摘要:

The hypothesis that progesterone (P) activates estrous behavior in estrogen-primed female rats via a protein synthetic mechanism was examined. The protein synthesis inhibitor anisomycin was applied intracerebrally via 28-gauge bilateral implants to neural sites implicated in the mediation of estrous responsiveness. Results showed that anisomycin blockade of P-activated estrous behavior was neural site specific. Animals with anisomycin placed in the ventromedial hypothalamus (VMH) (n = 27) showed low levels of lordosis and solicitation behavior 4 h after the subcutaneous administration of 500 µg P, whereas animals with anisomycin implants in the preoptic area (n = 11) or the midbrain area in the region of the interpeduncular nucleus (n = 11) displayed high levels of estrous behavior. No deficits in open-field activity were observed following localized anisomycin treatment, and all animals appeared to be healthy. Results of the present study are consistent with the hypothesis that P acts to promote estrous behavior via a receptor-mediated genomic protein synthetic mechanism, and provide additional evidence that the VMH is the primary site of P action

ISSN:0028-3835    

DOI:10.1159/000123914

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Vasopressin analogs, which markedly differed in the ratio of pressor versus antidiuretic activity and also in ACTH/β-endorphin-releasing activity, were used in the present study. The ability of vasopressin and these analogs to enhance the release of adrenocorticotropin- (ACTH-IR) and β-endorphin-like immunoreactivity (β-EI) induced by synthetic ovine corticotropin-releasing factor –CRF–(1–41)– was studied in vitro using incubated rat anterior pituitary quarters. Arginine vasopressin (AVP) potentiated the action of CRF-(1–41) 2- to 4-fold. Vasopressin analogs, which possess direct CRF-like activity when given alone, also enhanced β-EI release caused by CRF-(1–41); the lowest concentration able to potentiate CRF-(1–41) activity was closely correlated with the EDso value of these analogs for direct CRF-like activity. The vasopressin analog 1-(β-mercapto-β, β-cyclopentamethylenepropionic acid)-2-(O-methyl)tyrosine-8-arginine-vasopressin blocked the release of ACTH-IR induced by AVP; however, this analog failed to prevent the potentiation by AVP of ACTH-IR release caused by CRF-(1–41), but enhanced itself the action of CRF-(1–41). Two analogs, which exhibited no direct CRF-like activity and which also did not antagonize the CRF-like activity of AVP, markedly enhanced the ACTH-IR and β-EI response to CRF-(1–41). These data indicate that the potency of vasopressin analogs to enhance the action of CRF-(1–41) is not related to their reported vasopressor or antidiuretic activity and provide some evidence that the structural requirements for potentiation by vasopressin of CRF-(1–41) action may be different also from those parts of the vasopressin molecule which confer the ability to induce ACTH-IR/β-EI rele

ISSN:0028-3835    

DOI:10.1159/000123915

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Recent reports on the effects of progesterone on the frequency of pulsatile LH release in several species have compelled a reevaluation of the regulation of pulsatile LH secretion by gonadal steroids in the rat. Long-term ovariectomized (OVX) adult rats were given Silastic implants filled with estradiol-17β in oil, and blood samples were taken every 5 min for 3 h, either 1 or 2 days later. Compared with the control group (empty Silastic capsules), estrogen-treated animals had significantly lower mean plasma LH concentrations, because of a significant increase in the time between pulses, pulse amplitude not being significantly affected. In a second experiment, it was determined that progesterone alone had no significant effect on pulse amplitude, frequency or mean plasma LH concentrations. In a third experiment, OVX animals received estrogen-filled (or empty) capsules on 1 day followed by progesterone-filled (or empty) capsules on the next day, and frequent blood samples were taken on the following day. Two-way analysis of variance showed significant inhibitory effects of estrogen on mean LH levels, pulse amplitude and pulse frequency. Progesterone lowered the pulse amplitude significantly, but had no effect on pulse frequency, unlike its reported effects in other species. There were no significant interactions between estrogen and progesterone on any parameter tested, indicating that there is no synergism between the two steroids under these conditions. We conclude that estrogen is the principal ovarian hormone restraining LH secretion in the long-term OVX rat and that progesterone has only a modest effect, even in the presence of estrogen

ISSN:0028-3835    

DOI:10.1159/000123916

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The dependence of periovulatory gonadotropin secretion on LHRH was assessed with the use of a potent LHRH antagonist [ALHRH; (Nac-L-Ala1, p-Cl-D-Phe2, D-Trp3,6) LHRH]. Blood samples were collected hourly from 14.00 h proestrus (P) through 09.00 h estrus (E) from intact cycling female rats. ALHRH was administered at 09.00 or 13.00 h Pbefore the proestrous increases in gonadotropins had commenced or at 23.00 h P after the LH and primary FSH surges had occurred but preceding the secondary FSH surge. Antagonist given at 09.00 or 13.00 h P completely blocked the LH release with levels remaining undetectable in most animals (<30 ng/ml) throughout the sampling period. However, administration of antagonist at these times failed to block completely the primary FSH surge although peak values were reduced when compared with controls, which displayed normal gonadotropin surges. In addition, ALHRH administered at 23.00 h failed to alter the magnitude or other characteristics of the secondary FSH surge when compared with controls.

