ISSN:0028-3835    

DOI:10.1159/000125641

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The aim of this study was to establish whether the nocturnal peak concentrations of circulating melatonin are affected by a single dose of 7,12-dimethylbenz[a]anthracene (DMBA) in female Sprague-Dawley rats as used for mammary tumor induction. Prior to this, the circadian rhythms of melatonin (N-acetyl-5-methoxytryptamine) and 6-sulfatoxymelatonin, the main metabolic product of melatonin, were determined in female Sprague-Dawley rats. The cosinor analysis revealed significant circadian rhythms with very similar acrophases around 1.00 a.m. for both substances. To enable explanations for possible changes in plasma melatonin after DMBA treatment, the biosynthesis in the pineal and the major metabolic product in the liver, 6-sulfatoxy-melatonin, were measured 2 and 7 days after DMBA. Plasma melatonin was depressed by 31–37% (p < 0.05) 2 and 7 days after DMBA but the pineal melatonin content remained unchanged. 2 days after DMBA, pineal serotonin and N-acetylserotonin showed a transient elevation of 35% (p < 0.025) and 25% (p < 0.05), respectively. The plasma concentrations of 6-sulfatoxymelato-nin were the same in DMBA- and vehicle-treated animals. An elevation of the 6-sulfatoxymelatonin/melatonin ratio indicated a relative increase in the metabolism of melatonin due to DMBA. The absence of an absolute increase in 6-sulfatoxymelatonin after DMBA could be caused by an additional shift within the spectrum of different metabolic products of melatonin due to the carcinogen. Possible mechanisms are discusse

ISSN:0028-3835    

DOI:10.1159/000125642

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The effects of dopamine (DA) on voltage-dependent potassium currents were investigated in rat lactotrophs maintained in primary culture. Lactotroph cells were identified using the reverse hemolytic plaque assay. Membrane currents and potentials of lactotroph cells were recorded using the patch-clamp recording technique in the ‘whole-cell’ configuration. In the presence of cobalt (2 mM), two types of voltage-dependent K+currents were recorded, a voltage-activated delayed K+ current (IK) and a voltage-activated transient K+current (IA). The current IK was activated at membrane potentials varying from –20 to + 40 mV and did not inactivate during prolonged voltage steps (up to 25 s); it was blocked by tetraethylammonium (10 mM). The current IA was activated at membrane potentials higher than –45 mV and showed a voltage-dependent inactivation between –110 and –40 mV; it was slightly inhibited by 4-aminopyridine (5 mM). Under current-clamp conditions, the majority of the cells (60%) showed spontaneous Ca2+-dependent action potentials (APs) while silent cells (40%) were excitable by depolarizing current pulses. Bath application of 10 nM DA evoked a hyperpolarizing response, blocked spontaneous APs and decrease the amplitude of evoked APs. Only the hyperpolarizing response faded during the course of the whole cell recording experiments. Under voltage-clamp conditions, DA induced a reversible increase in both voltage-dependent outward K+ currents, without modifying their thresholds. Steady-state inactivation of IA was not affected by DA. These DA-induced responses were dose-dependent and they involved D2 receptor activation. They were mimicked by the specific D2 receptor agonist bromocriptine (10 nM) and blocked by the specific D2 receptor antagonist sulpiride (100 nM), the D1 antagonist SCH 23390 being ineffective. The ability of DA to increase voltage-dependent K+ currents cannot be observed without GTP in the recording pipette. It was pertussistoxin-sensitive but was affected neither by bath application of 1 mM for skolin nor by the presence of 500 µM cyclic AMP with 500 µM 3-isobutyl-l-methylxan-thine in the pipette solutions. We conclude that in lactotroph cells DA specifically increases two voltage-dependent K+ currents via a pertussis-toxin-sensitive guanine nucleotide regulatory protein and appears to be independent of intracellular cyclic AMP. This effect leads to a decrease in the excitability of the cell, explaining in part the inhibitory effect of DA on prol

