摘要:

Normal or pregnant rats were treated orally for 21 days or throughout pregnancy with water or increasing doses of morphine and killed on days 7, 14, and 21 of pregnancy and 1 day post partum. At these time intervals, plasma, pituitary, and hypothalamic concentrations of β-endorphin and methionine enkephaline were measured in normal and pregnant rats. Moreover, pituitary and hypothalamic concentrations of the two peptides were also measured in fetuses and newborn. Plasma β-endorphin and methionine enkephalin increased significantly during pregnancy without any specific effect of morphine. Pituitary concentrations of β-endorphin were not modified either by pregnancy or morphine treatment, while methionine enkephalin concentrations increased on days 7 and 11 of pregnancy, in both water- and morphine-treated rats. The pattern of the two peptides in the hypothalamus is completely superimposable to the one present in the pituitary with the exception of an increase of β-endorphin on day 21 of pregnancy, which is more evident in control animals. Consistently with our observations in human newborn and the neurological dysfunctions we observed in them, the concentrations of both the peptides are significantly increased in the hypothalamus of fetuses and newborn of morphine-treated mothers, while in the pituitary only β-endorphin concentrations are incre

ISSN:0028-3835    

DOI:10.1159/000124897

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The effects of dopamine on proopiomelanocortin (POMC) gene expression were compared in primary cultures of the anterior and intermediate lobes of the rat pituitary. A single-stranded POMC complementary DNA was used to quantitate POMC messenger RNA levels. Treatment with dopamine (1 µM) for 48 h reduced POMC messenger RNA levels in the intermediate lobe by 77%, but had no effect on POMC gene expression in the anterior lobe. Dopamine D2 receptors were implicated in the response, as bromocriptine (100 nM) reproduced the dopamine inhibition. The responses to dopamine and bromocriptine were antagonized by haloperidol (10 µM). The decrease in POMC messenger RNA levels was dose dependent with ED50 values of about 50 and 0.1 nM for dopamine and bromocriptine, respectively. The accumulation of POMC-derived peptides, β-endorphin and α-melanocyte-stimulating hormone, over 2 days was measured by radioimmunnoassay and was shown to parallel the changes in POMC synthesis. The dopamine-induced inhibition of intermediate lobe POMC synthesis was unaffected by isoprenalin (5 µM) and corticotropin-releasing factor (10 nM), although these treatments had stimulatory effects when tested alone. Activating adenylate cyclase with forskolin (1 µM) or treatment with 8-bromocyclic adenosine monophosphate (1 mM) doubled POMC messenger RNA levels, and, when tested against these stimuli, bromocriptine still produced a 30% inhibition of POMC gene expression. These observations suggest that D2 receptor induced inhibition of POMC gene expression is not only mediated by a decrease in cyclic adenosine monophosphate levels. When cells were pretreated with pertussis toxin (100 ng/ml), the bromocriptine-induced inhibition was almost completely lost, suggesting that the dopaminergic inhibition is mediated by guanosine triphosphate binding pro

