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Cortisol augments synthesis of growth hormone, but does not alter synthesis of prolactin and proopiomelanocortin, in the 120- to 125-day fetal ovine pituitary.

In adult animal pituitaries or in cultured pituitary tumor cells, glucocorticoids are regulators of GH, PRL, and proopiomelancortin (POMC) synthesis. However, ovine fetal plasma cortisol concentrations are low until shortly before parturition, suggesting that cortisol may not normally regulate hormone synthesis in the fetal pituitary. To investigate whether cortisol could affect fetal synthesis of GH, PRL, and POMC, we obtained fetal pituitary tissue from normal fetuses and from fetuses which had received cortisol infusion for 48 h. Tissues were labeled in short term organ culture and the newly synthesized proteins were displayed by two-dimensional gel electrophoresis and autoradiography. Results were quantified by computerized integration of the area and density of the autoradiographic spots after high resolution television scanning. Cortisol infusion augmented synthesis of GH in comparison to controls (P = 0.01), but did not alter PRL synthesis. Cortisol also did not inhibit POMC synthesis in either the anterior pituitary or the neurointermediate lobe. These data suggest that the pituitary-adrenocortical slow feedback inhibition of POMC synthesis is not functional in the ovine fetus at 120 to 125-days gestation, but that pituitary somatotropes are responsive to glucocorticoids at this stage of fetal development.

Animals↗

Redox-sensing release of human thioredoxin from T lymphocytes with negative feedback loops.

Thioredoxin (TRX) is released from various types of mammalian cells despite no typical secretory signal sequence. We show here that a redox-active site in TRX is essential for its release from T lymphocytes in response to H2O2 and extracellular TRX regulates its own H2O2-induced release. Human T cell leukemia virus type I-transformed T lymphocytes constitutively release a large amount of TRX. The level of TRX release is augmented upon the addition of H2O2, but suppressed upon the addition of N-acetylcysteine. In the culture supernatant of a Jurkat transfectant expressing the tagged TRX-wild type (WT), the tagged TRX protein is rapidly released at 1 h and kept at a constant level until 6 h after the addition of H2O2. In contrast, another type of transfectant expressing the tagged TRX mutant (C32S/C35S; CS) fails to release the protein. H2O2-induced release of TRX from the transfectant is inhibited by the presence of rTRX-WT in a dose-dependent manner. Preincubation of the transfectant with rTRX-WT for 1 h at 37 degrees C, but not 0 degrees C, results in a significant suppression of the TRX release, reactive oxygen species, and caspase-3 activity induced by H2O2, respectively. Confocal microscopy and Western blot analysis show that extracellular rTRX-WT added to the culture does not obviously enter T lymphocytes until 24 h. These results collectively suggest that the oxidative stress-induced TRX release from T lymphocytes depends on a redox-sensitive event and may be regulated by negative feedback loops using reactive oxygen species-mediated signal transductions.

Apoptosis↗

Tyrosine phosphorylation of Sprouty proteins regulates their ability to inhibit growth factor signaling: a dual feedback loop.

Sprouty proteins are recently identified receptor tyrosine kinase (RTK) inhibitors potentially involved in many developmental processes. Here, we report that Sprouty proteins become tyrosine phosphorylated after growth factor treatment. We identified Tyr55 as a key residue for Sprouty2 phosphorylation and showed that phosphorylation was required for Sprouty2 to inhibit RTK signaling, because a mutant Sprouty2 lacking Tyr55 augmented signaling. We found that tyrosine phosphorylation of Sprouty2 affected neither its subcellular localization nor its interaction with Grb2, FRS2/SNT, or other Sprouty proteins. In contrast, Sprouty2 tyrosine phosphorylation was necessary for its binding to the Src homology 2-like domain of c-Cbl after fibroblast growth factor (FGF) stimulation. To determine whether c-Cbl was required for Sprouty2-dependent cellular events, Sprouty2 was introduced into c-Cbl-wild-type and -null fibroblasts. Sprouty2 efficiently inhibited FGF-induced phosphorylation of extracellular signal-regulated kinase 1/2 in c-Cbl-null fibroblasts, thus indicating that the FGF-dependent binding of c-Cbl to Sprouty2 was dispensable for its inhibitory activity. However, c-Cbl mediates polyubiquitylation/proteasomal degradation of Sprouty2 in response to FGF. Last, using Src-family pharmacological inhibitors and dominant-negative Src, we showed that a Src-like kinase was required for tyrosine phosphorylation of Sprouty2 by growth factors. Thus, these data highlight a novel negative and positive regulatory loop that allows for the controlled, homeostatic inhibition of RTK signaling.

