol maintained constant nidatory oestrogen concentrations. The nidatory stimulus was provided by crushing the uterus with a haemostat or by the intrauterine instillation of arachis oil. The decidual response was assessed by measuring changes in uterine weight or by examining the stroma for the presence of alkaline phosphatase. Sensitivity to the oil was first observed approximately 14 h after the insertion of the oestradiol implant but this sensitivity had waned by 32 h and was absent at 40 h. Crushing the uterus initiated a decidual response in mice treated with progestin alone but if the oestradiol implant was inserted then the uterus was responsive to crushing 24 h after insertion but not at 45 h. The traumatic decidual cell reaction (crushing), although not requiring nidatory oestradiol for its successful initiation, was nevertheless subject to the refractoriness that followed oestradiol sensitivity.

Tissue spaces during development and regression of the decidual cell reaction in ovariectomized, steroid-treated mice

Changes in the extracellular and blood spaces of the uterus were assessed from the distribution volumes of 51Cr-EDTA and 51Cr-labelled red blood cells during the development and regression of the artificially induced decidual cell reaction in ovariectomized, steroid-treated mice. The normally high values for uterine extracellular space (0.35-0.40 microliter/mg) fell to less than 0.20 microliter/mg in association with decidual growth. Uterine blood space increased from around 0.02 microliter/mg to 0.03-0.05 microliter/mg with decidual development. Induction of decidual regression by removal of s.c. progesterone implants caused a rapid decline in tissue blood volume to reach control values (0.01-0.02 microliter/mg) within 24 h and preceded any reduction in uterine weight. Uterine vascular permeability, as determined from the tissue accumulation of 125I-labelled human serum albumin, fell with a similar time course. Tissue extracellular space returned to the higher control values within 48 h of initiating decidual regression.

Failure of platelet-activating factor (PAF-acether) to induce decidualization in mice and failure of antagonists of PAF to inhibit implantation

The possible role of platelet-activating factor (PAF) in the uterine responses associated with implantation was investigated. Attempts to trigger a decidual cell response in the uteri of hormonally sensitized, ovariectomized mice by instilling PAF-acether (1-1000 ng) intraluminally were unsuccessful. The effect of PAF antagonists on implantation was investigated in females ovariectomized on Day 3 of pregnancy and treated with progesterone. Implantation was induced in these females by injection of 10 ng oestradiol-17 beta on Day 8. Hourly intraperitoneal injections of three PAF antagonists (WEB 2086, CV 3988 and BN 52021 at doses of 1.2-1.4 mg/kg) given over a 24-h period starting 1 h before the injection of oestradiol-17 beta had no significant effect on the occurrence of implantation sites. Intraluminal injection of WEB 2086 (15 micrograms) or BN 52021 (5 micrograms) either 3 h before or 6 h after the nidatory oestradiol also had no significant inhibitory effect on implantation. SRI 63-441 given once daily over the first 4 days of pregnancy at a dose of 40 micrograms/30 g body weight had no inhibitory effect on the establishment of pregnancy. These results are not consistent with a critical role for PAF in implantation in mice.

A study of the early morphological changes initiated in the uterine luminal epithelium by substances (oil and carrageenan) which induce the decidual cell reaction in mice

Oil, carrageenan or saline were injected into the uteri of ovariectomized mice treated with hormones on schedules which would sensitize, partly sensitize or not sensitize the uterus to an intraluminal decidual stimulus. The uterine epithelium was examined histologically at various times over the succeeding 5 h. Saline did not produce any morphological change whereas almost immediately after the injection of oil or carrageenan epithelial cell death was apparent in the uterus, regardless of hormone treatment. Within 45 min the dead cells had been removed and the epithelium was re-established. Oil droplets were still present in the uterus after 5 h and these were able to stimulate a decidual reaction in partly sensitized animals when oestrogen was administered 18-44 h after the oil instillation, well after the re-establishment of the epithelium. It is suggested that the early transient cell death in the uterine epithelium is not responsible for triggering the decidual reaction but that it is the contact of the oil droplet with an intact epithelium which triggers the response when the hormonal conditions so allow.