ISSN:0028-3835    

DOI:10.1159/000124898

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Median eminence (ME) luteinizing-hormone-releasing hormone (LHRH)-degrading activity (LHRH-DA) may play a role in regulating the availability of releasable LHRH. Incubation of LHRH with ME tissue supernatant yields LHRH(1-5) and LHRH(6-10) degradation fragments, as detected by high-performance liquid chromatography (HPLC) analysis, suggesting a 5–6 cleavage of the decapeptide. Since these fragments are also present after incubation of LHRH with α-chymotrypsin (α-CH), we examined the possibility that the irreversible inhibitor of α-CH, N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), might inhibit LHRH-DA and affect LHRH release. Irreversible inhibitors of trypsin-like proteases [N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), and phenylmethylsulfonylfluoride (PMSF)] were used as controls. LHRH-DA was determined by HPLC estimation of the loss of synthetic LHRH incurred when the peptide was incubated with aliquots of ME supernatant in the presence or absence of the inhibitors. LHRH release from ME fragments was assessed by radioimmunoassay after incubating the tissue with the inhibitors in Krebs-Ringer bicarbonate buffer. The LHRH-DA in both the incubation medium and the ME tissue was determined at the end of the incubation. TPCK (0.5–100 µM) added to ME tissue supernatant inhibited LHRH-DA in a dose-dependent manner. In contrast, when TPCK was added to medium in which intact ME were being incubated to assess LHRH release, the LHRH-DA of these ME was inhibited only at the 25-, 50- and 100-µM doses of TPCK, suggesting a relative inability of the inhibitor to reach endopeptidase pools in intact tissue. These same doses of TPCK increased LHRH release from the incubated ME. The effect of TPCK (at 50 or 100 µM) on prostaglandin E2 (PGE2) formation was abolished by indomethacin; however, indomethacin blocked only the effect of 50 µM TPCK, but not 100 µM TPCK, on LHRH release. This suggests that at high doses TPCK increases LHRH release through a PGE2-independent mechanism. No evidence of tissue damage after 100 µM TPCK was detected, as assessed by the absence of lactate dehydrogenase levels in the incubation medium. Neither LHRH-DA nor LHRH release were affected by TLCK or PMSF. TPCK at either a low (12.5 µM) or a high (50 µM) dose failed to enhance the effect of norepinephrine on LHRH release, indicating that 5,6 endopeptidase activity may not act acutely to regulate the pool of releasable LHRH. Our results indicate that (1) TPCK is a potent inhibitor of an endopeptidase which degrades LHRH at its Tyr5-Gly6 bond, and (2) TPCK releases LHRH from the ME not by damaging the nerve terminals or by inhibiting endopeptidase activity, but rather through activation of a cell-membrane-dependent signal transduc

ISSN:0028-3835    

DOI:10.1159/000124899

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Adrenalectomized rats displayed a deficiency in retention of an immobility response acquired during an initial 15-min forced swimming procedure (Porsolt swimming test) and measured 24 h later in a 5-min retest session. The deficit could be restored dose dependently with the glucocorticoid dexamethasone (µg range) administered 15 min after the initial test. The antiglucocorticoid RU 38486 administered subcutaneously (1 and 10 mg/kg) inhibited the dexamethasone effect and caused a parallel shift in the dose-response curve of dexamethasone. Intracerebroventricular administration of RU 38486 to intact rats immediately before the initial test attenuated retention of acquired immobility over a 100,000-fold lower dose range (ng) and increased the plasma corticosterone level. Local administration of 1 ng RU 38486 in the dentate gyrus of the hippocampus also diminished the percentage immobility, but did not influence the adrenocortical response. Injections of RU 38486 in parafascicular and paraventricular nucleus were ineffective on behaviour. In the latter nucleus the antiglucocorticoid disinhibited the activity of the hypothalamus-pituitary-adrenal axis. Intracerebroventricular pretreatment with promegestone did not interfere with RU 38486 action, ruling out involvement of its antiprogestin properties. Intracerebroventricular or subcutaneous treatment of intact rats with the antimineralocorticoid RU 28318 was not effective. Finally, adrenalectomized rats replaced with corticosterone delivered via subcutaneously implanted 100-mg corticosterone pellets showed normal behavioural performance, while a 25-mg implant did not. The present study with local infusions of RU 38486 indicates that glucocorticoid feedback via type 2 receptors exerts a long-term influence on behaviour in the hippocampus and controls the activity of the hypothalamus-pituitary-adrenal axis in the paraventricular nucleus

