Estrogen Implants Research Articles

The progesterone blockade of the luteinizing hormone surge is overcome by RU486.

Progesterone can prevent the oestrogen-induced and spontaneous preovulatory luteinizing hormone (LH) surges but the mechanisms underlying this effect remain poorly understood. Using a follicular phase ovariectomised (OVX) ewe model and by elevating progesterone in the presence of oestrogen to inhibit the LH surge, we investigated whether the progesterone receptor antagonist, RU486, could block the inhibitory effects of progesterone. Accordingly, intravaginal progesterone implants were inserted into OVX Ile-de-France ewes (n = 18), bearing 10 mm Silastic 17beta-oestradiol implants. Ten days later, the progesterone implants were removed, whereupon new implants were inserted immediately into 12 ewes: six of which were also injected with 100 mg RU486 dissolved in 10 mL vehicle (10% alcohol in peanut oil) and six received vehicle only. The remaining six ewes were injected with vehicle only. RU486 and vehicle injections were made again 12 and 24 h later. After the last injection, oestrogen concentrations were raised to peak follicular phase levels in all ewes by subcutaneous insertion of four 3-cm 17beta-oestradiol implants. Blood samples were collected every 2 h for 40 h starting 9 h after the insertion of the oestrogen implants. As expected, the six ewes treated only with oestradiol had a LH surge whereas no ewes given the implants in the presence of progesterone surged. RU486 completely blocked the inhibitory effect of progesterone. There were no differences in the time of LH surge onset, duration over which LH levels remained above their half-maximal concentration or magnitude of the LH surge between the two groups showing surges. Our study suggests strongly that the progesterone-mediated blockade of the ovine oestrogen-induced LH surge is not through allopregnanolone activation of the GABA(A) receptor. Rather, our study demonstrates that this effect is transduced by the classic nuclear progesterone receptor.

Estrogen Implants in the Lateral Habenular Nucleus Do Not Stimulate the Onset of Maternal Behavior in Female Rats

The natural onset of maternal behavior in the rat is hormonally mediated. Estrogen, progesterone, and prolactin administered to ovariectomized females in amounts and sequences that produce circulating levels similar to those found during pregnancy stimulate the onset of maternal behavior. In fact, maternal behavior can be stimulated by estrogen alone, administered either peripherally or by implant in the central nervous system. The lateral habenula (Lhb), which is a necessary component in the neural circuit that supports maternal behavior, contains a subset of neurons with estrogen receptors. The present study investigated whether estradiol implants directly in the Lhb are sufficient to stimulate maternal behavior. Female rats, hysterectomized and ovariectomized on day 16 of pregnancy, received estrogen implants in the Lhb or, as a positive control, in the medial preoptic area (MPOA). An additional control group received cholesterol implants in the Lhb. All females were tested for pup retrieval, nest building, crouching behavior, locomotor activity, and carrying behavior. Estradiol implants into the Lhb did not stimulate the onset of maternal behavior. Females with estrogen implants in the Lhb scored significantly lower in pup retrieval and crouching behavior compared to females with implants in the MPOA and were not significantly different from females with cholesterol implants in the Lhb. There were also no significant differences in overall activity or carrying behavior among the groups.

Effects of long-term estrogen implants in beef heifers.

Crossbred beef heifers (n = 78) were assigned randomly to one of three treatments. Heifers received either no implant, one estradiol-releasing implant (Compudose), or two estradiol-releasing implants. Heifers were implanted at birth and then reimplanted every 150 d. Calves were maintained with the cows until weaning at approximately 200 d of age. Heifers were placed in the feedlot as one group and fed a growing diet for 56 d. Following the growing phase, heifers were segregated into their respective treatment groups and fed until selected by industry buyers for harvest. Beginning at 1 yr of age and continuing every 14 d until puberty or harvest, heifers were palpated per rectum, and blood samples were collected for determination of ovarian activity and attainment of puberty. Serum progesterone of > or =1 ng/mL and(or) palpation of a detectable corpus luteum were criteria of puberty. At weaning and again at harvest, an x-ray was taken of the left front leg of six heifers selected randomly from each group. Metacarpal bones III and IV from the same animals were collected at harvest and transected for determination of epiphyseal plate closure. The x-ray scores and the actual measurements had a correlation of .94. Epiphyseal plate closure occurred in a dose-related manner, with heifers on the higher dose of estrogen having earlier plate closure than heifers on the lower dose. At harvest, reproductive tissues and carcass data were collected for all heifers. Eighteen of 25 untreated control heifers (P < .05), 6 of 26 heifers treated with one implant, and 2 of 26 heifers treated with two implants attained puberty by the end of the experiment. No differences (P > .10) were detected among treatment groups for carcass traits. These data suggest that early and continuous treatment of heifers with estradiol implants can retard reproductive function.

