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R Robbins

Publications and source records attributed to R Robbins.

16 recordsLinked to original sources
PubMed1992

Regulation of plasminogen activators and type-1 plasminogen activator inhibitor by cyclic AMP and phorbol ester in rat astrocytes.

Two plasminogen activators (PAs): tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), as well as the type-1 plasminogen activator inhibitor (PAI-1) are synthesized and secreted by rat astrocytes. Preliminary studies suggest that PA activity plays a role in astrocyte development and differentiation. We have examined the regulation of the PA system by the cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) in purified rat astrocyte cultures. PKA activity was increased by exposing cultured astrocytes to forskolin or dibutyryl cyclic AMP, whereas PKC activity was stimulated with phorbol-12-myristate 13-acetate (PMA). Activation of both second-messenger pathways produced a time- and dose-dependent increase in the total PA activity. However, based on SDS-PAGE/zymography we found that forskolin increased t-PA activity and reduced u-PA activity, whereas PMA treatment caused a significant increase in u-PA activity without altering t-PA activity. Reverse zymography analysis revealed that astrocyte PAI-1 activity is decreased by forskolin and increased by PMA. Together, these results demonstrate that the components of the PA system in rat astrocytes are independently and reciprocally regulated by PKA and PKC. Our findings raise the possibility that the plasminogen activator system could be involved in some of the actions of growth factors and/or neuromodulators that modulate PKC or PKA in astrocytes.

Animals↗
PubMed1992

Involvement of protein kinase-C in the mitogenic effect of insulin-like growth factor-I on rat astrocytes.

Insulin-like growth factor-I (IGF-I) stimulates the proliferation of many cell types, including astrocytes. Astrocytes are a population of brain cells highly enriched in IGF-I receptors, which unlike neurons, retain the ability to proliferate in the adult brain. Although astrocyte proliferation in response to IGF-I is well documented, the intracellular mechanisms that mediate this phenomenon are poorly defined. Interestingly, activation of protein kinase-C (PKC) by IGF-I has been observed in several cell types. In this report we first characterized the mitogenic effects of IGF-I on highly purified type I rat astrocyte cultures. Next, we determined whether IGF-I activates PKC in our cultures. Finally, since astrocyte proliferation is stimulated by both IGF-I and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA), we decided to test the possible involvement of PKC in the mitogenic activity of IGF-I on astrocytes. IGF-I stimulated the DNA synthesis rate in rat astrocytes. Analysis of the time course revealed that IGF-I (10 nM) induces maximal stimulation of [3H]thymidine incorporation (a 4-fold increase) 16-18 h after exposure. TPA also stimulated mitogenesis in our cultures. The dose-response of [3H]thymidine incorporation induced by IGF-I and TPA indicated that 10 nM was the lowest concentration producing a maximal effect for both agents. Analysis of proteins by Western blot revealed that 10 nM IGF-I translocates PKC(alpha), the predominant PKC isoform in astrocyte cultures, from the cytosol to the membrane fraction within 20 min. A similar activation of PKC was achieved with 100 nM TPA. When astrocytes were exposed to IGF-I (10 nM) and TPA (10 nM) in combination, [3H]thymidine uptake was significantly higher than the uptake induced by either IGF-I (10 nM) or TPA (10 nM) alone. However, the effect of IGF-I plus TPA was not fully additive. In a second experiment, the mitogenic effect of IGF-I was partially abolished in cells depleted of PKC by preincubation with high concentrations of TPA (300 nM). Finally, incubation of astrocytes with the PKC inhibitor H-7 at 20 microM, a concentration that completely blocked the mitogenic action of TPA, only reduced the ability of IGF-I to stimulate DNA synthesis by 50%. In summary, our results demonstrate that IGF-I can rapidly activate PKC in astrocytes, and that PKC activation is involved in the mitogenic effect of IGF-I on these cells. However, we conclude that IGF-I also stimulates astrocyte proliferation through PKC-independent pathways.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Pulmonary surveillance using bronchoscopy and bronchoalveolar lavage during high-dose antineoplastic therapy.

Pulmonary failure is a major contributor to morbidity and mortality during marrow aplasia following high-dose antineoplastic therapy. For this reason, we initiated a pulmonary surveillance program for patients undergoing high-dose chemotherapy for leukemia or bone marrow transplantation. As part of this program, bronchoscopy with BAL was performed prior to therapy and at the onset of granulocytopenia. Thirty-three of the first 57 patients managed in this program developed some evidence of pulmonary complications. Twelve patients died in aplasia; all had pulmonary failure. Forty patients had clinically significant abnormalities on the bronchoscopy before treatment including 12 of 19 patients who had normal findings on chest x-ray films, physical examination, and pulmonary function testing, and no fever. Twenty-seven patients had clinically significant abnormal bronchoscopy or BAL at the onset of granulocytopenia. Thirteen patients required additional bronchoscopy. No patient required an open lung biopsy. Pulmonary surveillance using bronchoscopy with BAL is useful in the detection of pulmonary disease prior to the initiation of and following high-dose antineoplastic therapy.

