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Biomedical subjects

W Vale

Publications and source records attributed to W Vale.

At least 145 records · Page 8Linked to original sources
PubMed1990

A 90-day subcutaneous toxicity and fertility study of a LHRH antagonist in rats.

[Ac-D2Nal1,4Cl-DPhe2,D3Pal3,Arg5,DGlu6+ ++ (anisole adduct),DAla10]-GnRH (Nal-Glu) is an antagonist of LHRH and has the potential to be utilized as an antigonadal agent. A study was undertaken to evaluate the toxicological effects of Nal-Glu in rats. Nal-Glu, dissolved in 5% mannitol in water containing 9 ml/liter benzyl alcohol, was administered subcutaneously. In subchronic studies, groups of 12 male and 12 female rats received 0, 50, 250, or 1250 micrograms/kg body weight (BW) Nal-Glu for 90 days and were killed on Day 91. Additional groups of male and female rats were given the high dose of Nal-Glu (1250 micrograms/kg BW) or vehicle for either 30 or 90 days. Their fertility was assessed by mating them with normal animals. Unlike some other LHRH antagonists, Nal-Glu exhibited a low potency for causing in vitro histamine release from rat peritoneal mast cells. Furthermore, in acute in vivo studies, Nal-Glu was less active in the induction of peripheral edema. In the subchronic study, all doses of Nal-Glu were well tolerated and there were no apparent systemic toxic effects. The pharmacological effects of Nal-Glu were quite evident, however. Nal-Glu treatment led to a significantly decreased body weight gain in the males and a significantly increased body weight gain in the females. There was a dose-dependent decrease in weights of gonads and reproductive organs in both the sexes. Some of the hematological and serological parameters were significantly different in Nal-Glu-treated animals. However, most of the values were within the normal range and are considered to be of no toxicological significance. Histopathological evaluations were made in the control and high-dose groups only. In the male, a seminiferous tubular degeneration and atrophy of the interstitial cells was seen. The prostate and seminal vesicles were also atrophied and the epididymides were devoid of spermatozoa. In the females, the ovaries and uteri were atrophic. The injection site of Nal-Glu-treated rats had inflammatory changes indicative of a local irritating action of the drug. All other tissues had normal histomorphology. Both male and female rats became infertile when 1250 micrograms/kg Nal-Glu was administered for 30 days. Normal fertility was restored 8 weeks after cessation of 90-day treatment. It is concluded that repeated administration of Nal-Glu leads to reversible infertility in both male and female rats. Although it was irritating at the site of injection. Nal-Glu had no systemic toxicological effects.

Animals↗
PubMed1990

Cyclic hexapeptides related to somatostatin. Synthesis and biological testing.

As a continuation of our program to study the structure-function relationship of the peptide hormone somatostatin, we report the synthesis and biological potencies of a series of cyclic hexapeptide analogs related to somatostatin. The parent peptide of this series was designed by Veber and coworkers, c[-Pro6-Phe7-D-Trp8-Lys9-Thr10-Phe11-], and has been reported to be superactive in the inhibition of the release of growth hormone. (The superscript numbers refer to the positions of residues in native somatostatin). The series of analogs has been designed to examine the role of the so-called bridging region, Phe11-Pro6, which has been postulated to be important in maintaining the proper conformation of the biologically active tetrapeptide, Phe-D-Trp-Lys-Thr. We have incorporated peptidomimetics and the retro-inverso modification into the bridging region of the molecule, with the aim of affecting the conformational preferences found in the parent peptide. Results from the biological assay--in vitro inhibition of growth hormone--and the conformational analysis (adjoining paper) of our analogs will provide insight into the relationship between structure and biological activity of somatostatin.

Amino Acid Sequence↗
PubMed1990

Activin-A modulates growth hormone secretion from cultures of rat anterior pituitary cells.

