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Biomedical subjects

W Vale

Publications and source records attributed to W Vale.

At least 235 records · Page 13Linked to original sources
PubMed1987

A new cytotoxin specific for the target cells of corticotropin-releasing factor.

To develop a cytotoxic agent selective for pituitary corticotropes, an analog of CRF, [Nle21,38,Arg36]rat (r) CRF, was conjugated to the plant toxin gelonin using glutaraldehyde as a cross-linking agent. In a two-step synthesis, glutaraldehyde was first coupled to the amino-terminal of the CRF analog. This was then reacted with gelonin to form a product, which contained 20 mol [Nle21,38,Arg36]rCRF/mol gelonin, as indicated by amino acid analysis. Efficacy and specificity of the gelonin-[Nle21,38,Arg36]rCRF conjugate were assessed in cultured rat anterior pituitary cells 3 days after a 12-h exposure to the cytotoxic conjugate, CRF, or gelonin. While pretreatment with the cytotoxic gelonin-[Nle21,38,Arg36]rCRF conjugate decreased cellular ACTH content by 74%, pretreatment with appropriate concentrations of CRF had no significant effect on cellular ACTH content. The ACTH secretory response to 2.5 nM CRF was completely eliminated by pretreatment with the gelonin-[Nle21,38,Arg36]rCRF conjugate; in contrast, pretreatment with identical doses of CRF had minimal effect. Neither pretreatment with CRF nor pretreatment with the gelonin-[Nle21,38,Arg36] rCRF conjugate had any effect on the content of LH or the LH secretory response to GnRH. These results indicate the efficacy and specificity of the conjugate of [Nle21,38,Arg36]rCRF to gelonin in eliminating CRF target cells.

Adrenocorticotropic Hormone↗
PubMed1987

Gonadotropins and testosterone escape from suppression during prolonged luteinizing hormone-releasing hormone antagonist administration in normal men.

The ability of prolonged administration of a LHRH antagonist, [Ac-delta 3Pro1,4F-D-Phe2,D-Trp3,6]LHRH (4F-antagonist), to suppress serum gonadotropin and testosterone levels was studied in normal men. The 4F-antagonist was given either as a continuous 13.3 micrograms/kg X h sc infusion for 72 h or as intermittent sc injections of 100 micrograms/kg every 6 h for 7 days. Serum FSH, LH, and testosterone levels decreased in the period immediately following initiation of 4F-antagonist administration. However, an escape toward baseline levels for each of these hormones occurred during prolonged antagonist administration. When men receiving the continuous infusion were challenged with iv bolus doses of 50 micrograms LHRH, the response of LH after the first 12 h of 4F-antagonist administration was similar to that before its administration. This gonadotropin and testosterone escape suggests that, at the doses used, the inhibitory action of the antagonist on gonadotropin secretion is progressively lost. The initial decrease in androgen levels could serve to augment endogenous LHRH release, which, in turn, overcomes the pituitary effects of the antagonist, or to augment endogenous LH secretion directly. These results demonstrate that the pituitary can escape from the suppressive effects of prolonged LHRH antagonist administration and partially restore serum gonadotropin and testosterone levels to normal in man.

Adult↗
PubMed1987

Adenosine 3',5'-monophosphate, prostaglandins, and epinephrine stimulate the secretion of immunoreactive gonadotropin-releasing hormone from cultured human placental cells.