Estrogen-mediated neuroprotection after experimental stroke in male rats.

We have previously shown that 17beta-estradiol reduces infarction volume in female rats. The present study determined whether single injection or chronic implantation of estrogen confers neuroprotection in male animals with middle cerebral artery occlusion (MCAO) and whether there is an interaction with endogenous testosterone. Male Wistar rats were treated with 2 hours of reversible MCAO. In protocol 1, acute versus chronic estrogen administration was examined in groups receiving the following: Premarin (USP) 1 mg/kg IV, immediately before MCAO (Acute, n=13, plasma estradiol=171+/-51 pg/mL); 7 days of 25 microg (E25, n=10, 10+/-3 pg/mL) or 100 microg 17beta-estradiol (E100, n=12, 69+/-20 pg/mL) by subcutaneous implant; or saline (SAL, n=21, 3+/-1 pg/mL). Laser-Doppler flowmetry was used to monitor the ipsilateral parietal cortex throughout the ischemic period and early reperfusion. At 22 hours of reperfusion, infarction volume was determined by 0 2,3,5-triphenyltetrazolium chloride staining and image analysis. In protocol 2, rats were castrated to deplete endogenous testosterone and then treated with estradiol implants: castration only (CAST, n= 13, estradiol=5+/-2 pg/mL), sham-operated (SHAM, n= 10, 4+/-2 pg/mL), estradiol implant 25 microg (CAST+E25, n=16, 7+/-2 pg/mL) or 100 microg (CAST+E100, n=14, 77+/-14 pg/mL). Cortical infarct volumes were reduced in all estrogen-treated groups: Acute (21+/-4% of ipsilateral cortex), E25 (12+/-5%), and E100 (12+/-3%) relative to SAL (38+/-5%). Caudate infarction was similarly decreased: Acute (39+/-7% of ipsilateral striatum), E25 (25+/-7%), and E100 (34+/-6%) relative to SAL (63+/-4%). Castration did not alter ischemic outcome; cortical and caudate infarction (percentage of respective ipsilateral regions) were 37+/-5% and 59+/-5% in CAST and 39+/-7% and 57+/-5% in SHAM, respectively. Estrogen replacement reduced infarction volume in castrated animals in cortex (19+/-4% in CAST+E25 and 12+/-4% in CAST+E100) and in caudate (42+/-6% in CAST+25 and 20+/-7% in CAST + 100). Laser-Doppler flowmetry results during ischemia and reperfusion was not different among groups. Both acute and chronic 17beta-estradiol treatments protect male brain in experimental stroke. Testosterone availability does not alter estradiol-mediated tissue salvage after MCAO.

The effect of hormone replacement therapy on the oxidation of low density lipoprotein in postmenopausal women

