Daily Injections Of Estradiol Benzoate Research Articles

Sexual dimorphism of liver endoplasmic reticulum stress susceptibility in prepubertal rats and the effect of sex steroid supplementation.

What is the central question of this study? Is there sexual dimorphism in the occurrence of hepatic endoplasmic reticulum stress? What is the main finding and its importance? The transition from prepubertal to the adult age is associated with an increase in the unfolded protein response markers in the liver of male rats, which is probably due to an increase in serum testosterone levels. Male rodents present a higher predisposition to obesity and insulin resistance than females. These disorders have been associated with endoplasmic reticulum (ER) stress. To investigate a possible sexual dimorphism in the hepatic occurrence of ER stress, we evaluated the expression of ER stress markers in the livers of male and female rats in two phases of sexual development. In the first experimental model, male and female prepubertal and adult Wistar rats were used. Adult males presented higher body mass and greater mass of the adipose tissue and liver than adult females. Prepubertal animals presented no differences in these parameters between males and females. Despite this finding, the hepatic expression levels of Bip, Ire1α and Xbp1s mRNA were lower in prepubertal males than in females, while in adult animals, they did not differ between sexes. In the second experimental model, we anticipated the sexually mature phase by daily injections of testosterone propionate for 10days in prepubertal males or by daily injections of oestradiol benzoate for 7days in prepubertal females. Oestradiol administration in prepubertal females did not change any of the parameters evaluated. Testosterone administration to prepubertal males led to a higher body mass and greater expression of Bip, Ire1α, Atf4 and Xbp1s in the liver. These findings suggest that the increased ER stress predisposition observed in males during puberty is due to an increase in testosterone levels, indicating that ER stress is sexually dimorphic before puberty due to the lack of testosterone in males.

Estradiol modulates recovery of REM sleep in a time-of-day-dependent manner.

Ovarian hormones are thought to modulate sleep and fluctuations in the hormonal milieu are coincident with sleep complaints in women. In female rats, estradiol increases waking and suppresses sleep. In this study, we asked whether this effect is mediated via circadian or homeostatic regulatory mechanisms. Ovariectomized female rats received daily injections of estradiol benzoate (EB) or sesame oil that mimicked the rapid increase and subsequent decline of circulating estradiol at proestrus. In one experiment, animals were sleep deprived for 6 h starting at lights-on, so that recovery began in the mid-light phase; in the second experiment, animals were sleep deprived starting in the mid-light phase, so that recovery began at lights-off. EB suppressed baseline rapid eye movement (REM) and non-REM (NREM) sleep and increased waking in the dark phase. In both experiments, EB enhanced REM recovery in the light phase while suppressing it in the dark compared with oil; this effect was most pronounced in the first 6 h of recovery. By contrast, NREM recovery was largely unaffected by EB. In summary, EB enhanced waking and suppressed sleep, particularly REM sleep, in the dark under baseline and recovery conditions. These strong temporally dependent effects suggest that EB consolidates circadian sleep-wake rhythms in female rats.

Arginine vasopressin regulation in pre- and postpubertal male rats by the androgen metabolite 3β-diol

Arginine vasopressin (AVP) is a nonapeptide expressed in several brain regions. In addition to its well-characterized role in osmoregulation, AVP regulates paternal behavior, aggression,circadian rhythms, and the stress response. In the bed nucleus of the stria terminalis (BST), AVP gene expression is tightly regulated by gonadal steroid hormones. However, the degree by which AVP is regulated by gonadal steroid hormones in the suprachiasmatic nucleus (SCN) and medial amygdala (MeA) is unclear. Previous studies have shown that AVP expression in the brain of gonadectomized rats is restored with testosterone, 17beta-estradiol, and 5alpha-dihydrotestosterone(DHT) replacement. In addition, we have demonstrated that 3beta-diol, a metabolite of DHT,increased AVP promoter activity in a neuronal cell line and that the effects of 3beta-diol on AVP promoter activity were mediated by estrogen receptor-beta. To test whether 3beta-diol has a physiological role in the regulation of central AVP expression in vivo, we gonadectomized pre- and postpubertal male rats and followed with once daily injections of estradiol benzoate (EB),DHT-propionate, 3beta-diol-dipropionate, or vehicle. The SCN, BST, and MeA were analyzed for AVP mRNA expression using in situ hybridization. In the BST, intact juveniles had significantly fewer AVP-expressing cells than adults. GDX abolished all AVP mRNA expression in the BST in both age groups, whereas treatment with EB restored >80% and DHTP <10% of the AVP expression. Interestingly, 3beta-diol-proprionate was more effective at inducing AVP expression in juveniles than in adults, suggesting that the regulation of AVP by 3beta-diol might be age dependent [corrected].

