Acute Estradiol Research Articles

Effect of ovarian steroids on basal and oxytocin-induced prostaglandin F2alpha secretion from pig endometrial cells.

These studies were undertaken to determine how treatment with 100 nM progesterone and/or 10 nM oestradiol-17beta acutely (3 h; Experiment 1) or chronically (72 h; Experiments 2-4) influenced basal and oxytocin (OT)-stimulated prostaglandin (PG) F(2alpha) secretion, in enriched cultures of pig endometrial luminal epithelial, glandular epithelial and stromal cells obtained on Day 16 (Experiments 1, 2 and 4) or Day 12 (Experiment 3) after oestrus. In Experiment 1, acute treatment with progesterone stimulated PGF(2alpha) secretion from each cell type on Day 16, whereas acute oestradiol treatment inhibited the stimulatory action of progesterone on PGF(2alpha) secretion only in glandular epithelial cells. In Experiment 2, OT stimulated phospholipase (PL) C activity in luminal epithelial cells on Day 16 only in the presence of chronic oestradiol treatment. For glandular epithelial cells on Day 16, OT stimulated PLC activity only in the presence of chronic treatment with steroid. In stromal cells on Day 16, OT stimulated PLC activity in the absence of steroids and the response to OT was further enhanced by oestradiol. In the absence of chronic treatment with steroid, OT did not stimulate PGF(2alpha) secretion from luminal epithelial cells, but oestradiol induced a response to OT. For glandular epithelial cells, OT-induced PGF(2alpha) secretion was not altered by steroids, whereas the stimulatory response to OT was inhibited by oestradiol or progesterone in stromal cells. For endometrial cells obtained on Day 12 after oestrus in Experiment 3, OT only stimulated PGF(2alpha) release from glandular epithelial and stromal cells. For luminal epithelial cells obtained on Day 16 after oestrus and cultured under polarizing conditions in Experiment 4, secretion of PGF(2alpha) occurred preferentially from the basolateral surface and was stimulated by OT more from the basolateral surface than from the apical surface. Oxytocin-induced PGF(2alpha) secretion from the apical surface was enhanced by chronic treatment with oestradiol, whereas that from the basolateral surface was enhanced by chronic treatment with progesterone. In summary, oestradiol enhanced OT-induced PGF(2alpha) secretion from the apical surface of luminal epithelial cells and reduced the response of stromal cells to OT, actions that may contribute to the reorientation of PGF(2alpha) from endocrine secretion (i.e. towards the uterine vasculature) to exocrine secretion (i.e. towards the uterine lumen) during pregnancy recognition in pigs.

Myometrial maxi-K channel β1 subunit modulation during pregnancy and after 17β-estradiol stimulation

Myometrial maxi-K channels are modulated by β subunits. We aimed to determine whether β subunits are modulated to affect uterine excitability during gestation. RNase protection analyses revealed that mouse β1 subunit transcripts are regulated during gestation with peak expression at day 14 of pregnancy. Immunohistochemical analysis indicates an increase of this subunit during gestation. Upregulation of the β1 transcript occurs with 4-day exposure to 17β-estradiol but not progesterone, and acute estradiol exposure has no effect on β1 transcript expression. These findings verify that β1 subunit transcript is regulated in mouse myometrium during gestation and estrogens may contribute to this increase.

Lack of effects of acute estradiol on mood in postmenopausal women

Chronic treatment with estrogen is believed to improve mood in postmenopausal women, and recent preclinical evidence suggests that estradiol may also affect mood and behavior through acute neuronal membrane-mediated effects on the central nervous system. This study was designed to characterize potential mood effects of single doses of transdermal estradiol in healthy postmenopausal women who were not taking hormone replacement therapy (HRT). Twelve women participated in a five-session, within-subjects, double-blind study, in which they received placebo, transdermal estradiol (0.2, 0.4, and 0.8 mg), or d-amphetamine (15 mg, oral) in a randomized order. Amphetamine was included as a positive control. Dependent measures included self-report measures of mood, physiological measures, and plasma hormone levels. Despite dose-dependent increases in plasma estradiol levels, and despite the fact that d-amphetamine produced its prototypic stimulant-like effects in these postmenopausal women, estradiol did not produce effects on mood. The finding that acute administration of exogenous estradiol did not alter mood suggests that more chronic exposure to estradiol is needed to produce mood-enhancing effects.

