bluuebunny/crossref_metadata_2025 huggingface dataset:
Random and Non‐Random Coincidence Between Luteinizing Hormone Peaks and Follicle‐Stimulating Hormone, Alpha Subunit, Prolactin and Gonadotropin‐Releasing Hormone ulsations
Authors: Veldhuis Johannes D. , Iranmanesh Ali , Clarke Lain , Kaiser Donald L. , Johnson Michael L.
Published: September 2006

We have examined the co‐pulsatility of luteinizing hormone (LH) and prolactin, LH and follicle‐stimulating hormone (FSH), and LH and α subunit in normal men. We tested whether the degree of physiologically observed co‐pulsatility (peak coincidence) significantly exceeded expected random concordance between independently pulsating hormone series. To this end, computer simulations were used to create synthetic endocrine time series pulsating randomly and independently at known frequencies. Resultant predictions of the mean, variance and probability distribution of the number of randomly coincident peaks permitted us to test the null hypothesis that physiologically observed hormone co‐pulsatility was due to chance peak associations alone. Physiological observations were made in 33 normal men and in six ovariectomized ewes subjected to combined hypothalamo‐pituitary and jugular venous catheterization. The following salient results were obtained: 1) random peak coincidence rates between independently pulsating hormone series were substantial at high pulse frequencies, but such random rates were significantly exceeded in the case of gonadotropin‐releasing hormone and LH peaks (P< 0.0001); 2) random coincidence was further increased when coincidence was defined as peak maxima occurring not only simultaneously but also within some defined time window (e.g. ±10 min, as commonly done in the literature); 3) significant co‐pulsatility could be demonstrated for simultaneous LH and FSH pulsations in normal men (P< 0.0001); 4) coincidence rates for 10‐min lagged (but not for simultaneous) LH and prolactin pulses were significantly more likely than chance associations; 5) observed coincidence between LH and a subunit pulses significantly exceeded expected (random) peak overlap (P<0.001); and 6) in contrast, hormone peaks in different men were only randomly associated.

We conclude that based upon the means, variances and probability distributions calculated here, available reports on peak coincidence between pulsatile neuroendocrine time series must be re‐examined in the light of high rates of random coincidence observed between independently pulsating hormone series.
Multifaceted Interaction of Corticosteroids with the Intracellular Receptors and with Membrane GABAA Receptor Complex in the Rat Brain
Authors: Sutanto Win , Handelmann Gail , de Bree Freddy , de Kloet E. Ronald
Published: September 2006

In vitro assays using crude synaptosomal membrane preparations from the cortex and cytosolic fraction of hippocampus have shown that in the brain, steroids can bind to the intracellular corticosteroid receptors as well as to the membrane‐bound GABA‐receptor complex. Corticosteroid, deoxycorticosterone and spironolactone bound with higher affinity to the mineralocorticoid (relative binding affinity (IC50 in nM) 1.2, 3.9 and 4.9, respectively) than to the glucocorticoid receptors (IC50 5.2, 14.0 and 88.0 nM, respectively) in hippocampal cytosol. They enhanced significantly the binding of [35S]t‐butylbicyclophosphorothionate to cortical membrane. Steroids such as 3α,5α‐tetrahydroxydeoxycorticosterone and 3a‐hydroxy‐5α‐dihydroprogesterone displaced the binding of [35S]t‐butylbicyclophosphorothionate with IC50 (in nM) of 236.7 and 315.0, respectively. In the presence of 10 to 12.5μM added GABA, they bound with higher affinity (IC50 18.0 and 20.5 nM, respectively). Pentobarbital also bound to this site with IC50 of 430,000 and 240,000 nM, respectively, in the absence and presence of GABA. These compounds also enhanced the binding of [3H]flunitrazepam which was not affected by the presence of added GABA. They showed no affinity for mineralocorticoid or glucocorticoid receptors.

Data from this study showed that steroids which preferentially bound to the mineralocorticoid receptor sites (corticosterone, deoxycorticosterone and spironolactone) also enhanced the binding of [35S]t‐butylbicyclophosphorothionate to their recognition sites. Steroids which did not interact with the intracellular receptors (3α,5α‐tetrahydroxydeoxycorticosterone and 3a‐hydroxy‐5α‐dihydroprogesterone) displaced [35S]t‐butylbicyclophosphorothionate binding and enhanced [3H]flunitrazepam binding.
Medial Preoptic Microimplants of the Antiestrogen, Keoxifene, Affect Luteinizing Hormone‐Releasing Hormone mRNA Levels, Median Eminence Luteinizing Hormone‐Releasing Hormone Concentrations and Luteinizing Hormone Release in Ovariectomized, Estrogen‐Treated Rats
Authors: Petersen Sandra L. , Cheuk Chad , Hartman Richard D. , Barraclough Charles A.
Published: September 2006