The oxidative modification of low density lipoprotein (LDL) is important in the pathogenesis of atherosclerosis, and oestrogen has been shown to inhibit copper and cell mediated oxidation of LDL in vitro. We have investigated the effect of oral and transdermal oestrogens (oestradiol valerate 1 mg, conjugated equine oestrogens 0.625 mg and patches releasing 50 μg oestradiol daily), oestrogen implants (oestradiol 50 mg) and oral combined oestrogen and progestogen (oestradiol valerate 2 mg with medroxyprogesterone acetate 5 mg and oestradiol valerate 2 mg with norethisterone acetate 1 mg), on the susceptibility of LDL to oxidation in postmenopausal women (total n=56). Oxidation of LDL was initiated by the addition of copper ions, and monitored by measurement of conjugated dienes. Changes in fasting serum levels of total cholesterol, LDL, HDL and triglycerides were also evaluated, as were changes in LDL composition. Total cholesterol decreased by 5.5% ( P<0.05) with CEE, 6.8% with oestradiol implants ( P<0.05), 9.3% with oestradiol+MPA ( P<0.01) and 10% with oestradiol+norethisterone ( P<0.05). There were reductions in LDL with oral oestradiol valerate (7.8%) ( P<0.05), CEE (13.8%) ( P<0.01) and oestradiol combined with MPA (12.7%) ( P<0.05). HDL increased by 7.1% ( P<0.01) and 6.3% ( P<0.05), with oestradiol valerate and CEE respectively, and decreased by 9% ( P<0.05) with implants and by 14.7% with oestradiol combined with norethisterone ( P<0.01). Triglycerides were significantly increased with CEE (14.9%) and reduced with oestradiol implants (15.2%) (both P<0.05). While there was no change in the ratio of `cholesterol ester' to `free cholesterol' within LDL with any of the HRT preparations, a reduction in total cholesterol and cholesterol ester content of LDL occurred with transdermal oestradiol and a reduction in free cholesterol occurred with oestradiol plus MPA. Although we found a small but significant decrease in plasma hydroperoxide concentration four weeks after insertion of the oestradiol implant from 1.17±0.06 to 1.03±0.04 μmol/l ( P<0.05), we found no significant change in the lag time to oxidation, or in the maximum rate of propagation of the reaction, after treatment with any of the above forms of hormone replacement therapy. This study does not therefore support the role of oestrogens as antioxidants in vivo.

Effect of exogenous estradiol on plasma concentrations of somatotropin, insulin-like growth factor-I, insulin-like growth factor binding protein activity, and metabolites in ovariectomized angus and braham cows

To determine the effect of breed and estradiol-17β on selected hormones and metabolites, ovariectomized (⪖3 mo) Angus ( n = 14) and Brahman ( n = 12) cows were paired by age and body weight and randomly assigned as either nonimplanted controls (CON) or implanted with estradiol (E2) for 45 d. After Day 7 and through Day 42, plasma concentration of somatotropin was greater for E2 than CON cows (treatment X day, P < 0.05). During an intensive blood sampling on Day 36, E2 cows tended (P < 0.10) to have greater somatotropin pulse amplitudes than CON cows, but other parameters of somatotropin release were not affected (P > 0.10) by E2 treatment. The effect of breed was apparent on Day 36 as Brahman cows had greater (P < 0.05) somatotropin pulse amplitude, basal secretion, and mean concentration than Angus cows. Overall, plasma concentration of IGF-I was greater (P < 0.01) for E2 than CON cows (158.3 vs. 104.2 ng/ml) and was greater for Brahman than Angus cows (164.1 vs. 98.4 ng/ml). However, there was a trend (P < 0.10) for a treatment X breed X day interaction for IGF-I (i.e., the magnitude of increase in IGF-I concentration was greater in E2-Angus than E2-Brahman cows). After Day 7 and through Day 42, total plasma IGF binding protein (IGFBP) activity was greater (P < 0.01) for E2 than CON cows. Ligand blotting revealed at least five forms of IGFBP activity, and E2 cows had greater (P < 0.05) binding activity of IGFBP-3 and the 30- and 32-kDa IGFBP than CON cows. Brahman cows had greater (P < 0.05) IGFBP-3 and the 32-kDa IGFBP than Angus cows. After Day 14 and through Day 42, concentration of urea nitrogen (PUN) was greater (P < 0.001) for CON than E2 cows (treatment X day, P < 0.001). Brahman had greater (P < 0.01) PUN than Angus cows (16.6 vs. 14.2 mg/dl). Plasma concentration of glucose was greater (P < 0.01) for E2 than CON cows (78.9 vs. 76.4 mg/dl) but was not affected (P > 0.10) by breed. In summary, these data suggest that some, but not all, of the positive effects of estradiol on peripheral concentration of IGF-I and IGFBP activity can be attributed to increased somatotropin. Moreover, breed influenced basal and E2-induced secretion of somatotropin and IGF-I such that differences between Brahman and Angus cows in plasma IGF-I concentrations were abated within 3 wk of estradiol implantation. Thus, breed influences the metabolite and hormonal response of cattle to estrogenic implants.