Adaptor Proteins, Signal Transducing↗

Dynamics and contribution of mechanisms mediating renal blood flow autoregulation.

We investigated dynamic characteristics of renal blood flow (RBF) autoregulation and relative contribution of underlying mechanisms within the autoregulatory pressure range in rats. Renal arterial pressure (RAP) was reduced by suprarenal aortic constriction for 60 s and then rapidly released. Changes in renal vascular resistance (RVR) were assessed following rapid step reduction and RAP rise. In response to rise, RVR initially fell 5-10% and subsequently increased approximately 20%, reflecting 93% autoregulatory efficiency (AE). Within the initial 7-9 s, RVR rose to 55% of total response providing 37% AE, reaching maximum speed at 2.2 s. A secondary RVR increase began at 7-9 s and reached maximum speed at 10-15 s. Response times suggest that the initial RVR reflects the myogenic response and the secondary tubuloglomerular feedback (TGF). During TGF inhibition by furosemide, AE was 64%. The initial RVR rise was accelerated and enhanced, providing 49% AE, but it represented only 88% of total. The remaining 12% indicates a third regulatory component. The latter contributed up to 50% when the RAP increase began below the autoregulatory range. TGF augmentation by acetazolamide affected neither AE nor relative myogenic contribution. Diltiazem infusion markedly inhibited AE and the primary and secondary RVR increases but left a slow component. In response to RAP reduction, initial vasodilation constituted 73% of total response but was not affected by furosemide. The third component's contribution was 9%. Therefore, RBF autoregulation is primarily due to myogenic response and TGF, contributing 55% and 33-45% in response to RAP rise and 73% and 18-27% to RAP reduction. The data imply interaction between TGF and myogenic response affecting strength and speed of myogenic response during RAP rises. The data suggest a third regulatory system contributing <12% normally but up to 50% at low RAP; its nature awaits further investigation.

Acetazolamide↗

Ethanol inhibits asialoglycoprotein receptor synthesis but augments its mRNA expression in a human hepatoma cell line.

The effect of ethanol on the expression of asialoglycoprotein receptor protein and its mRNA was studied in a human hepatoma cell line, HepG2. The number of asialoglycoprotein receptors on the cell surface was decreased to 60% of the control level, without a loss in affinity, by incubating the cells with 100 mM ethanol. The decrease in cell surface asialoglycoprotein receptors was paralleled by a decrease in total receptor numbers, including intracellular and surface receptors. The internalization of asialoglycoprotein was also diminished, to 44% of that in control cells. The decreases in cell surface receptors and total receptor numbers were partially restored by 2 mM 4-methylpyrazole, suggesting that ethanol metabolites participated in the diminution of asialoglycoprotein receptor expression. However, the steady-state expression of asialoglycoprotein receptor mRNA was increased in ethanol-treated cells and further augmented by a longer ethanol exposure. These paradoxical results, i.e., the decrease of asialoglycoprotein receptor protein and the increase of its mRNA expression, suggest that the reduction in the asialoglycoprotein receptor protein is a post-transcriptional event and that a possible feedback regulatory mechanism may control asialoglycoprotein receptor gene transcription and/or impair the degradation of its mRNA.

Alcohol Dehydrogenase↗

Mechanisms of augmented field potential responses in the rat olfactory bulb.