We examined the temporal changes in plasma luteinizing hormone (LH) levels, median eminence luteinizing hormone‐releasing hormone (LHRH) concentrations and LHRH mRNA levels in estrogen‐treated, ovariectomized rats with empty or antiestrogen‐ containing microcannulae stereotaxically implanted into the medial preoptic area. Neither treatment disrupted the negative feedback effects of estrogen on LH secretion, but antiestrogen (Keoxifene) blocked the afternoon LH surges. In rats exhibiting LH surges, median eminence LHRH concentrations were similar at 0800, 1200 and 1600 h, but they were significantly elevated by 2000 h. In contrast, no alterations in LHRH concentrations occurred in the Keoxifene‐treated group. LHRH mRNA levels in control rats were significantly elevated at 1200, 1600 and 2000 h compared with 0800 h, but LHRH mRNA levels in Keoxifene‐treated rats did not change significantly over the time period examined. When we compared treatment effects over time we saw that serum LH levels were significantly higher in control than Keoxifene‐treated rats only at 1600 and 2000 h. Median eminence LHRH concentrations did not differ between treatment groups until 2000 h when control animals had significantly higher levels than those of Keoxifene‐treated animals. LHRH mRNA levels in Keoxifene‐treated rats were significantly higher than those of controls at 0800 hand significantly lower at 1600 h. No differences in LHRH mRNA levels were detected between groups at either 1200 h or 2000 h. In summary, although it was not clear on which neuronal system estrogen acted, depriving medial preoptic neurons of this steroid in systemically estrogenized rats certainly disrupted the neural mechanisms involved in surge, but not basal LH release. In addition, neither LHRH mRNA levels nor median eminence LHRH concentrations showed variations within the period studied when the estrogen‐sensitive mechanisms involved in LH release were disrupted. Therefore, the changes in LHRH mRNA levels and LHRH concentrations in the median eminence seen in surging animals probably resulted from the same neural events which triggered LH release.
The Brain Renin‐Angiotensin System and the Regulation of Prolactin Secretion in Female Rats: Influence of Ovarian Hormones
Authors: Myers Lin S. , Steele Marianne K.
Published: September 2006

This study was designed to investigate the effects of exogenous and endogenous angiotensin II (All) on prolactin release in ovariectomized rats, with and without estrogen and progesterone pretreatment. In the first series of experiments, All or vehicle was injected into the third cerebral ventricle of conscious, freely‐moving rats. In both treated and untreated rats, administration of 50 ng All suppressed prolactin levels within 15min of injection, compared to vehicle‐injected rats. In untreated rats, prolactin levels returned to baseline values by 30 min, while in treated rats, prolactin levels remained suppressed for an hour.

In the second series of experiments, the involvement of endogenous brain All in tonically suppressing prolactin release was assessed by administering either All receptor blockers (saralasin or sarthran) or an All synthesis inhibitor (enalaprilat, an inhibitor of the conversion of angiotensin I to All). Neither All receptor blockade nor converting enzyme inhibition resulted in any change in prolactin levels in untreated levels in untreated rats. However, following treatment with ovarian steroids, infusion of saralasin or injection of enalaprilat resulted in a significant increase in plasma prolactin tilers. During saralasin infusion, prolactin levels were significantly increased by 15 min and continued to be higher than controls at 60 min. After enalaprilat administration, prolactin levels did not rise significantly until 90 min and then remained elevated up to 120 min post‐injection. These latter results suggest that at least one h is required for maximal inhibition of angiotensin synthesis in the brain.

These data demonstrate that low doses of All suppressed basal prolactin secretion in both untreated and ovarian steroid‐treated, ovariectomized rats. However, treated rats appeared to be more sensitive than untreated animals to the prolactin‐lowering effects of centrally administered All. The lack of prolactin response in untreated rats when brain All synthesis was inhibited or All receptors were blocked suggests that, in the absence of ovarian steroids, endogenous All was not acting tonically to suppress prolactin secretion. Following exposure to ovarian steroids, however, the endogenous brain All system appeared to be activated and involved in controlling prolactin release.
Atrial Natriuretic Factor is Released into Hypophysial Portal Blood: Direct Evidence that Atrial Natriuretic Factor may be a Neurohormone Involved in Hypothalamic Pituitary Control
Authors: Lim Alan T. , Sheward W. John , Copolov David , Windmill Dallas , Fink George
Published: September 2006

Atrial natriuretic factor (ANF) is produced in atriomyocytes (1, 2), released as a 28 amino‐acid peptide into the systemic circulation and probably plays an important role in fluid and electrolyte balance (3, 4). The facts that immunoreactive ANF (ir‐ANF) is also present in nerve terminals in the external layer of the median eminence (ME) (5), ir‐ANF can be released from the hypothalamus in vitro by potassium depolarization (6) and specific ANF binding sites are present at a high concentration in rat pituitary tissue (7) suggest that ANF may be involved in hypothalamic‐pituitary regulation. We report here that ir‐ANF concentrations in hypophysial portal blood are about two to four times greater than in peripheral plasma from hypophysectomized as well as pituitary‐intact adult female rats. These results show for the first time that ir‐ANF is secreted from the hypothalamus into the hypophysial portal circulation at a concentration (≈10−9 M) consistent with a role for ANF as a hypothalamic‐pituitary regulator or modulator.
Effects of Neonatal Exposure to Estradiol on Prolactin Secretion and Activity of the Tubero‐lnfundibular Dopamine System in Young Adulthood: Comparison with Neonatal Prolactin Deficiency*
Authors: Crowley William R. , Shah Girish V. , Watanobe Hajime , Grosvenor Clark E.
Published: September 2006