The acute effects of estradiol benzoate on amygdala-kindled seizures in male rats

Using amygdaloid-kindling model of epilepsy, effects of acute estradiol treatment on seizure parameters were investigated in male rats. Fully kindled male rats were treated with various doses of estradiol benzoate (EB, 10, 30 and 50 μg/kg, i.p.) and kindling parameters such as seizure stage (SS), afterdischarge duration (ADD) and stage 5 duration (S5D) were elicited at various times (0.25, 1.5, 3 h and every 24 h for 96 h) post-drug administration. While the 10-μg/kg dose of EB failed to change seizure parameters, administration of the 30- and 50-μg/kg doses caused significant prolongation of ADD and S5D (was not changed significantly by the latter dose) at various time intervals post-drug administration. Pretreatment with the 3 mg/kg dose of tamoxifen citrate (TAM) inhibited the EB (30 μg/kg) effect, while pretreatment with the 10-mg/kg dose produced significant prolongation of ADD and S5D. These results suggest that in male amygdaloid kindled rats, acute estradiol treatment leads to an intensification of seizure that is manifested by increases in ADD and S5D. As the effect is evident 0.25 h post-EB administration and duel action of TAM in opposing the EB effect at low doses and potentiating it at the higher doses, the possibility of a genomic effect may be ruled out. The variable effects of TAM might be explained by its partial agonistic property on estrogen receptors

Memory retention is modulated by acute estradiol and progesterone replacement.

Ovarian hormones alter spine density of hippocampal granule and pyramidal cells in young adult and aging female rats (P. Miranda, C. L. Williams, & G. Einstein, 1999; C. S. Woolley, 1998). The present study used a delayed matching-to-place version of the water maze to investigate a behavioral correlate of these hormone-induced changes in hippocampal connectivity in 3- and 8-month-old female rats. When primed with 10-microg injections of estradiol 72 and 48 hr before testing, the memory retention of ovariectomized rats was improved compared with retention after priming with oil. A single injection of progesterone maintained this enhancement if testing occurred within 8 hr of the progesterone injection but not if testing occurred more than 24 hr after the progesterone injection. These findings indicate that estradiol and progesterone alter memory retention and suggest that these changes may be the result of hormone-induced increases in hippocampal connectivity.

Memory retention is modulated by acute estradiol and progesterone replacement.

Memory retention is modulated by acute estradiol and progesterone replacement.

C-Fos gene expression pattern in the hypothalamus and the preoptic area of defeminized rats

The object of the present study was to determine the c-fos gene expression pattern in the hypothalamus (HYP) and the preoptic area (POA) after estradiol and testosterone priming during the critical period of sexual differentiation of the rat brain. Three-day-old female rats were injected s.c. with a single dose of 17β-estradiol (200 μg), testosterone enantate (200 μg) or vehicle (corn oil). HYP and POA were dissected 2 h, 24 h and 14 days after treatments and on the day of vaginal opening (VO). Other animals, previously treated as above, were acutely injected with 17β-estradiol (5 μg) on the day of VO; HYP and POA were obtained 3 h later. Total RNA was extracted and processed for semiquantitative RT-PCR. We observed that c-fos gene expression was markedly increased in POA of the animals treated with estradiol or testosterone 2 h after treatments, while a non-significant increase in c-fos gene expression was observed in the HYP of these animals. We found a significant increase in c-fos expression in HYP and POA on the day of VO in both estradiol and testosterone defeminized rats. Interestingly, the acute estradiol administration on the day of VO did not induce c-fos gene expression in either HYP or POA of defeminized animals, instead a diminution in its expression was observed in animals treated with testosterone in POA. The overall results suggest that estradiol and testosterone imprinting during critical postnatal period of sexual differentiation of the brain permanently modifies the regulation of c-fos gene expression.