ISSN:0028-3835    

DOI:10.1159/000125650

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Prenatal plus neonatal administration of methimazole (MMI), a procedure provoking marked hypothyroidism in rats, increased by about 100% the thymic content of oxytocin and severely (by approximately 80%) decreased the thymus weight, compared to euthyroid counterparts. Adult-onset, propylthiouracyl (PTU)-induced hypothyroidism, while provoking thymic involution, or thyroxine (T4) hyperthyroidism, did not affect oxytocin concentrations. Thymic involution and increases in thymus oxytoxin could also be obtained with repeated administration of the potent glucocorticoid dexamethasone. However, since corticosterone, unless subchronically injected at largely supraphysiological doses, was previously shown to have no influence on thymic parameters of young adult rats, a major involvement of the neonatal adrenal axis in oxytocin alterations could be excluded. It is suggested that the ontogenesis of thymic oxytocin production is under thyroid control.

ISSN:0028-3835    

DOI:10.1159/000125643

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The use of magnetic beads coated with anti-IgG antibodies should allow simultaneous purification and depletion of differing anterior pituitary cell types labelled with anti-hormone antibodies. This technique would be expected to give very similar results to fluorescence-activated cell sorting (FACS). Magnetic bead separation of dispersed, labelled anterior pituitary cells is cheap, easy and quick to perform (time from the end of anti-hormone antibody labelling to completion of purification is approximately 30 min) and the resulting cells are viable for at least 24 hours after purification. While the cell recovery for beads and FACS, 94% (SEM ± 4.4) vs. 89% (SEM ± 3.9) and purity of 88% (SEM ± 2.2) vs. 96.7% (SEM ± 1.7) for lactotrophs and purity of 87% (SEM ± 1.9) vs. 98% (SEM ± 1) for somatotrophs are similar, the results for depletion by the magnetic bead separation method are disappointing, only 30–40% of the labelled lactotrophs or somatotrophs cells bind to the beads and thus only a sub-population of cells may be purified by this method. These results are explicable on the basis of the sensitivity of the two techniques. Pituitary cells co-incubated with two specific anti-prolactin antibodies (one raised in rabbit and one in sheep) demonstrate that removal by Dynal magnetic beads (coated with rabbit IgG antibody) of those prolactin molecules bound to the rabbit anti-prolactin antibody also removed those prolactin molecules bound to a sheep anti-prolactin antibody. In contrast, co-incubating cells with the rabbit anti-prolactin antibody and a sheep anti-growth hormone antibody did not remove growth hormone labelling when the prolactin bound to the beads was removed. We hypothesise that during exocytosis at 4 °C, the hormone core of the secretory granule is transiently trapped within the lipid bi-layer of the surface membrane prior to discharge and it is at this point that the intact hormone core is labelled with the anti-hormone antisera. Removal of the prolactin core by the bead separation technique would simultaneously remove the prolactin bound to the sheep anti-prolactin antibody yet in no way affect growth hormone which might be present on a neighbour

ISSN:0028-3835    

DOI:10.1159/000125644

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The relationship between noradrenergic (NA) stimulatory and γ-aminobutyric acid (GABA)-mediated inhibitory systems in the control of luteinizing hormone (LH) secretion was examined in ovariectomized rats. Stimulation of the GABAA receptor by an intraventricular (i.c.v.) administration of a GABAA agonist, muscimol, significantly attenuated the LH secretory response to the subsequent i.c.v. injection of NA in estrogen-primed rats. On the other hand, blockade of α-adrenergic receptors by phenoxybenzamine did not interfere with the stimulatory effect of an i.c.v. injection of a GABAA antagonist bicuculline. In a different series of experiments, ovariectomized animals had been treated with i.c.v. injections of 6-hydroxydopamine (6-OHDA) or its vehicle. An i.c.v. injection of muscimol or phentolamine significantly inhibited the estrogen-induced surge of LH secretion in vehicle-treated rats. Muscimol also inhibited the existing pulsatile LH secretion in vehicle-treated, estrogen-unprimed animals. In animals in which hypothalamic NA terminals were presumed to be destroyed by 6-OHDA, the inhibitory effect of phentolamine was significantly diminished while that of muscimol was unaltered. These results permit the following conclusions: (1) the central GABAergic system inhibits LH secretion via GABAA receptors; (2) this inhibitory GAB A system operates without mediation by the NA system, and (3) the GABAergic non-NA-mediated system can affect physiological patterns of pituitary LH secretion in female rat

