摘要:

Complex interactions of the pituitary, hypothalamus, and pineal involving MIF-1 (Pro-Leu-Gly-NH2) were shown many years ago. One of the largest changes consisted of increased amounts of an MIF-1-like material in the plasma of hypophysectomized rats as measured by the skin lightening of darkened frogs. The present study used radioimmunoassay to measure immunoreactive Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) in intact, hypophysectomized, pinealectomized, and superior cervical ganglionectomized (SCG) rats. Samples were collected every 4 h for 24 h. Plasma concentrations of Tyr-MIF-1-like immunoreactivity were higher in hypophysectomized rats and lower in pinealectomized rats than in the intact or SCG groups, which were not reliably different from each other. In most groups, the highest plasma concentrations appeared to occur about 04.00 h, a time at which brain concentrations of Tyr-MIF-1-like immunoreactivity were low. However, no diurnal rhythm in plasma was seen in the pinealectomized rats. At none of the times did brain concentrations of immunoreactive peptide differ among the four groups. By high-performance liquid chromatography of plasma, the main peak of immunoreactivity was found to elute at the same position as Tyr-MIF-1 supporting the natural occurrence of this tetrapeptide. Thus, this study demonstrates that the concentration of immunoreactive Tyr-MIF-1 in plasma is increased by hypophysectomy.

ISSN:0028-3835    

DOI:10.1159/000124722

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The purpose of this investigation was to elucidate the differences in the nature and time course of changes in in vitro prolactin (PRL) cell activity between blinded and blind/pinealectomized female hamsters. Adult female golden hamsters were either left intact, blinded and sham-pinealectomized (Blind/Sham) or blinded and pinealectomized (Blind/ Pinx). Twelve weeks after surgeries, animals were killed by decapitation and randomized hempituitaries were incubated for a total of either 30, 60, 90, 120, 180 or 240 min. PRL release in vivo, as estimated by monitoring serum titers of immunoreactive PRL (IR-PRL), was markedly reduced in Blind/Sham animals; pinealectomy completely prevented this depression. PRL storage was assessed by measuring total levels (i.e., medium + pituitaries) of IR-PRL in vitro. Total, pituitary and media values of IR-PRL were all significantly depressed in Blind/Sham females. Pinealectomy of blinded animals almost completely prevented these reductions. PRL synthesis, as evaluated by measuring the amount of 3H-leucine incorporated into PRL in vitro, was profoundly reduced in Blind/Sham females. Surprisingly, pinealectomy failed to prevent the blinding-induced decrease in PRL production. From these data, we conclude that in the light-deprived female hamster the pineal gland inhibits PRL storage and release, while the depression in PRL synthesis may be independent of a pineal influence.

ISSN:0028-3835    

DOI:10.1159/000124723

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

For determination of the roles of histamine and its receptors, H1 and H2, in the control of basal and estrogen-induced LH-RH secretion, the mediobasal hypothalamus (MBH) and/or pituitary was excised from normally cycling female rats and perifused in an in vitro sequential double chamber perifusion system. Administration of 10–7M histamine caused significant release (90–170% increase, p < 0.05) of LH from the pituitary in sequence with the MBH, whereas 10–7M histamine had no effect on LH release from the pituitary perifused alone; administration of 10–5M 2-methylhistamine, an H1 agonist, induced significant release (50–120% increase, p < 0.05) of LH-RH from the MBH, and addition of 10–5M mepyramine, and H1 antagonist, abolished this LH-RH release. The LH concentrations in the efflux were not affected by the administration of the H2 agonist 4-methylhistamine. Estradiol caused significant release of LH-RH from the MBH and LH from the pituitary in sequence with the MBH. The estradiol-induced release of LH-RH and LH were completely abolished by perifusion with medium containing 10–5M mepyramine. The H2 receptor antagonist ranitidine did not affect estradiol-induced LH release. Histamine did not change the LH release induced by 20 ng LH-RH. These findings suggest that histamine induces release of hypothalamic LH-RH, and that histamine H1 receptors in the hypothalamus are involved in the basal and estradiol-induced

ISSN:0028-3835    

DOI:10.1159/000124724

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

An in vitro perifusion system was used to investigate immunoreactive β-endorphin (β-END-I) release from adult human hypothalami in response to dopamine (DA) and the DA receptor antagonist haloperidol (HAL). Administration of a 1 µM pulse of DA consistently elicited a mean (±SE) 88 ± 9% increase (p< 0.05, n = 5) in β-END-I release, whereas 1 µM HAL had no effect. Administration of 1 µM DA during three perifusions in which 1 µM HALwas added to the medium failed to alter basal β-END-I release. In contrast, DA did evoke an acute 230 + 31% increase (p< 0.05) in β-END-I release during three matching perifusions with medium containing the α-adrenergic antagonist phentolamine. These studies demonstrate that DA can stimulate in vitro release of β-END-I from the adult human hypothalamus by a DA receptor mediat