Previous results from this laboratory indicate that female rats who consume milk deficient in prolactin (PRL) during the neonatal period subsequently display hyperprolactinemia, associated with decreased activity in the tubero‐infundibular dopamine (DA) system and decreased lactotrope responsiveness to DA receptor stimulation. The present studies tested whether these neuroendocrine consequences of neonatal PRL deficiency can be mimicked by exposure of neonatal rats to estradiol. Female rats were injected sc with 1 mUg estradiol benzoate or oil vehicle on postpartum Days one to 3, while in other experiments, females were made neonatally deficient in PRL through treatment of their mothers with the DA agonist bromocriptine, a treatment that reduces the levels of PRL in milk. Females treated neonatally with estradiol benzoate, as well as offspring of the bromocriptine‐treated mothers, displayed hyperprolactinemia as young adults, as compared to their respective vehicle‐matched controls, and in both cases, this was abolished by ovariectomy, indicating dependence upon ovarian secretions. As reported previously in neonatal PRL‐deficient females, neonatal estradiol benzoate‐treated animals also exhibited reduced steady state levels and decreased turnover rates of DA in the median eminence when 35 days of age. DA levels and turnover rates in this region were still significantly reduced on postpartum Day 60. The DA agonist bromocriptine suppressed PRL release to a similar extent in cultured anterior pituitary cells from neonatal estrogen‐treated and control rats, suggesting normal responsiveness of DA receptors on lactotrope cells in both groups. The present results confirm the ability of estradiol treatment or induction of a PRL deficiency during the early neonatal period to induce subsequent hyperprolactinemia in female rats, and further indicate that the hyperprolactinemic conditions resulting from either neonatal manipulation are dependent on the ovary and are associated with decreased levels and turnover of DA in the median eminence during the prepubertal period. Although these findings suggest that increased exposure to estradiol during the neonatal period may underlie the similar effects of neonatal PRL deficiency, the further observations in neonatal estrogen‐treated rats that 1) decreased DA turnover in the median eminence persists at Day 60, and 2) lactotrope responsiveness to DA is normal, differ from results obtained previously in PRL‐deficient rats. Thus, enhanced exposure to estrogen during the neonatal period does not appear to account for all of the neuroendocrine consequences of neonatal PRL deficiency.
Evidence for the Co‐Expression of Oxytocin and Vasopressin Messenger Ribonucleic Acids in Magnocellular Neurosecretory Cells: Simultaneous Demonstration of Two Neurohypophysin Messenger Ribonucleic Acids by Hybridization Histochemistry
Authors: Kiyama Hiroshi , Emson Piers C.
Published: September 2006

A novel enzyme‐labelled oligonucleotide probe specific for oxytocin messenger ribonucleic acid (mRNA) and a radiolabelled oligonucleotide probe specific for vasopressin mRNA were used together to visualize both oxytocin and vasopressin mRNA's in hypothalamus sections from salt loaded (2% saline) rats. The results demonstrate that the majority of magnocellular neurons contain only oxytocin or vasopressin mRNA, however a small number of neurons, 1% to 2%, contained both oxytocin and vasopressin transcripts.
Direct Stimulation of Growth Hormone Secretion by Galanin in the Domestic Fowl*
Authors: Cheung A. , Hall T. R.
Published: September 2006

Galanin, a novel peptide originally isolated from porcine intestine, has a wide distribution in the nervous system and is known to enhance the release of growth hormone in mammals, though the mechanism of its actions is still subject to debate. In the current study, the effects of galanin on growth hormone secretion in the domestic fowl were investigated. Intravenous injections of galanin into both 8‐week old and 18‐week old female Hubbard broilers produced marked increases in plasma growth hormone, similar in magnitude to that evoked by human growth hormone‐releasing factor. Galanin produced dose‐related increases in growth hormone release, with a peak response occurring within 10 min of administration. Growth hormone release in response to a maximal challenge of growth hormone‐releasing factor was further augmented when galanin was given at the same time. Galanin stimulated growth hormone release from chick hemipituitary glands in vitro, a response which was not dependent upon hypothalamic input. In addition, galanin potentiated the actions of growth hormone‐releasing factor on growth hormone release in vitro and these responses were reversed by somatostatin. These results show that galanin is able to stimulate growth hormone release in the domestic fowl by acting directly on the pituitary gland.
Atrial Natriuretic Peptide Secretion from Fetal Rat Diencephalon in Culture
Authors: Levin Ellis R. , Loughlin Sandra E. , Kaplan Gary
Published: September 2006

The presence of a distinct brain pool of the atrial natriuretic peptides (ANP) has been established. To determine the molecular forms and regulation of secretion of ANP, we studied fetal rat diencephalic neurons and glia in primary culture. ANP immunoreactivity determined by radioimmunoassay was found only in the neuron predominant cultures. The neurons contained mainly ANP (103–126) and less ANP (102–126), but secreted only ANP (103–126) into the medium after potassium and glutamate‐dependent depolarization. Little, if any, ANP (99–126), the predominant form which circulates in plasma and originates from the heart, was secreted. The ability of potassium and glutamate to cause a mean 50% increase of ANP secretion above baseline was abolished after deleting calcium chloride from the medium. In contrast, hypo‐ or hyperosmolarity or increased sodium content in the incubation medium did not influence ANP secretion. These studies indicate that regulative secretion of ANP occurs from primary cultures of predominantly diencephalic neurons, probably accounting for the high concentrations of these peptides in this area of the brain. The forms of ANP contained within the cells and secreted after depolarization are different from ANP secreted from neonatal rat atrial myocytes. In contrast to myocytes, varying sodium or osmolarity did not cause ANP secretion. We postulate that influences on ANP production/secretion in the brain may be distinct from the heart.
Relationship of Gonadal Hormone Administration, Sex, Reproductive Status and Age to Monoamine Oxidase Activity Within the Hypothalamus
Authors: Luine Victoria , Hearns Michelle
Published: September 2006