Olfactory bulb field potential and single unit responses to paired pulse stimulation of the lateral olfactory tract were observed in the rat. In agreement with previous reports, surgical levels of barbiturate anesthesia prolonged the period of diminution of the field potential responses to the test pulse relative to the effect seen under light anesthesia. Very deep barbiturate anesthesia (sufficient to depress the EEG) led to decreased responses to the primary pulse but augmented responses to the test pulse. Urethane and ether anesthesia produced augmented test responses without severely depressing the EEG and without producing a period of diminished test responses. Single unit recordings failed to show external plexiform layer units excited at the time of maximal augmentation of the field potential. Simultaneous single unit and field potential recordings showed that prolonged diminution of the field potential response was associated with prolonged suppression of unit responses to the test pulse, while augmented field potential responses were associated with decreased suppression of unit responses to the test pulse. These observations are most easily explained by the assumption of temporal facilitation in the synaptic output of mitral and tufted cells. This facilitation is masked by feedback inhibition under some conditions, particularly under barbiturate anesthesia.

Anesthesia, General↗

Augmented humoral and anaphylactic responses in Fc gamma RII-deficient mice.

Despite its widespread distribution on both lymphoid and myeloid cells, the biological role of the low-affinity immunoglobulin-G receptor, Fc gamma RII, is not fully understood. Defects in this receptor or its signalling pathway in B cells result in perturbations in immune-complex-mediated feedback inhibition of antibody production. We now report that Fc gamma RII-deficient animals display elevated immunoglobulin levels in response to both thymus-dependent and thymus-independent antigens. Additionally, the effector arm of the allergic response is perturbed in these mice. Mast cells from Fc gamma RII-/- are highly sensitive to IgG-triggered degranulation, in contrast to their wild-type counterparts. Fc gamma RII-deficient mice demonstrate an enhanced passive cutaneous analphylaxis reaction, the result of a decreased threshold for mast-cell activation by Fc gamma RIII cross-linking. These results demonstrate that Fc gamma RII acts as a general negative regulator of immune-complex-triggered activation in vivo for both the afferent and efferent limbs of the immune response. Exploiting this property offers new therapeutic opportunities for the treatment of allergic and autoimmune disorders.

Animals↗

Two distinct antigen-specific suppressor factors induced by the oral administration of antigen.

The feeding of sheep erythrocytes (SRBC) to mice leads to the production of two distinct T cell-derived suppressor factors by spleen cells. Each has been characterized for specificity, genetic restrictions, and cellular interactions. Fraction I has a 60,000-75,000 mol wt, is specific for antigen, and is suppressive of primary in vitro anti-SRBC responses at all times. It is not restricted by major histocompabitility complex (MHC)- or Igh-linked genes, but it fails to suppress spleen cells derived from any strain of mouse with a B10 background. It acts on an Lyt-2+ T cell to increase suppressive activity. An antiserum has been prepared against this factor that reacts with other, unrelated T cell suppressor factors. Fraction II has an approximately 30,000-40,000 mol wt, is specific for antigen, and has a dual effect on in vitro anti-SRBC responses. On day 3 of culture, it leads to augmentation of the response, whereas at day 5 it suppresses the response. It is not restricted by MHC genes, but it is restricted by Igh-linked genets. It acts by activating an Ly-1 t cell to both help and induce feedback suppression. These factors, and the antisera prepared against them, should allow more precise dissection of the molecular pathways by which immunoregulatory cells communicate with one another.

Administration, Oral↗

Evidence for an inhibitory influence of rat placental lactogen on prolactin release in vitro.

Incubation of placental tissue from Day 11 pregnant rats for increasing periods of time resulted in proportionately more rat placental lactogen (rPL) release. The amount of placental tissue incubated correlated directly with the amount of rPL released into the medium. When placentas were coincubated with anterior pituitaries from ovariectomized rats, prolactin release was significantly inhibited. When media from incubations which had contained varying numbers of Day 11 placentas for 24 h were added to vials containing anterior pituitaries, prolactin release was inhibited, proportionate to the amount of rPL in the media. Media from incubations of Day 9 placentas, which contained very little rPL, had no effect on prolactin release. When medium containing anterior pituitary tissue was incubated for 24 h, pituitaries removed, and the medium incubated with placental tissue for an additional 24 h, there was no difference in prolactin levels compared to incubation medium not containing placental tissue. Addition of a trypsin inhibitor to the medium containing placental tissue did not augment the amount of prolactin remaining after a 24-h incubation. Thus it would appear that the placenta does not release a substance into the medium that destroys prolactin. This suggests that secretions from the placenta, presumably rPL, can exert a negative feedback on prolactin secretion at the level of the anterior pituitary.