ISSN:0028-3835    

DOI:10.1159/000125645

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Medroxyprogesterone acetate (MPA), a synthetic progestin that reduces plasma testosterone levels, has been used in the treatment of male sex offenders. It also reduces the sexual activity of male macaques. To investigate its sites and mechanisms of action, 11 adult male cynomolgus monkeys were castrated and 7 and 21 h later were pretreated with 20 mg progesterone s.c. (Prog, n = 3), or 5 mg dihydrotestosterone propionate s.c. (DHTP, n = 3) or oil vehicle (controls, n = 5). Twenty-four hours after castration, all males were injected i.v. with 5 mCi [3H]-MPA, and killed after 60 min. Left halves of the brains were processed for thaw-mount autoradiography to identify the neurons accumulating radioactivity, and right halves were analyzed by high performance liquid chromatography (HPLC) to measure the uptake of [3H]-MPA in nuclear fractions. In males pretreated with oil, there were labeled neurons in the ventromedial nucleus (n.), arcuate n., medial preoptic n. and anterior hypothalamic area. In progester-one-pretreated males, labeling was reduced by 84–100% compared with controls (p < 0.001), but in DHTP-pretreated males there was no effect, and labeling was not significantly different from control levels. Nuclear concentrations of [3H]-MPA measured by HPLC in controls were highest in the hypothalamus, amygdala, preoptic area and pituitary gland. Pretreatments with progesterone reduced the nuclear concentrations of [3H]-MPA in hypothalamus, preoptic area and pituitary gland by 82–95% compared with controls (p < 0.05), but DHTP pretreatments had no effect. Progesterone pretreatments did not reduce concentrations of [3H]-MPA in blood or in tissue supernatants, and the blockade of labeling appeared to be limited to nuclear uptake mechanisms. Results indicated that MPA was bound predominantly to progestin and not androgen receptors in neuronal nuclei, suggesting that the effects of MPA in the brain of the male primate may be mediated by progestin-target neur

ISSN:0028-3835    

DOI:10.1159/000125646

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

We have previously demonstrated that neurons in the rostral arcuate nucleus expressing the messenger RNA (mRNA) for pro-opiomelanocortin (POMC) are responsive to modulation by physiological levels of testosterone. It is uncertain, however, whether testosterone’s action is mediated through direct activation of androgen receptors or through aromatization to estradiol and subsequent binding to estrogen receptors. We examined this question by evaluating the effectiveness of estradiol and dihydrotes-tosterone (DHT), a nonaromatizable androgen, in reversing the castration-induced diminution of POMC mRNA in the arcuate nucleus. Using in situ hybridization, we measured POMC mRNA content within arcuate neurons of intact, castrated, castrated testosterone-replaced, castrated estradiol-replaced, and castrated DHT-replaced male rats. Adult male rats were castrated and implanted (s.c.) with a Silastic capsule filled to one of the following specifications: crystalline testosterone (30 mm; n = 4); 17β-estradiol (E2) diluted 1:1 with cholesterol (5 mm; n = 4); DHT (40 mm; n = 4); or empty (30 mm; n = 4). Control, sham-operated animals (n = 4) were left intact. Analysis of the results showed that following castration, POMC mRNA content was significantly reduced in cells of the arcuate nucleus (intact: 152 ± 3 grains/cell vs. castrate: 110 ± 3 grains/cell). Replacement with physiological levels of testosterone prevented the decline in POMC mRNA levels (castrated testosterone-replaced: 143 ± 6 grains/cell), as did replacement with physiological levels of estrogen (castrated estrogen-replaced: 149 ± 8 grains/cell). Treatment with DHT failed to prevent the postcastration decline in POMC mRNA content (castrated DHT-treated: 118 ± 4 grains/cell). These results show that whereas testosterone and estrogen prevent the postcastration decline in POMC mRNA, the nonaromatizable androgen DHThad no such effect. Based on these observations, we conclude that the ability of testosterone to stimulate POMC gene expression is likely to be mediated through aromatization and subsequent activation of estrogen re