Mechanisms for Differential Effects of Estrogen on Tyrosine Hydroxylase (TH) Gene Transcription

There are conflicting findings regarding the ability of estrogen to regulate TH gene expression in vivo, with some reports of elevation, reduction or no change. The basis for these discrepancies is unclear and may result from differences in dose, duration, mode of administration, or estradiol receptor (ER) subtype expressed. We found that in the nucleus of the solitary tract of OVX female rats, the response of the TH gene depends on the mode of estrogen administration. Daily injections of estradiol benzoate (EB) at 25 μg/kg for 16 days led to a greater than 2‐fold rise in TH mRNA, while administration of 17‐β estradiol (E2) (0.1 mg, 21 day release) for a similar time by pellets, triggered a 90% reduction in TH mRNA compared to vehicle treated controls. Another important parameter is the ER subtype. Many catecholaminergic cells express both ERα and ERβ. To study the mechanism and effect of ER subtypes, we co‐transfected PC12 cells with expression vectors for ERα or ERβ and TH reporter constructs. E2 elevated TH promoter driven reporter activity with ERα, while it triggered a reduction with ERβ. Further studies found that in the presence of ERα, the membrane impermeable E2‐BSA triggered a similar elevation of TH promoter activity requiring the CRE/CaRE motif. CREB and its phosphorylation at Ser133 were required for the response to E2 or E2‐BSA. The findings reveal several ways whereby estrogen can regulate TH transcription.

Sexual Behavior Activity Tracks Rapid Changes in Brain Estrogen Concentrations

Estrogens are classically viewed as hormones that bind to intracellular receptors, which then act as transcription factors to modulate gene expression; however, they also affect many aspects of neuronal functioning by rapid nongenomic actions. Brain estrogen production can be regulated within minutes by changes in aromatase (estrogen synthase) activity as a result of calcium-dependent phosphorylations of the enzyme. To determine the effects of rapid changes in estrogen availability on male copulatory behavior, we mimicked in male mice the rapid upregulation and downregulation of brain estrogen concentration that should occur after inactivation or activation of aromatase activity. A single injection of different aromatase inhibitors [Vorozole, 1,4,6-androstatrien-3,17-dione (ATD), or its metabolite 17-OH-ATD (1,4,6-androstatrien-17beta-ol-3-one)] almost completely suppressed male sexual behavior (mounts and intromissions) expressed 10-20 min later by C57BL/6J mice but did not affect behavior in aromatase knock-out (ArKO) mice, activated by daily injections of estradiol benzoate, thereby confirming the specificity of the behavioral inhibition observed in wild-type mice. The rapid ATD-induced inhibition was reversed by the simultaneous injection of a large dose of estradiol. A single injection of estradiol to ArKO mice also activated male sexual behavior within 15 min. Thus, rapid increases or decreases in brain estrogen concentrations are followed within minutes by corresponding changes in male sexual behavior. Sexual behavior can thus be used to monitor changes in local estrogen concentrations and analyze the mechanisms mediating the rapid decline in estrogen signaling that takes place after inhibition of estrogen synthesis.