Acute Effects of Estradiol Pretreatment on the Response to d-Amphetamine in Women

Little is known about the interactions between ovarian hormones and responses to psychoactive drugs in humans. Preclinical studies suggest that ovarian hormones such as estrogen and progesterone have direct and indirect central nervous system actions and that these hormones can influence behavioral responses to psychoactive drugs. In the present study, we assessed the subjective and physiological effects of d-amphetamine (AMPH; 10 mg p.o.) after pretreatment with estradiol. Two groups of healthy, regularly cycling women participated in two sessions scheduled during the early follicular phases of two menstrual cycles. One group received estradiol patches (Estraderm TTS; 0.8 mg) which elevated plasma estradiol levels to approximately 750 pg/ml on both sessions; the other group received placebo patches on both sessions. Both groups received AMPH (10.0 mg) and placebo in a randomized and counterbalanced order on the two sessions. Dependent measures included self-report questionnaires, physiological measures, and plasma hormone levels. Most of the subjective and physiological effects of AMPH were not affected by acute estradiol treatment. Nevertheless, estradiol pretreatment increased the magnitude of the effects of AMPH on subjective ratings of ‘pleasant stimulation’ and decreased ratings of ‘want more’. Also, estradiol produced some subjective effects when administered alone: It increased subjective ratings of ‘feel drug’, ‘energy and intellectual efficiency’, and ‘pleasant stimulation’. These results provide limited evidence that the stimulating effects of AMPH are increased by acute estradiol pretreatment.

Effects of tamoxifen on serotonin transporter and 5-hydroxytryptamine 2A receptor binding sites and mRNA levels in the brain of ovariectomized rats with or without acute estradiol replacement

Estradiol-17β (E 2), in its positive feedback mode for gonadotropin release in the female rat, induces expression of the genes for the 5-hydroxytryptamine 2A receptor (5-HT 2AR) and the serotonin transporter (SERT) in the dorsal raphe nucleus (DRN) with a concomitant increase in the densities of 5-HT 2AR and the SERT in rat forebrain. The forebrain regions affected are those which, in humans, are concerned with the control of mood, mental state, cognition and emotion. Here we have used the mixed estradiol agonist/antagonist, tamoxifen, to determine whether this action of estradiol is mediated by cytoplasmic estradiol receptors. Acute treatment (∼32 h) of ovariectomized rats with estradiol benzoate (EB) increased significantly the amount of 5-HT 2AR mRNA and SERT mRNA in the DRN and the densities of 5-HT 2AR and SERT binding sites in the forebrain. These effects of EB were completely blocked by tamoxifen. Treatment with tamoxifen alone had no effect on either gene expression or the density of binding sites. Together, these data show that tamoxifen acts as a pure estradiol antagonist with respect to serotonergic mechanisms in brain. Detailed analysis of the effects of estradiol and tamoxifen on the DRN showed that SERT gene expression is constitutive only in the posterior DRN; in the anterior DRN, SERT gene expression appears to depend upon estrogen induction which is blocked by tamoxifen. Our findings strongly suggest that estradiol receptors are involved in mediating estradiol action on central serotonergic mechanisms and are relevant for our understanding of the effects of antiestrogens as well as estradiol on mood, mental state and cognition.

Estradiol protects against ischemic injury.

Clinical studies demonstrate that estrogen replacement therapy in postmenopausal women may enhance cognitive function and reduce neurodegeneration associated with Alzheimer's disease and stroke. This study assesses whether physiologic levels of estradiol prevent brain injury in an in vivo model of permanent focal ischemia. Sprague-Dawley rats were ovariectomized; they then were implanted, immediately or at the onset of ischemia, with capsules that produced physiologically low or physiologically high 17beta-estradiol levels in serum (10 or 60 pg/mL, respectively). One week after ovariectomy, ischemia was induced. Estradiol pretreatment significantly reduced overall infarct volume compared with oil-pretreated controls (mean+/-SD: oil = 241+/-88; low = 139+/-91; high = 132+/-88 mm3); this protective effect was regionally specific to the cortex, since no protection was observed in the striatum. Baseline and ischemic regional CBF did not differ between oil and estradiol pretreated rats, as measured by laser Doppler flowmetry. Acute estradiol treatment did not protect against ischemic injury. Our finding that estradiol pretreatment reduces injury demonstrates that physiologic levels of estradiol can protect against neurodegeneration.