ISSN:0028-3835    

DOI:10.1159/000125647

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The central actions of atrial natriuretic peptide (ANP) in rats include inhibition of arginine vasopressin (AVP) release, and less consistently, ACTH suppression and hypotension. To explore any such inhibitory actions on basal and stimulated levels of AVP and ACTH, we have studied the effect of intracerebroventricular (ICV) infusion of ANP on the hemodynamic and hormonal response to acute hemorrhage in conscious sheep. Two groups of 5 sheep received rat ANP(101–126) by ICV infusion (0.5 µg bolus followed by 0.5 µg/h for 3 h, or 5 µg bolus followed by 5 µg/h for 3 h) as well as artificial cerebrospinal fluid control infusions in random order. One hour after the start of the ICV infusion, acute hemorrhage (15 ml/kg BW within 10 min) was performed. Basal levels before hemorrhage of mean arterial pressure (MAP), heart rate and plasma hormones were unaltered by either dose of ICV ANP. After hemorrhage, the fall in MAP and rise in heart rate were similar in each group. However, compared to control infusions the response to hemorrhage of ACTH (433 ± 147 to 2,175 ± 588 vs. control 541 ± 103 to 893 ± 244 ng/1; p < 0.016) and angiotensin II (AII) (18 ± 3 to 94 ± 23 vs. control 18 ± 4 to 58 ± 8 pmol/l; p < 0.001) were significantly greater during high-dose ANP infusion. Although peak AVP levels more than doubled those observed on the control day, the increase did not reach statistical significance (p < 0.1053). Plasma concentrations of cortisol, aldosterone, epinephrine and norepinephrine were not significantly different in control and ANP-treated groups. In conclusion, while central ANP infusion does not alter basal hemodynamic or hormone levels in sheep, the ACTH, AII and AVP responses to hemorrhage are increased. Since the augmented hormone response cannot be attributed to vasodepression, activation by ANP of a central facilitator (such as brain norepinephrine) or suppression of an inhibitor (such as brain natriuretic peptide or opioids

ISSN:0028-3835    

DOI:10.1159/000125648

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

It was shown previously that the severity of motoneuron loss induced by nerve transection in rats 3 or 6 weeks of age was correlated inversely with the level of testosterone in circulation [Yu, W.H.A., Exp. Neurol. 102: 230–235, 1988], and that administration of testosterone to female rats attenuated axotomy-induced neuronal cell loss in a dose-dependent manner [Yu, W.H.A., J. Neurosci. 9: 3908–3914, 1989]. The present study was undertaken to examine whether elevation of the level of plasma testosterone in gonadally intact male rats by exogenous testosterone would likewise reduce neuronal cell loss. Following unilateral transection of the hypoglossal and facial nerves at 3 or 6 weeks after birth, rats received subcutaneous injections of 0.5, 1.0, or 2.0 mg testosterone propionate (TP) dissolved in 0.1 ml sesame oil or an equal volume of vehicle alone twice weekly for the first 4 postaxotomy weeks, and once weekly thereafter for additional 6 weeks. Results indicated that males axotomized at 3 weeks of age and treated with 1.0 or 2.0 mg TP had nearly twofold greater neuronal cell loss than oil-treated controls. The resultant cell loss was similar to that of castrated males or females without TP treatment despite the fact that TP treatment significantly elevated the plasma testosterone level. Neuronal cell loss in males axotomized at 6 weeks of age, however, was unaffected by TP treatment. Although testicular atrophy was noted in all TP-treated rats, the damage appeared to be greater in the testis of the 3-week-old than that of 6-week-old rats, as manifested by the castration-like effect of neuronal cell loss in prepubertal rats. It is concluded that testosterone treatment could not totally eliminate neuronal cell loss from axotomy and that the presence of normal, functioning testes is essential for potentiating the effect of testosterone on neuronal survi

ISSN:0028-3835    

DOI:10.1159/000125649

出版商:S. Karger AG    

年代:1990

数据来源: Karger