bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Response of Lactotrophs and Somatotrophs to a Joint Application of Vasoactive Intestinal Peptide and Thyrotrophin‐Releasing Hormone in the Rat
Authors: Bluet‐Pajot M. T. , Durand D. , Mounier F. , Léonard J. F. , Kordon C.
Published: September 2006

We have studied the responses of growth hormone, prolactin and thyrotrophin to vasoactive intestinal peptide and thyrotrophin‐releasing hormone added either together or separately under various in vivo (free‐moving, intact animals or rats bearing hypothalamic lesions) or in vitro (perifused anterior pituitary fragments) conditions. Thyrotrophin‐releasing hormone or vasoactive intestinal peptide stimulated prolactin release in all cases and the individual effects of both peptides were additive when administered together. Vasoactive intestinal peptide, but not thyrotrophin‐releasing hormone, induced a growth hormone response in intact rats. In contrast, both peptides stimulated growth hormone release in lesioned rats as well as in perifused anterior pituitary fragments. In that case, the effect of vasoactive intestinal peptide on growth hormone release was not additive with that of thyrotrophin‐releasing hormone, either in vivo or in vitro. Thyrotrophin release was slightly stimulated by vasoactive intestinal peptide, whereas it responded markedly to thyrotrophin‐releasing hormone. The effect of thyrotrophin releasing‐hormone was not further affected by simultaneous vasoactive intestinal peptide administration.

These data suggest that additivity of the effect of second messengers generated as a response to thyrotrophin‐releasing hormone and vasoactive intestinal peptide are specific of the target cell type.
Autoradiographic Study of Binding and Internalization of a Luteinizing Hormone‐Releasing Hormone Antagonist [D‐Nal1, D‐Cpa2, A‐D‐Trp3, D‐Arg6, D‐Ala10]LHRH by Rat Pituitary Gonadotrophs
Authors: Badr Mohamed , Pelletier Georges
Published: September 2006

The binding and intracellular pathway of the radioiodinated luteinizing hormone‐releasing hormone (LHRH) antagonist [D‐Nal1, D‐Cpa2, D‐Trp3, D‐Arg6, D‐Ala10]LHRH in pituitary gonadotrophs was studied as a function of time after iv injection of label into intact and castrated female rats. In semithin (1 |im) sections, silver grains were exclusively localized over about 10% of anterior pituitary cells in intact animals. In castrated animals, only the large castration cells were labeled. In control rats injected with both iodinated antagonist and an excess of unlabeled peptide, no significant labeling could be detected. At the ultrastructural level, the silver grains were exclusively localized in gonadotrophic cells. The time‐course study showed that 30 min and 60 min after injection a high proportion of the silver grains was associated with the plasma membrane. Six h after injection, an appreciable proportion of the label was found over intracellular organelles, especially lysosomes and secretory granules. These results indicate that the potent LHRH antagonist used in the present experiments binds selectively to gonadotrophs and is subsequently internalized but at a much lower rate than that observed with LHRH agonists. This slow internalization of the LHRH antagonist might be related to the normal endocytic processes which occur independently of receptor activation.
Biogenic Amine and Corticotrophin‐Releasing Factor Concentrations in Hypothalamic Paraventricular Nucleus and Biogenic Amine Levels in the Median Eminence of Normal Dogs, Chronic Dexamethasone‐Treated Dogs, and Dogs with Naturally‐Occurring Pituitary‐Dependent Hyperadrenocorticism (Canine Cushing's Disease)
Authors: Peterson Mark E. , Palkovits Miklós , Chiueh Chuang C. , Graves Thomas K. , Mezey Eva , Vale Wylie , Krieger Dorothy T.
Published: September 2006

We measured dopamine, norepinephrine, serotonin and epinephrine concentrations in the paraventricular nucleus and median eminence, and corticotrophin‐releasing factor levels in the paraventricular nucleus. Tissue was isolated by micropunch technique from hypothalami of normal dogs, dogs treated for one week with dexamethasone (1 mg/kg/day) and dogs with spontaneous pituitary‐dependent hyperadrenocorticism. Concentrations of corticotrophin‐releasing factor and most of the neurotransmitters were found to be similar between our three groups of dogs. However, we found the mean dopamine concentration in the median eminence tissue to be significantly decreased in dogs with Cushing's disease and in steroid‐treated dogs. Epinephrine levels were elevated in the hypothalamic paraventricular nucleus of steroid‐treated dogs.
Effect of Centrally Administered Oxytocin on the Association Between Cortical Electroencephalogram and Milk Ejection in the Rat
Authors: Wakerley J. B. , Foreman C. T. , Ingram C. D.
Published: September 2006

The milk‐ejection reflex of the rat is closely associated with synchronized activity of the cortical electroencephalogram (EEG), and the frequency of milk ejections has been shown to be greatly facilitated by central oxytocin. The following experiments were undertaken to examine the changes in the EEG during facilitation of the reflex by central oxytocin. Intracerebroventricular injection of 1 mU (2.2 ng) oxytocin during suckling caused a rapid increase in the frequency of milk ejections but no change in the predominantly synchronized pattern of the EEG. However, after a delay (11.3 ± 0.8 min, mean ± SE) there appeared to be an increasing proportion of desynchronization, which correlated with cessation of the facilitated milk‐ejection responses. Hence, the observed EEG desynchronization may signal activation of mechanisms inhibitory to the milk‐ejection reflex.

In the absence of the suckling stimulus oxytocin also caused a change to desynchronization. However, this effect was more pronounced and commenced after a much shorter latency (1.7 ± 0.4 min, mean ± SE; P < 1.001), suggesting that the desynchronizing effect of oxytocin on the EEG can be attenuated by the suckling stimulus.