Activins, initially identified as FSH-releasing proteins, have now been shown to exert effects on other cell types of the anterior pituitary, including the somatotrophs. In the present study the inhibitory action of activin-A (beta A beta A) on GH secretion was characterized using primary cultures of rat anterior pituitary cells. Activin-A suppressed basal GH secretion for up to 72 h (the longest time tested). Immediately after the treatment period with activin-A, when the cells were thoroughly washed and further incubated with or without rat GH-releasing factor (rGRF), basal and stimulated GH secretion were partially inhibited as well. In parallel, activin-A pretreatment diminished rGRF-stimulated cAMP accumulation. The effects of activin-A were time- and concentration-dependent, with half-maximal inhibition occurring in the range of 20-30 pM activin-A. A minimum pretreatment time of 3 h was required for maximal effect, and when rGRF and activin-A were added simultaneously, no inhibition was evident. Secretory responses of activin-A-pretreated cells to rGRF were influenced by glucocorticoids. When cells were cultured in the presence of the synthetic glucocorticoid dexamethasone, pretreatment (72 h) with activin-A attenuated rGRF-stimulated GH secretion only during short (1-h), but not longer (3-h), exposure periods to the neuropeptide. In the absence of dexamethasone, rGRF-stimulated GH secretion was inhibited at all incubation times tested (up to 3 h). A 3-h exposure to the protein factor did not alter total (cellular plus secreted) immunoreactive GH levels, suggesting that the inhibition of secretion with the shorter treatment was not secondary to attenuated GH biosynthesis. However, longer (72-h) treatment with activin-A decreased total GH levels, indicating lower GH biosynthetic rates, as previously shown. Somatostatin is recognized as the primary negative modulator of GH secretion. Activin-A and SRIF inhibited GH secretion additively, suggesting distinct mechanisms of action for each. GH secretion in response to other secretagogues, such as 12-O-tetradecanoyl-phorbol-13-acetate, forskolin, cholera toxin, and 8-bromo-cAMP, was also suppressed after activin-A pretreatment. The presence of the RNA synthesis inhibitor actinomycin-D completely blocked the inhibitory effect of a 3-h activin-A pretreatment on subsequent rGRF-stimulated GH secretion. Pertussis toxin was only partially effective in preventing the inhibition by activin-A. The results of this study indicate that activin-A plays a crucial role as a modulator of somatotropic function, inhibiting GH secretion at the level of the secretory process and secondary to the inhibition of GH biosynthesis.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Central corticotropin-releasing factor mediates the suppressive effect of stress on natural killer cytotoxicity.

CRF acts within the brain to elicit changes in neuroendocrine, autonomic, and behavioral activity similar to that observed after stress. A reduction of splenic natural killer (NK) activity has also been described after the central administration of CRF. In this study we examined whether the central release of CRF plays a physiological role in mediating stress-induced suppression of NK cytotoxicity. Four sessions of footshock stress (1.5 mamp; 1-sec duration; 60-Hz sine wave; delivered randomly twice per min for 30 min) over a 48-h period significantly (P less than 0.001) reduced splenic NK activity in the rat. Pretreatment of the animals by central administration of polyclonal CRF antibodies completely antagonized the stress-induced suppression of NK cell activity. In contrast, the peripheral immunoneutralization of CRF was ineffective. Measurement of circulating levels of ACTH and corticosterone demonstrated that stress-induced elevations of ACTH and corticosterone were significantly (P less than 0.05) attenuated by peripheral anti-CRF serum, but not by centrally administered anti-CRF. These findings suggest that endogenous brain CRF coordinates the suppressive effect of footshock stress on NK cytotoxicity independently of pituitary-adrenal activation.

Adrenocorticotropic Hormone↗
PubMed1990

Cytokines act within the brain to inhibit luteinizing hormone secretion and ovulation in the rat.

Alterations of immune activity are often accompanied by reproductive disorders. Because interleukins mediate the host's response to immune activation, we first examined the effect of the central injection of several lymphokines on LH secretion by gonadectomized rats. We then studied the ability of the most potent lymphokine in this system, interleukin-1 beta (Il-1 beta), to interfere with the proestrous LH surge and ovulation in the intact female rat as well as the dependence of this effect on the activation of opiate receptors. Finally, we investigated the possibility that increased brain levels of Ils, as induced by the central administration of a bacterial endotoxin, might also alter the normal ovulatory process. After intracerebroventricular (icv) injection, Il-1 beta, Il-6, and tumor necrosis factor all lowered plasma LH levels in castrated rats. On a molar basis, Il-1 beta was the most potent inhibitor of LH secretion. In gonadectomized animals, 2.5 and 10 ng Il-1 beta administered icv significantly (P less than or equal to 0.01) decreased plasma LH levels for 6 h, while the effect of 40 ng lasted up to 12 h. By contrast, FSH secretion was only measurably altered by 40 ng Il-1 beta 8 and 12 h posttreatment. In intact cycling female rats, icv injection of 40 ng Il-1 beta or 400 ng Il-1 alpha at 0830 h on the morning of proestrus significantly (P less than 0.01 and P less than 0.05, respectively) interfered with the proestrous surge of LH. In contrast, the peripheral administration of either lymphokine was without measurable effect. Centrally injected Il-1 beta (40 ng at 0830 h on proestrus) also blocked ovulation in most animals, while a dose of 25 ng injected iv was ineffective. Finally, we observed that the icv injection of endotoxin (a lipopolysaccharide), also interfered with ovulation. The possible involvement of opiate-dependent pathways in mediating the inhibitory action of Il-1 beta on reproductive processes was tested by implanting naloxone pellets 16-24 h before lymphokine treatment. The pellets, which released 200, 400, or 800 micrograms naloxone/h (corresponding to approximately 0.6, 1.32, or 2.64 mg/kg BW.h), had no effect on ovulation by themselves. When given before icv Il-1 beta, all naloxone regimens countered the effect of the cytokine, with the 800-micrograms/h dose restoring ovulation in eight of nine rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1990