ISSN:0028-3835    

DOI:10.1159/000124725

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present experiments sought to identify brain regions in which implants of an antiestrogen would antagonize the ability of a systemic estradiol treatment to activate sexual behavior in female rats. In experiment 1, ovariectomized female rats were implanted subcutaneously with 5-mm Silastic capsules containing a 5% concentration of estradiol and injected with 500 µg progesterone 2 days later, 4–5 h before testing for sexual behavior. Bilateral intracranial implants of 1% crystalline concentrations of the high-affinity antiestrogens monohydroxytamoxifen (TAM) or keoxifene placed into the ventromedial nucleus of the hypothalamus (VM) 24 h prior to estradiol treatment significantly reduced lordosis responsivity compared with control females receiving empty cannulae. Implants of 1% TAM into the medial preoptic area or medial amygdala 24 h prior to estradiol hat no significant effect on lordosis. Similarly, implants of 1% TAM into the VM 12 h after estradiol had no effect on lordosis. In experiment 2, lordosis was activated by subcutaneous implants of Silastic capsules containing 1% estradiol plus 500 µg progesterone. In this experiment, implants of 1% TAM into the VM 24 h prior to estradiol significantly reduced lordosis only if both cannulae tips were in, or adjacent to, the VM. Females receiving intracranial 1% TAM, but whose cannulae (even unilaterally) were outside the VM, had levels of lordosis equivalent to those of control females. Increasing the concentration of intracranial TAM to 10% virtually eliminated lordosis in females with bilateral implants in the VM, whereas females receiving intracranial 10% TAM in the region of, but outside, the VM showed no evidence of a lordosis deficit. These results indicate that selectively blocking estradiol receptors in VM neurons can antagonize the effects of systemically delivered estradiol on lordosis. Taken together with previous data, these results suggest that stimulation of VM estrogen receptors is both necessary and sufficient for the hormonal activation of lordosis in r

ISSN:0028-3835    

DOI:10.1159/000124726

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Recent evidence suggests that increased plasma prolactin (PRL) levels could be modifying the synthesis and release of catecholamines (CA) from the adrenal medulla. In order to study this possibility, female rats bearing an anterior pituitary gland, from a litter-mate donor, under the right kidney capsule since day 30 of life and their sham-operated controls were sacrificed by decapitation 45 days after the transplant operation. Plasma PRL and CA levels and CA content in the adrenal medulla were analyzed. A significant increase in plasma PRL levels was shown in grafted (22 ± 2 µg/1) when compared to control rats (6 ± 0.3 µg/1), together with a significant increase in plasma norepinephrine (NE) (4.2 ± 1.1 µg/1 vs. 1.7 ± 0.7 µg/1) and epinephrine (E) (2.9 ± 0.6 µg/1 vs. 1.6 ± 0.2 µg/1). Similar plasma dopamine (DA) levels were found in both groups (0.6 ± 0.2 µg/1 vs. 0.8 ± 0.3 µg/1). An increase in adrenal DA content (29.1 ± 6.8 ng/mg protein), together with a decrease in NE (33.3 ± 6.8 ng/mg protein) and E content (65.9 ± 11.8 ng/mg protein) was detected in grafted as compared to control rats (DA: 12.0±3.6 ng/mg protein; NE: 79.3 ± 22.1 ng/mg protein; E: 184.2± 39.2 ng/mg protein). We can conclude from these data that the elevation of circulating PRL levels induced by a pituitary graft is able to increase the synthesis and release of CA from the adrenal m

ISSN:0028-3835    

DOI:10.1159/000124727

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The ability of vasopressin to stimulate the accumulation of 3H-labelled inositol phosphates was studied in vitro using prelabelled rat anterior pituitary quarters. [8-Arginine] vasopressin activates inositol lipid breakdown in this system in a time- and dose-dependent manner; vasopressin (3 × 10–7M) resulted in a 1.8-fold stimulation of inositol phosphate accumulation over control accumulation after 10 min. This response to vasopressin is inhibited by the specific V1 antagonist (CH2)5Tyr(Me)AVP. Both oxytocin and the selective V2 agonist DDAVP also show some agonist activity, but are considerably less potent than arginine vasopressin. Corticotrophin-releasing factor alone had no effect on inositol phosphate production, whilst a high dose given in conjunction with vasopressin resulted in a diminution of the response below that found with the same concentration of vasopressin alone. Anterior pituitaries from vasopressin-deficient Brattleboro rats also show a phosphatidylinositol response to vasopressin. Pituitaries from rats that had been adrenalectomized 4 days earlier showed no increase in inositol phosphate accumulation in response to vasopressin. Daily administration of dexamethasone (40 µg/day) reversed this effect of adrenalectomy. This reversal was not seen when dexamethasone (40 µg/ml) was added to the incubation medium of adrenalectomized rat pituitary quarters. These results confirm that the rat anterior pituitary contains functional vasopressin receptors capable of activating inositol phospholipid metabolism and that this biochemical response is modified by changes in the hypothalamo-pituitary-adrenal