These results demonstrate two phases in the action of central oxytocin in the suckled rat. During the initial phase, the milk‐ejection reflex is facilitated and although there may be a concomitant desynchronizing influence on the EEG this is prevented by the influence of the suckling stimulus. In the later phase, this desynchronizing influence predominates and is accompanied by cessation of milk‐ejection responses.

Although milk ejections were generally restricted to periods of a synchronized EEG as previously reported, during the oxytocin‐induced change to desynchronization a number of milk ejections were observed to occur in the absence of a synchronized EEG. These results provide further evidence that the association between milk ejection and the EEG state is not an absolute causal relationship.
Triiodothyronine Regulates Insulin‐Like Growth Factor‐I Binding to Cultured Rat Pituitary Cells*
Authors: Geary E. Stewart , Lim Matthew , Ceda Gian Paolo , Ro Sandy , Rosenfeld Ron G. , Hoffman Andrew R.
Published: September 2006

Triiodothyronine (T3) stimulates the synthesis of growth hormone and enhances the growth of neoplastic rat pituitary somatomam‐motrophs (GH cells) in culture. Moreover, T3 has been shown to stimulate the production and secretion of an autocrine growth factor by these cells. We have previously demonstrated the presence of specific receptors for insulin‐like growth factors (IGF) on GH cells. Since GH3 cells contain mRNA encoding IGF‐I, it has been suggested that IGF‐I might act in an autocrine fashion in these cells. Therefore, it was of interest to learn how T3 affects IGF‐I binding to GH3 cells. T3 increased [125I]IGF‐I binding in a time ‐ and dose‐dependent manner. After 48 h of exposure to T3, an increase in IGF‐I binding was seen with 10−11M T3, maximizing with 10−8M T3. When cells were exposed to 10−8 T3, [125I]IGF‐I binding reached a maximum of 218 ± 20.8% of control (±SEM, P < 0.002) after 72 h of incubation. Scatchard analysis indicated that T3 did not alter the Kd of IGF‐I for its receptor, but that the total receptor number was increased. Dexamethasone (10−7M) inhibited the T3‐induced increase in IGF‐I binding, but glucocorticoid alone did not substantially alter receptor number. No significant change in insulin or IGF‐II binding was seen after hormone treatment. 10−8 M T3 or IGF‐I increased the growth of the GH3 cells by ≥30%. Our data indicate that T3 upregulates IGF‐I binding in GH3 cells without altering insulin binding and thereby provides a means for enhancing potential autocrine regulation in this cell line.
The Expression of the Kallikrein Gene Family in the Rat Pituitary: Oestrogen Effects and the Expression of an Additional Family Member in the Neurointermediate Lobe
Authors: Clements Judith A. , Matheson Bronwyn A. , MacDonald Raymond J. , Funder John W.
Published: September 2006

Using a series of oligonucleotide probes (18 to 21 mers) specific for members of the rat kallikrein/tonin gene family (PS, S1, S2, S3, K1, P1), we have shown by Northern blot analysis that the oestrogen‐dependent kallikrein gene expressed in the male and female rat anterior pituitary is true kallikrein (PS). In addition, we have demonstrated that oestrogen treatment may also induce PS gene expression in the male and female rat neurointermediate lobe. None of the other five rat arginyl‐esteropeptidase genes so far described (S1, S2, S3, K1, P1) was found to be expressed in the anterior pituitary or neurointermediate lobe under these conditions. However, the demonstration of an additional hybridization signal in the male neurointermediate lobe using a relatively non‐specific PS gene probe suggests the expression of another, as yet uncharacterized, kallikrein gene family member in this tissue.
Electrical Stimulation of Specific Brainstem Nuclei Suppresses Growth Hormone‐Releasing Hormone‐Induced Growth Hormone Secretion in the Pentobarbital Anaesthetized Rat
Authors: Koibuchi Noriyuki , Kato Masakatsu , Kakegawa Tadao , Suzuki Mitsuo
Published: September 2006

To clarify the neural mechanism related to suppression of growth hormone (GH) secretion, biphasic electrical stimulation was delivered into several brainstem nuclei in the pentobarbital anaesthetized rat. A concentric bipolar stimulating electrode was implanted chronically one week prior to the electrical stimulation. Ninety min before the electrical stimulation, the rats were anaesthetized by ip injection of pentobarbital and a silastic cannula was inserted into the right atrium for blood sampling. Blood samples were withdrawn five times (0, 10, 20, 30 and 60 min) during the experiment. Electrical stimulation was delivered for 10 min just after the first blood sampling. One min after the onset of the stimulation, human GH‐releasing hormone was injected iv to induce GH secretion. Electrical stimulation of several brainstem nuclei, i.e. the locus coeruleus, the rostral portion of the nucleus tractus solitarius and the lateral reticular nucleus suppressed GH secretion and the central gray of the pons showed a tendency for the suppression of GH secretion. On the other hand, electrical stimulation of the parabrachial nucleus and the caudal portion of the nucleus tractus solitarius did not suppress GH secretion. These suppressions were nullified by prior electrolytic lesioning of the hypothalamic periventricular nucleus where the major cell bodies of somatostatin immunoreactive fibres in the median eminence originate. These results indicate that electrical stimulation of several brainstem nuclei excites somatostatin neurons in the periventricular nucleus which are responsible for the suppression of GH secretion.
Differential Effects of Pre‐Weaning Stress on Adrenocorticotrophin and Prolactin Response to Novel Stimuli in Adult Rats
Authors: Hamamura Mitsuko , Onaka Tatsushi
Published: September 2006