Steroid hormones modulate the release of immunoreactive gonadotropin-releasing hormone from cultured human placental cells.

The aim of the present study was to evaluate whether steroid hormones or opiate receptor agonists participate in the mechanisms regulating the release of immunoreactive GnRH (irGnRH) from cultured human placental cells. No significant changes in irGnRH concentrations were found in the culture medium after 48-h incubation of estradiol, estriol, or progesterone. Both estriol and estradiol augmented, while progesterone decreased, the irGnRH release induced by 8-bromo-cAMP. The stimulatory effect of estriol or estradiol was reversed by the concomitant addition of progesterone. The secretagogue effect of activin on irGnRH release from cultured placental cells was increased by the presence of estriol and reduced by the addition of progesterone. The action of estriol was counteracted by both tamoxifen, an estrogen antagonist, and progesterone. The inhibitory effect of progesterone was completely reversed by RU 486, a specific receptor antagonist. The addition of morphine, methionine-enkephalin, or UP50, 488H which preferentially bind mu-, delta-, and kappa-opiate receptors, respectively, did not decrease basal irGnRH release from cultured human placental cells. However, both morphine and UP50, 488H significantly inhibited 8-bromo-cAMP-induced GnRH release. The present results showed that steroid hormones and opiate receptor agonists influence irGnRH release from human cultured cells, suggesting that local interaction between steroids and peptides modulates irGnRH release from human placenta.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Presence and synthesis of inhibin subunits in human decidua.

A growing number of studies provided the evidence that human decidua is a pregnancy-related tissue capable of hormone production and metabolism. The aim of the present study was to evaluate the possible presence of inhibin subunits in human decidua. Tissue samples were collected in pregnant women during the first (8 weeks) and second trimester (18 weeks) of gestation and at term (40 weeks). Immunohistochemical data were obtained using affinity purified polyclonal antisera raised in rabbit against porcine alpha, beta A, or beta B subunits. Levels of the respective inhibin subunits were evaluated by Northern blot analysis using cDNA probes encoding sequences corresponding to each subunit. The present results indicated that human decidua contains and synthesizes inhibin alpha, beta A, and beta B subunits. The immunohistochemical data showed that decidual cells were stained with both inhibin alpha and beta B antisera, showing a similar localization. On the other hand, cells stained with inhibin beta A antisera were sparse and followed a distribution pattern different from that of cells stained with alpha or beta B antisera. The first inhibin alpha and beta B subunit mRNAs were both expressed in first trimester of pregnancy, and those mRNA levels showed a gestational related increase. The beta A subunit mRNA was expressed at very low levels at term and could not be detected earlier during pregnancy. The present data showed that human decidua actively produces inhibin subunits with a gestational-related profile. The results suggest that decidua may be a further source of inhibin-related proteins during pregnancy and emphasize the endocrine competence of human decidua.

Abortion, Spontaneous↗
PubMed1990

Inhibition of somatotroph growth and growth hormone biosynthesis by activin in vitro.