Acute Estradiol and Progesterone Administration Reduced Cardiovascular and Catecholamine Responses to Mental Stress in Menopausal Women

Steroid hormones are involved in the regulation of sympathoadrenal activity. Since the effect of sex steroids on the cardiovascular system and catecholamine secretion could also be exerted through an acute, nongenomic mechanism, we have studied the response to mental stress (color word test, CWT) in a group of 15 menopausal women during estrogen (100 µg of estradiol by patch), progesterone (100 mg i.m.) or placebo administration. Systolic blood pressure (SBP) increased during CWT in the three sessions (F = 11.0, p < 0.001) but the area under the curve of SBP was higher during placebo (2,855 ± 131 mm Hg·min) than during estradiol (2,585 ± 139 mm Hg·min) and progesterone (2,553 ± 179 mm Hg·min, p < 0.05 for both). Plasma epinephrine increased during CWT in the three sessions (F = 31.1, p < 0.001) and the plasma epinephrine response to mental stress was higher during placebo than during estradiol administration (F = 4.3, p < 0.01). The area under the curve of epinephrine was 10,342 ± 1,348 pmol/min·l during placebo and 7,280 ± 818 pmol/min·l during estradiol (p < 0.03). The plasma glycerol levels at the end of CWT were higher during placebo (0.26 ± 0.04 nmol/l) than during estradiol (0.19 ± 0.03 mmol/l) and progesterone (0.17 ± 0.04 mmol/l) administration (p < 0.05 for both). No significant differences were found in the responses of diastolic blood pressure, heart rate, norepinephrine and cortisol to mental stress during placebo and estradiol or progesterone administration. This study demonstrates that acute steroid administration is able to modify the cardiovascular and catecholamine response to mental stress in menopausal women.

Prenatal androgens time neuroendocrine puberty in the sheep: effect of testosterone dose.

In sheep, prenatal exposure to androgens during a critical period for sexual differentiation of the brain (30-90 days of gestation; 145 days is term) can advance the timing of puberty in females and prevent the preovulatory LH surge. The present study tests the hypothesis that in sheep, the timing of neuroendocrine sexual maturation is related to the amount of prenatal steroid exposure. In addition, we determined if different steroid requirements exist for sexual differentiation of the tonic and surge modes of gonadotropin secretion. Testosterone was administered weekly to three groups of pregnant ewes from days 30-90 of gestation at doses of 200, 80, or 32 mg/week. The resulting androgenized female lambs together with control males and females (n = 5-7/group) were gonadectomized at 3 weeks of age, and gonadal steroids were replaced with a SILASTIC brand estradiol-filled capsule. LH concentrations were measured from biweekly blood samples. Sustained increases in circulating LH were considered to reflect the initiation of neuroendocrine puberty. In male lambs, LH secretion started to increase at 8.3 +/- 0.9 weeks of age (mean +/- SEM). The two highest doses of prenatal androgen advanced the onset of neuroendocrine sexual maturation in females. In the 200 mg androgenized females, the pubertal LH rise (10.2 +/- 2.0 weeks) began about the same time as in males. In the 80 mg treatment group, LH concentrations increased at 16.2 +/- 1.5 weeks, which was later than in males, but well before that in normal females (27.1 +/- 0.7 weeks). For females treated with the lowest dose of androgen (32 mg), the pubertal LH increase (24.6 +/- 1.9 weeks) began about the same time as in normal females. To test the function of the LH surge system, LH was measured every 2 h for 60 h after an acute increase in circulating estradiol was produced by implanting additional estrogen capsules. All control females produced a surge in response to acute estradiol stimulation. LH surges did not occur in males, 200 mg androgenized females, or 80 mg androgenized females. Of six females from the 32 mg treatment group, two produced LH surges in response to the stimulatory feedback action of estradiol. We conclude that the greater the amount of prenatal testosterone, the earlier the initiation of the pubertal LH rise. Moreover, the finding that low doses of testosterone (32 mg/week) are capable of abolishing the LH surge without significantly advancing the timing of puberty supports our hypothesis that different steroid requirements exist for sexual differentiation of tonic and surge modes of LH secretion.