Emotional responsiveness is reduced in adult animals which have been exposed to stress during their first few weeks of life (1, 2). The stress of ‘handling’, daily removal of pups from their mother during the pre‐weaning period, also leads to a reduced corticosterone response to novel stimuli in adult life (3). In rats, exposure to novel stimuli results in the concomitant release of prolactin (PRL) and corticosterone (4–6). Here we show that, in male rats handled daily during the pre‐weaning period of life and tested in adult life for their hormonal responses to exposure to novel audio‐visual stimuli, the consequent secretion of adrenocorticotrophin (ACTH) is attenuated, but that of PRL is not. Thus, pre‐weaning handling results in permanent changes in a neural system specific to the control of ACTH secretion rather than affecting pathways common to neuroendocrine responses to emotional stimuli (7).
Proopiomelanocortin, Preproenkephalin‐A and Preprocholecystokinin mRNA in the Hypothalamus of CCI4‐Treated Rats
Authors: Brini Anna , De Giuli Morghen Carlo , Bianchi Mauro , Rovati Lucio C. , Panerai Alberto E.
Published: September 2006

It has previously been shown that β‐endorphin (BE) and cholecystokinin (CCK) concentrations decrease in brain areas of rats or humans affected by severe liver disease (SLD). We now report the increase of proopiomelanocortin (POMC) and preprocholecystokinin mRNA in the hypothalamus and cortex of rats with experimental SLD, suggesting an increased post‐translational turnover of BE and CCK in this experimental condition.
The Effects of a Growth Hormone‐Releasing Peptide and Growth Hormone‐Releasing Factor in Conscious and Anaesthetized Rats
Authors: Clark R. G. , Carlsson L. M. S. , Trojnar J. , Robinson I. C. A. F.
Published: September 2006

The growth hormone (GH) releasing ability of GH‐releasing factor (GRF) and a GH‐releasing hexapeptide, CHRP, have been studied in anaesthetized and conscious male and female rats. The GH responses to GHRP in anaesthetized rats were inconsistent, and this peptide was much less potent than GRF. Continuous iv infusions of GRF or GHRP both caused an initial GH release which was not maintained, and further GH release could be elicited by injection of GRF during an infusion of GHRP and vice versa. In contrast, conscious rats were much more sensitive to GHRP. Infusions of GHRP or GRF both caused an initial GH release. With GRF infusions, GH release continued in the normal episodic pattern whereas with GHRP infusion, GH secretion remained elevated over baseline and the normal pulsatile rhythm was disrupted. Plasma GH levels fell after stopping GHRP infusion, without an immediate resumption of normal GH pulsatility. Conscious male rats responded intermittently to injections of GRF given iv every 45 min, but when such serial injections of GRF were given during a continuous iv infusion of GHRP, the GH responses to GRF became regular and more uniform. These results suggest that GHRP prevents the normal cyclic refractoriness to GRF in male rats by disrupting cyclic somatostatin release. The greater potency of GHRP in conscious rats may also depend on the release of endogenous GRF since passive immunization with an anti‐GRF serum reduced the plasma GH response to GHRP infusion. Thus in the conscious animal, GHRP may release GH by complex actions at both a hypothalamic and pituitary level.
Estrogen Alters Oxytocin mRNA Levels in the Preoptic Area
Authors: Caldwell J. D. , Brooks P. J. , Jirikowski G. F. , Barakat A. S. , Lund P. K. , Pedersen C. A.
Published: September 2006

Estrogen has numerous effects on immunoreactive levels of oxytocin (OXT) centrally, particularly in the preoptic lateral subcommissural nucleus (LSN). In this study in situ hybridization of a 38‐base oligodeoxyribonucleotide (38mer) complementary to OXT mRNA revealed that estrogen treatment altered the pattern of OXT production in the rostral LSN and the more caudal anterior commissural nucleus. Rats were injected with 20 ng estradiol benzoate or sesame oil vehicle im 4 and 5 days after ovariectomy. On the sixth day all animals were perfused with paraformaldehyde‐glutaraldehyde and their brains sectioned to 10 μm thickness in a −10 °C cryostat. Coronal brain sections were taken from four parallel levels of the preoptic‐anterior hypothalamic area. These sections were mounted and hybridized in situ to a [l125]‐labeled 38mer for 16 h at 37 °C. Washed and dried slides were processed for autoradiography and analyzed with a light microscope. The effect of estrogen on OXT production differed between the rostral and caudal sections in both the LSN and periventricular (PeV) areas. Estrogen significantly increased OXT mRNA levels in LSN cells while decreasing hybridization in the anterior commissural nucleus cells. Changes in frequency patterns in the PeV paralleled those in the LSN with a significant drop of hybridization in the caudal PeV. Neurons hybridizing 38mer probe were also found in several other areas including the ventral medial preoptic area, lateral hypothalamus, bed nucleus of the stria terminalis and the nucleus triangularis septi. OXT mRNA levels were affected by estrogen treatments and this effect differed between the preoptic area and anterior hypothalamus. The sensitivity of LSN oxytocinergic cells to estrogen has implications for estrogen‐sensitive OXT‐enhanced reproductive behaviors.
Effects of Orchidectomy on Nigro‐Striatal Dopaminergic Function: Behavioral and Physiological Evidence
Authors: Dluzen Dean E. , Ramirez Victor D.
Published: September 2006