Hypothalamic sites of action for testosterone, dihydrotestosterone, and estrogen in the regulation of luteinizing hormone secretion in male sheep.

Testosterone (T) inhibits LH secretion partly by acting at unknown sites within the brain to inhibit GnRH secretion. We tested the hypothesis that the preoptic area (POA) and arcuate-ventromedial region (ARC/VMR), areas rich in androgen and estrogen (E) receptors, are neural sites at which T and the T metabolites, dihydrotestosterone (DHT) and estrogen (E), act to suppress LH secretion. Bilateral guide cannulae were surgically implanted into either the POA or ARC/VMR of castrated male sheep. Experiments were conducted under a long day photoperiod to maximize the inhibitory effect of the steroids. In Exp 1, all sheep (n = 6/site) sequentially received bilateral implants of cholesterol (CHOL), T, or E at each site. Jugular blood samples were taken at 10-min intervals for 4 h both immediately before implant insertion and 5 days later. In Exp 2, all sheep (n = 6/site) sequentially received bilateral implants of CHOL, DHT, or E at each site according to a latin square design. Blood samples were taken before and 7 days after implant insertion. In Exp 3, which followed the same design as Exp 2, implants of E, T, or DHT were placed only in the ARC/VMR. In the final experiment, the effects of T and CHOL implants in the ARC/VMR were compared. Neither T, DHT, nor CHOL implants at either site affected LH secretion. In contrast, E treatment in the ARC/VMR suppressed mean plasma LH levels (P < 0.01), primarily due to an increase in interpulse interval (P < 0.01). Estrogen implants in the POA caused a small, but nonsignificant (P > 0.05), decrease in mean LH levels in the first experiment and an increase in LH interpulse interval (P < 0.05) in the second experiment. These results suggest that the ARC/VMR and possibly the POA are sites at which E acts to reduce GnRH secretion in male sheep.

Evidence for a direct neuronal pathway from the suprachiasmatic nucleus to the gonadotropin-releasing hormone system: combined tracing and light and electron microscopic immunocytochemical studies.

The timing and occurrence of the preovulatory luteinizing hormone (LH) surge in the female rodent are critically dependent on the integrity of the suprachiasmatic nucleus (SCN). Destruction of the SCN leads to a cessation of the ovarian cycle, whereas implantation of estrogen in ovariectomized rats results in daily LH surges. The anatomical substrate for these effects is not known. Previous studies involving lesions of the SCN have suggested the presence of a direct vasoactive intestinal polypeptide (VIP)-containing pathway to gonadotropin-releasing hormone (GnRH) neurons. To further investigate the direct connection between the SCN and the GnRH system, we have used tract-tracing with the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PhaL) in combination with an immunocytochemical staining for GnRH in light and electron microscopic studies. Small, unilateral PhaL deposits, especially when they were placed in the rostral ventrolateral portion of the SCN, revealed a bilateral projection to the preoptic area, where PhaL-immunoreactive fibers were regularly found in close apposition to GnRH neurons. Ultrastructural studies showed synaptic interaction of PhaL-containing fibers with GnRH-immunoreactive (IR) cell bodies, thus demonstrating a direct SCN-GnRH connection. Taken together, these data provide evidence for the existence of a monosynaptic pathway from the SCN to the GnRH system in the hypothalamus of the female rat. We suggest that this pathway may contain at least VIP as a putative transmitter and may play a role in the circadian regulation of the estrous cycle in the female rat.

Psychological effects of continuation versus discontinuation of hormone replacement therapy by estrogen implants: A placebo-controlled study