The emission and elicitation of mouse ultrasonic vocalizations: the effects of age, sex and gonadal status

Subject' mice of varying gonadal status (castrate males; intact or neonatally gonadectomized females and males) were paired for 3-min with intact 'stimulus' females and ultrasonic vocalizations were monitored. Vocalization patterns from home cages differed from the test pairings. The results suggested that the age, experience and gonadal status of the subject influenced the vocalizations from the pair. As the source of ultrasonic calls from these vocally intact pairs could not be individually identified, the 'subjects' were paired with a range of ultrasonically silent (inferior laryngeal nerve-transected) stimulus animals. Vocalizations were detected from all combinations of animals. Gonadally intact females were most effective in eliciting ultrasonic vocalizations from the subjects and gonadally intact males were least effective. The responses of castrate males were lower than from intact males. Anesthetized adults of either sex elicited only poor vocalization responses from other adults. Ultrasonic calls have often previously been studied using vocally intact 'subject' and 'stimulus' animals: the present results confirm the difficulty of establishing who is who in such situations.

The effects of different anaesthetic agents on the estimation of uterine vascular permeability in mice

Vascular permeability in the uterus and other tissues of mice was assessed using the accumulation of 125I-human serum albumin 30 min after its intravenous injection. The anaesthetic agent employed for the 125I-albumin injection differentially affected the estimates of vascular permeability: intraperitoneal (i.p.) tribromoethanol of pentobarbitone sodium produced significantly higher values for the uterus and body wall than ether. The i.p. administration of either Saffan or pentobarbitone sodium reduced estimates of vascular permeability in the duodenum. These results emphasize the importance of the choosing a suitable anaesthetic agent in vascular studies of the uterus and other abdominal tissues.

Environmental ultrasound in laboratories and animal houses: a possible cause for concern in the welfare and use of laboratory animals

Many laboratory animals are known to be sensitive to sounds (ultrasounds) beyond the nominal upper limit (20 kHz) of the human hearing range. Sources of sound in laboratories and animal houses were examined to determine the extent of ambient ultrasound. Of 39 sources monitored, 24 were found to emit ultrasonic sounds. Many of these (e.g. cage washers and hoses) also produced sound in the audible range. Running taps, squeaky chairs and rotating glass stoppers created particularly high sound pressure levels and contained frequencies to over 100 kHz. The oscilloscopes and visual display units investigated provided particular cause for concern as they emitted sounds that were entirely ultrasonic and therefore were apparently silent. Ambient ultrasound therefore appears to be common in laboratories and animal houses. It is suggested that its effect on laboratory animals should be investigated and guidelines on acceptable levels be formulated.

Use of a single-injection tissue-sampling technique to study steroid uptake by the decidualized endometrium of the mouse

A tissue-sampling paired-tracer method was used to investigate the effect of plasma proteins on uptake by the decidualized endometrium of [3H]progesterone, [3H]oestradiol and [3H]corticosterone. When injected arterially in protein-free Ringer, the extraction of progesterone and oestradiol was 100%, while that of corticosterone was only 60%. The addition of 4% albumin or injection in mouse plasma resulted in significant decreases in progesterone extraction to about 80% and 65% respectively. Injection in pregnant guinea-pig plasma reduced progesterone extraction further (to 33%). While neither 4% albumin nor mouse plasma had any significant effect on the uptake of oestradiol, neonatal rat plasma reduced oestradiol extraction to 40%. These results are consistent with high-affinity binding proteins having a limiting effect on the availability of steroids to target tissues.

Long-term monitoring of mouse ultrasonic vocalizations

The temporal pattern of ultrasonic vocalizations by mice in an undisturbed 'home' environment can now be assessed using a system based on amplitude discrimination. Within a chosen frequency band, vocalizations of sufficient intensity are detected by an amplitude discriminator. The output from a pulse generator is sent to a microcomputer which records the time of the incoming event. The system has been validated for monitoring ultrasonic vocalizations in the mouse.

Uterine blood flow during the development and regression of the decidual cell reaction in ovariectomized, steroid-treated mice

Uterine blood flow was assessed in mice by measuring organ uptake of intravenously injected [14C]butanol. In ovariectomized mice, injection of 100 ng oestradiol-17 beta increased blood flow 5-fold over that of untreated controls. The injection of oestradiol-17 beta in progesterone-treated mice also increased uterine blood flow at the time of maximal sensitivity to a decidual stimulus, but not 4 days later. Absolute values of blood flow increased during development of the decidual cell reaction in proportion to the increase in uterine weight, reaching maximal values 96 h after decidual induction. When progesterone injections were stopped 72 h after decidual induction, a rapid decrease in absolute and relative blood flow values preceded the decrease in uterine weight. This decrease in uterine blood flow occurred within 12 h of removing a subcutaneous implant containing progesterone. These results are consistent with the view that increased uterine blood flow during decidual development may be necessary to support the rapid increase in uterine weight at implantation and the subsequent decrease in both relative and absolute uterine blood flow on withdrawal of progesterone may promote decidual regression in the mouse.