In the present experiments, we examined the effect of castration upon two indices of nigro‐striatal dopaminergic function in the male rat. In Experiment I, differences in spontaneous locomotor behavioral activity between intact and castrated male rats were examined. The total distance traveled, horizontal activity and mean revolutions of castrated male rats were significantly greater than that of intact males. No significant differences between intact and castrated males were obtained for vertical activity. In Experiment II, the spontaneous in vitro dopamine release from the corpus striatum of intact and castrated rats as sampled during the light‐phase (1500 h) and dark‐phase (2400 h) of the photoperiod was examined. At both time periods, the spontaneous in vitro dopamine release of castrated males was significantly greater than that of intact males. Both intact and castrated males showed statistically significant increases in dopamine release at the 2400 h compared to the 1500 h time period. To examine if testicular hormones were responsible for these castration induced changes in dopamine release, in Experiment III we treated castrated male rats with testosterone propionate. Administration of testosterone propionate (0.1 mg/day × 5 days) significantly reduced in vitro dopamine release compared to untreated or castrated male rats receiving vehicle treatment. These results demonstrate that testicular hormones, most likely testosterone, have a markedly suppressive effect upon the nigro‐striatal dopaminergic system as evidenced from changes in spontaneous behavioral activity and in vitro dopamine release.
Oestrogen‐Insensitive Progestin Receptors in the Central Nervous System: Physicochemical and Immunoreactive Characteristics
Authors: Cerbón Marco A. , Martineíz Maryam , Pérez‐Palacios Gregorio
Published: September 2006

The intracellular effects of progesterone in the central nervous system are exerted via two distinct receptors: The classical oestrogen‐regulated progestin receptor and the non‐oestrogen‐inducible progestin receptor. To assess whether the oestrogen‐insensitive receptor is related to the oestrogen‐dependent receptor or whether it is a different binding macromolecule, its physicochemical and immunoreactive characteristics (immunoprecipitation with polyclonal anti‐uterine progesterone receptor antisera) were studied in neural tissues of the female rat. The results disclosed that the dissociation constant (Kd, 0.4–0.5 ± 10−9 M), stereospecificity and sedimentation coefficient (7–8 S) in linear sucrose gradients of the oestrogen‐insensitive progestin receptor were identical to those reported for the oestrogen‐regulated progestin receptor, although its saturation binding capacity was significantly lower. Results of in vitro nuclear acceptor assays revealed that the progestin receptor complexes from cerebellum and cerebral cortex, were able to specifically bind to cell nuclei preparations in a fashion similar to that observed with the uterine progestin receptor, although to a lesser extent. Interestingly, a similar nuclear uptake of receptor complexes was noticed when standardized cerebellum and uterus cytosol preparations with a similar receptor content were used. The anti‐uterine progesterone receptor immunoglobulins used in the immunoprecipitation studies were able to specifically recognize the progestin receptor populations of the anterior pituitary and hypothalamus (oestrogen‐regulated receptors) as well as those of the cerebellum and cerebral cortex (oestrogen‐insensitive receptors). The results presented show that both the oestrogen‐sensitive and the oestrogen‐insensitive cytosol progestin receptors in brain bind the same progesterone‐like molecules used as radioligands and also react with the same antibody when tested in an immunoprecipitation radioassay. The striking similarities found in binding kinetics, physicochemical characteristics and immunoreactive behaviour in the two progestin receptors studied demonstrated that both macromolecules belong to the same family of proteins in spite of their different sensitivity to oestrogens. The overall data seem to suggest a common origin of the two progestin receptor populations in brain but with different mechanisms of hormonal regulation.
Regulation of Anterior Pituitary Gonadotrophin Subunit mRNA Levels by Gonadotrophin‐Releasing Hormone in the Ewe
Authors: Mercer Julie E. , Clarke Lain J.
Published: September 2006

Levels of mRNA for the common a subunit and for the β subunits of luteinizing hormone (LH) and follicle‐stimulating hormone (FSH) were measured in the pituitary glands of ovariectomized hypothalamo‐pituitary disconnected ewes. A control group (n = 7) received 250 ng pulses of gonadotrophin‐releasing hormone (GnRH) each hour for one week. To examine the effects of changing GnRH pulse amplitude four sheep were given 250 ng pulses of GnRH for one week and then 25 ng pulses for one week. Plasma LH and FSH concentrations were lowered by reducing the GnRH pulse amplitude but pituitary levels of mRNA for a subunit were increased. Levels of mRNA for FSHβ and LHβ were similar with 25 ng and 250 ng pulses of GnRH. To examine the importance of pulsatile versus continuous GnRH inputs, a group of sheep was given a constant infusion of 250 ng/h GnRH for one week. Compared to sheep given 250 ng pulses of GnRH the mRNA levels for LHβ and FSHβ were lower in sheep given a constant infusion of GnRH; levels of a subunit mRNA were similar in the two groups. To examine the short‐term effects of removing GnRH inputs, ovariectomized, hypothalamo‐pituitary disconnected ewes that had been receiving 250 ng pulses of GnRH each hour were deprived of GnRH for 6 h (n = 4) or 30 h prior to slaughter; levels of mRNA for the three subunits were similar to control values in both of these groups.

These studies show that wide variation in GnRH pulse amplitude has little effect on mRNA levels for the gonadotrophin subunits but message levels are affected by the mode of GnRH input (constant versus pulsatile). The maintenance of gonadotrophin subunit mRNA levels for at least 30 h after GnRH deprivation suggests that these mRNA species have a long half‐life or that transcription continues after GnRH withdrawal.
Immunoreactive Prolactin in the Cerebrospinal Fluid of Estrogen‐Treated and Lactating Rats as Determined by Push‐pull Perfusion of the Lateral Ventricles
Authors: Rubin Beverly S. , Bridges Robert S.
Published: September 2006