There is conflicting evidence regarding the effects of hormone replacement therapy (HRT) with estrogens on psychological and symptoms of menopause. Forty women already attending a menopause clinic for continuing HRT by estrogen implants were studied in a randomized, double-blind, placebo-controlled study of estrogen reimplantation versus implantation of a placebo preparation. Assessment included self rating with visual analog scales, standardized psychological and menopause rating scales (Hospital Anxiety and Depression Scale, Self-Concept Questionnaire, Cognitive Failures Questionnaire, Greene Menopause Index), and interview with the Present State Examination. No difference in outcome with regard to either psychological or symptoms was found 2 months after entry to the study between the women who received an active implant and those who received a placebo implant, in spite of the former group having a significant rise in estradiol levels. The only effect of HRT on physical symptoms was a nonsignificant reduction in flushes. Psychiatric morbidity of the study population was high with nearly half being psychiatric cases according to the Present State Examination at both initial assessment and follow-up. At entry to the study nearly all the women had levels of estradiol in the premenopausal range and four had supraphysiological levels. It appears likely that women were returning requesting a new implant because of symptoms related to nonhormonal factors. Women receiving continuing HRT for menopausal symptoms should be reassessed both for hormonal status and current psychosocial factors when they present with recurrent symptoms, especially those of a psychological or nature.

Psychological effects of continuation versus discontinuation of hormone replacement therapy by estrogen implants: A placebo-controlled study

There is conflicting evidence regarding the effects of hormone replacement therapy (HRT) with estrogens on psychological and psychiatric symptoms of menopause. Forty women already attending a menopause clinic for continuing HRT by estrogen implants were studied in a randomized, double-blind, placebo-controlled study of estrogen reimplantation versus implantation of a placebo preparation. Assessment included self rating with visual analog scales, standardized psychological and menopause rating scales (Hospital Anxiety and Depression Scale, Self-Concept Questionnaire, Cognitive Failures Questionnaire, Greene Menopause Index), and interview with the Present State Examination. No difference in outcome with regard to either psychological or psychiatric symptoms was found 2 months after entry to the study between the women who received an active implant and those who received a placebo implant, in spite of the former group having a significant rise in estradiol levels. The only effect of HRT on physical symptoms was a nonsignificant reduction in flushes. Psychiatric morbidity of the study population was high with nearly half being “psychiatric cases” according to the Present State Examination at both initial assessment and follow-up. At entry to the study nearly all the women had levels of estradiol in the premenopausal range and four had supraphysiological levels. It appears likely that women were returning requesting a new implant because of symptoms related to nonhormonal factors. Women receiving continuing HRT for menopausal symptoms should be reassessed both for hormonal status and current psychosocial factors when they present with recurrent symptoms, especially those of a psychological or psychiatric nature.

Anabolic implant effects on visceral organ mass, chemical body composition, and estimated energetic efficiency in cloned (genetically identical) beef steers.

Six sets of four genetically identical Brangus steers (n = 24; X BW 409 kg) were used to determine the effect of different anabolic implants on visceral organ mass, chemical body composition, estimated tissue deposition, and energetic efficiency. Steers within a clone set were randomly assigned to one of the following implant treatments: C, no implant; E, estrogenic; A, androgenic, or AE, androgenic + estrogenic. Steers were slaughtered 112 d after implanting; visceral organs were weighed and final body composition determined by mechanical grinding and chemical analysis of the empty body. Mass of the empty gastrointestinal tract (GIT) was reduced approximately 9% (P < .10) in steers implanted with estrogen alone or in combination with an androgen. Liver mass was increased (P < .10) from 6 to 14% by implants. Steers implanted with the AE combination had greater (P < .10) daily protein accretion (163.4 g/d) than either E (128.8 g/d) or A (137.1 g/d), and, because the combination improved gain above C (101.1 g/d), this demonstrates the additive effects of a combination implant on protein deposition. Anabolic implants did not alter (P > .10) the efficiency of ME utilization. In general, estrogenic implants decreased GIT, androgenic implants increased liver, and all implants increased hide mass. Steers implanted with an AE combination had additive effects on protein deposition compared with either implant alone. The NEg requirements for body gain are estimated to be reduced 19% by estrogenic or combination implants.

Administration of ovarian steroid hormones does not change the reward effectiveness of lateral hypothalamic stimulation in ovariectomized rats

The effect of two schedules of steroid hormone administration on the reward effectiveness of lateral hypothalamic stimulation was examined in ovariectomized Long-Evans female rats. In Experiment 1, estrogen and progesterone were administered on a 4-day schedule so as to mimic the hormonal profile of the estrous cycle; in Experiment 2, silastic implants of progesterone and estrogen were used to induce steroid hormone levels similar to those observed in mid- and late pregnancy. In both experiments, hormone administration was sufficient to induce characteristic behaviors: lordosis in Experiment 1 and a change in sucrose preference and body weight in Experiment 2. In contrast, hormone administration did not change the reward effectiveness of the electrical stimulation in either Experiment 1 or Experiment 2.