ISSN:0028-3835    

DOI:10.1159/000123917

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In the present experiment we used push-pull perfusion (PPP) on-line with high performance liquid chromatography with electrochemical detection (HPLC-EC) to measure the concentration of neuroactive substances collected in perfusates from the caudate nucleus (CN) of conscious, freely moving rats. To validate the suitability of such an approach, both chromatographic and biological procedures were used. The chromatographic performances of four pure standards, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-HIAA) were examined under the conditions of the experiment and the release of these four chemicals by amphetamine (AMPH) locally infused into the CN or systemically administered to conscious rats used as an index of biological validation. Distinct dose-response curves were obtained for each standard injected into the HPLC-EC singly or mixed together in perfusion medium (modified Krebs-Ringer’s Phosphate, KRP, pH 7.4). Moreover, each standard in the chromatogram appeared as a well-defined elution band with a different retention time. The brain perfusate samples did not contain factors interfering with the normal operation of the HPLC-EC or measurement of the the concentration of added standards. The recovery of pure DA, DOPAC, 5-HIAA and HVA added to the perfusate samples was 97, 87, 98 and 114%, respectively. No decrements in peak heights were observed in the chromatograms when a 1-ng dose mixture of the four standards dissolved in medium and maintained at 4°C was injected into the HPLC-EC at regular intervals for a 60-min period after initial preparation. In addition, similar concentration levels of DA (8.03 ± 0.72 vs. 8.51 ± 0.62 ng/mg) were detected in male rat corpus striatum (CS) fragments extracted with either perfusion medium or with 0.1 VHCIO4; however, higher levels of DOPAC were found using perfusion medium than 0.1 N NClO4 (1.85 ± 0.16 vs. 1.15 ± 0.15 ng/mg). To validate biologically the preparation, AMPH was infused either locally into the CN or administered systemically. Infusion of this psychostimulant directly into the CN of a diestrous rat evoked a clear dose-response in DA output (from a basal level of 10–15 pg/min to a maximum of 150 pg/min) without modifying HVA or 5-HIAA output. However, an apparent decrease in DOPAC output immediately following the 10–6 M dose of AMPH was noticed. When two consecutive doses of AMPH (10–3 M) were infused into the CN of a diestrous rat at 2-hour intervals, similar increases in DA output were recorded. The basal and AMPH-stimulated output of DA from the CN of proestrous and diestrous rats were also estimated by measuring the concentration of this amine in perfusate samples with an already validated radioenzymatic assay (REA). Comparable data was obtained (5–15 pg/min, DA basal output), corroborating the authenticity of DA determinations by HPLC-EC. In addition, when AMPH was administered intraperitoneally the expected changes in behavior and DA output were also observed in a fully awake diestrous rat. Therefore, the present data based on chromatographic and biological validations indicate that the PPP on-line with HPLC-EC can be used advantageously to examine the effect of drugs and hormones in the in vivo output of several neuroactive substances from the CN of conscious, freely moving rats. Moreover, it will be possible to correlate behavioral events with in vivo output of bio

ISSN:0028-3835    

DOI:10.1159/000123918

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Previous experiments showed that haloperidol (Haldol) blocked LH release and ovulation when injected on the day of proestrus in the female rat. The present studies were designed to investigate the mechanism of Haldol blockade and the possibility that bromocriptine (CB) might counteract the effect. One hour prior to subcutaneous injection of an effective dose of Haldol (0.25 mg/kg at 09.30 h), CB was injected intraperitoneally at one of four doses (2.5, 5.0, 7.5, or 10.0 mg/kg at 08.30 h). Bromocriptine was effective at restoring LH release and ovulation, and the optimal dose for this particular experiment was found to be 7.5 mg/kg. The highest dose (10.0 mg/kg), however, resulted in no significant increase in ovulation. Treating animals with CB (5.0, 10.0, or 20.0 mg/kg at 08.30 h) followed by control vehicle showed that high doses of CB caused a significant inhibition of LH release and ovulation. After 20.0 mg/kg there was no significant surge of LH, and although ovulation did occur it was significantly suppressed when compared to control animals (p = 0.017). These results showed that appropriate doses of CB counteract the Haldol blockade of LH release and ovulation. The suppression of Haldol-induced PRL secretion by low-dose CB, without the significant restoration of ovulation, supported the hypothesis that the Haldol blockade was mediated via a direct effect of Haldol on central nervous system control mechanisms. While CB alone exerted a profound inhibition of PRL at low doses, it had no effect on LH release. CB at high doses, however, was inhibitory to both LH release and ovulation.