Immunoreactive (ir) prolactin levels in the cerebrospinal fluid were measured in push‐pull perfusion samples collected from the lateral cerebral ventricles in freely‐moving ovariectomized rats prior to and after estrogen treatment, and in rats during pregnancy and lactation. Ir‐prolactin levels in cerebrospinal fluid were elevated throughout the perfusion period in ovariectomized animals given estrogen and in Day 8 lactating females following the onset of nursing by their young. Cerebrospinal fluid perfusates collected from ovariectomized animals prior to estradiol treatment and from females on Days 18 and 22 of gestation contained levels of ir‐prolactin that were below the limit of detectability of the prolactin radioimmunoassay. Data from previous studies in our laboratory suggest that pituitary prolactin is involved in the mediation of maternal responsiveness. Where and how prolactin exerts its actions in this regard remains to be determined. Results of the present study indicate that detectable levels of ir‐prolactin are present in the cerebrospinal fluid of nulliparous females after exposure to an estradiol regimen known to shorten their latency to display maternal responsiveness and in lactating females actively exhibiting maternal behavior. Once in the cerebrospinal fluid, prolactin should have access to neural target sites behind the blood‐brain barrier. The presence of ir‐prolactin in the cerebrospinal fluid of females in the present study is consistent with a role for this protein hormone, acting at the level of the central nervous system, in the facilitation of maternal responsiveness as well as in the regulation of other neural and neuroendocrine processes.
Relationship of Substance P‐lmmunoreactive Nerve Fibers with Somatotropes of the Anterior Pituitary in the Monkey
Authors: Ju Gong , Liu Shaojun
Published: September 2006

In a previous study, substance P‐immunoreactive nerve fibers were demonstrated in the pars distalis of the anterior pituitary in the monkey. The present work investigated their relationship with somatotropes. Pituitaries of Macaca mulatta monkeys were frozen, sectioned and double immunostained with antisera against substance P and human growth hormone. Substance P‐immunoreactive nerve fibers, with many varicosities, were found in close proximity to somatotropes. It is suggested that a direct neural factor may be involved in the regulation of growth hormone secretion.
The Effect on Vasopressin Release of Microinjection of Cholinergic Agonists into the Paraventricular Nucleus of Conscious Rats
Authors: Shoji Masaru , Share Leonard , Crofton Joan T. , Brooks David P.
Published: September 2006

We have studied in conscious unrestrained rats under basal conditions the effect of activation of muscarinic and nicotinic receptors in the paraventricular nucleus on vasopressin secretion and mean arterial blood pressure. The microinjection of oxotremorine (0.2, 2 or 20 ng), a specific muscarinic agonist, produced a substantial, dose‐dependent, transient increase in the plasma vasopressin concentration. There was also a rise in mean arterial blood pressure and a bradycardia that followed the same time‐course as the change in plasma vasopressin levels. The microinjection of nicotine (0.1, 1 or 10 HQ) into the paraventricular nucleus had only questionable effects on vasopressin release and mean arterial blood pressure; heart rate was unaffected. These findings suggest that muscarinic receptors may be of primary importance in the paraventricular nucleus in the Cholinergic stimulation of vasopressin release.
Effects of Glucose on Thyrotrophin‐Releasing Hormone, Growth Hormone‐Releasing Hormone, Somatostatin and Luteinizing Hormone‐Releasing Hormone Release from Rat Hypothalamus in vitro
Authors: Lewis B. M. , Dieguez C. , Ham J. , Page M. D. , Creagh F. M. , Peters J. R. , Scanlon M. F.
Published: September 2006

Increasing concentrations of D‐glucose (1 to 25 mM) inhibited somatostatin, thyrotrophin‐releasing hormone (TRH) and growth hormone‐releasing hormone (GHRH) release from incubated adult rat hypothalami in a stereospecific manner. In contrast, the effects of D‐ and L‐glucose on luteinizing hormone‐releasing hormone release were virtually identical. Increasing concentrations of D‐glucose also inhibited somatostatin release following depolarization with high K+, but had no obvious effect on depolarization‐induced TRH or GHRH release when compared with L‐glucose.

In conclusion, D‐glucose exerts a potent, dose‐related modulatory action on the release of rat hypothalamic TRH and GHRH as well as somatostatin in vitro. Further studies are required to establish any physiological relevance of glucose in the modulation of these hypothalamic neuropeptides.
Arcuate Nucleus and Preoptic Area Involvement in Beta‐Endorphin‐lnduced Release of Prolactin in Conscious Ovariectomized Rats†
Authors: Voogt James L. , Reseh Garth , Turkington Susan
Published: September 2006

The ability of ß‐endorphin (ß‐END) to release prolactin and the ability of naloxone to block prolactin's release when delivered to specific hypothalamic areas via push‐pull perfusion was studied in unrestrained, conscious, Ovariectomized rats. Perfusion of either the arcuate nucleus or the preoptic area with ß‐END for 15 to 30 min caused a large, brief increase in plasma prolactin levels. Perfusion for a longer time period (120 min) resulted in peak prolactin levels at 60 min, with a return to baseline by 120 min, suggesting that ß‐END primarily acts to induce a sequence of events that culminates in prolactin release, but other factors are needed to maintain this release over long periods of time. Perfusion of the arcuate nucleus for two 15‐min periods 90 min apart resulted in two surges of prolactin. When naloxone, the opiate receptor antagonist, was added to the perfusate, ß‐END was not capable of stimulating prolactin release. These results provide a model to answer whether endogenous ß‐END has a role in the neuroendocrine regulation of prolactin surges and what the location is of the opiate neurons involved in this neuronal pathway.
Cardiovascular and Steroid Responses to Graded Haemorrhage in Rats with Adrenal Regeneration Hypertension
Authors: Foulkes R. , Gardiner S. M. , Bennett T.
Published: September 2006