Cell culture and biochemical procedures were used to identify and study the possible mechanisms regulating the secretion of GnRH-like immunoreactivity (GnRH-LI) from human placenta. Monolayer primary cultures of trophoblasts were established after mechanical and enzymatic dispersion of normal human term placenta. The cultured cells stained immunocytochemically positive with anti-GnRH serum, and GnRH-LI extracted from the cells eluted from high performance liquid chromatography with the same retention time as authentic GnRH. One week after plating, exposure to high concentrations of K+ or to various doses of veratridine, a Na+ ionophore, increased GnRH-LI release into the culture medium. This effect was reversed by Ca2+ antagonists (cobalt, EGTA, and verapamil). Dibutyrylcyclic AMP, forskolin, theophylline, and theobromine also increased GnRH-LI concentrations in the medium of cultured placental cells in a dose-related manner, as did prostaglandins E2 and F2 alpha and epinephrine. The effect of epinephrine on GnRH-LI concentrations was mimicked by isoproterenol and reversed by propranolol, suggesting an effect mediated by beta-adrenergic receptors. These results indicate that GnRH-LI release from cultured human placental cells is stimulated by the opening of ionic channels and activation of the adenylate cyclase/cAMP system, and that prostaglandins and epinephrine may be involved in the regulation of GnRH-LI release from human placenta.

Adenosine Monophosphate↗
PubMed1987

Growth hormone-releasing factor induces c-fos expression in cultured primary pituitary cells.

GH-releasing factor (GRF) and somatostatin regulates the secretion and biosynthesis of GH as well as the proliferation of GH-producing cells. In order to further characterize the mitogenic effect of GRF, we studied the expression of the proto-oncogene c-fos in primary pituitary cells. Maximal induction of c-fos mRNA was observed 20-60 min after stimulation with 5 nM GRF, returning to basal levels after 2 h. Somatostatin-14 (5 nM) partially inhibited the GRF induced c-fos expression. Forskolin and phorbol 12, 13 dibutyrate induced c-fos gene in cultured primary pituitary cells with similar kinetics. Transcription of the fos gene was accompanied by biosynthesis of the fos protein. Indirect immunofluorescence using a fos specific antibody, showed exclusive nuclear localization of the fos protein. These data demonstrate that GRF and somatostatin, in addition to regulating GH secretion and somatotroph proliferation, can also regulate the expression of c-fos proto-oncogene in primary somatotrophs.

Animals↗
PubMed1986

Inhibin-mediated feedback control of follicle-stimulating hormone secretion in the female rat.

The secretion of follicle-stimulating hormone (FSH) by the anterior pituitary gland is regulated by the interaction of hypothalamic and gonadal hormones. Recently, proteins termed inhibins that selectively suppress FSH secretion have been purified and characterized from the gonadal fluids of several species. Antibodies to a synthetic peptide encompassing the amino terminal 25 residues of the recently characterized porcine inhibin were used to develop a specific radioimmunoassay (RIA) for inhibin and to neutralize endogenous inhibin during the estrous cycle of the rat. The administration of 20 international units of pregnant mare serum gonadotropin (PMSG) stimulated the secretion of inhibin in intact immature female rats, whereas ovariectomy caused an abrupt decrease in plasma inhibin concentrations that were not prevented by the injection of PMSG. The infusion of a polyclonal antiserum to inhibin, from 12 noon on proestrus to 1 a.m. on the morning of estrus, as well as its acute intravenous injection during diestrus I or II, caused an increase in plasma FSH (but not luteinizing hormone) concentrations. These results support the hypothesis of a feedback loop between the release of ovarian inhibin and FSH in the female rat.

Animals↗
PubMed1986

Corticotropin releasing factor receptor-mediated stimulation of adenylate cyclase activity in the rat brain.