Activity of Type A monoamine oxidase (MAO) was measured in microdissected samples from preoptic‐hypothalamic and hindbrain areas of young male and female rats, and aged female rats. Administration of estradiol and progesterone, in doses sufficient to facilitate lordosis behavior and induce a luteinizing hormone surge in ovariectomized, but not castrated rats, was associated with sexually dimorphic changes of MAO activity within the hypothalamus. Forty‐two h following estradiol benzoate administration, increased MAO activity was measured in the ventromedial nucleus (VML) and midbrain central gray of females, while decreased MAO activity was measured in the VML and arcuate‐median eminence (ArME) of males. Progesterone administration to estradiol benzoate‐primed rats was associated with decreased MAO activity in the VML and medial preoptic nucleus (mPOA) of females and decreased activity in the dorsal raphe nucleus of males. Activity of MAO on diestrus, proestrus and estrus was assessed in ten preoptic‐hypothalamic and hindbrain sites. Differences between days of the cycle were limited to the mPOA, ArME and VML. While activities were generally lowest at estrus, these areas exhibited different patterns of activity across the cycle. Activity was highest at proestrus in the mPOA and highest at diestrus in the VML and ArME. Activity of MAO in some areas of 25‐month old, diestrus rats was altered as compared to young, cycling rats; however, ageing was not associated with widespread changes in MAO activity. In the suprachiasmatic nucleus, aged rats showed approximately 30% less activity than young rats. In the mPOA, VML and ArME, activity in aged females was different from some, but not all, days of the estrous cycle. These results show that MAO activity changes within specific hypothalamic sites when the neuroendocrine axis is altered. Since the changes are present in areas where activity of rnonoaminergic systems is critical for initiating gonadotrophin surges and inducing lordosis behavior, these results provide initial evidence that catabolism of monoamines by MAO may contribute to rnonoaminergic regulation of reproductive function.
Effect of Naloxone on the Secretion of Corticosterone Induced by Gamma‐Hydroxybutyric Acid in Male Rats
Authors: Miguez M. I. , Aldegunde M.
Published: September 2006

The effect of intraperitoneally administered γ‐hydroxybutyrate on the hypothalamo‐hypophysial‐adrenocortical axis was studied. A significant increase in plasma corticosterone was induced by the administration of γ‐hydroxybutyrate (100 mg/kg). The lack of antagonism of this action of γ‐hydroxybutyrate by picrotoxin or bicuculline pretreatments (GABAergic antagonists), suggests independence from the GABAergic system. Neither dopaminergic nor serotoninergic systems intervened in the γ‐hydroxybutyrate‐stimulating effect on the hypothalamo‐hypophysial‐adrenocortical axis. Both corticosterone release and synthesis in adrenocortical cells was not significantly affected by γ‐hydroxybutyrate, suggesting that this is possibly due to a central action of γ‐hydroxybutyrate. The increase in corticosterone levels was probably mediated by an opioid receptor, since a strong similarity existed between the effects of γ‐hydroxybutyrate and those of morphine. Moreover, the results show that the opioid‐receptor involvement was demonstrated by the naloxone‐sensitivity of the γ‐hydroxybutyrate effects.
Secretion of GAWK, a Presumed Product of Chromogranin B Processing, by a Human Medullary Thyroid Carcinoma Cell Line: Effect of Phorbol Ester, Forskolin and Calcium‐lonophore
Authors: Iguchi H. , Kameya T. , Kadoya K. , Shimaoka K.
Published: September 2006

GAWK was isolated from human pituitary glands and presumed to be a processing product of human Chromogranin B. In the present studies, we investigated effects of phorbol ester (TPA), forskolin and Ca2+‐ionophore (A23187) on GAWK secretion using a human medullary thyroid carcinoma‐derived cell line (TT‐cell). A dose‐responsive stimulation of GAWK‐like immunoreactivity (LI) secretion was found in the presence of TPA as well as forskolin. A23187 caused an increase of GAWK‐LI secretion and addition of TPA together with A23187 revealed an additive effect on the GAWK‐LI secretion. These findings indicate that GAWK‐LI is a secretory peptide in the TT‐cells and suggest that A and C kinase, and possibly Ca2+‐calmodulin transduction systems are involved in the GAWK‐LI secretion by the TT‐cells. TT‐cells may provide a good model for the investigation of regulation of Chromogranin secretion.
Expression of Histamine H1‐Receptors in Xenopus Oocytes Injected with Messenger Ribonucleic Acid from Bovine Adrenal Medulla: Pertussis Toxin Insensitive Activation of Membrane Chloride Currents
Authors: Meyerhof Wolfgang , Schwärzt Jürgen R. , Höllt Volker , Richter Dietmar
Published: September 2006

Histamine H2‐receptors have been identified in Xenopus oocytes previously microinjected with poly(A) + ribonucleic acid from bovine adrenal glands. Bath application of histamine to ribonucleic acid‐primed oocytes evoked concentration‐dependent, oscillating membrane currents under voltage‐clamp conditions. H1‐receptor specific antagonists clemastine, doxepin, pyrilamine, promethacine, diphenylhydramine, dephenylpyraline and chlorpheniramine, but not H2‐receptor antagonists, cimetidine and ranitidine, inhibited histamine‐induced responses. Membrane currents evoked by bath‐applied histamine were insensitive to pertussis toxin, carried by chloride ions and dependent on intracellular but not extracellular calcium.
Arginine Vasopressin‐Anti‐Idiotypic Immunostaining of Human Brain Cells
Authors: Joseph S. A. , Pilcher W. H. , Knigge K. M. , Abood L G. , Michael G. J.
Published: September 2006

Polyclonal anti‐idiotypic antibodies, generated against the IgG fraction of antisera to arginine vasopressin (AVP), were shown to recognize two proteins in rat brain and bovine pituitary associated with [3 H]AVP binding. Immunochemical analyses with these antisera revealed reactivity in paraventricular and supraoptic nucleus neuronal elements and in terminals of the posterior pituitary in the human central nervous system. With the use of a dual immunocytochemical staining technique employing both the anti‐idiotype and idiotype for AVP it was possible to demonstrate a pattern of AVP‐anti‐idiotypic‐immunoreactivity on AVP neuronal elements which suggests the existence of autoreceptors.
Changes in Feeding Activity, Plasma Luteinizing Hormone, and Testes Weight in Ring Doves Following Hypothalamic Injections of Prolactin
Authors: Foreman Kenneth T. , Lea Robert W. , Buntin John P.
Published: September 2006