Blood pressure (BP) and plasma steroid responses to haemorrhage (2 ml + 1 ml + 1 ml at 20‐min intervals) were assessed in sham‐operated (SO) rats and in rats with adrenal regeneration hypertension (ARH). Experiments were carried out between 0700 and 1000 h (a.m.) and between 1400 and 1700 h (p.m.), because rats with ARH have BPs that are higher a.m. than p.m. There were no differences in the BP responses following haemorrhage in SO or ARH rats either a.m. or p.m., although ARH rats were unable to increase their plasma steroid levels. Pretreatment with captopril alone, d(CH2)5 DAVP alone, or captopril and d(CH2)5DAVP augmented the early hypotensive responses to haemorrhage but did not influence the later compensated levels of BP in either group of rats. There were no clear‐cut a.m. to p.m. differences in the changes in BP in any of the drug‐treated groups of SO or ARH rats. Under all conditions studied, the compensated level of systolic BP in ARH rats, 20 min after the final bleed, remained higher a.m. than p.m., indicating that this difference was not dependent on the renin‐angiotensin system and vasopressin and suggesting that the sympathetic nervous system and/or other factors might be involved.
Interactions Between Opioid Peptides and Adrenaline‐Containing Neurons Modulate Luteinizing Hormone Secretion in Male Rats
Authors: Martensz N. D. , Goldstone A. P. , Stuart E. , Everitt B. J.
Published: September 2006

There is increasing evidence that the opioid inhibition of luteinizing hormone (LH) secretion is mediated, at least in part, by catecholaminergic mechanisms. This study determined the effects of selective manipulation of noradrenergic and adrenergic systems on the ability of opiate receptor blockade to induce the release of LH in adult male rats.

Selective depletion of hypothalamic noradrenaline levels by 80% following 6‐hydroxydopamine infusions into the central tegmental tract did not alter the 2‐ to 3‐fold increase in serum LH levels following opiate receptor blockade with naloxone (2.5 mg/kg). In contrast, both selective depletion of hypothalamic adrenaline by prior treatment with the phenylethanolamine N‐methyltransferase inhibitor, LY134046 (2 × 50 mg/kg) and non‐selective depletion of all three catecholamines with α‐methyl‐p‐tyrosine (250 mg/kg), abolished the naloxone‐induced increase in LH.

These results suggest that the inhibition of LH secretion by endogenous opioid peptides is influenced by catecholaminergic neurotransmission and further support the view that adrenaline rather than noradrenaline or dopamine is of importance in this context.
Biochemical and Immunocytochemical Assessment of Neural Progestin Receptors Following Estradiol Treatments that Eliminate the Sex Difference in Progesterone‐Facilitated Lordosis in Guinea‐Pigs
Authors: Olster Deborah H. , Blaustein Jeffrey D.
Published: September 2006

A single injection of estradiol benzoate (10 μg), while highly effective in ovariectomized female guinea‐pigs, does not prime castrated males to display progesterone‐facilitated lordosis. In contrast, adult males and females exhibit the same, high degree of progesterone‐facilitated lordosis when primed with two, 2.0 μg injections of free estradiol‐17ß (pulse regimen). We compared neural progestin receptor induction after these different estradiol treatments by in vitro radioligand binding assays and immunocyto‐chemistry. Binding assays confirmed previous observations of lower concentrations of cytosol progestin receptors in the mediobasal hypothalamus‐preoptic area in estradiol benzoate‐treated males than in females. No such sex difference was observed in animals that had been exposed to the behaviorally effective estradiol pulse regimen; rather, hypothalamic‐preoptic area progestin receptor concentrations in these animals did not differ from the low levels observed in males treated with the behaviorally ineffective estradiol benzoate regimen. Immunocytochemical analysis revealed progestin receptor‐immunoreactivity in fewer cells in the medial preoptic nucleus‐anterior hypothalamic nucleus, periventricular preoptic area and arcuate nucleus of estradiol pulse‐ as compared to estradiol benzoate‐treated males and females. Estradiol benzoate treatment induced progestin receptor‐immunoreactivity in more cells in the medial preoptic area and ventrolateral hypothalamus than estradiol pulses in males, but not in females. Surprisingly, in these regions estradiol benzoate‐treated males had significantly more progestin receptor‐immunoreactive cells than females.

These experiments yield two major findings: First, as has been shown in rats, the display of progesterone‐facilitated lordosis is not inflexibly differentiated according to sex in guinea‐pigs. Furthermore, reduced concentrations of estradiol‐induced progestin receptors in the hypothalamus and preoptic area cannot account for the lack of progesterone‐facilitated lordosis that is observed following priming with estradiol benzoate in males. Secondly, in the medial preoptic area and ventrolateral hypothalamus of female guinea‐pigs, estradiol pulses are as effective as estradiol benzoate in inducing progestin receptors. These observations, taken together with the finding of equal behavioral efficacy of the two estradiol treatments, are consistent with the hypothesis that estradiol‐induced progestin receptors in these regions of the brain are involved in progesterone‐facilitated lordosis in female guinea‐pigs.
Synchronous Pulsatile Release of Luteinizing Hormone and Immunoreactive Beta‐Endorphin from the Human Pituitary in vitro
Authors: Rossmanith W. G. , Yen S. S. C. , Rasmussen D. D.
Published: September 2006