Short-Term Estrogen Replacement Increases β-Preprotachykinin mRNA Levels in Uninjured Dorsal Root Ganglion Neurons, but Not in Axotomized Neurons

Dorsal root ganglion (DRG) neurons that mediate nociception express the high affinity NGF receptor (trkA) gene and the preprotachykinin (PPT) gene. NGF has been shown to regulate both of these DRG neuronal genes. Our laboratory has shown that these genes are also regulated by estrogen. Long-term daily estrogen replacement, in adult ovariectomized (OVX) rats, causes a coordinate decline in trkA and β-PPT mRNA levels in lumbar DRG neurons, while short-term estrogen replacement increases trkA mRNA levels in uninjured as well as in axotomized lumbar DRG neurons. The purpose of the current study was to test the hypothesis that short-term estrogen replacement increases DRG β-PPT mRNA levels in lumbar DRG neurons of OVX rats and that the increase is dependent on target-derived NGF. Sciatic nerve transection (SNT) was used to eliminate target-derived NGF in L4 and L5 DRGs in adult OVX rats. Seven days later, one-half of the SNT and one-half of the animals that had received sham sciatic nerve transactions (SHAM) received two daily injections of estradiol benzoate (EB). The remaining rats received two daily injections of vehicle alone. Quantitative in situ hybridization analyses of sections from L4 and L5 DRGs showed that two daily injections of EB significantly increased β-PPT mRNA levels in DRGs of SHAM animals, but had no effect on β-PPT mRNA levels in DRGs from SNT animals. These data coupled with our earlier observations of the effect of short-term estrogen replacement on DRG trkA mRNA levels, indicate that the regulation of DRG β-PPT mRNA levels by estrogen requires target-derived NGF.

Estrogen desensitizes 5-HT 1A receptors and reduces levels of G z, G i1 and G i3 proteins in the hypothalamus

The present study investigated whether estrogen would desensitize hypothalamic serotonin 1A (5-HT 1A) receptors by examining the neuroendocrine response to 8-OH-DPAT, a 5-HT 1A agonist. Rats were ovariectomized, allowed to recover for 5 days, then given 2 daily injections of estradiol benzoate or vehicle (10 μg/day, s.c.). Twenty-four hours after the second injection, rats were challenged with a sub-maximal dose of 8-OH-DPAT (50 μg/kg, sc) or saline 15 min prior to sacrifice. 8-OH-DPAT produced a significant increase in plasma oxytocin, ACTH and corticosterone levels in ovariectomized rats. While estrogen treatment for 2 days did not alter basal hormone levels, it did significantly reduce the magnitude of oxytocin, ACTH and corticosterone responses to 8-OH-DPAT. The reduction in hormone responses was accompanied by a significant reduction in hypothalamic levels of G z, G i1 and G i3 proteins (by 50%, 30% and 50%, respectively). These findings suggest that a reduction in these G proteins may contribute to the mechanisms underlying estrogen-induced desensitization of 5-HT 1A receptors. The desensitization of 5-HT 1A receptors has been suggested to underlie the therapeutic effects of antidepressant 5-HT uptake inhibitors (SSRIs). Thus, the present results suggest that estrogen or estrogen-like substances in combination with SSRIs may prove effective in developing novel therapeutic strategies for neuropsychiatric disorders in women.

Exogenous estrogen acts differently on production of estrogen receptor in the preoptic area and the mediobasal hypothalamic nuclei in the newborn rat

Expression of the estrogen receptor (ER) in the preoptic area (POA) and the mediobasal hypothalamus (MBH) in newborn female rats was studied by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISHH). The number of ER immunoreactive (ER-IR) cells decreased and expression of ER mRNA was suppressed in the arcuate (ARH) and the ventromedial (VMH) hypothalamic nuclei by daily injections of estradiol benzoate (EB) for ten consecutive days. In contrast, in the POA, expression of ER mRNA was not suppressed by EB treatment, while the ER immunoreactivity and the number of ER-IR cells was decreased by EB treatment. Results of quantification of ER mRNA by reverse transcription-polymerase chain reaction correlated well with results from ISHH: that is, ER mRNA expression decreased in the MBH but not in the POA. Thus, estrogen affects ER gene expression differently in these two brain regions.

Exogenous estrogen acts differently on production of estrogen receptor in the preoptic area and the mediobasal hypothalamic nuclei in the newborn rat

Expression of the estrogen receptor (ER) in the preoptic area (POA) and the mediobasal hypothalamus (MBH) in newborn female rats was studied by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISHH). The number of ER immunoreactive (ER-IR) cells decreased and expression of ER mRNA was suppressed in the arcuate (ARH) and the ventromedial (VMH) hypothalamic nuclei by daily injections of estradiol benzoate (EB) for ten consecutive days. In contrast, in the POA, expression of ER mRNA was not suppressed by EB treatment, while the ER immunoreactivity and the number of ER-IR cells was decreased by EB treatment. Results of quantification of ER mRNA by reverse transcription-polymerase chain reaction correlated well with results from ISHH: that is, ER mRNA expression decreased in the MBH but not in the POA. Thus, estrogen affects ER gene expression differently in these two brain regions.