Corticotropin releasing factor (CRF)-stimulated adenylate cyclase activity and receptor binding were examined in rat brain homogenates using a potent synthetic CRF analog--[D-Tyr3,D-Pro4,Nle18,21,alpha-helical]CRF3-41 (alpha-hel CRF3-41). Binding of alpha-hel CRF3-41 in the rat brain was saturable, reversible, of high affinity and exhibited relevant peptide specificity. This analog also stimulated adenylate cyclase activity of various brain regions; the greatest magnitude of stimulation was in the cerebral cortex followed by the septum, cerebellum and thalamus. Adenylate cyclase stimulation in the cerebral cortex was concentration-dependent with an ED50 of 2.5 +/- 0.4 nM for alpha-hel CRF3-41 and an ED50 of 16 +/- 2 nM for ovine and rat CRF. Maximal stimulation was comparable for all peptides. Agonist-stimulated adenylate cyclase activity was competitively blocked by the CRF antagonists. The inactive CRF analog, ovine CRF1-39, at concentrations less than 1 microM, did not significantly stimulate adenylate cyclase. Adrenalectomy, which has been reported to modulate CRF receptor number and CRF-stimulated adenylate cyclase activity in the anterior pituitary, had no effect on CRF receptor binding or CRF-stimulated adenylate cyclase activity in the cerebral cortex. These results suggest that, as in the anterior pituitary, at least some of the physiological responses mediated by CRF receptors in the brain utilize the cyclic nucleotide regulatory pathway as a post-receptor mechanism.

Adenylyl Cyclases↗
PubMed1986

Corticotropin releasing factor (CRF) receptor antagonist blocks activating and 'anxiogenic' actions of CRF in the rat.

The effectiveness of a recently synthesized corticotropin releasing factor (CRF) antagonist, alpha-helical CRF9-41, in reversing the locomotor activating and proconflict effects of CRF was evaluated. The CRF receptor antagonist (50, 100 and 200 micrograms, i.c.v.) produced a dose-related attenuation of the response-suppressing effects of CRF in a conflict model of anxiety. The antagonist also effectively suppressed the marked locomotor activation produced by CRF. No discernible intrinsic effects on behavior were noted when the antagonist was administered alone. These results suggest that the behavioral effects of CRF are receptor-mediated phenomena and point to the potential usefulness of a CRF antagonist in understanding the function of endogenous CRF in mediating responses to stressful stimuli.

Animals↗
PubMed1986

Stress-induced inhibition of reproductive functions: role of endogenous corticotropin-releasing factor.

In the adult castrated male rat, exposure to inescapable, intermittent electroshocks inhibited the pulsatile pattern of luteinizing hormone release and markedly lowered its plasma concentrations. The central administration of the corticotropin-releasing factor (CRF) antagonist alpha-helical ovine CRF residues 9 to 41 reversed the inhibitory action of stress. Neither its peripheral injection, nor the intraventricular injection of the inactive CRF analog des-Glu to Arg ovine CRF was effective. These results suggest that endogenous CRF may mediate some deleterious effects of noxious stimuli on reproduction.

Adrenocorticotropic Hormone↗
PubMed1986

Neuropeptides and NADPH-diaphorase activity in the ascending cholinergic reticular system of the rat.

A major group of cholinergic neurons is present in the midbrain and pontine tegmentum. These cells could be selectively stained using either monoclonal antibodies to choline acetyltransferase, the pharmacohistochemical acetylcholinesterase procedure, or reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. Using these three techniques, the precise distribution of this cell group was determined. By combining these techniques with immunohistochemical staining for various neuropeptides, examples of peptide-cholinergic coexistence could be demonstrated in this cell group. Approximately 30% of these cholinergic neurons displayed substance P immunoreactivity. Most of these cells also showed corticotropin-releasing factor immunoreactivity and bombesin/gastrin-releasing peptide immunoreactivity. These results therefore provide evidence for the coexistence of various neuropeptides together with NADPH-diaphorase activity in the ascending cholinergic reticular system.

Acetylcholinesterase↗
PubMed1986

The effect of intravenous, subcutaneous, and intranasal GH-RH analog, [Nle27]GHRH(1-29)-NH2, on growth hormone secretion in normal men: dose-response relationships.