ISSN:0028-3835    

DOI:10.1159/000124900

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The effect of testosterone on growth hormone (GH) secretory pattern during a 6-hour continuous infusion of human GH-releasing factor (GRF) (1–44) NH2 was observed in unrestrained adult female Wistar rats. Rats had been ovariectomized or sham operated 6 weeks previously. Three weeks after the ovariectomy, the rats received sesame oil or testosterone propionate at a dose of 1 or 2 mg s.c. daily for 21 days. All rats were provided with two indwelling cannulae: one in the right atrium for undisturbed blood collection and the other in the inferior vena cava for vehicle or GRF infusion. Vehicle or GRF was administered by an infusion pump at a dose of 50 ng/kg/min for 6 h. Serial blood specimens were obtained every 20 min. Sham-operated adult female Wistar rats exhibited a high-frequency, low-amplitude pulsatile GH secretion during a 6-hour vehicle infusion. When they received a 6-hour continuous infusion of GRF, the amplitudes of GH pulses and baseline GH values were markedly augmented, but the pulse frequency remained unaltered. The GH secretory pattern during a 6-hour vehicle infusion among ovariectomized rats was similar to that of sham-operated female rats, whereas the magnitude of elevation of GH pulse and baseline level in ovariectomized rats were significantly lower than in sham-operated rats. The ovariectomized female rats that had received 2 mg testosterone for 21 days showed a low-frequency, regularly timed, high-amplitude pulsatile GH secretion, and GH values during the intervening period were low. This GH secretory pattern was indistinguishable from that in adult male rats. During a 6-hour continuous infusion of GRF, baseline GH levels in rats given testosterone were less than one tenth of those in sham-operated female rats, while the amplitudes of the GH pulses were augmented to almost three times that of sham-operated female rats. Thus, the masculine GH secretory pattern was clearly preserved and even exaggerated during the stimulation. The reversal of GH secretory pattern was dependent on the dose of testosterone. GH secretion in the presence of a continuous infusion of GRF is determined largely by phasic release of somatostatin. Therefore, our results suggest that the treatment of adult female rats with testosterone masculinizes the GH secretory pattern by reducing the frequency of intermittent diminution of somatostatin release and augmenting the inhibitory tone mediated by somatostatin during the intervening period

ISSN:0028-3835    

DOI:10.1159/000124901

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Neuronal and glial cells cultured from neonatal rat brains showed staining for both angiotensin I and II using the peroxidase-antiperoxidase method. In glial cell extracts of normotensive Wistar-Kyoto rats, the concentrations of angiotensin I and II were 12.47 ± 2.71 (n = 4) and 66.73 ± 13.28 fmol/mg protein (n = 4). Angiotensin I and II found in neuronal cell extracts of normotensive Wistar-Kyoto rats were 11.29 ± 2.99 (n = 4) and 60.25 ± 12.77 fmol/mg protein (n = 4). No significant difference was found in the concentration of angiotensin I and II in both cell types from the same rat strain. Angiotensin I concentrations of 16.83 ± 3.43 fmol/mg protein (n = 5) determined in neuronal cell extracts derived from spontaneously hypertensive rats did not differ significantly from those found in neuronal cell extracts of Wistar-Kyoto rats. However, neuronal cell extracts from spontaneously hypertensive rats revealed values of 25.19 ± 4.31 fmol angiotensin Π/mg protein (n = 4). This was significantly different (p < 0.05) and represented a 58% reduction in the angiotensin II levels in neuronal cells from spontaneously hypertensive rats compared to Wistar-Kyoto rat cultures. Angiotensin I and II measured in the growth medium containing 10% plasma-derived horse serum was below the detection limit of both radioimmunoassays. No difference in the angiotensin I and II levels was found in cells kept in serum-free medium. The angiotensin I and II immunoreactive material determined in the cell extracts could be characterized on reversed-phase high pressure liquid chromatography as (Ile5)-angiotensin I and II. (Ile5)-angiotensin III was not dete