Microinjections of ovine prolactin were administered unilaterally to the ventromedial hypothalamic nucleus and the preoptic‐suprachiasmatic region in adult male ring doves in an attempt to determine the site(s) at which intracranial injections of prolactin act to alter feeding behaviour and gonadotropin secretion in this species. Food intake and body weight were measured daily during a 6‐day pretreatment period and the 5‐day treatment period that immediately followed. During the treatment period, birds received twice daily injections (0.5 μl) of either 2.5 ng ovine prolactin or saline vehicle. An additional group of birds with cannulae in the ventromedial nucleus were given twice daily injections of 25 ng ovine prolactin. Although food consumption was unaffected by low dose prolactin treatment, birds given 25 ng prolactin injections into the ventromedial nucleus showed a significant augmentation in food intake. Injections of 25 ng prolactin into the preoptic area also increased feeding; however, the magnitude of this hyperphagic response, as expressed relative to pretreatment levels, was less than that observed following prolactin injection into the ventromedial nucleus. No differences were observed between prolactin‐treated and vehicle‐treated birds in either cannulation group when testes weights and plasma luteinizing hormone concentrations were compared at the end of the treatment period. However, the possibility that prolactin influenced changes in luteinizing hormone and testes weight relative to baseline values could not be assessed due to constraints imposed by the experimental paradigm used. These results suggest that prolactin‐sensitive neurons in the ventromedial hypothalamic region and the preoptic area are potential sites of prolactin action in promoting hyperphagia in ring doves. However, the role of these sites in mediating prolactin‐induced suppression of gonadotropin secretion in this species remains to be clarified.
Castration Reduces the Nocturnal Rise of Pineal Melatonin Levels in the Male Rat by Impairing its Noradrenergic Input
Authors: Hernandez G. , Abreu P. , Alonso R. , Santana C. , Moujir F. , Calzadilla C. H.
Published: September 2006

The effects of castration and testosterone treatment on pineal day‐night rhythms were studied in male rats. Bilateral gonadectomy was performed at 21 days of age. Testosterone propionate was given subcutaneously to castrated animals in a dose of 10 μg/100 g body weight during two consecutive days before sacrifice. Animals were killed 40 days after gonadectomy at four different times of a 12:12 h light‐dark cycle (1600, 2400, 0400 and 0800h). Tyrosine hydroxylase activity was measured in individual pineals by means of high‐performance liquid chromatography determination of L‐DOPA formed. Pineal levels of norepinephrine, dopamine, 5‐hydroxytryptamine and 5‐hydroxyindole acetic acid were determined by high‐performance liquid chromatography with amperometric detection, while pineal melatonin content was measured by radioimmunoassay. Castration abolished the day‐night rhythms of pineal tyrosine hydroxylase activity and norepinephrine content, both by elevating their daytime levels and by blocking their nocturnal rise. In addition, gonadectomy drastically modified pineal indoleamine metabolism by increasing daytime levels of both 5‐hydroxytryptamine and 5‐hydroxyindole acetic acid, and by reducing the nocturnal elevation of pineal melatonin content. Testosterone treatment was unable to prevent the effect of orchidectomy on pineal rhythms of tyrosine hydroxylase activity, 5‐hydroxytryptamine or 5‐hydroxyindole acetic acid content, however it partially restored the day‐night pineal rhythms of both norepinephrine and melatonin content. These results are indicative of a possible participation of reproductive hormones in the control of pineal rhythmic activity in the male rat. Apparently, since gonadectomy abolished the nocturnal rise of both pineal tyrosine hydroxylase activity and norepinephrine content, the primary site of action of reproductive hormones could be at the level of the superior cervical ganglion.
Negative Feedback by Corticosterone is the Major Mechanism Responsible for Corticotropin‐Releasing Factor‐Induced Desensitization
Authors: Miyanaga Ken , Miyabo Susumu , Ooya Eiichi
Published: September 2006

Subcutaneous infusion of ovine corticotropin‐releasing factor (oCRF) to male rats at a rate of 0.1 μg/h for 4 days did not alter the rise of plasma adrenocorticotropin (ACTH) and corticosterone induced by 3‐min ether exposure. In contrast, 1.0 μg/h oCRF for 4 days virtually abolished the ACTH response to ether, whereas a substantial corticosterone response was preserved. Intravenous administration of phenoxybenzamine (5 mg/kg) prior to ether stress completely inhibited the corticosterone response. Plasma ACTH and corticosterone responses in chronic CRF‐treated rats to an intravenous bolus injection of 2.0 μg oCRF were also markedly blunted by pretreatment with subcutaneous oCRF 1.0 μg/h for 4 days. Adrenalectomized rats given corticosterone in the drinking fluid at a concentration of 80 μg/ml showed a plasma corticosterone pattern mimicking the normal diurnal rhythm. Basal plasma ACTH and thymus weight were within normal limits. In these rats, the magnitude of ACTH rise to ether stress did not differ between the chronic CRF‐treated rats and the vehicle‐treated rats. In cultured pituitary cells prepared from animals infused with oCRF 1.0 μg/h for 4 days, the basal and CRF‐stimulated ACTH release was reduced by 46%. We conclude that among the possible mechanisms proposed for ‘desensitization’ during long‐term infusion of CRF, negative feedback by elevated corticosterone at both brain and pituitary levels is the primary factor. The results also suggest the existence of non‐ACTH‐mediated catecholaminergic systems in the stress‐induced adrenocortical activation.
Isolation, Amino‐Acid Sequence, Synthesis and Biological Properties of Urotensin I from Hippoglossoides elassodon
Authors: McMaster D. , Itoh H. , MacCannell K. L. , Rivier J. , Rivier C. , Vale W. , Fryer J. N. , Tran T. N. , Lederis K.
Published: September 2006