A 29 amino acid analog of growth hormone releasing hormone (GH-RH)-40 was given intravenously, subcutaneously, and intranasally to normal men to determine its effectiveness in stimulating growth hormone (GH) release. The GH-RH analog, [Nle27]GH-RH(1-29)-NH2, is an amidated 29 amino acid peptide that has one amino acid substitution at position 27. This peptide stimulates GH secretion when given by the intravenous, subcutaneous, and intranasal routes without adverse effect. The degree of GH stimulation was variable among subjects and the greatest amount of stimulation occurred with the highest doses. GH stimulation occurred in a dose-responsive manner after all three routes of administration. A tenfold higher subcutaneous dose was required to stimulate a comparable amount of GH secretion as compared with intravenous administration, and a thirtyfold higher intranasal than intravenous dose was required to stimulate approximately one fifth the amount of GH release. For comparison, one dose of GH-RH-40, 1 microgram/kg, was administered intravenously. GH secretion after 1 microgram/kg GH-RH-40 and 1 microgram/kg Nle27 GH-RH was comparable between the two groups of subjects. Stimulation of GH secretion by Nle27 GH-RH occurred within 5 minutes of intravenous and within 10 minutes of subcutaneous and intranasal administration; peak GH levels were observed within 30 minutes. GH levels declined and returned to near baseline levels 2 hours after administration of the analog.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Intranasal↗
PubMed1986

Single dose responses to the gonadotropin-releasing hormone agonist analogue [(imBz 1)-D-His6,Pro9-NEt]GnRH.

The agonist analogue of gonadotropin-releasing hormone (GnRH), [(imBz1)-D-His6,Pro9-NEt]GnRH, has a potency 200 times that of the native hormone in vitro. In single dose studies in man, this analogue resulted in 2- to 4-fold elevation of LH and FSH, and demonstrated a prolonged duration of activity. [(imBz1)-D-His6,Pro9-NEt]GnRH appears to be safe and, as with other analogues of GnRH, may have application to clinical medicine.

Adult↗
PubMed1986

Inhibin A-subunit cDNAs from porcine ovary and human placenta.

Inhibin, a gonadal protein that preferentially suppresses the secretion of pituitary follicle-stimulating hormone, has been isolated from porcine follicular fluid and characterized as a 32-kDa protein composed of 18-kDa and 14-kDa subunits. In the present work, oligonucleotide probes predicted from amino-terminal inhibin amino acid sequences have been used to isolate, from a porcine ovarian lambda gt11 cDNA library, clones encoding the 18-kDa subunit, or A chain, of inhibin. DNA sequence analysis showed that the inhibin A chain is initially synthesized as a larger precursor protein and is predicted to be a glycopeptide. Inhibin A-chain mRNA is present specifically in the gonads, and its synthesis can be induced by treatment of the animal with gonadotropins. The porcine probe was used to isolate a human inhibin A-subunit cDNA from a placental cDNA library. The human precursor is highly homologous to its porcine counterpart and is predicted to generate an 18-kDa glycosylated inhibin A subunit.

Amino Acid Sequence↗
PubMed1986

Growth hormone-releasing factor stimulates proliferation of somatotrophs in vitro.

The mitogenic effect of the hypothalamic peptides growth hormone-releasing factor (GRF) and somatostatin on cultured growth hormone (GH)-producing cells (somatotrophs) was studied. Using autoradiographic detection of [3H]thymidine uptake and immunocytochemical identification of GH-producing cells, we show that 5 nM GRF causes a 20-fold increase in the percentage of somatotrophs labeled with [3H]thymidine. The total number of somatotrophs in GRF-treated cultures was increased by 60%. Somatostatin had no measurable effect on the labeling index by itself, but it partly inhibited the GRF-induced increase in both the labeling index and the total number of cells. Forskolin caused an increase in both the percentage of somatotrophs with a [3H]thymidine-labeled nucleus and the somatotroph number similar to that caused by GRF. GH secretion as well as cellular GH content in the GRF- or forskolin-treated cells increased with culture time over the entire period, whereas secretion and content of GH gradually decreased in control or somatostatin-treated cultures during the entire culture period. These data suggest that GRF and somatostatin regulate the mitotic activity of GH-producing cells and that the effect of GRF is possibly mediated by cyclic AMP.

Animals↗
PubMed1986

Nocturnal pulsatile growth hormone releasing hormone treatment in growth hormone deficiency.