Use of genetically identical (clone) steers to determine the effects of estrogenic and androgenic implants on beef quality and palatability characteristics

Six sets of four genetically identical Brangus steers (n = 24; mean weight = 413 kg, SD = 19.8) were used to study the effects of estradiol and trenbolone acetate on beef quality and palatability characteristics. Steers in each clone set were randomly assigned to the following treatment groups: 1) a nonimplanted control; 2) a single estrogenic implant, containing 20 mg of estradiol benzoate and 200 mg of progesterone; 3) a single androgenic implant, containing 140 mg of trenbolone acetate; or 4) a single combination implant, containing 24 mg of 17-beta estradiol and 120 mg of trenbolone acetate. Following implantation, the steers were fed a high-concentrate finishing diet for a period of 112 d. Compared with control steers, implanted steers had higher (P < .05) average daily gains and heavier (P < .05) finished live weights and carcass weights. However, there were no differences (P > .05) among treatment groups with respect to their effects on growth rate, live weight, carcass weight, dressing percentage, fat thickness, longissimus muscle area, percentage of kidney, pelvic, and heart fat, or USDA yield grade. Moreover, marbling scores for implanted steers were not statistically different from marbling scores for control steers. However, a comparison among implant types showed that steers implanted with the estrogenic implant had significantly lower marbling scores than did steers implanted with the androgenic or combination implants. Use of androgenic and combination implants had no effect (P > .05) on beef tenderness of strip loin, top sirloin, or top round steaks; however, use of estrogenic implants decreased (P < .05) tenderness of top sirloin steaks.

Effect of ovarian steroids on footshock avoidance learning and retention in female mice

Mice were trained to avoid footshock in a T-maze, with retention tested one week later. Adult male CD-1 mice made their first avoidance during acquisition after fewer trials than random cycling females and with less variability. Female mice in diestrus, when plasma levels of progesterone are low, learned to avoid footshock faster than females in estrus. Ovariectomized (OVX) mice learned in fewer trials than intact random cycling mice. Similar differences, though of a smaller magnitude, were found on the retention tests (i.e. males had better retention than females, mice in diestrus showed better retention 8 days later when in the same part of the estrous cycle than thse in estrus, and OVX mice had better retention than cycling females). OVX mice with estrogen implants learned faster than those with progesterone implants or progesterone plus estrogen implants. Hormonal status did not affect sensitivity to acoustic or footshock stimuli as measured by a startle reflex, nor did it affect activity. Pretraining administration of amphetamine, picrotoxin and strychnine attenuated the impairing effect of progesterone on acquisition. The possibility that progesterone may impair learning and to some extent, retention by facilitating the GABAergic activity and thereby reducing arousal level is discussed.

Changes in bone mineral density and bone-specific alkaline phosphatase in ovariectomized ewes

An animal model of human osteoporosis which adequately meets many of the criteria needed to test new therapeutic agents is currently unavailable. The old ewe may serve this purpose, as changes in bone remodeling occur within 3 months, and a difference in bone mass has been indicated 6 months after ovariectomy. In the current study, we have measured longitudinal changes in bone mass and bone-specific alkaline phosphatase (BSAP) for six months in 7-9 year old ovariectomized (OVX) ewes. Thirty ewes were divided into three groups: sham-treated (n = 9), OVX (n = 12) and OVX with estrogen implants (OVXE, n = 9). Bone mineral density (BMD) was determined at 0, 3 and 6 months in the vertebrae (L4-L6/L5-L7), calcaneus (CAL) and distal radius (DR) using dual-energy X-ray absorptiometry (DEXA). Bone-Specific Alkaline Phosphatase (Tandem-R Ostase; Hybritech) was determined at monthly intervals. Body weight did not significantly change in any group during treatment compared to sham, although a trend of increasing body weight at 3 and 6 months was apparent in both OVX groups. Luteinizing hormone increased in all OVX ewes as a function of time as expected, demonstrating successful ovariectomies. Uterine weight was significantly increased (p < 0.01) in the OVXE animals compared to Sham and OVX groups. BMD did not change significantly during the 6-month treatment period in the CAL or DR. BMD in the vertebrae (L4-L6/L5-L7) was significantly lower in the OVX group compared to sham (p < 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of season on LH secretion in ovariectomized Australian cashmere does