F093 effects of acute and short-term estradiol administration on serum nitric oxide levels in postmenopausal women

F093 effects of acute and short-term estradiol administration on serum nitric oxide levels in postmenopausal women

Prediction of ovarian response to exogenous gonadotropin stimulation: Utilization for collection of primate oocytes for fertilization in vitro

The predictive value of 2 tests for ovarian response to controlled ovarian hyperstimulation in the cynomolgus monkey model was evaluated. The tests utilized were: 1) the cycle Day 3 (Day 1 = onset of menses) FSH value and 2) the acute estradiol (E 2) response to a GnRH agonists (GnRHa) administered on Day 3. Both tests were performed during the cycle preceding control ovarian hyperstimulation. Subsequently, monkeys (n = 26) were stimulated with Metrodin T (Days 2–6, 25IU/d) and Pergonal T (Day 7 to hCG administration, 25IU/d). Laparoscopic oocyte retrieval was performed 32 to 34 after hCG administration. Analysis of the data revealed that Day 3 FSH values could not predict whether an animal would respond well to control ovarian hyperstimulation in a subsequent cycle (P = 0.77). However, the E 2 change 24 h post-GnRHa administration was significantly greater for animals responding well to control ovarian hyperstimulation compared with the animals deleted after 6 d of stimulation (P = 0.042). The mean change in E 2 levels in animals taken to aspiration was 97.8 pg/ml compared with only 21.6 pg/ml for the deleted animals. This differential response of E 2 production after GnRHa treatment was used to correctly identify (by discriminant analysis) 78% of the animals subsequently deleted for poor response. Thus, the increase in serum E 2 level after GnRHa, but not the basal FSH level, was found to be predictive of ovarian response to stimulation in the cynomolgus monkey.

The Effects of Testosterone and Estradiol on Mast Cell Number in the Harderian Gland of the Frog, Rana esculenta

The Harderian gland (HG) of the frog Rana esculenta contains mast cells in the interstitial tissue. The mast cell number (MCN) is influenced by sex hormones. Gonadectomy in both sexes provoked a decrease in MCN in January, while no effect was observed in September. Sex hormone-replacement therapy gave different results; estradiol treatment in castrated males and females always increased MCN, while testosterone did not. Acute estradiol treatment provoked an increase in MCN on days 2 and 4 of treatment and the morphology of the glandular compartment appeared normal. On days 8, 10 and 12 of treatment the MCN drastically decreased. The majority of glandular acini appeared strongly disorganized and the interstitial tissue became hypertrophic in concomitance with an increased vascularization. Our results suggest that estradiol acts by stimulating mast cells and acute estradiol treatment provokes proliferation of interstitial connective tissue together with glandular cells damage.

Effects of estrogen replacement therapy on peripheral vasomotor function in postmenopausal women

Hormone replacement therapy is associated with a reduction in cardiovascular events in postmenopausal women. We have recently found that acute 17β-estradiol administration improves endothelium-dependent vasodilation in both the peripheral and coronary circulations of postmenopausal women. The current study was undertaken in 33 estrogen-deficient postmenopausal women ( mean age 59 ± 7 years) to determine if short-term estrogen replacement therapy also improves endothelium-dependent vasodilation in peripheral circulation. Acute intraarterial infusion of estradiol, which increased forearm venous estradiol levels from 16 ± 11 to 345 ± 202 pg/ ml, potentiated forearm vasodilation induced by the endothelium-dependent vasodilator acetylcholine by 49 ± 67% ( p <0.001). Acute estradiol also potentiated vasodilation induced by the endothelium-independent vasodilator nitroprusside by 5 ± 31% ( p = 0.04). However, after 3 weeks of transdermal estradiol administration (0.1 mg/day), which achieved an estradiol level of 120 ± 57 pg/ ml, the vasodilator responses to acetylcholine and to sodium nitroprusside were unchanged from initial measurements obtained before acute administration of estradiol. Repeat intraarterial infusion of estradiol in 8 women, while receiving transdermal estradiol, increased forearm venous estradiol levels to 268 ± 105 pg/ ml and again potentiated the vasodilator response to acetylcholine to a similar degree as that observed in the initial study after acute administration of estradiol. Thus, although acute intraarterial infusion of 17β-estradiol potentiates endothelium-dependent vasodilation in the forearms of postmenopausal women, this effect is not maintained with a 3-week cycle of systemic estradiol administration. The different effects of acute and chronic estradiol may be due to the lower plasma levels achieved with chronic estrogen administration.