The effects of daily exposure to oestrous or anoestrous gilts and sows on the attainment of puberty in the gilt

Seventy Large White/ Landrace crossbred gilts were allocated by litter of origin and liveweight to one of five treatments: (1) no contact with stimulus animals (control); (2) daily exposure to an anoestrous gilt; (3) daily exposure to an oestrous gilt; (4) daily exposure to an anoestrous sow; (5) daily exposure to an oestrous sow. All treatments were imposed for 20 min daily from a mean gilt age of 159 days for 100 days. Fourteen ovariectomised female pigs were used to provide the treatments, seven of these being designated small (mean liveweight 78.9 ± 4.1 kg) and seven designated large (mean liveweight 192.0 ± 15.0 kg). These ovariectomised females were treated on a rotational basis with two daily injections of oestradiol benzoate (OB) to induce oestrus, oestrus being taken as days 4 and 5 following the first injection. Anoestrous females were selected from within the same group, but females that had been treated with the OB were not used from the day of injection for at least 10 days. Results show that a significantly higher proportion of gilts reached puberty within the experimental period when given daily contact with stimulus animals than when not stimulated ( P < 0.05). Exposure to large stimulus females tended to reduce gilt age at puberty (204.2 vs. 216.3 days) and significantly increased ( P < 0.05) the proportion of gilts attaining puberty by days 29 (0.46 vs. 0.15) to 40 (0.54 vs. 0.19) of the experimental period compared with exposure to small stimulus females. The sexual status of the exposure female exerted no influence on the timing of gilt puberty (mean age at puberty 210.3 vs. 207.7 days and proportion pubertal within the experimental period 0.82 vs. 0.85 for treatments involving exposure to anoestrous and oestrous females respectively). These data indicate that exposure to ‘strange’ females can induce early puberty in the gilt. They further suggest that differences in the stimulus value to prepubertal gilts of exposure to ‘strange’ female pigs may occur, and that any differences that do occur are likely to be due to the size, rather than the sexual status, of the exposure female.

Androgen Treatment Decreases Estrogen Receptor Binding in the Ventromedial Nucleus of the Rat Brain: A Quantitative in Vitro Autoradiographic Analysis

Androgens oppose the actions of estrogen on a number of neuroendocrine functions in the rat including prolactin and gonadotropin secretion and the activation of the female pattern of sex behavior. Although in nonneural tissues antiestrogenic actions of androgens have been related to actions at the level of the estrogen receptor, previous attempts to demonstrate effects of nonaromatizable androgens on estrogen receptor levels in the brain have been unsuccessful, possibly because of the poor anatomical resolution of the methods used. We have used a new in vitro autoradiographic assay combined with an 125I-labeled estrogen receptor ligand to test the hypothesis that the nonaromatizable androgen, 5α-dihydrotestosterone (5α-DHT), may act to reduce estrogen binding in specific regions of the brain involved in reproductive neuroendocrine and behavioral responses. This in vitro autoradiographic method allows selective measurement of occupied estrogen receptors in tissue sections. Gonadectomized/adrenalectomized rats were divided into two groups per sex. All animals received daily injections of estradiol benzoate (EB: 40 μg/kg body wt) for 4 days. Animals in the 5α-DHT treatment group received 5α-DHT (10 mg/kg body wt) every 12 h for 4 days, while animals in the control group received vehicle injections. Animals were killed 4 h after the final EB/5α-DHT injection and their brains processed for in vitro autoradiography. As previously reported, higher levels of estrogen binding were observed in the ventrolateral aspect of the ventromedial nucleus (vIVMN) and the periventricular and medial preoptic area of the female compared to the male. 5α-DHT treatment resulted in an overall decrease in estrogen binding which attained statistical significance only in the vIVMN of the female. This effect of 5α-DHT was inhibited by flutamide, a nonsteroidal androgen receptor antagonist, confirming that the effect was mediated through the androgen receptor system. When similarly treated female rats were injected (iv) with a saturating dose of unconjugated estradiol 1 h before sacrifice to occupy and thus detect all available receptor, a similar 5α-DHT-induced decrease in estrogen-binding capacity in the vIVMN was observed. Thus, it is unlikely that 5α-DHT treatment resulted in downregulation of estrogen receptor occupation through a local effect on estrogen metabolism. These data demonstrate for the first time that nonaromatizable androgens can act in the brain to downregulate estrogen receptor. As the vIVMN is the principal site for regulation of female sex behavior in the female rat, these findings support the hypothesis that androgens may act to inhibit estrogen-induced female sex behavior by decreasing estrogen receptor binding.