Activin-A, a homodimeric protein composed of two inhibin beta A-subunits, was first isolated from gonadal fluids based upon its ability to stimulate FSH secretion and biosynthesis, but was also observed to suppress GH secretion. The present report describes the effects of activin on the biosynthesis of GH and the proliferation of pituitary somatotrophs. In pituitary cells cultured in the presence of 0.7 nM activin for 3 days, GH secretion was decreased by 50% compared to the control value. Inhibition of GH biosynthesis, measured by quantitative immunoprecipitation of [35S]methionine-labeled cells, could be observed after 24 h of activin treatment, and maximal (70%) inhibition of GH biosynthesis was observed after 3 days. Activin inhibited basal as well as GH-releasing factor (GRF)-, glucocorticoid-, and thyroid hormone-stimulated GH biosynthesis. Inhibin, which is known to reverse the effect of activin on FSH secretion, did not reverse the effect of activin on GH biosynthesis. Treatment of somatotrophs with activin for 3 days completely inhibited the growth-promoting effect of GRF on somatotrophs. However, no effect of activin on GRF-stimulated expression of the c-fos protooncogene was observed. These data demonstrate that activin, in addition to its stimulatory effect on FSH secretion, is able to inhibit both expression of GH and growth of somatotropic cells.

Activins↗
PubMed1990

Structure of the human melanin concentrating hormone mRNA.

The melanin-concentrating hormone (MCH) is a cyclic neuropeptide which induces skin paling and may be involved in the control of the pituitary adrenal axis in teleost fishes. We have recently cloned and characterized the salmon and rat MCH mRNAs and we report in the present paper the cloning and sequencing of the human counterpart. The deduced human MCH (hMCH) precursor is 165 amino acids long and as for rat and salmon, encodes the MCH peptide at the C-terminus. The human and rat MCH precursors are very similar to one another but differ extensively from the salmon counterpart. Strong sequence conservation was found in the regions of mammalian prohormones encoding the novel putative neuropeptides named NGE and NEI which we had originally identified in the rat MCH precursor. Furthermore, sequence identities, with perhaps functional implications, were found among the MCH, human ANF, and aplysia peptide A hormone precursors.

Amino Acid Sequence↗
PubMed1990

Pituitary mammosomatotroph adenomas develop in old mice transgenic for growth hormone-releasing hormone.

It has been shown that mice transgenic for human growth hormone-releasing hormone (GRH) develop hyperplasia of pituitary somatotrophs and mammosomatotrophs, cells capable of producing both growth hormone and prolactin, by 8 months of age. We now report for the first time that old GRH-transgenic mice, 16 to 24 months of age, develop pituitary mammosomatotroph adenomas. These findings provide conclusive evidence that protracted stimulation of secretory activity can cause proliferation, hyperplasia and adenoma of adenohypophysial cells.

Adenoma↗
PubMed1990

Corticotropin-releasing factor and parturition: plasma and amniotic fluid levels and placental binding sites.

We evaluated levels of corticotropin-releasing factor in the plasma and amniotic fluid of women who had spontaneous vaginal delivery or elective cesarean. Corticotropin-releasing factor binding sites were also studied in placental tissue collected from vaginal or cesarean birth. Plasma samples were collected hourly from seven women from the onset of labor until delivery, and from ten women before and during elective cesarean. Amniotic fluid samples were collected from 40 women at different stages of labor and from ten women during elective cesarean. Maternal plasma corticotropin-releasing factor levels increased during labor, showing the highest values at delivery. No significant differences in amniotic fluid immunoreactive corticotropin-releasing factor levels were observed at the different stages of cervical dilatation. At cesarean, maternal plasma levels did not differ significantly from those found before surgery, and in the amniotic fluid they were similar to those found in pregnancy. The number of 125I-corticotropin-releasing factor binding sites in placental tissue was higher after vaginal than after cesarean delivery. These results suggest that corticotropin-releasing factor secretion is activated by the stress of labor.

Adult↗
PubMed1989

Widespread expression of corticotropin-releasing factor messenger RNA and immunoreactivity in the rat olfactory bulb.

Immunohistochemical, in situ hybridization histochemical, and Northern blot methods were used to demonstrate and characterize the distribution of corticotropin-releasing factor immunoreactivity (CRF-IR) and mRNA in the rat olfactory system. Northern analysis demonstrated the presence of an mRNA species in the olfactory bulb indistinguishable from, and in greater abundance than, CRF mRNA isolated from whole hypothalamus. Results from hybridization histochemical and immunohistochemical studies converged to indicate that CRF is expressed in a majority of mitral and tufted cells in the main and accessory bulbs, and in subsets of granule and periglomerular cells. Consistent with cellular localizations in primary output neurons, a dense network of fine CRF-immunoreactive varicosities was demonstrated in the external plexiform layer of the olfactory bulb and in layer Ia of piriform cortex. Other acknowledged terminal fields of the projection neurons of the main and accessory bulbs also displayed CRF-IR. The results suggest that CRF is the most broadly distributed neuroactive agent yet charted in olfactory bulb somata. This peptide may serve as a modulator or co-transmitter of importance in several cell types in the main and accessory olfactory bulbs, including the principal output neurons.