ISSN:0028-3835    

DOI:10.1159/000124728

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In unanaesthetized rats chronically prepared with venous and intracerebral cannulae, noradrenaline injected into the region of the supraoptic nuclei caused a dose-dependent increase in plasma vasopressin, measured by radioimmunoassay. A similar response was obtained with phenylephrine, but not with either clonidine or isoprenaline. The secretion of vasopressin was not secondary to change in arterial pressure, since similar injections of noradrenaline resulted in a small increase in arterial pressure, measured in the anaesthetized rat. These results suggest that noradrenaline stimulates alpha-1-adrenoceptors, presumably located on vasopressin-secreting neurones, thereby causing these cells to secrete vasopressin into the circulation. Tyramine injections also resulted in a prompt elevation in plasma vasopressin, indicating that endogenous noradrenaline is capable of releasing vasopressin.

ISSN:0028-3835    

DOI:10.1159/000124729

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The autoregulatory feedback control of prolactin, which is mediated by tuberoinfundibular dopamine (DA) neurons, is altered in the aged rat; this is evidenced by increased circulating concentrations of prolactin and decreased activity of these neurons. In the present study the action of prolactin on tuberoinfundibular DA neurons in young and aged female rats was estimated by measuring the rate of DA synthesis (dopa accumulation following the administration of a decarboxylase inhibitor) in the median eminence. The rate of dopa accumulation in the median eminence of the aged (26 months) rat was reduced to 50–60% of that in the young (3 months) rat. The acute systemic administration of haloperidol, a DA antagonist which increases serum concentrations of prolactin or intracerebroventricular infusions of prolactin increased the rate of dopa accumulation in the median eminence of both young and aged rats by the same relative amount. The administration of haloperidol and prolactin increased the rate of DA synthesis to a greater extent in young than in aged rats. The administration of bromocriptine, a DA agonist which reduces serum concentrations of prolactin, decreased the rate of dopa accumulation in the median eminence of both young and aged rats. In young animals the intracerebroventricular administration of prolactin reversed the bromocriptine-induced decrease in DA synthesis in the median eminence after 4 h and caused a further increase after 12 h. Qualitatively similar effects were seen in the aged rats; however, prolactin-treated young rats had much higher levels of DA synthesis than aged rats. Studies were undertaken to determine the response of DA synthesis in the median eminence of young and aged rats to chronically elevated prolactin. In these studies elevated serum prolactin was sustained by eleven daily injections of haloperidol. The rate of dopa accumulation in the median eminence of both young and aged rats was increased by the same relative amount but not to the same absolute levels. Despite the age-related decrease in the basal activity of tuberoinfundibular DA neurons, these neurons in young and aged rats are equally responsive to prolacti

ISSN:0028-3835    

DOI:10.1159/000124730

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Recent studies have suggested zinc to be a possible modulator of hormone secretion from the anterior pituitary. The three aims of the present study were: (1) to estimate the total amount of zinc in the gland by instrumental analysis; (2) to visualize the zinc at light and electron microscopical levels, and (3) to estimate the amount of zinc that can be visualized by histochemical techniques. PIXE measurement showed the total amount of zinc to be 74 ng/mg dry weight in males and 100 ng/mg dry weight in females, which is a highly significant difference. Histochemically, the zinc was shown by a modified Timm method and the selenium method to be localized to the secretory granules, and to a smaller extent to the Golgi apparatus of the somatotrophs, corticotrophs and thyrotrophs. Chelation of tissue zinc by intravital dithizone treatment effectively blocked subsequent selenium and Timm staining in the secretory granules, and PIXE assays of the chelated metal (extracted into CCU) showed it constitued less than 5% of the total zinc in the tissue. It is concluded from the study that zinc is present in the anterior pituitary of rats in rather high amounts and that loosely bound zinc, which is suggested to exert a biological effect by itself, can be located to the parts of the cells responsible for production, storing and release of hormones.

ISSN:0028-3835    

DOI:10.1159/000124731

出版商:S. Karger AG    

年代:1987

数据来源: Karger