ISSN:0028-3835    

DOI:10.1159/000124902

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Experiments were carried out to investigate the hypothalamic control mechanism for prolactin (PRL) and luteinizing hormone (LH) secretion in the female rat. Anterior medial preoptic nucleus (AMPO) or suprachiasmatic nucleus (SCN) lesions were produced by passing 5–10 µA of direct current (tip negative). Persistent estrus (PE) began as early as 6 days and as late as 30 days after electrolytic lesioning. Blood samples obtained during diestrus, proestrus and estrus revealed well-described profiles of plasma PRL and LH in sham-lesioned animals, indicating that our cannulation and blood sampling procedure had no adverse effects on the plasma hormone levels. Individual sham-operated animals sampled on successive or alternate proestrous afternoons showed precise timing of the PRL and LH surges. However, when a shift occurred in the PRL surge a comparable shift would also occur in the LH surge, indicating a coupling between the mechanisms regulating the PRL and the LH surge. The AMPO-, SCN- or combine-lesioned PE animals exhibited low basal levels of plasma PRL and LH. Small secretory bursts occurred one to three times during the 6-hour sampling periods. Animals with incomplete SCN lesions had plasma PRL titers significantly higher than the other 3 groups. Plasma progesterone levels were significantly lower in the PE animals (p < 0.01), whereas plasma estrogen levels were not significantly different from proestrous controls. These experiments indicate that during the afternoon of proestrus, the surges of plasma PRLand LH are very precise in the time of onset. Moreover, the mechanisms controlling the surge of PRL and LH are temporally coupled. Lesions of the AMPO or the SCN cause very low levels of plasma PRL in the presence of elevated plasma estrogen levels, and accumulation of LH-releasing hormone in neurons throughout the preoptic-hypothalamic continuum. In conclusion, these data indicate that the AMPO and the SCN act as a unit to initiate the surge of PRL and

ISSN:0028-3835    

DOI:10.1159/000124903

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Portions of sheep anterior pituitary lobe tissue were extracted under acid conditions and assayed for the two neurophysins (oN-III and oN-I/II) by radioimmunoassay. In all tissues examined, oN-III and oN-I/II immunoreactivi-ties were detected. Using a combination of isoelectric focusing and polyacrylamide gel electrophoresis, the neurophysins of the anterior pituitary gland behaved like oN-III and oN-I/II. oN-III of the anterior pituitary was purified by affinity chromatography and high-performance liquid chromatography. This corticotroph oN possessed an amino acid analysis similar to that of oN III and an N-terminal amino acid sequence, including residues 1–24, identical to that of authentic oN-III. These findings support the work of others who have identified neurohypophysial hormones in the anterior pituitary glan

ISSN:0028-3835    

DOI:10.1159/000124904

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Met-enkephalin concentrations in the anterior pituitary gland were shown to decline dramatically within the first 24 h after reserpine treatment, with effects apparent as early as 6 h. This was followed by subsequent repletion and late augmentation of Met-enkephalin levels 3 weeks following reserpine. Treatment with the alpha-1-adrenergic agonist me-thoxamine had no effect, whereas the alpha-1-antagonist prazosin lowered Met-enkephalin concentrations. Treatment with the dopamine agonists bromocriptine or apomorphine had no effect, but haloperidol treatment increased anterior pituitary Met-enkephalin which was reversed by concomitant bromocriptine administration. We postulate that the changes in anterior pituitary Met-enkephalin following reserpine were related to alterations in the monoamine neurotran-smitters. Adrenergic and dopaminergic mechanisms may have opposing roles in the maintenance of Met-enkephalin concentrations in the anterior pituitary gland.

ISSN:0028-3835    

DOI:10.1159/000124905

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Basal plasma concentrations of growth hormone (GH) were monitored in both normal and estradiol-primed male rats by the collection of sequential blood samples from freely moving rats, via chronic intraatrial cannulae. Blood was sampled every 2 min for a period of 80 min and plasma GH levels determined by radioimmunoassay. The normal male rats displayed a pulsatile release of GH, while the estradiol-primed male rats exhibited a relatively steady level of plasma GH concentration. The rats exposed to high levels of estradiol (1.59 ± 0.42 nmol/l plasma) also had a higher mean value of basal GH concentration. An injection of 100 µg/kg of bovine neurophysin II did not alter GH release in the normal male rats. However, it did significantly elevate GH levels in the estradiol-primed animals to a mean peak level approximately six times the mean basal level. The administration of 100 µg/kg of bovine neurophysin I to estradiol-primed male rats did not produce any change in plasma GH levels and thus eliminates the possibility of the nonspecific stimulation of neurophysin II on GH relea

ISSN:0028-3835    

DOI:10.1159/000124906

出版商:S. Karger AG    

年代:1988

数据来源: Karger