Animals↗

The cochlear amplifier: augmentation of the traveling wave within the inner ear.

PURPOSE OF REVIEW: There have been many recent advancements in our understanding of cochlear function within the past ten years. In particular, several mechanisms that underlie the sensitivity and sharpness of mammalian tuning have been discovered. This review focuses on these issues. RECENT FINDINGS: The cochlear amplifier is essentially a positive feedback loop within the cochlea that amplifies the traveling wave. Thus, vibrations within the organ of Corti are sensed and then force is generated in synchrony to increase the vibrations. Mechanisms that generate force within the cochlea include outer hair cell electromotility and stereociliary active bundle movements. These processes can be modulated by the intracellular ionic composition, the lipid constituents of the outer hair cell plasma membrane, and the structure of the outer hair cell cytoskeleton. SUMMARY: A thorough understanding of the cochlear amplifier has tremendous implications to improve human hearing. Sensorineural hearing loss is a common clinical problem and a common site of initial pathology is the outer hair cell. Loss of outer hair cells causes loss of the cochlear amplifier, resulting in progressive sensorineural hearing loss.

Acoustic Stimulation↗

Prolactin enhancement of its own uptake at the choroid plexus.

The choroid plexus contains PRL receptors that function in part to transport PRL from the blood into the cerebrospinal fluid (CSF). The blood PRL concentration of female rats was altered by 1) three daily injections of haloperidol (chronic hyperprolactinemia) with or without bromocriptine administration 4 h before death, 2) bromocriptine alone for 4 h (acute hypoprolactinemia), and 3) a single vascular injection of ovine PRL (acute hyperprolactinemia). Changes in the uptake of PRL by the choroid plexus was assessed by quantitative in vivo autoradiography after the injection of radiolabeled PRL. Correlation of changes in PRL uptake at the choroid plexus with changes in PRL transport from blood to CSF was evaluated by subjecting CSF samples to sodium dodecyl sulfate-polyacrylamide gel electrophoresis after vascular injection of radiolabeled PRL. Autoradiography revealed that both chronic and acute hyperprolactinemia resulted in a significant increase in the uptake of radiolabeled PRL by the choroid plexus compared to that in untreated control animals. In contrast, bromocriptine had no effect on PRL uptake at the choroid plexus relative to that in control (untreated) animals. Chronic hyperprolactinemia, but not acute hyperprolactinemia, resulted in a significant increase in the transport of radiolabeled PRL from the blood to the CSF compared to that in untreated controls. The results are consistent with the up-regulation of PRL receptors in the choroid plexus by circulating PRL and the consequent augmentation of transport of PRL from blood to CSF.

Animals↗

Interactions of TGF-dependent and myogenic oscillations in tubular pressure.

We have previously shown that there are two oscillating components in spontaneously fluctuating single-nephron blood flow obtained from Sprague-Dawley rats (Yip K-P, Holstein-Rathlou NH, and Marsh DJ. Am J Physiol Renal Physiol 264: F427-F434, 1993). The slow oscillation (20-30 mHz) is mediated by tubuloglomerular feedback (TGF), whereas the fast oscillation (100 mHz) is probably related to spontaneous myogenic activity. The fast oscillation is rarely detected in spontaneous tubular pressure because of its small magnitude and the fact that tubular compliance filters pressure waves. We detected myogenic oscillation superimposed on TGF-mediated oscillation when ambient tubular flow was interrupted. Two well-defined peaks are present in the mean power spectrum of stop-flow pressure (SFP) centering at 25 and 100 mHz (n = 13), in addition to a small peak at 125-130 mHz. Bispectral analysis indicates that two of these oscillations (30 and 100 mHz) interact nonlinearly to produce the third oscillation at 125-130 mHz. The presence of nonlinear interactions between TGF and myogenic oscillations indicates that estimates of the relative contribution of each of these mechanisms in renal autoregulation need to account for this interaction. The magnitude of myogenic oscillations was considerably smaller in the SFP measured from spontaneously hypertensive rats (SHR, n = 13); consequently, nonlinear interactions were not observed with bispectral analysis. Reduced augmentation of myogenic oscillations in SFP of SHR might account for the failure in detecting nonlinear interactions in SHR.