ISSN:0028-3835    

DOI:10.1159/000123919

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Male rats aged between 15 and 75 days were orchidectomized or only anesthetized. After various periods from 2 h to 42 days, 8 animals of both groups were sacrificed. Serum concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) as well as the hypothalamic luteinizing hormone-releasing hormone (LHRH) content were determined by radioimmunoassay. At the times studied within 15 days of castration, no significant change in hypothalamic LHRH content was observed in rats orchidectomized at 21 days of age. However, when studied 3–6 weeks after castration, those animals showed a reduced hypothalamic LHRH content. No differences were observed between anesthetized and orchidectomized rats aged 15,18 or 21 days and studied 1 week later. In contrast, castration of 75-day-old rats resulted in a significant reduction of the hypothalamic LHRH content after 2–15 days. A significant decrease was also observed 1 week after orchidectomy of rats aged 24–50 days. 1 day after orchidectomy, LH and FSH serum levels were markedly increased in 21- as well as 75-day-old rats. In the latter, serum LH concentrations did not change any further whereas in the former a plateau was only seen after 1 week. In rats orchidectomized at various ages ranging from 15 to 50 days, no consistent differences appeared in serum gonadotropin concentrations evaluated 7 days later. According to these data, variations in hypothalamic LHRH content after orchidectomy differ according to age and maturity. In 15- to 21-day-old rats, the age-related increase in hypothalamic LHRH content was not immediately affected by castration as it was in older animals. This might suggest that (1) changes in sensitivity to gonadal factors according to age are primarily localized in the hypothalamus, (2) some maturational processes in the hypothalamus are not dependent on the presence of gonadal fa

ISSN:0028-3835    

DOI:10.1159/000123920

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Infusion of oxytocin into one vertebral artery of anesthetized dogs did not alter plasma vasopressin concentration, blood pressure or heart rate. However, there was a significant (p < 0.01) increase in plasma renin activity (PRA; Δ = 7.6 ± 2.3 ng/ml · h). A 35% hemorrhage caused blood pressure to fall by 9.4 ± 4.0 mmHg (p < 0.01) and PRA to rise by 8.8 ± 2.7 ng/ml · h (p < 0.05). In 8 dogs that were subjected to a similar hemorrhage and that also received an intravertebral infusion of oxytocin, blood pressure was maintained and PRA increased by 14 + 4.3 ng/ml · h (p < 0.05). Heart rate and plasma vasopressin responses were similar in both hemorrhage groups. The results indicate that oxytocin prevented the fall in blood pressure associated with a hemorrhage, possibly by increasing renin r

ISSN:0028-3835    

DOI:10.1159/000123921

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Male Sprague-Dawley rats were maintained on either a normal or low-sodium diet for 5 weeks to examine whether dietary sodium restriction alters angiotensin II (Ang II) receptors. The receptor sites in the hypothalamus-thalamus-septum (H-T-S) region of the brain, the adrenal glands and bladder visceral smooth muscle were measured by saturation isotherm binding assays using 125I-Ang II. Compared to control rats, the low-sodium diet group showed a smaller weight gain, reduced water intake, elevated hematocrit, and decreased urinary sodium concentration. In addition, sodium-depleted rats had a 10-fold elevation in plasma renin activity. However, neither binding affinity of 125I-Ang II to the brain H-T-S region nor its density was significantly different between the two groups. In contrast, both the 125I-Ang II binding density and dissociation constant in the adrenal gland were significantly elevated, while the binding density of 125I-Ang II in the bladder smooth muscle was significantly decreased in the sodium-restricted group. These results suggest that dietary sodium depletion does not alter Ang II receptors in the rat brain areas wherein Ang II exerts the majority of its central actions.

ISSN:0028-3835    

DOI:10.1159/000123922

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The developmental pattern of hypophyseal luteinizing hormone (LH) during fetal and early postnatal life, and the capacity of fetal and early postnatal pituitaries to synthesize, release and store LH in the absence of any hypothalamic influence were investigated. Pituitary radioimmunoassayable LH was detectable by fetal day 12; its level remained low up to fetal day 17 and thereafter continued to increase up to postnatal day 2 with sharp rises occurring between day 17 and 18 of gestation and after birth. Cultured fetal and early postnatal pituitary primordia were able to synthesize, to release and store the hormone, however, the pattern of these cellular functions varied according to the animal age when explantation was performed. Data derived from cultured pituitaries showed a gradual rise in the daily hormone content of the medium between fetal day 13 to 17. From fetal day 19 onwards, however, the daily discharge of LH decreased. These findings suggest that the fetal and early postnatal pituitary has the capacity to synthesize and release LH, furthermore after a period of independent differentiation hypothalamic signals appear to be required for pituitary hormone release.

ISSN:0028-3835    

DOI:10.1159/000123923

出版商:S. Karger AG    

年代:1984

数据来源: Karger