Adult↗
PubMed1991

The role of endogenous opiates in athletic amenorrhea.

We hypothesized that menstrual disturbances in female athletes arise from opioid-induced abnormalities in gonadotropin and/or prolactin (PRL) secretion. To investigate this hypothesis, we measured luteinizing hormone, follicle-stimulating hormone, and PRL levels in eumenorrheic and amenorrheic athletes during thyrotropin-releasing hormone and gonadotropin-releasing hormone tests at baseline, after naloxone infusions, after exercise to exhaustion, and after similar exercise during naloxone infusions. Contrary to our hypothesis, amenorrheic runners did not have significant alterations in basal, postexercise, or stimulated hormone levels compared with eumenorrheic runners. In addition, opioid blockade by naloxone did not enhance gonadotropin release by amenorrheic athletes.

Adult↗
PubMed1990

Functional loss of chemotactic factor inactivator in the adult respiratory distress syndrome.

The adult respiratory distress syndrome (ARDS) is often characterized by a neutrophilic alveolitis, which may be mediated in part by the neutrophil chemoattractant, C5a. Chemotactic factor inactivator (CFI) can decrease C5a-directed neutrophil chemotaxis. Thus, a loss of CFI activity in the ARDS lung could lead to an increased ability of C5a to attract neutrophils. Lung CFI levels were measured antigenically and functionally in bronchoalveolar lavage (BAL) fluid obtained from 29 patients with ARDS and in 14 normal control subjects. Antigenic levels of CFI were found to be markedly elevated in ARDS BAL fluid (1,855 +/- 437 ng/ml) compared with that in normal BAL (29 +/- 10 ng/ml, p less than 0.005), but, in contrast, CFI functional activity was markedly decreased in ARDS BAL fluid compared with that in normal BAL fluid (31 +/- 7% inhibition versus 76 +/- 5% inhibition, p less than 0.01). Furthermore, although purified CFI readily inhibited the ability of C5a to attract neutrophils (92% inhibition), this activity was decreased when BAL fluid from patients with ARDS was incubated with CFI (47 +/- 10%, p less than 0.01). These findings suggest that patients with ARDS are functionally deficient in CFI, leading to an increased ability of C5a to attract neutrophils.

Aminopeptidases↗
PubMed1986

Somatostatin receptors are biologically active before they are inserted into the plasma membrane.

We have examined the biological activity of intracellular somatostatin (SRIF) receptors in cultured rat anterior pituitary cells. We used digitonin-permeabilized cells to introduce free SRIF intracellularly and chloroquine-treated cells to promote intracellular accumulation of SRIF via a receptor-mediated pathway. At a concentration of 0.001%, digitonin (3-min incubation at 37 C) allowed [125I]SRIF to enter the cells without affecting cell viability. Autoradiography of [125I]SRIF demonstrated its association with secretion vesicles (28%), nuclei (25%), and other intracellular organelles. An acid wash technique that removes cell surface-bound ligand revealed that both digitonin-permeabilized cells and chloroquine-treated cells accumulated approximately twice as much intracellular SRIF as did control cells. The biological activities of intracellular SRIF accumulated via two different pathways, receptor mediated and through digitonin-produced pores in the plasma membrane, were different. In chloroquine-treated cells, the accumulation of intracellular SRIF did not result in its additional biological effect. SRIF inhibited GH-releasing factor-induced GH release from 578 +/- 12 to 168 +/- 9 ng/10(6) cells X 30 min, which did not differ from the control value. Cells incubated with digitonin demonstrated normal basal (160 +/- 9 ng/10(6) cells X 30 min) and GH-releasing factor-stimulated GH release (564 +/- 11 ng/10(6) cells X 30 min). However, the inhibitory action of SRIF in these cells was approximately 30% greater (98 +/- 8 ng/10(6) cells X 30 min) than that in either control or chloroquine-treated cells, suggesting that SRIF freely admitted intracellularly produces additional biological activity. These observations confirm the presence of the intracellular receptors and suggest that these receptors exist in a biologically active form.

Animals↗
PubMed1985

Somatostatin and the cerebral cortex.