An experiment was conducted to define the seasonal changes in LH secretion in ovariectomized does with oestrogen implants and the effect of immunization against melatonin. Fifteen mature Australian cashmere goats were ovariectomized and given either no further treatment or one or two implants containing oestradiol; another similar group of 15 does were immunized against melatonin before ovariectomy and oestrogen treatment. LH concentrations and livemasses were recorded every week for 2 years. Livemasses of both groups showed a distinct seasonal pattern with a summer maximum and a winter minimum irrespective of treatment. LH concentrations also showed distinct seasonal patterns with a significant interaction between the number of implants and the time of the year. In the nonimmunized does, the presence of a constant low dose of oestrogen (one implant) resulted in low concentrations of LH except from May to August, the normal period of spontaneous ovulatory activity in intact does. In contrast, nonimmunized does receiving a high dose of oestrogen (two implants) showed a rise in LH concentrations in February, and concentrations remained high until August. Immunization against melatonin abolished this differential LH secretory pattern, and both doses of oestrogen were associated with a short period of high LH concentration between May and September. These results indicate that a negative feedback effect of oestrogen results in low LH secretion for most of the year and that hypothalamic sensitivity to LH decreases for only a short period between May and August.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction by estrogens of lipid peroxidation and lipid peroxide-derived malonaldehyde-DNA adducts in male Syrian hamsters: role of lipid peroxidation in estrogen-induced kidney carcinogenesis.

Estrogen-induced kidney carcinogenesis in male Syrian hamsters has previously been postulated to be mediated by free radicals generated by redox cycling of catecholestrogen metabolites. As part of our examination of this hypothesis, we have studied the induction of lipid peroxidation and lipid peroxide-derived malondialdehyde (MDA)-DNA adducts in kidney and liver of hamsters treated with single injections of diethylstilbestrol (DES) or with estradiol (E2) implants for various lengths of time. Treatment of hamsters with 50 and 100 mg/kg DES increased concentrations of both lipid hydroperoxides and of MDA-DNA adducts. In hamsters treated with E2 implants for up to 50 days, lipid peroxide levels in liver were double control values 3 h after hormone implantation, and then decreased to plateau values of 30% over controls. Those in kidney rose to 2- to 3-fold above controls 3 days after hormone implantation and then decreased to plateau values of 51% above controls. MDA-DNA adduct levels were two or three times higher than those of controls in liver and kidney of hamsters treated with hormone implants for 3 and 7 days. Renal lipid peroxide concentrations were raised by chronic treatment with E2, but not by weakly carcinogenic estrogens ethinylestradiol or 2-fluoroestradiol. In contrast, MDA-DNA adduct levels were raised by all three steroidal estrogens 3 days after estrogen implantation. The increases in lipid peroxides and in MDA-DNA adducts in estrogen-treated hamsters support a mechanism of carcinogenesis by free radical generation via redox cycling of catcholestrogen metabolites. Lipid peroxides are postulated to play a dual role in estrogen-induced carcinogenesis, (i) as cofactors for cytochrome P450-mediated formation of catecholestrogen metabolites and their redox cycling, and (ii) as precursors of MDA, a DNA adduct-forming endogenous electrophile.

Dexamethasone-induced hyperglycemia in obese Avy/a (viable yellow) female mice entails preferential induction of a hepatic estrogen sulfotransferase.