Prenatal testosterone differentially masculinizes tonic and surge modes of luteinizing hormone secretion in the developing sheep.

In sheep, prenatal exposure to androgens during a critical period for sexual differentiation can masculinize tonic luteinizing hormone (LH) secretion and defeminize the LH surge. The present study investigated the possible independent control of these two modes of LH secretion, as revealed by their developmental history. Specifically, we tested the hypothesis that separate critical periods exist for androgenization of tonic and surge LH secretion. Pregnant ewes were treated weekly with testosterone cypionate (200 mg in oil). As a control and to induce robust masculinization of reproductive neuroendocrine function, one group of females received testosterone from day 30 to 86 of gestation (LONG group). To determine if masculinization of tonic LH secretion develops separately from that of the LH surge, two additional groups were treated from day 30 to 51 (EARLY group) or 65-86 (LATE group). At birth, the external genitalia of the LONG- and EARLY-treated females were masculinized; those of the LATE-treated group were normal. At 2 weeks of age, all androgenized females, together with normal males and females (n = 8 each), were gonadectomized and steroids replaced using an estradiol-filled Silastic capsule. First, to determine the timing of the pubertal decrease in steroid sensitivity, circulating LH was monitored twice weekly. Second, to test the function of the LH surge system, LH was measured every 1-2 h for 60 h after an acute increase in estradiol at 9 months of age. With regard to tonic LH secretion, in control males and LONG-treated females, a sustained increase in tonic LH in the presence of constant steroid feedback occurred at 7.1 +/- 0.3 and 10.9 +/- 1.7 weeks of age, respectively (mean +/- SE). In control females, tonic LH increased at 27.1 +/- 0.8 weeks. Despite the differences in their genitalia, EARLY and LATE testosterone treatment produced intermediate effects: LH secretion increased at 19.3 +/- 1.2 and 20.4 +/- 0.8 weeks, respectively. In response to acute estradiol stimulation, all control females produced a surge of LH that peaked 18.4 +/- 0.6 h after steroid treatment. For the control males and LONG-treated females, LH concentrations were not sustained above unsuppressed pretreatment levels throughout the 60-hour sampling period. All but 4 of the 18 EARLY- and LATE-treated females responded to estradiol stimulation with a surge of LH that peaked at 29.8 +/- 1.6 and 31.8 +/- 1.3 h, significantly later than that of control females.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Estradiol Modulation of Electrical Activity of the LHRH Pulse Generator in the Ovariectomized Rat: Restoration by Naloxone

Whether estrogen has the brain as a site of its negative feedback action was investigated by checking the acute effect of estradiol-17 beta (E2) on the electrical activity of the luteinizing hormone-releasing hormone (LHRH) pulse generator in ovariectomized rats fitted with chronically implanted electrode arrays in the medial basal hypothalamus. Before subcutaneous E2 implantation, the hypothalamic multiunit activity (MUA) exhibited, at an average frequency of 2.43/h, characteristic increases (volleys), each of which was associated with the initiation of an LH pulse. Within 2 h after E2 implantation, the frequency of MUA volleys was reduced significantly, probably associated with decreases in the frequency of LH pulses. The decrease in the amplitude of LH pulses occurred later than 2 h, but this effect was considered not to be mediated by the brain since the duration of MUA volleys was not changed. Since the mean serum LH concentration started to decrease within 2 h after E2 implantation, it was concluded that the acute inhibitory E2 effect on LH release is mediated by the brain. On the day after E2 implantation, intravenous infusion of naloxone (2 mg/kg/h) promptly elicited intermittent MUA volleys each of which was associated with an LH pulse. This suggests that operation of the LHRH pulse generator in the ovariectomized condition is restrained by the action of E2 with the mediation of endogenous opioid peptide neurons.