A 41‐residue urotensin I neuropeptide (H‐UI) was isolated from urophyses of the marine teleost Hippoglossoides elassodon (the flathead sole). The peptide was recognized by its partial cross‐reactivity in a radioimmunoassay developed for Catostomus (sucker) Ul (S‐UI), and was purified by reversed‐phase high‐performance liquid chromatography. The amino‐acid sequence was shown to be H‐Ser‐Glu‐Glu‐Pro‐Pro‐Met‐Ser‐lle‐Asp‐Leu‐Thr‐Phe‐His‐Met‐Leu‐Arg‐Asn‐Met‐lle‐His‐Arg‐Ala‐Lys‐Met‐Glu‐Gly‐Glu‐Arg‐Glu‐Gln‐Ala‐Leu‐lle‐Asn‐Arg‐Asn‐Leu‐Leu‐Asp‐Glu‐Val‐NH2. H‐UI is 66% homologous with S‐UI and 63% homologous with Cyprinus (carp) Ul (C‐UI). Like S‐ and C‐UI, H‐UI is about 50% homologous with the frog skin peptide sauvagine and with Catostomus and mammalian corticotropin‐releasing factors. H‐UI had similar vasodilatory effects in mammals, and similar adrenocorticotropin‐releasing effects (in rat and goldfish) to S‐UI, C‐UI, sauvagine and the corticotropin‐releasing factors, but had relatively low potency (e.g. 10% to 30% of the vasodilatory potency of S‐ and C‐UI) in all the bioassay systems studied.
Ovarian Steroid Regulation of Pulsatile Luteinizing Hormone Release During Early Gestation in the Rat
Authors: Gallo Robert V. , Bona‐Gallo Antonella , O'Sullivan David
Published: September 2006

The object of this study was to examine ovarian regulation of pulsatile luteinizing hormone (LH) secretion during early gestation. This was done primarily by analyzing pulsatile LH release in rats that were either sham ovariectomized (OVX) on Day 7 of pregnancy, implanted with empty Silastic capsules, and bled on Day 8, or OVX on Day 7, immediately implanted with Silastic capsules producing plasma levels of estradiol and/or progesterone characteristic of Day 7 to 8 of pregnancy, and bled on Day 8. In addition, the role of progesterone in regulating pulsatile LH secretion was also examined by administration of the progesterone receptor antagonist, RU486, on Day 7 and examining pulsatile LH release on Day 8 of pregnancy. OVX caused a marked increase in LH pulse amplitude and frequency within 24 h. Replacement with physiological plasma levels of estradiol or progesterone alone had no suppressive effect on this OVX‐induced increase in pulsatile LH secretion. Restoration of physiological plasma levels of both estradiol and progesterone returned LH pulse amplitude to values seen in sham OVX controls, and prevented the OVX‐induced increase in LH pulse frequency. The group mean LH pulse frequency tended to be less in estradiol + progesterone‐treated rats than in sham OVX controls, but this difference was not statistically significant. RU486 blocked uterine progesterone receptors as evidenced by endometrial hemorrhaging. In agreement with the OVX + steroid replacement data, RU486 administration also resulted in increases in LH pulse amplitude and frequency. These data demonstrate that the frequency and amplitude of LH pulses on Day 8 of gestation are held in check by negative feedback signals coming from the ovary. Neither steroid alone exerts any suppressive influence over pulsatile LH secretion during early gestation, but both steroids acting together exert a prominent negative feedback regulation on the pulsatile LH release process.
Cell‐Specific Expression of the Rat Oxytocin Gene in Transgenic Mice
Authors: Young W. Scott , Reynolds Kay , Shepard Emily A. , Gainer Harold , Castel Mona
Published: September 2006

The genes for the posterior pituitary hormones oxytocin (OT) and vasopressin (VP) are expressed in magnocellular neurons of the hypothalamus. Previous attempts to obtain cell‐specific expression of OT and VP transgenes in mice have been unsuccessful using constructs containing only the OT or VP genes. As the endogenous genes are located near each other on the same chromosome, we investigated four transgenic mouse lines incorporating a single 5.2 k bp construct of rat genomic deoxyribonucleic acid with 1.63 k bp and 3.55 k bp of the OT and VP genes, respectively. Rat OT transcripts were detected only in transgenic mouse OT neurons of the paraventricular and supraoptic nuclei in two lines. The levels of endogenous and transgene OT transcripts increased in response to 10 days of lactation. Furthermore, rat OT‐associated neurophysin immunoreactivity was detected in magnocellular cell bodies as well as in the posterior pituitary of the transgenic but not the control mice. Cell‐specific rat VP expression was not detected in these transgenic mice.
Heterologue Conversion of Amphibian Hydrin 2 into Vasotocin Through Bovine Granule Alpha‐Amidating Enzyme
Authors: Rouillé Yves , Chauvet Jacqueline , Acher Roger
Published: September 2006

Hydrin 2 (vasotocinyl‐Gly), found along with vasotocin in the neurohypophysis of frogs and toads but not of other vasotocin‐bearers such as birds and reptiles, is believed to act on water permeability of frog skin, whereas vasotocin mainly fulfils the antidiuretic function on the kidney. In order to understand the peculiar regulation of provasotocin differential processing in amphibians, conversion of hydrin 2 into vasotocin has been attempted using bovine pituitary granule α‐amidating enzyme. Generated vasotocin has pharmacological properties and Chromatographic behaviour in high‐performance liquid chromatography identical to those of synthetic vasotocin. However, the low yield of conversion (5% to 10%) suggests that additional factor(s) might be involved in the physiological processing.
Inhibition by Brain Natriuretic Peptide of Vasopressin Neurons in the Supraoptic Nucleus and Neurons in the Region of the Anteroventral Third Ventricle in Rat Hypothalamic Slice Preparations
Authors: Yamamoto S. , Inenaga K. , Yamashita H.
Published: September 2006