Chin marking behavior, sexual receptivity, and pheromone emission in steroid-treated, ovariectomized rabbits

The effect of daily injections of estradiol benzoate (1 or 10 μg) and of progesterone (10 mg) on chin marking activity, sexual receptivity, and emission of nipple-search pheromone in ovariectomized rabbits was investigated. Both estradiol treatments resulted in a significant increase in all three measures over baseline and control group levels within 1–3 days, and withdrawal in a return to pretreatment levels within 2 weeks (Experiment I). In contrast, the administration of progesterone to such estradiol-primed does resulted in an almost immediate suppression of chin marking and lordosis, but in marked enhancement of pheromone emission and aggressive behavior (Experiment II). However, progesterone given alone to nonprimed does had no effect on any of these measures (Experiment III). The response profiles resulting from these treatments correspond well to patterns reported for intact does during estrus (= estradiol alone), pregnancy (= estradiol plus progesterone), and at parturition (= progesterone withdrawal).

Effect of 5 alpha-dihydrotestosterone on sexual receptivity and neural progestin receptors in ovariectomized rats given pulsed estradiol.

Experiments were carried out to examine the mechanism whereby 5 alpha-dihydrotestosterone (DHT) antagonizes the stimulatory effects of estrogen plus progesterone (P) on sexual receptivity (lordosis) in the ovariectomized rat. Estradiol (E2; 1 microgram s.c. in 10% ethanol) was administered in a discontinuous (pulsed) treatment regimen thought to mimic phase requirements of estrogen action; two injections of E2 were given either 6 or 12 h apart (first injection, Hour 0). Progesterone (0.5 mg in oil) was injected at Hour 20, and behavioral testing occurred at Hour 24. Dihydrotestosterone (2.5 mg s.c. in 10% ethanol/propylene glycol) inhibited lordosis when it was given before (-12 or -3 h), between (+3, or -3 and +3 h), or after (+8 h) the two E2 injections, but was not effective when given at +20 h. Significant inhibition of E2 + P-induced lordosis was achieved by 2.5 but not 1.0 or 0.2 mg DHT at -3 h, while uterine weights in the same animals were reduced significantly by 2.5 and 1.0 mg DHT. Serum E2 and DHT concentrations peaked rapidly after injection, declining to near baseline by 3 and 12 h, respectively. Induction of cytosolic progestin receptors (cPR) in the preoptic area and medial basal hypothalamus by estrogen was not prevented by DHT when animals were given the two pulsed E2 injections or daily injections of estradiol benzoate, although P was able to override the inhibitory behavioral effects of DHT in the latter but not the former group.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent attempts to improve synchronisation of ovulation and to induce superovulation in the mare

SummaryRecent experiments designed to improve synchronisation and stimulation of ovulation in mares are described. The addition of daily injections of oestradiol benzoate to a routine synchronisation protocol, that utilised intravaginal sponge administration of a progestogen, ally I trenbolone, for seven days followed by an injection of prostaglandin at the time of sponge removal, reduced pituitary follicle stimulation hormone (FSH) secretion during treatment, increased the interval from sponge removal to ovulation but did not improve synchronisation of ovulation. Addition of daily injections of testosterone to the protocol reduced the secretion of pituitary luteinising hormone (LH), but not FSH, during treatment and it did improve synchronisation of ovulation.Attempts to stimulate follicular growth with an anti‐oestrogen, tamoxifen, during late anoestrus or after synchronisation treatment during the breeding season were unsuccessful; FSH and LH secretion rates and follicular growth were not stimulated. Treatment of mares with an extract of horse pituitary glands during successive oestrous cycles to give a total of six treatments per mare during the breeding season induced the growth of a mean of 3.3 mature follicles but only a mean of 1.8 ovulations in each treated cycle. This treatment regime did not seem to exhaust the pool of follicles that can be stimulated in subsequent cycles.