A unique subset of interneurons which are rich in immunoreactive somatostatin (IRS) exists in the cerebral cortex. The regulation of IRS secretion by these cells is reviewed. Acetylcholine, glutamic acid and several neuropeptides including VIP, CCK, and metenkephalin have been identified as IRS secretagogues. The types of molecules which stimulate IRS release, the electrophysiologic effects of somatostatin, and the recognition of abnormal IRS levels in human CNS diseases were all used to formulate a working model of the role of the somatostatinergic cell in ongoing cerebral cortical function.

Amino Acids↗
PubMed1985

Early extubation after high-dose fentanyl anaesthesia for aortocoronary bypass surgery: reversal of respiratory depression with low-dose nalbuphine.

To investigate the possibility of selective reversal of narcotic-induced respiratory depression following fentanyl anaesthesia, we studied 20 patients after aortocoronary bypass surgery. All patients were anaesthetized with fentanyl, 40 micrograms . kg-1 and oxygen, with isoflurane as indicated. In a random double blind fashion either incremental doses of nalbuphine, or normal saline were administered approximately four hours after cardiopulmonary bypass. Respiratory depression was evaluated using blood gas and end tidal CO2 (PETCO2) measurement, and in addition, a ventilatory response to CO2 was obtained preoperatively and at selected intervals postoperatively. Despite randomization, patients with more respiratory depression were assigned to nalbuphine. There appeared to be a reversal of respiratory depression with nalbuphine, indicated by a fall in the resting PETCO2 value. This apparent reversal of respiratory depression was associated with a significant increase in pain, requiring treatment in three patients. We conclude that low-dose nalbuphine is not an acceptable method of antagonism of respiratory depression in this group of patients. Many patients who did not receive nalbuphine were able to breathe adequately at an earlier stage than was previously suspected. Close monitoring of the respiratory system may permit earlier extubation without the requirement of a narcotic antagonist after this dose of fentanyl.

Anesthesia, General↗
PubMed1985

Insulin receptors on cultured hypothalamic cells: functional and structural differences from receptors on peripheral target cells.

We have studied the functional and structural characteristics of insulin receptors on cultured rat hypothalamic cells. The receptors on these cells are specific for insulin, but have a lower binding affinity than that measured in nonneuronal tissues. Neither acute (2-h) nor long term (24-h) exposure of the hypothalamic cells to high insulin concentrations resulted in receptor down-regulation. However, insulin is internalized in these cells and accumulated in the presence of the lysomotropic agent chloroquine. Acute exposure to insulin does not alter initial rate of 2-deoxyglucose transport in hypothalamic cells, but does cause a stimulation of aminoisobutyric acid uptake. Photoaffinity labeling of the receptors of the hypothalamic cells with a biologically active photosensitive insulin revealed a major specifically labeled band of 115K mol wt and a minor band of 40K mol wt under disulfide-reducing conditions compared to bands of 125K and 90K mol wt seen after labeling of the insulin receptors of adipocytes. The receptor proteins in hypothalamic cells under nonreducing conditions (420K, 370K, and 310K mol wt) were also smaller than those in adipocytes. Thus, the insulin receptors of cultured hypothalamic cells differ from insulin receptors on peripheral target tissues in both functional and structural aspects.

Adipose Tissue↗
PubMed1974

Detecting the enterotoxigenicity of Staphylococcus aureus strains.

An optimal sensitivity plate method for examining large number of staphylococcal strains for production of the known enterotoxins (A-E) is presented. Small volumes of relatively concentrated enterotoxin are produced by the semi-solid agar, cellophane-over-agar, or sac culture techniques. Detection of the enterotoxin in the supernatant fluid is accomplished with the optimal sensitivity plate method. In this method small plastic petri dishes (50 mm) were used for a modified Ouchterlony of high sensitivity.

Agar↗
PubMedDate not supplied

Interictal spikes and hippocampal somatostatin levels in temporal lobe epilepsy.

We investigated the relationship between somatostatin-like immunoreactivity (SSLI) and interictal spikes (IIS) in human temporal lobe epileptic tissue. IIS counted manually from depth electrode recordings obtained preoperatively were expressed as spike frequency in anterior, middle, and posterior portions of hippocampus. SSLI was determined by radioimmunoassay (RIA). An inverse relationship between SSLI in the entorhinal cortex (EC) and IIS frequency in hippocampus was present (r = -0.55, p = 0.06). No correlation between IIS and SSLI in CA4, CA3, CA1, or the dentate was evident. This finding suggests a role of the EC in generation, regulation, or expression of interictal paroxysmal electrical activity in temporal lobe epilepsy (TLE), for which somatostatin may be a marker.

Electroencephalography↗