Effects of Acute Estradiol on 5-Hydroxytryptamine and Dopamine Receptor Subtype mRNA Expression in Female Rat Brain

The aim of the present study was to determine the effect of estradiol-17β, in its positive feedback mode for the release of prolactin and luteinizing hormone (LH), on gene expression of 5-hydroxytryptamine (5-HT) and dopamine receptors. Gene expression was determined by measurement of the levels of receptor mRNA by in situ hybridization in brain sections from adult female rats. The animals were ovariectomized under halothane anesthesia on the morning of diestrus, given a sc injection of either estradiol benzoate (EB) or oil (vehicle), and killed between 1600-1700 h of the next day, presumptive proestrus. The injection of EB in this preparation is known to stimulate a massive surge of LH and prolactin in the late afternoon of presumptive proestrus. The injection of EB produced a significant increase in silver grain densities representing 5-HT 2 receptor mRNA in the dorsal raphe nucleus (DRN) and a significant reduction in these grain densities in the medial septum and diagonal band of Broca. The number of cells expressing 5-HT 2 receptor mRNA was increased by 290% in the DRN and decreased by 25% in the medial preoptic area. Estradiol had no effect on silver grain densities, or numbers or percentages of cells expressing 5-HT 2 receptor mRNA in any of the other nine brain regions or choroid plexus studied, and had no effect on the levels of 5-HT 1A, 5-HT 1C, D 1, or D 2 receptor mRNA in any region studied. These data suggest that the 5-HT 2 receptor is a key receptor involved in mediating the positive feedback stimulation by estradiol-17β of LH and prolactin release. Since estradiol increases 5-HT levels in the DRN, the data raise the intriguing possibility that estrogen positive feedback on LH and prolactin release is mediated by a feed-forward 5-HT drive which results in increased 5-HT release at DRN-derived nerve terminals on hypothalamic neurons which control LH and prolactin release.

Dynamic patterns of medial preoptic mu-opiate receptor regulation by gonadal steroid hormones.

The density of mu-opiate receptors located in the medial preoptic area (MPOA) of the rat hypothalamus is cyclical and sexually dimorphic. The hormonal regulation of MPOA mu-receptors was examined in ovariectomized rats treated with a variety of hormone regimens. In experiment 1, animals received acute estradiol (E2), progesterone (P), or prolactin (PRL), or E2 followed in 48 h by either P or vehicle by subcutaneous injection. Brains were removed 3 h after the final injection. In experiment 2, animals were implanted with empty or E2-filled Silastic capsules, and received either P or vehicle by injection 48 h later, at which time E2 capsules were removed. One group received E2 implants which remained in place following sham removal surgery. Brains and trunk blood for radioimmunoassay of E2 and P were collected 3, 27 or 51 h after the final injection. Frozen brain sections were prepared, incubated in [3H]D-Ala2,MePhe4,Gly-ol5-enkephalin, which selectively labels mu-receptors, and analyzed using quantitative receptor autoradiography. P treatment significantly increased MPOA mu-receptors, but only 27 h after E2 priming. Neither shorter P exposure, nor E2, P or PRL alone affected MPOA mu-receptor density. Following this delayed E2,P-induced increase, mu-receptor density subsequently decreased in the presence of absence of E2. The results suggest that E2,P treatment produces a gradual and transient increase of MPOA mu-receptor density. The subsequent decrease of receptor density is independent of the presence of E2 and may be related to receptor turnover. The time course of this effect is consistent with that of the estrus cycle. Such hormone-induced regulation of MPOA mu-receptor density could influence the physiologic effects of opiates on gonadotropin secretion and reproductive behavior in cycling females.