An in vitro perifusion system employing very frequent (30 s) perifusate collectionswas utilized to investigate the relationship between pulsatile release of luteinizing hormone (LH) and immunoreactive β‐endorphin (iβ‐END) during individual perifusions of adult human anterior hemipituitaries. Each of six hemipituitaries released LH and iβ‐END in a distinctlypulsatile fashion, with pulses occurring approximately every 3.2 min for each. Power spectral analysis revealed that pulsatile release of both LH and iβ‐END occurred in a rhythmic pattern, with a periodicity of 3.1 and 3.2 min, respectively, and that the periodicity of pulsatile LH and iβ‐END release was correlated within individual perifusions. Moreover, the relative amplitudes (% change) of the synchronous LH and iβ‐END pulses were correlated. The effluent fractions from two of the perifusions were also assessed for thyrotropin, and it was determinedthat thyrotropin pulses were synchronized to both LH and iβ‐END pulses. These studies confirm that LH and iβ‐END are released from human anterior pituitaries in vitro in an intrinsically pulsatile fashion, and demonstrate that the LH and iβ‐END pulses tend to occur rhythmically and in synchrony and proportion with each other. Furthermore, correlation of thyrotropin pulses to both the LH and iβ‐END pulses suggests a common fundamental intrapituitary pulse generating mechanism.
Large Molecular Weight Immunoreactive Corticotrophin‐Releasing Hormone has Bioactivity on Superfused Ovine Pituitary Cells
Authors: Chan E‐C. , Thomson M. , Madsen G. , Boettcher B. , Falconer J. , Smith R.
Published: September 2006

Human placental extracts fractionated with Sephadex G‐50 produced three peaks of corticotrophin‐releasing hormone immunoreactivity, a large molecular weight peak (Mr30,000), an intermediate peak (4,758 < Mr < 10,000) and a low molecular weight peak coeluting with the 41‐residue hormone. All three peaks of immunoreactivity stimulated the release of β‐endorphin‐like immunoreactivity from ovine pituitary cells superfused in vitro. No response was observed from unstimulated cells superfused in parallel. Gel chromatography indicated that intermediate and small molecular weight forms of human corticotrophin‐releasing hormone immunoreactivity remained intact after contact with the ovine pituitary cells, whereas the large molecular weight material dissociated to produce 41‐residue hormone immunoreactivity. The secreted β‐endorphin immunoreactivity was shown by gel chromatography to comprise both β‐lipotrophin‐like and the 31‐residue β‐endorphin‐like immunoreactivity. The data show that the intermediate and low molecular weight forms of placental corticotrophin‐releasing hormone immunoreactivity are bioactive and suggest that the intermediate form is a hormone precursor, possibly procorticotrophin‐releasing hormone125–196, and the small form is identical to the hypothalamic hormone. The results with the larger molecular weight material indicate that it is likely to be a complex of the mature 41‐residue hormone and a binding protein.
Estrous Cycle Variations in Gonadotropin‐Releasing Hormone, Substance P and Beta‐Endorphin Contents in the Median Eminence, the Arcuate Nucleus and the Medial Preoptic Nucleus in the Rat: A Detailed Analysis of Proestrus Changes
Authors: Parnet P. , Lenoir V. , Palkovits M. , Kerdelhué B.
Published: September 2006

The concentrations of gonadotropin‐releasing hormone, substance P and β‐endorphin were measured in the median eminence, the arcuate nucleus and the medial preoptic nucleus of 4‐day cycling female rats. Very well marked estrous cycle‐related fluctuations were registered for these neuropeptides in these areas. The largest variations in concentrations of peptide levels were observed in the median eminence. Substance P concentration was highest throughout the day of proestrus as compared to the three others days of the cycle. At the time of the preovulatory luteinizing hormone surge, on the afternoon of proestrus, there was a marked increase in gonadotropin‐releasing hormone concentration and a marked decrease in β‐endorphin concentration.
The Biosynthesis of Melanin‐Concentrating Hormone in a Fish
Authors: Bird David J. , Baker Bridget I. , Eberle Alex , Swann Ray W.
Published: September 2006

This work investigated the biosynthesis of a neurohypophysial hormone, melanin‐concentrating hormone (MCH), in the trout. Sephadex G‐75 chromatography showed the presence of several large MCH‐immunoreactive molecules in hypothalamic and pituitary gland extracts, with different retention times on high‐performance liquid chromatography from the mature MCH1–17. About 10% of the total MCH‐immunoreactivity in the hypothalamus was attributable to large molecular weight forms but these contributed less than 1% to the immunoreactivity in the neurointermediate lobe. Both [35 S]methionine and [3 H]leucine were injected into the hypothalamus near the MCH perikarya (nucleus lateralis tuberis region) of anaesthetized fish, after which the fish were killed at intervals of up to 8 h post‐injection and the basal hypothalami, pituitary pars distales and neurointermediate lobes were extracted in acid. MCH‐related immunoprecipitates from these extracts were fractionated by sodium dodecyl sulphate polyacrylamide gel electrophoresis or by Sephadex G‐50 chromatography. The results show the incorporation of radiolabel into 15.3 K and 11.3 K precursors within 0.75 h, and their conversion, via several smaller intermediates, to a molecule resembling MCH1–17. The results are discussed in relation to the known cDNA sequence of salmon MCH. Labelled MCH first appeared in the neurointermediate lobe 4 h after injection, giving an estimated transit rate of 0.4 mm/h.
The Effect of Anteroventral Third Ventricular Lesions on the Changes in Cholecystokinin Receptor Density in the Rat Supraoptic Nucleus Following Saline Drinking
Authors: Blackburn R. E. , Dayt N. C. , Leng G. , Hughes J.
Published: September 2006