It is not entirely clear whether or not atrial natriuretic peptide (ANP) directly inhibits vasopressin neurons in the supraoptic nucleus (SON) and paraventricular nucleus. Recently, a novel peptide, brain natriuretic peptide (BMP), which has been isolated from the brain, has been shown to have a similar action to ANP on the regulation of vasopressin release. Intracerebroventricular injection of both BNP and ANP inhibits stimulus‐evoked increases of plasma vasopressin level. The present study was undertaken: 1) to investigate whether BNP affects the activity of neurons in the region of the anteroventral third ventricle (AV3V) and SON which are involved in the control of body fluid homeostasis and blood pressure regulation, 2) to reassess effects of ANP on SON neurons, and 3) to test whether BNP exerts its effects by mechanisms which are different from those of ANP. Extracellular recordings were made from 213 AV3V and 110 SON spontaneously firing neurons in the rat coronal hypothalamic slice preparation. Of the AV3V neurons tested, BNP inhibited 86 (40%) and excited 2 (1%) while 125 neurons remained unaffected. A dose‐response relationship was obtained for 7 AV3V neurons at different BNP concentrations ranging from 10−11 M to 10−6 M; the firing rates of all 7 neurons decreased. The threshold concentration to evoke inhibitory responses was approximately 10−10M in the AV3V. When BNP and ANP were applied to the same neuron, most AV3V neurons which were inhibited by BNP were also inhibited by ANP and the neurons which were unaffected by BNP were also unaffected by ANP. Thus, these two peptides probably have a similar action on AV3V neurons. When BNP and angiotensin II were applied to a group of 60 neurons in the AV3V, most of the responsive neurons showed either inhibitory responses to BNP or excitatory responses to angiotensin II. Both BNP and ANP were applied to a group of 110 SON neurons: BNP (10 −7 M) inhibited 52 (75%) of 69 phasic (putative vasopressin) neurons, while BNP affected none of the 41 non‐phasic (putative oxytocin) neurons. By contrast, ANP inhibited only 20 (29%) of 69 phasic neurons tested but it also had no effect on 41 non‐phasic neurons tested. Our results are consistent with the suggestion that BNP is involved in the regulation of vasopressin release by acting on SON neurons and AV3V neurons.
Thyrotrophin‐Releasing Hormone Raises Cytosolic Free Calcium Concentration in Human Adenomatous Somatotrophs and Corticotrophs; Comparison with in vivo Responsiveness to Thyrotrophin‐Releasing Hormone in Patients with Acromegaly or Cushing's Disease
Authors: Spada Anna , Reza‐Elahi Farzin , Lania Andrea , Pandiella Atanasio , Bassetti Monique , Bazzoni Nicoletta , de Alamo Paloma Gil , Faglia Giovanni
Published: September 2006

The effect of thyrotrophin‐releasing hormone (TRH) on intracellular free Ca2+ concentration, [Ca2+)i, was investigated with the fluorescent dye fura‐2 in cell suspensions obtained from 13 human growth hormone‐secreting adenomas and 6 adrenocorticotrophin‐secreting adenomas. Preoperatively, 9 out of 13 acromegalic patients showed a positive growth hormone response to TRH administration while none of the 6 patients with Cushing's disease had a plasma adrenocorticotrophin increase after TRH injection. In all the growth hormone‐secreting adenomas the addition of TRH (100 nM) caused a significant rise in [Ca2+]i (from a resting level of 133±40 (±SD) to a value of 284±119 nM at 100 nM TRH, n = 42; P<0.001). The transient induced by TRH was found to have a dual origin, one due to Ca2+ mobilization from intracellular stores which was maintained in presence of EGTA (3mM) and verapamil (10 μM) and a plateau phase due to Ca2+ influx from the extracellular media. Somatostatin (0.1 μM) lowered both resting [Ca2+]i and TRH‐induced transients. The effect of gonadotrophin‐releasing hormone on [Ca2+]i was evaluated on cell suspensions obtained from 6 growth hormone‐secreting adenomas. Gonadotrophin‐releasing hormone (100 nM) caused a marked rise in [Ca2+]i (from 179±25 to 283±15nM) on the cell suspension obtained from the only in vivo responsive adenoma while it was ineffective in the remaining 5. Although TRH was ineffective in modifying plasma adrenocorticotrophin levels in all patients with Cushing's disease, in 5 out of 6 tumors the addition of 100 nM TRH caused a significant rise in [Ca2+]i (from 102.5 ± 36 to 163±66 nM, n = 22; P < 0.005). However, the effect of TRH on [Ca2+]i was significantly lower than that caused by arginine vasopressin, a physiological stimulator of adrenocorticotrophin release ([Ca2+]i values; 145±78 nM at 100 nM TRH versus 300±140 at 10 nM arginine vasopressin, n = 15; P<0.05). Moreover, the effect of arginine vasopressin on [Ca2+]i was detectable at concentrations as low as 0.1 nM while TRH was effective at concentrations higher than 1 nM. By contrast, gonadotrophin‐releasing hormone was ineffective in increasing [Ca2]i in all the adrenocorticotrophin‐secreting adenomas studied. Collectively, these data indicate that sensitivity to TRH is present in almost all the growth hormone‐ and adrenocorticotrophin‐secreting adenomas independently of the responsiveness of the individual patients to the peptide.
Determination of Enkephalins in Rat Cerebrospinal Fluid with High‐Performance Liquid Chromatography‐Electrochemical Detection: Increased Concentrations During Lactation are Controlled by Sucking
Authors: Forsberg G. , Bednar I. , Qureshi G. A. , Eneroth P. , Sodersten P.
Published: September 2006