Effects of estrogen and progesterone on serum prolactin and luteinizing hormone levels in ovariectomized turkeys ( Meleagris gallopavo)

Serum prolactin (PRL) and luteinizing hormone (LH) levels from mature female turkeys were determined following ovariectomy and daily subcutaneous injections for 4 or 9 days of 0.002–2.0 mg/kg estradiol benzoate (EB), 0.05–2.0 mg/kg progesterone (P), or their combinations. Serum PRL levels were increased ( P < 0.05) at the onset of sexual maturity in intact controls, but not in ovariectomized turkeys. Injection of 0.02 mg/kg EB into ovariectomized turkeys resulted in elevated ( P < 0.05) serum PRL levels after 8 treatment days. Higher doses failed to elicit a response of greater magnitude. EB at doses of 0.02–2.0 mg/kg reduced LH levels while 0.002 mg/kg EB increased LH levels above ( P < 0.05) those of ovariectomized controls. The 1.0-mg/kg P dose increased ( P < 0.05) serum PRL within 24–48 hr of administration while the 0.05-, 0.5-, or 2.0-mg/kg P doses failed to elicit a response. When P was injected in doses of 0.5–2.0 mg/kg, LH levels were decreased in a dose-response manner. The injection of EB combined with P had a variable effect on serum PRL levels. The 0.5- or 1.0-mg/kg dose of P facilitated (advanced in time) the rise in serum PRL level induced by 0.02 mg/kg of EB. In contrast, the positive feedback effect of 0.2 mg/kg of EB was blocked when administered with 0.5 mg/kg of P. Serum LH levels were dramatically decreased by all steroid combinations used. These results indicate that daily injections of EB and/or P in ovariectomized turkeys have a variable effect on serum PRL and LH levels depending upon the dose, the duration of treatment, or the ratio between EB and P.

Suppression of lordotic responsiveness in the female rat during mesencephalic electrical stimulation

The effects of biphasic electrical stimulation of the mesencephalic median (MRN) and dorsal raphe (DRN) nuclei, as well as the adjacent periaquenductal gray (PAG), on lordotic behavior were investigated in ovariectomized rats primed with three daily injections of estradiol benzoate (2 μg). Animals were tested between 4–8 hours after a progesterone (0.5 mg) injection on day four which normally facilitates high levels of receptivity during this period. Although stimulation of the MRN had no significant effect on lordosis, DRN activation at 100 Hz (0.5 msec pulse duration) or 10 Hz (2 msec pulse duration) caused a marked and immediate suppression (53% and 56%, respectively) in receptivity. This suppression does not appear to be due to activation of serotoninergic neurons originating in the DRN since pretreatment with an inhibitor of serotonin synthesis (parachlorophenylalamine, 320 mg/kg) essentially did not modify the suppression, thus providing no evidence in support of an inhibitory role for serotonin in lordotic behavior. Activation within the PAG adjacent to the DRN at 10 Hz (0.5 or 2 msec pulse duration) produced an immediate, dramatic decrease (81% and 80%, respectively) in receptivity. The suppressions induced by DRN and PAG stimulation appear most likely to be due to activation of a descending pathway inhibitory to the lordosis reflex at medullary or spinal cord levels.