Autoradiography and computerized image analysis were used to study the density of Cholecystokinin binding sites in the supraoptic nucleus of sham‐lesioned and anteroventral third ventricle (AV3V)‐lesioned animals in which the magnocellular system had been activated by salt‐loading with 2% saline for 48 h. Rats were maintained in metabolic cages for 5 to 7 days prior to a sham‐ or AV3V‐lesioning procedure, and the ratio of sodium intake:urinary sodium output used as a measure of sodium excretion. Following the sham or lesion procedure half of the rats had their drinking water replaced with 2% saline and the other half were maintained on normal drinking water. Neurohypophysial hormone levels were measured by specific radioimmunoassay in trunk blood samples taken 48 h after the saline or water treatment. The AV3V‐lesioned group of animals were characterized by an inability to excrete the excess sodium load and by a failure to increase secretion of both oxytocin and vasopressin into the general circulation in response to the salt‐stimulus. Despite this inappropriate response, [125 l]cholecystokinin octapeptide binding in the oxytocin‐rich dorsal portion of the supraoptic nucleus was similarly elevated in both sham‐ and AV3V‐lesioned rats following 2 days of saline treatment. These results suggest that the magnocellular oxytocin system is capable of responding to an osmotic stimulus even when the release of hormone has been severely impaired.
Effects of Different Opioid Receptor Antagonists on the Electrically‐Evoked Release of Endogenous Dopamine from the Isolated Neural Lobe of the Rat Pituitary Gland in vitro
Authors: Racké K. , Hering B. , Weber I.
Published: September 2006

Isolated neural lobes of the rat pituitary gland were incubated in Krebs‐HEPES solution which contained the dopamine uptake inhibitor GBR 12921 and in some experiments additionally pargyline. The release of endogenous dopamine evoked by electrical stimulation of the pituitary stalk was determined by high‐performance liquid chromatography with electrochemical detection. (±)‐ Naloxone increased the evoked dopamine release maximally by 440% (EC50 209 nM). The (+)‐enantiomer of naloxone (up to 10 μM) did not affect the release of dopamine. The preferential κ‐opioid receptor antagonist MR 2266 increased the evoked dopamine release maximally by 135% (EC50 7 nM). MR 2267, the inactive (+)‐enantiomer of MR 2266, had no effect on dopamine release. The δ‐opioid receptor selective antagonist ICI 174864 increased the release of dopamine maximally by 120% (EC50 10 nM). The non‐selective opioid receptor agonist etorphine up to 10 μM had no effect on the evoked dopamine release. In conclusion, endogenous opioids in the neurohypophysis strongly inhibit the release of endogenous dopamine from this gland. Activation of κ‐ and δ‐opioid receptors appears to be involved in the inhibitory action of the endogenous opioids on the neurohypophysial release of dopamine.
Dose‐Related Effects of Progesterone and 5 Alpha‐Dihydroprogesterone upon Estrogen‐Induced Prolactin Release
Authors: Brann Darrell W. , Putnam Carla D. , Mahesh Virendra B.
Published: September 2006

Previous work from our laboratory has shown that progesterone causes a rapid reduction of pituitary nuclear estrogen receptors. This effect is accompanied by a loss of estrogen action such as estrogen‐induced progesterone receptor synthesis and prolactin release. Recent work has demonstrated that the effect of progesterone on estrogen receptor depletion is dose‐related. Therefore the purpose of this study was to examine the effect of different doses of progesterone upon estrogen‐induced prolactin release. Progesterone exhibited a multiphasic effect on estrogen‐induced prolactin release. The 0.8 mg/kg body wt and 3.2 mg/kg body wt doses of progesterone significantly inhibited estrogen‐induced prolactin release, whereas the intermediate dose, 2.0 mg/kg, was without effect. Progesterone is rapidly metabolized to 5α‐dihydroprogesterone in the pituitary, and this metabolite has recently been shown to deplete pituitary estrogen receptors similar to progesterone. Thus the effect of 5α‐dihydroprogesterone onstrogen‐induced prolactin release was also examined. 5α‐dihydroprogesterone was found to exhibit a multiphasic effect similar to progesterone in inhibiting estrogen‐induced prolactin release. The 0.4 mg/kg and 2.0 mg/kg doses of 5α‐dihydroprogesterone significantly inhibited estrogen‐induced prolactin release, whereas the 0.8 mg/kg dose was ineffective. The effect of 5α‐dihydroprogesterone required estrogen priming and was blocked by the antiprogestin, RU486, suggesting progesterone receptor mediation.
Evidence for a Short Feedback of Prolactin on the Tubero‐Infundibular Endings: Differential Effect on the Release of [3 H]Gamma‐Aminobutyric Acid and [3 H]Dopamine from Superfused Median Eminence
Authors: Felman K. , Tappaz M.
Published: September 2006

Release experiments were undertaken on the tubero‐infundibular terminals of the hypothalamic median eminence. Isolated median eminences were preloaded with [3 H]y‐aminobutyric acid (GABA) or [3 H]dopamine in such conditions that non‐specific uptake was pharmacologically impaired. Each median eminence was continuously superfused with Krebs bicarbonate medium and tritium releases were evoked with high potassium solutions. The evoked release was estimated by measuring the total radioactivity of which actual dopamine and GABA represented more than 60% and 80%, respectively. The experiments were done by applying two successive 5‐min pulses of potassium, the second in the presence of prolactin. These stimulations were submaximal: for each, a KCl concentration was chosen that gave about half the maximal response (45 mM for GABA and 30 mM for dopamine); the responses were suppressed by calcium‐free medium. Rat prolactin induced a significant increase of dopamine‐evoked release in a dose‐dependent manner with a maximum (30%) at 25 μg prolactin/ml of medium. Over the same range of concentration a significant but still weak (10%) increase of evoked GABA was observed only with the highest prolactin concentration (25 μg prolactin/ml). At the same concentrations, ovine prolactin induced a markedly reduced effect on dopamine release and had no effect on GABA release. Spontaneous releases of dopamine and GABA were not affected by prolactin. These results show that prolactin enhances acutely and directly, but differently, the evoked release of GABA and dopamine by the median eminence. This differential effect may reflect either a differential regulation or a greater heterogeneity of GABAergic endings. Our data give support for a short feedback exerted by prolactin directly on the tubero‐infundibular neurons.