Animals↗

Dual Diagnosis Motivational Interviewing: a modification of Motivational Interviewing for substance-abusing patients with psychotic disorders.

Motivational Interviewing (MI) is a brief treatment approach for helping patients develop intrinsic motivation to change addictive behaviors. While initially developed to target primary substance using populations, professionals are increasingly recognizing the promise this approach has for addressing the motivational dilemmas faced by patients who have co-occurring psychiatric and psychoactive substance use disorders. Unfortunately, this recognition has not lead to a clear explication of how MI might be adopted for specific diagnostic populations of dually diagnosed patients. In this article we describe how we have applied the principles and practices of MI to patients who have psychotic disorders and co-occurring drug or alcohol use problems. Specifically, we provide two supplemental guidelines to augment basic MI principles (adopting an integrated dual diagnosis approach, accommodating cognitive impairments and disordered thinking). We present recommended modifications to primary MI skill sets (simplifying open-ended questions, refining reflective listening skills, heightening emphasis on affirmation, integrating psychiatric issues into personalized feedback and decisional balance matrices). Finally, we highlight other clinical considerations (handling psychotic exacerbation and crisis events, recommended professional qualifications) when using MI with psychotic disordered dually diagnosed patients.

Adult↗

Studies of hyperthymic mice. I. The influence of multiple thymus grafts on the size of the peripheral T cell pool and immunological performance.

Following the implantation of syngeneic chromosomally marked thymuses under the kidney capsule of normal adult mice, donor T cells were found in the blood and other lymphoid organs. The mice were found to have increased numbers of Thy.1-positive cells in spleen and lymph nodes, increased peripheral blood lymphocyte levels and also augmented immune responses to sheep erythrocytes. The contribution made by an individual graft to the donor T cell pool was independent of the number of thymuses grafted as was the growth of the grafts themselves. The results reaffirm that there is no homeostatic feedback control of thymus growth in adult mice.

Animals↗

Predominant role of tumor necrosis factor-alpha in human monocyte IL-10 synthesis.

In previous studies it has been shown that the bacterial endotoxin LPS induces an initial burst of inflammatory cytokine synthesis in human monocytes, which is followed by substantial IL-10 production; the IL-10 then down-regulates the inflammatory cytokine production as well as IL-10 production itself. Herein we tested the hypothesis that IL-10 production in human monocytes is under control of one of the cytokines induced by LPS. Accordingly, we cocultured purified human peripheral blood monocytes with a panel of cytokines including TNF-alpha, IL-1 alpha, IL-1 beta, IL-6, granulocyte macrophage-CSF, transforming growth factor-beta, and IFN-alpha and then measured IL-10 mRNA production using a semiquantitative reverse transcription-polymerase chain reaction technique. We found that TNF-alpha had a major effect on IL-10 mRNA production, inducing a 20- to 120-fold increase over baseline production. In contrast, IL-1 alpha, IL-1 beta, IL-6, granulocyte macrophage-CSF, transforming growth factor-beta, and IFN-alpha had little effect (< 3-fold). The induction of IL-10 mRNA by TNF-alpha in monocytes was dose dependent and began between 8 and 24 h after the addition of TNF-alpha; this suggests that the increased IL-10 mRNA level was due to de novo mRNA synthesis rather than mRNA stabilization; this latter finding was corroborated by actinomycin-D time course studies, which showed that the half-life of IL-10 was less than 1 h and was not significantly altered by TNF-alpha. These studies concerning IL-10 mRNA induction by TNF-alpha were corroborated by studies of IL-10 protein secretion: TNF-alpha alone, but not IL-1 alpha, IL-1 beta, or IL-6 induces substantial IL-10 secretion. Furthermore, LPS induces a large amount of IL-10 secretion that is largely inhibited (50 to 75%) by anti-TNF-alpha but not by antibodies to other inflammatory cytokines. Finally, TNF-alpha augments LPS-induced IL-10 secretion. Taken together, these findings suggest that TNF-alpha is unique among the inflammatory cytokines in its role as an inducer of IL-10 in human monocytes, as such, it induces a molecule that provides negative feedback to its own production.