Animals↗
PubMed1989

Neurotransmitters and peptides modulate the release of immunoreactive corticotropin-releasing factor from cultured human placental cells.

The substances stimulating the release of immunoreactive corticotropin-releasing factor from cultured human placental cells were investigated. Monolayer primary cultures of trophoblast cells from pregnant women at term were used. The immunoreactive corticotropin-releasing factor released in the culture medium eluted from high-performance liquid chromatography with the same retention time as human corticotropin-releasing factor. Norepinephrine and acetylcholine increased immunoreactive corticotropin-releasing factor release into the culture medium in a dose-related manner. Epinephrine was partially active, whereas dopamine and serotonin did not induce significant changes of immunoreactive corticotropin-releasing factor release from placental cultures. Angiotensin II, interleukin-1, oxytocin, and arginine-vasopressin also increased placental immunoreactive corticotropin-releasing factor release in a dose-related manner, whereas other peptides (vasoactive intestinal peptide, substance P, somatostatin, atrial natriuretic factor, interleukin-2) were ineffective. These results showed that several neurotransmitters and peptides stimulate the release of immunoreactive corticotropin-releasing factor from placental cells, suggesting their possible involvement in the physiologic regulation of placental immunoreactive corticotropin-releasing factor release during pregnancy and parturition.

Acetylcholine↗
PubMed1989

Fluorescent and cytotoxic analogs of corticotropin-releasing factor: probes for studying target cells in heterogeneous populations.

The procedures briefly outlined above described the syntheses of two conjugates of CRF. In each case a molecule with a specific biochemical or physical property was conjugated to an analog of CRF to enable association of the particular property with only CRF-target cells. Thus, by conjugating gelonin or fluorescein to CRF it becomes possible to selectively impair the cellular function of, or fluorescently label, CRF-target cells among mixed populations. These methodologies are still in the early stages of development, and it can be expected that they will become more refined and improved as workers with specialized experience (in synthetic methods, microscopy, cell culture, etc.) continue this work.

Animals↗
PubMed1989

Activation of ganglionic tyrosine hydroxylase by peptides of the secretin-glucagon family: structure-function studies.

The hydroxylation of tyrosine to dopa is the rate-limiting reaction in catecholamine biosynthesis. It has been previously reported that secretin, vasoactive intestinal peptide and peptide histidine isoleucine amide, all members of the secretin-glucagon family of peptides, increase dopa synthesis in superior cervical ganglia in vitro. We report here that two other members of this peptide family, rat growth hormone-releasing factor and helodermin H38, a component of Gila monster venom, also increase the rate of dopa synthesis, while glucagon-like peptides I and II and a number of other peptides tested produce no effect. Since analogs of cAMP also increase dopa synthesis, it is of particular interest that all of the peptides that increase catechol synthesis also raise the levels of this cyclic nucleotide in the superior cervical ganglion. Helodermin H38 stimulated the rate of dopa synthesis and the level of cAMP with similar potencies (EC50S of approximately 10 nM) and with maximal effects of two- and two-fold, respectively. By either measure, rat growth hormone-releasing factor produced a two-fold increase at 10 microM and a three- to four-fold increase at 30 microM. Analogs of peptides of the secretin-glucagon family with a deletion or modification of the N-terminal histidine were much less effective in these assays at the concentrations tested than were their parent compounds, demonstrating an important role for this amino acid in conferring activity on these peptides. In addition to increasing dopa synthesis in intact tissue, incubation of ganglia with rat growth hormone-releasing factor, secretin, vasoactive intestinal peptide or peptide histidine isoleucine amide also increased the activity of tyrosine hydroxylase measured subsequently in ganglion homogenates. Thus, the peptidergic stimulation of dopa synthesis observed in the intact superior cervical ganglion appears to be due, at least in part, to the activation of tyrosine hydroxylase. Together with previous studies, these findings support the hypothesis that certain members of the secretin-glucagon family increase catecholamine synthesis in sympathetic neurons by a cAMP-dependent activation of tyrosine hydroxylase.

Amino Acid Sequence↗