We have treated five GH-deficient prepubertal children (4 M, 1 F) with GH releasing hormone 1-40 (GHRH1-40) in two dosage regimens over 9 months. Profiles of serum GH concentrations were obtained over 24 hours before treatment and nocturnal profiles were obtained serially throughout the study. GHRH was administered subcutaneously at night for four pulses using 1 microgram/kg/pulse in the first 3 months and 2 micrograms/kg/pulse for a further 6 months. All subjects demonstrated pituitary responsiveness to i.v. GHRH before treatment and at 3 and 6 months. GH secretion was induced in a pulsatile fashion in response to subcutaneous GHRH in three children from the first night of treatment. A self priming effect to successive GHRH pulses was evident and the response augmented with time and with the higher dose regimen. The growth velocity of these three children increased from a mean of 3.7 cm/year (range 3.7-3.8) before treatment to 5.5 cm/year (range 4.1-7.2) over the first 3 months and to 7.2 cm/year (range 4.8-9.2) over the following 6 months. In one subject entrainment of GH secretion to GHRH did not occur until the higher dose regimen and this was associated with a modest increase in growth velocity. One subject did not respond to treatment. Pulsatile administration of GHRH1-40 is effective in inducing GH secretion and promoting growth acceleration in some children with idiopathic GH deficiency. The optimal dose and mode of administration of GHRH have yet to be established.

Child↗
PubMed1986

Vasoactive intestinal peptide receptor antagonist [4Cl-D-Phe6, Leu17] VIP.

From structure-activity relationship studies of rat growth hormone-releasing factor (rGFR) on the vasoactive intestinal peptide (VIP) receptor in an in vitro preparation of exocrine pancreas, we predicted that [4Cl-D-Phe6, Leu17]VIP would be a competitive antagonist for the action of VIP. Micromolar concentrations of synthetic [4Cl-D-Phe6, Leu17]VIP competitively antagonized VIP-stimulated amylase release in the pancreatic preparation and VIP-stimulated short-circuit current changes in a colonic tumor cell line. In addition, [4Cl-D-Phe6, Leu17]VIP inhibited amylase release stimulated by rGRF, high concentrations of secretin (agents that act through the VIP receptor), and peptide contaminants in a preparation of natural glucagon. Finally, [4Cl-D-Phe6, Leu17]VIP did not inhibit the action of agonists for the secretin, GRF, or glucagon receptors.

Amylases↗
PubMed1986

Down-regulation of growth hormone releasing factor receptors following continuous infusion of growth hormone releasing factor in vivo.

The in vivo chronic infusion of growth hormone releasing factor (GRF) results in a loss of the pituitary growth hormone (GH) response to GRF as well as in a substantial depletion of pituitary GH content. To evaluate if the loss in response is due to the down-regulation of GRF receptors the specific GRF binding capacity of pituitary homogenates prepared from rats infused with saline or GRF (1 or 15 micrograms/h for 24 h) was determined. The pituitary binding capacity of animals infused with GRF was significantly reduced as compared to animals infused with saline.

Animals↗
PubMed1986

Clinical studies with GHRH in man.

GHRH was isolated from two GHRH-secreting pancreatic tumors which resulted in clinical acromegaly. Over 98% of acromegalic patients have a pituitary adenoma; however, acromegaly may occasionally result from ectopic or eutopic GHRH secretion. Administration of GHRH to normal adults stimulates growth hormone (GH) secretion; it may also stimulate GH release in some adults with GH deficiency in childhood and in a majority of GH-deficient children. Continuous infusion of GHRH to normal men stimulates GH secretion which augments naturally occurring GH pulses. GHRH is effective when administered subcutaneously and intranasally, but requires 30- and 300-fold higher doses, respectively. Intermittent subcutaneous GHRH therapy promotes acceleration of linear growth in GH-deficient children and appears promising as a treatment for these children.

Acromegaly↗