The effect of season and technique on synchronized and induced estrus and the induction of lambing in the ewe in a commercial setting

At 40 day intervals, groups of 87 to 142 commercial ewes of mixed breeding were subjected to a 5 day breeding period, following one of three estrus inducing or synchronizing treatments (intravaginal sponges containing 60 mg of medroxyprogesterone acetate) for 12 days with (progestin P.M.S.G. group) or without pregnant mares serum gonadotropin (P.M.S.G.) (Progestin group) at sponge removal, or a single injection of prostaglandin F 2α (breeding season and early anestrus only) (PGF 2α group)). Mean pregnancy rates (ewes lambing of those treated) and lambing percentages (lambs born per 100 ewes lambing) were 31 ± 4%, 169 ± 6%, 20 ± 5%, 105 ± 2% and 18 ± 8%, 118 ± 3%, respectively, for the three treatment groups above. Pregnancy rates for the progestin, P.M.S.G. group were 52% in late July, prior to the breeding season, 52% in September and declined to 14% in March (early anestrus). The time from the first of two daily injections of estradiol benzoate to lambing was 34.5 ± 4.4 hours in ewes 142 to 146 days pregnant.

Effects of estradiol benzoate and MER-25 on ethanol consumption in the ovariectomized rat.

Daily injections of estradiol benzoate (EB) administered to ovariectomized rats given continuous access to a 10% ethanol solution, to water, and to laboratory chow led to decreases in ethanol consumption. The suppression was transient; ethanol consumption returned to the level of oil-treated control animals after 14 days despite continued hormone administration. This pattern of change in ethanol consumption closely resembled previously reported effects of EB on food intake. It is proposed that a common mechanism was responsible for EB-induced suppression of both food and ethanol intake. Ethamoxytriphetol, MER-25, which antagonizes many estrogen-dependent effects but which mimics the action of EB on food intake, also led to decreases in ethanol consumption that paralleled those reported for food intake. These behavioral effects of EB and MEr-25 were shown not to be due to altered ethanol metabolism or to result from malaise developing out of an interaction between EB and ethanol. It is thus suggested that voluntary consumption of ethanol by the rat is largely due to its caloric content. The relevance of these results for several recent reports of decreased ethanol intake during pregnancy is discussed.

Inhibition of lordosis in rats by the antiestrogen CI-628 in the absence of progesterone.

A series of experiments assessed whether the ability of the antiestrogen CI-628 to inhibit estrogen-stimulated lordosis in adult ovariectomized rats depends upon its interference with the synergistic effects of estrogen with progesterone. In Experiment 1, the effect of CI-628 was contrasted in rats brought into estrus by a single subcutaneous injection of estradiol benzoate (EB) combined with an injection of progesterone (P) 42 hr later versus four daily injections of EB (without any P). CI-628 was given at the time of EB injection(s). CI-628 substantially and equally effectively antagonized lordotic responding in both conditions. In the absence of CI-628, rats receiving progesterone had significantly higher lordosis scores than the 4-day EB control animals. In Experiment 2, rats receiving CI-628 on only the first 2 of 4 days of EB injections had significantly decreased lordosis scores unless P was also given on the day of testing. This suggested that the EB from the latter injections was not acting as a progestin "mimic." In Experiment 3, lordotic responding stimulated by EB (without P) was inhibited by CI-628 in rats that were both ovariectomized and adrenalectomized. This suggested that adrenal progestins were not involved in the ability of CI-628 to inhibit lordosis. Taken together, the results suggest that the mechanism of action of CI-628 for the inhibition of lordosis does not depend upon its ability to antagonize an estrogen-induced increase in neural progestin receptors. Implications of this for estrogen-mediated behaviors, for which CI-628 has little or no antagonistic effects, are discussed.

Accumulation of L-dopa in the median eminence: an index of tuberoinfundibular dopaminergic nerve activity.

A microradioenzymatic assay for dihydroxyphenylalanine (dopa) was used to measure the concentration of this precursor of dopamine (DA) in different regions of the rat brain. The accumulation of dopa 30 min after the injection of 3-hydroxybenzylhydrazine (NSD 1015), an inhibitor of dopa decarboxylase, was measured in the striatum and median eminence to obtain a biochemical index of the activity of nigrostriatal and tuberoinfundibular DA nerves, respectively. Injections of a DA agonist, piribedil, reduced dopa accumulation in the striatum but not in the median eminence. Injections of a DA antagonist, haloperidol, increased dopa accumulation in the striatum 2 and 8 h after injection and in the median eminence 16 h after injection. Three daily injections of estradiol benzoate increased the accumulation of dopa in the median eminence but not in the striatum; the estrogen-induced increase of dopa accumulation in the median eminence was not observed in hypophysectomized rats. The effects of these pharmacological...