The sensitivity of the uterus of the mouse and rat to intraluminal instillation

The tissue accumulation of 125I-labelled human serum albumin 30 min after intravenous injection was used as an index of uterine vascular permeability. In ovariectomized mice, all sham and experimental instillation procedures produced a 6-10-fold increase in vascular permeability. Some effects were also manifest in the contralateral, control horn. In ovariectomized rats, instillation of saline and arachis oil increased vascular permeability 3-7-fold. After 3 or more days of progesterone treatment following oestradiol priming, fluorocarbon and arachis oil instillation produced marked vascular responses, but these were not restricted to the transient period in which the uterus would respond with decidualization. An IUD prevented the response to arachis oil instillation. These results indicate that the uterus is very sensitive to any manipulation and are consistent with decidualization representing a specialization of a normal uterine inflammatory response.

Intraluminally injected oil induces changes in vascular permeability in the 'sensitized' and 'non-sensitized' uterus of the mouse

After suitable sensitization of ovariectomized mice with progesterone and oestradiol, the intrauterine instillation of oil produces a massive decidual cell reaction. Vascular permeability, as reflected by the extra-vascular accumulation of 125I-labelled human serum albumin, increased after oil instillation and was maintained at 2-3 times control values for at least the next 3 days. Although oil instillation did not produce a decidual response in females treated with progesterone alone, an increase in vascular permeability (about 2 times control levels) still occurred. This response peaked 8 h after oil instillation and was not maintained. These results indicate that the progesterone-dominated uterus which has not been sensitized with oestradiol cannot be viewed as completely unresponsive to the stimulus of oil and demonstrate that a marked increase in vascular permeability is not itself sufficient to induce decidualization of progesterone-dominated uterine stromal cells. The uterine extravascular accumulation of 125I-labelled albumin was increased both in association with tribromoethanol anaesthesia and after oestradiol treatment of progesterone-primed animals. In pregnant mice, the appearance of Pontamine Sky Blue spots provided an earlier indication of implantation than did determination of total uterine extravascular 125I-labelled albumin accumulation.

The resistance of the mouse uterine lumen to flushing and possible contamination of samples by plasma and interstitial fluid

The hydrostatic pressures generated during controlled flushing of the mouse uterus increased at implantation and under conditions of uterine closure. These pressures may be responsible for inducing tissue damage during flushing. The possibility that samples collected by flushing might be contaminated with interstitial fluid or plasma was studied using intravenously administered 51Cr-labelled EDTA and 125I-labelled human serum albumin as markers. The presence of both tracers was detected in all flushings and was greatest in flushings from uteri with luminal closure and early implantation sites. These observations raise serious doubts about the validity of the flushing technique for analysing uterine luminal constituents in mice.

Time course of the changes in uterine vascular permeability associated with the development of the decidual cell reaction in ovariectomized steroid-treated rats

Uterine vascular permeability and tissue blood volume during the development of the oil-induced decidual cell reaction (DCR) in ovariectomized steroid-treated rats were assessed by measuring the extravascular accumulation of 125I-labelled human serum albumin and the tissue content of 51Cr-labelled red cells 30 min after intravenous administration. Within 15 min of oil instillation into one uterine horn, the vascular permeability of the horn was significantly elevated. Permeability rose to a sharp peak (10 times control levels) 9 h after oil instillation, but dropped to 5 times control values by 12 h and continued a steady decline over the next 7 days. Although a marked increase in uterine weight was associated with the development of the DCR, there was no significant change in blood volume/g tissue until 4 days after oil instillation.

Changes in prostaglandin levels in the sensitized and non-sensitized uterus of the mouse after the intrauterine instillation of oil or saline

Intrauterine instillation of oil, but not saline, induced both a decidual cell reaction and a marked elevation in the uterine PGF-alpha content of suitably sensitized ovariectomized mice. Uterine PGF-alpha concentrations were elevated within 5 min of the oil instillation, reached maximal levels within 30-60 min and then declined to near baseline levels again by 3 h. A similar increase in uterine PGF-alpha content in response to oil instillation was seen in non-sensitized females, although no decidual cell reaction developed. No significant changes in PGE or 6-oxo-PGF-1 content were observed. These results suggest that although the increase in uterine PGF-alpha content is not solely due to the distension of the uterus after intrauterine injection, the increase is not necessarily sufficient to induce a decidual cell reaction.