Base Sequence↗

The apparent paradox of the negative and positive feedback control system on gonadotropin secretion.

The separate and interactive effects of estradiol (E2) and luteinizing hormone-releasing factor (LRF) on the dynamics of LH storage and release were studied. Measurements were made of the serum gonadotropin responses to submaximal doses of LRF, given as brief pulses or infused over an extended period to normal women at various stages of the follicular phase of their menstrual cycles and to hypogonadal women with and without estrogen treatment. The two-pool concept of pituitary gonadotropin was verified; the dynamic responses of the two pools to the inputs of LRF and E2 were investigated and related to pituitary properties of sensitivity and reserve. Our results indicate that LRF appears to serve as a primary drive on the gonadotrophs, stimulating gonadotropin synthesis and storage (second pool), as well as release (first). E2 for the most part, amplifies the action of LRF except that it impedes LRF-induced release of gonadotropin. E2 augments the second pool activity (reserve) preferentially, and the relative activity of the first pool appears to be influenced by the E2-dependent self-priming effect of LRF. The interactions of the various elements of the system, when combined, provide a U-shaped curve to describe the over-all capacity of the gonadotrophs as a function of a broad range of E2 inputs. Negative and possitive feedback of E2 are revealed to operate by different mechanisms and to represent different segments of a single U-shaped curve rather than paradoxically disparate actions.

Estradiol↗

An auto-inducible vector conferring high glucocorticoid inducibility upon stable transformant cells.

A new gene expression system in mammalian cells was developed by using the glucocorticoid receptor (GR) as an inducible positive feedback factor. Mouse Ltk- cells were transfected with plasmids carrying the GR-encoding gene and the lacZ reporter gene, both of which were fused with the glucocorticoid-inducible enhancer/promotor of the mouse mammary tumor virus (MTV). The GR gene was first induced to supply the receptor protein, which further induced the expression of both GR and reporter genes. Stable transformants induced with dexamethasone, a synthetic glucocorticoid hormone, demonstrated beta-galactosidase activity 60-140-fold higher than uninduced controls. Similarly, the human alpha-interferon-encoding gene fused with the MTV enhancer/promoter was induced more than 12,000-fold. This system allowed us to increase the expression of the reporter or target genes without augmenting basal levels of expression significantly, and may be useful to investigate the unknown function of a cloned gene, particularly when the gene product of interest is cytotoxic or growth-inhibiting.

Animals↗

The angiotensin receptor antagonist 2-ethoxy-1-[[2'-(1H- tetrazol-5-yl) biphenyl-4-yl]methyl]-1H-benzimidazole-7-carboxylic acid (CV11974) attenuates the tubuloglomerular feedback response during NO synthase blockade in rats.

Nitric oxide (NO) produced in the juxtaglomerular apparatus may regulate the tubuloglomerular feedback (TGF) response. The inhibition of intrinsic NO results in significant renal hemodynamic changes, a phenomenon similar to that observed after angiotensin II (A-II) administration. We measured stop-flow pressure (Psf) during loop perfusion with artificial tubular fluid in Sprague-Dawley rats to establish whether alterations in TGF responsiveness during NO inhibition depend on the action of endogenous A-II. The NO synthase blocker N omega-nitro-L-arginine-methyl-ester (L-NAME: 10 mg/kg i.v.) significant increased TGF responsiveness, defined as the change in Psf on increasing loop flow from 0 to 40 nl/min compared with control (delta Psf: -21.3 +/- 2.6 vs. -9.7 +/- 0.6 mm Hg, P < .001). After concomitant treatment with the nonpeptide A-II type 1 receptor antagonist 2-ethoxy-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl]methyl]-1H-benzimidazole-7-carboxic acid (CV11974: 1 mg/kg i.v.) and L-NAME, the TGF response was attenuated significantly (delta Psf: -7.6 +/- 1.9 mm Hg, P < .001). On the other hand, Psf in the absence of loop perfusion was increased similarly by L-NAME treatment in the presence (53.7 +/- 2.2 mm Hg) or absence of CV11974 (Psf 50.7 +/- 3.2 mm Hg). These results suggest that augmentation of the TGF response by endogenous NO inhibition depends, at least in part, on the intrinsic A-II activity.

Angiotensin II↗