Methionine‐ and leucine‐enkephalin were measured in the cerebrospinal fluid of lactating rats by high‐performance liquid chromatography and electrochemical detection. The concentration of both peptides was high while the rats were nursing their litter. The concentration of methionine‐enkephalin decreased rapidly when the mother left her litter and increased equally rapidly after mother‐young reunion, provided the pups were allowed direct contact with the nipples of the mother. The level of leucine‐enkephalin did not change during the period of time the lactating rat normally stayed away from its litter but decreased after prolonged (12 h) mother‐pup separation. These results show that the concentration of methionine‐, but not leucine‐enkephalin in the cerebrospinal fluid fluctuates as the lactating rat interacts with its litter and is directly dependent upon the suckling stimulus. Although methionine‐enkephalin may contribute to the inhibition of sexual behaviour which occurs during lactation, the role of the enkephalins in the other behavioural and endocrine adaptations of lactation is unknown.
Oxytocin Receptor Binding in Female Prairie Voles: Endogenous and Exogenous Oestradiol Stimulation
Authors: Witt D. M. , Carter C. S. , Lnsel T. R.
Published: September 2006

Previous studies have demonstrated that oxytocin receptors in specific nuclei of rat forebrain are regulated by gonadal steroids. The current study used in vitro receptor autoradiography to investigate the distribution and regulation of oxytocin receptors in the forebrain of the female prairie vole (Microtus ochrogaster). In contrast to rats, in female prairie voles gonadal steroid secretion and oestrus behaviour result from male chemosignal stimulation and ovulation is induced by mating. Thus, the prairie vole brain provides an opportunity for investigating links between environmental stimuli, gonadal steroids and oxytocin receptors. Using a selective oxytocin receptor ligand [125l]d(CH2)5[Tyr(Me)2,Tyr‐NH29]ornithine vasotocin ([125I]OTA), specific binding was found in several regions including the anterior olfactory nucleus, the ventromedial nucleus of the hypothalamus, the bed nucleus of the stria terminalis, the amygdala and several cortical areas. Following ovariectomy, oestradiol benzoate (10 μg) administration increased oxytocin receptor binding 100% in the anterior olfactory nucleus, but did not affect receptors in other regions. Gonadallyintact females, exposed to male chemosignals, had significant increases in both endogenous oestradiol levels and anterior olfactory nucleus oxytocin receptor binding relative to gonadally‐intact females unexposed to male chemosignals. Following prolonged exposure to males with ad libitum mating, [125I]OTA receptor binding decreased to the levels found in unstimulated females. These results demonstrate that increases in oestrogen levels, of either exogenous or endogenous origin, can modulate oxytocin receptors in the brains of female prairie voles. In contrast to rats, oestrogen in female prairie voles appears to affect receptors in the anterior olfactory nucleus rather than the hypothalamus. We suggest that the species differences in oxytocin receptor distribution and gonadal steroid responsiveness reflect variations in reproductive physiology and possibly behaviour.
Reverse Haemolytic Plaque Assay Study of Corticotropin‐Releasing Hormone and Arginine Vasopressin Interaction in Ovine Corticotropes
Authors: Madsen G. , Chan E‐C. , Falconer J. , Ho K. Y. , Smith R.
Published: September 2006

Corticotropin‐releasing hormone and arginine vasopressin are known to interact in stimulating secretion of adrenocorticotropin‐related peptides from corticotropes. However, the mechanism mediating this interaction is uncertain. Recently, evidence has been provided using a reverse haemolytic plaque assay that in rat pituitary cells, arginine vasopressin potentiates the effects of corticotropin‐releasing hormone by increasing the percentage of target cells that secrete adrenocorticotropin. To determine whether a similar mechanism also operates in the sheep corticotrope, which is reportedly more sensitive to arginine vasopressin than that of the rat, a reverse haemolytic plaque assay for β‐endorphin secretion was used to study the response of ovine corticotropes to stimulation by increasing doses of corticotropin‐releasing hormone or arginine vasopressin (0.1 nM to 10.0 nM) alone or in combination.

In the reverse haemolytic plaque assay, β‐endorphin antiserum at 1:50 and complement at 1:10 were found to be optimal dilutions for plaque formation. A concentration‐dependent response curve to corticotropin‐releasing hormone was obtained with a significant increase in plaque area from basal to reach maximal levels at 1.0 nM. Arginine vasopressin also stimulated an increase in plaque area, however, plaques formed were significantly smaller than those caused by corticotropin‐releasing hormone. Since in the reverse haemolytic plaque assay, plaque area is related to the amount of hormone secreted by the cell, results demonstrate that although corticotropin‐releasing hormone and arginine vasopressin both stimulate β‐endorphin secretion from ovine corticotropes, corticotropin‐releasing hormone is a more potent secretagogue than arginine vasopressin in that it causes the formation of significantly larger plaques.

The addition of arginine vasopressin to low concentrations of corticotropin‐releasing hormone caused plaque areas to reach maximal levels at 0.1 nM whereas these levels were only attained at 1.0 nM when corticotropin‐releasing hormone was used alone. Therefore, arginine vasopressin interacts with corticotropin‐releasing hormone to increase corticotrope responses by increasing their secretory response to corticotropin‐releasing hormone. These data are consistent with previous work suggesting that arginine vasopressin increases the expression of corticotropin‐releasing hormone receptors on the corticotrope cell surface. However, no significant increase in the percentage of plaque‐forming cells was seen with either corticotropin‐releasing hormone or arginine vasopressin alone or in combination implying that there was no recruitment of previously non‐secreting cells.