Sex steroid sulfotransferases (ST) sulfurylate and thus inactivate estrogens or androgens, producing an androgenized or estrogenized state in the liver. The expression of diabetes in a number of animal models is sexually dimorphic and has been associated with steroidal states. Although the viable yellow (Avy) mutation produces an insulin-resistant obesity syndrome in mice of both sexes, only males develop chronic hyperglycemia. Hyperglycemia was rapidly induced in Avy/a females by dexamethasone (dex). This treatment completely suppressed both endogenous plasma corticosterone and hepatic corticosterone-binding globulin (CBG) mRNA within 24 h. Hyperglycemia in dex-implanted Avy/a females was accompanied by aberrant shifts in hepatic androgen/estrogen balance. This was effected by induction of estrogen sulfotransferase (EST) mRNA together with a > 10-fold increase in enzymatic activity. Similar dex-induced increases in androgen ST or phenol ST were not observed. Prior implantation of estrogen prevented development of hyperglycemia. The time-dependent spontaneous reversal of dex-induced hyperglycemia correlated with re-expression of CBG mRNA transcripts and reduced levels of EST transcripts and enzyme activity. Although dex-induced hyperglycemia was limited to Avy/a females, dex elicited hyperinsulinemia in lean a/a control mice of both sexes and exacerbated constitutive hyperinsulinemia in Avy/a males and females. In summary, dex-induced hyperglycemia in Avy/a females was associated with increased catabolism of hepatic estrogens mediated by induction of EST.

Preferential induction of c-fos immunoreactivity in vasoactive intestinal polypeptide-innervated gonadotropin-releasing hormone neurons during a steroid-induced luteinizing hormone surge in the female rat

In small rodents, reproduction is critically dependent on the integrity of the circadian oscillator of the brain, the suprachiasmatic nucleus (SCN). Lesions of the SCN induce persistent estrus (anovulation) in intact female rats, whereas estrogen implantation in ovariectomized rats results in daily LH surges, which disappear after SCN lesions. Vasoactive intestinal polypeptide (VIP), a peptide synthesized in cell bodies of the SCN, has been implicated in the regulation of LH release. Recently, we have provided immunocytochemical evidence for a VIP-containing neuronal projection from the SCN to the GnRH system. This suggests that VIP from the SCN may modulate LH release via a direct influence on GnRH neurons. To investigate the involvement of VIP input on GnRH neurons and SCN neurons in the generation of a LH surge, we used immunoreactive c-fos as a marker for cell activation in ovariectomized mature rats and immature rats treated with steroids. VIP-containing fibers were observed in apposition to a substantial portion of the GnRH neurons containing c-fos. Expression of c-fos was more frequently observed in VIP-innervated GnRH neurons than in GnRH neurons in general. This difference in activation was most pronounced during the onset of the LH surge. In SCN neurons, steroid treatment did not induce c-fos immunoreactivity before or during the LH surge. The present results indicate that VIP-containing fibers, possibly originating in the SCN, are involved in the initiation of the LH surge. In view of the reported inhibitory effects of VIP on LH release, it is suggested that the role of VIP input in this respect is permissive.

Preferential induction of c-fos immunoreactivity in vasoactive intestinal polypeptide-innervated gonadotropin-releasing hormone neurons during a steroid-induced luteinizing hormone surge in the female rat.

In small rodents, reproduction is critically dependent on the integrity of the circadian oscillator of the brain, the suprachiasmatic nucleus (SCN). Lesions of the SCN induce persistent estrus (anovulation) in intact female rats, whereas estrogen implantation in ovariectomized rats results in daily LH surges, which disappear after SCN lesions. Vasoactive intestinal polypeptide (VIP), a peptide synthesized in cell bodies of the SCN, has been implicated in the regulation of LH release. Recently, we have provided immunocytochemical evidence for a VIP-containing neuronal projection from the SCN to the GnRH system. This suggests that VIP from the SCN may modulate LH release via a direct influence on GnRH neurons. To investigate the involvement of VIP input on GnRH neurons and SCN neurons in the generation of a LH surge, we used immunoreactive c-fos as a marker for cell activation in ovariectomized mature rats and immature rats treated with steroids. VIP-containing fibers were observed in apposition to a substantial portion of the GnRH neurons containing c-fos. Expression of c-fos was more frequently observed in VIP-innervated GnRH neurons than in GnRH neurons in general. This difference in activation was most pronounced during the onset of the LH surge. In SCN neurons, steroid treatment did not induce c-fos immunoreactivity before or during the LH surge. The present results indicate that VIP-containing fibers, possibly originating in the SCN, are involved in the initiation of the LH surge. In view of the reported inhibitory effects of VIP on LH release, it is suggested that the role of VIP input in this respect is permissive.