Analysis of the LH surges induced by mating and LH-RH in the vole, Microtus agrestis

Female voles mated with a male and experiencing a single ejaculatory series exhibited a rapid and marked elevation of plasma LH levels. The profile of the LH surge had a broad peak 20-40 min after mating. Pentobarbitone sodium administered immediately after mating did not affect the magnitude of the surge. The LH response to exogenous LH-RH ws not affected by the state of receptivity of the female or by gonadectomy. There was no evidence of any priming effect of 25 ng LH-RH on the pituitary response to a second injection of LH-RH 20 or 60 min later. These results are consistent with the primary cause of the LH surge in the reflexly ovulating vole being a rapid secretion of LH-RH.

Effect of portacaval anastomosis and chronic underfeeding on the hypothalamic-pituitary-gonadal axis in the rat

Portacaval anastomosis (PCA) in the rat may be a useful experimental model for examining endocrine changes that occur during cirrhosis of the liver. A marked reduction in diet intake and body weight occurs in rats after establishing the shunt and studies were undertaken to determine the relationship of these effects to the testicular atrophy that also follows PCA. Control, sham-operated animals, experiencing a reduction in food intake similar to that of the animals with a PCA, showed reduced plasma levels of LH and testosterone but also exhibited a marked testicular response to LH. This was consistent with increased sensitivity of the hypothalamic-pituitary axis to the negative feedback of gonadal steroids in chronically underfed animals. Male rats with a PCA exhibited similarly reduced levels of LH and testosterone, but showed poor secretory responses of the pituitary gland to LH releasing hormone (LH-RH) and of the testis to LH. Testicular atrophy and cessation of spermatogenesis occurred in the animals with a PCA. These results suggested that the effects of PCA on the pituitary-gonadal axis cannot simply be explained as a consequence of the restricted intake of diet. This was confirmed by the responses to castration. In both fed and underfed sham-operated rats, castration resulted in a rapid and sustained increase in plasma LH and both groups showed a marked LH secretory response to LH-RH. In contrast, in animals with a PCA castration had little effect on plasma LH and the pituitary response to LH-RH was still poor. The effects of PCA cannot be simply explained by impeded metabolism of gonadal steroids causing increased negative feedback on the hypothalamic-pituitary axis.

Delayed pseudopregnancy in the mouse

Treatment of female mice with bromocriptine on Day 1 or 3 of pregnancy induced many of the females to return to oestrus. The incidence of extended cycles (7--10 days) and pseudopregnancies following this return to oestrus was significantly higher than in unmated control females. These observations are consistent with the existence of a 'mnemonic' component of the luteotrophic system in the mouse.

Effect of bromocriptine treatment on the ovulatory response to oestradiol benzoate in the reflex ovulator, Microtus agrestis

In some animals which ovulate spontaneously, oestrogen may stimulate prolactin secretion and high levels of prolactin may inhibit steroid-induced surges of LH. The possibility was investigated that such conditions were operating in the reflex ovulator Microtus agrestis to prevent spontaneous ovulation. However, bromocriptine treatment to suppress prolactin secretion did not enhance the poor ovulatory response to administration of oestradiol benzoate.

Pregnancy blockage and the memory of the stud male in the vole (Microtus agrestis)

When female voles were allowed contact with the stud male for only 1 h at the time of mating, 55% exhibited pregnancy failure when exposed to a strange male 48 h later. When females were made psuedopregnant by hormone treatment and vaginal stimulation (i.e. no stud male involved), 87% exhibited luteal failure when exposed to a strange male. It is suggested that the characteristics of the stud male are rapidly imprinted upon the female at the time of mating and that this imprinting is important in preventing the female showing a blocking response to this male upon any subsequent exposure.

Evidence for a coitally induced 'mnemonic' involved in luteal function in the vole (Microtus agrestis)

The development of luteal function in the vole is dependent on a neuroendocrine reflex which is initially activated by mating. Bromocriptine was used to destroy the CL initially induced by mating and fresh CL were induced by hormone treatment. The fate of such newly formed CL suggested that the luteotrophic effect of mating continued for about 10 days after mating, despite the destruction of the original mating-induced CL. The luteotrophic effect of mating therefore seems to be 'remembered'. A study of the fate of hormonally induced CL in females in which pregnancy had been blocked by exposure to a strange male suggested that the strange male may cause pregnancy failure by inhibiting or suppressing the luteotrophic 'mnemonic' activated by the stud mating.