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Biomedical subjects

R A Peterfreund

Publications and source records attributed to R A Peterfreund.

29 records · Page 2Linked to original sources
PubMed1984

Picrotoxinin and phorbol-12-myristate-13-acetate stimulate the secretion of multiple forms of somatostatin from cultured rat brain cells.

The molecular forms of somatostatin (SRIF) secreted by cultured fetal rat brain cells were resolved using reverse phase high performance liquid chromatography followed by radioimmunoassay. Multiple forms of SRIF-like immunoactivity were detected in media from cells treated with either picrotoxinin, phorbol-12-myristate-13-acetate, or high potassium. For stimulated cells, elevated levels of an SRIF-28-like molecule, an SRIF-14-like molecule, and a hydrophobic SRIF-like molecule were observed compared to basal conditions. All three forms of SRIF-like molecules were also detected in acid extracts of whole cells. The data are consistent with the possibility that secretion of multiple SRIFs , including SRIF-28, may be regulated by multiple effectors and mechanisms.

Animals↗
PubMed1984

Somatostatin analogs inhibit somatostatin secretion from cultured hypothalamus cells.

The effect of somatostatin (SRIF) analogs on the secretion of radioimmunoassayable SRIF (SRIF-LI) was studied in the model system of fetal rat hypothalamus cells maintained in long-term, primary dispersed culture. These experiments exploited the biologic activity of certain synthetic SRIFs which cross-react poorly in our standard RIA for SRIF. Carbachol-stimulated SRIF-LI secretion was suppressed by [DTrp8]-SRIF-14, [DTrp22]-SRIF-28 and the octapeptide, des-AA1,2,4,5,12,13[DTrp8]-SRIF. Effective concentrations of synthetic analogs were at or below 1 nM. des-Trp8-SRIF-14, an analog inactive in all other SRIF biological assays, was similarly ineffective in this assay system at doses up to 10 nM. Following removal of peptide by washing, peptide-treated and control cells responded similarly to depolarization with high potassium buffer. The data demonstrate a direct action of SRIF analogs on the hypothalamus to suppress SRIF-LI release and are consistent with the possibility that an endogenous peptide participates in 'ultrashortloop' negative feedback control of its own secretion in the intact animal.

Animals↗
PubMed1983

Methodological considerations in culturing peptidergic neurons.

Both explant and dispersed cell culture preparations of brain tissue provide a means to directly assess the functions of neuropeptide-containing brain cells isolated from the complex influences present in vivo. The validity of the approach depends on reproducibility of observations. In dispersed cell cultures, we find that cell responses, as determined by secretion of the peptide somatostatin, have remained relatively constant both quantitatively and qualitatively over numerous preparations. In addition, for pharmacologic studies on somatostatin secretion, data from several laboratories are in good agreement. The validity of the dispersed cell approach also depends on whether the pharmacologic and physiologic behavior of cells parallels that expected of excitable tissue. The variability of the explant cultures from culture dish to culture dish makes quantitative experiments, such as demonstrated with the dispersed cultures, difficult. On the other hand, explant cultures better maintain the integrity of the tissue components, so that interactions between neurons and glial cells could occur as in vivo. The long-term health and viability of neuropeptidergic cells in explant and dispersed culture make both preparations potentially useful models to examine central nervous system physiology. Future work with such preparations must eventually address the problems of culturing adult brain tissue, the precise nutrient and hormonal requirements of brain cells, so that undefined medium components, such as serum, can be eliminated from the culture environment, and the general question of whether observations made in vitro facilitate our understanding of intact brain physiology.

Animals↗
PubMed1983

Muscarinic cholinergic stimulation of somatostatin secretion from long term dispersed cell cultures of fetal rat hypothalamus: inhibition by gamma-aminobutyric acid and serotonin.

Regulation of somatostatin (SS) secretion was studied in an in vitro system using collagenase-dispersed cells from fetal rat hypothalamus maintained in long term monolayer culture. Cultured cells exhibit a measurable basal secretion of immunoactive SS (SSLI) which can be augmented by carbachol, acetylcholine, or oxotremorine. The EC50 for carbachol is about 1 microM. Atropine, but not hexamethonium, antagonizes the action of cholinergic agonists. Cobalt or tetrodotoxin pretreatment diminishes basal secretion and eliminates the response to carbachol. Serotonin, several serotonin agonists, and gamma-aminobutyric acid (GABA) suppress carbachol-induced secretion. The GABA blockers bicuculline or picrotoxinin reverse the effect of added GABA and by themselves also augment SSLI secretion. Picrotin is inactive. The direct response to either bicuiculline or picrotoxinin is prevented by cobalt or tetrodotoxin treatment. These observations are consistent with the presence of a muscarinic cholinergic receptor which acts by a mechanism depending on an action potential and calcium influx to enhance the release of SSLI from neurosecretory cells. The data also support the conclusion that GABAergic transmission occurs within the cultures to tonically inhibit SSLI secretion. GABAergic, cholinergic, and serotoninergic systems may thus interact at the level of the hypothalamus to modulate SS secretion in vivo and thereby influence anterior pituitary release of GH and TSH.

Animals↗
PubMed1983

Phorbol diesters stimulate somatostatin secretion from cultured brain cells.

Phorbol diester tumor promoters are potent cocarcinogens which also possess activity in a variety of biological assays. We have examined the effect of phorbol diesters on secretion of somatostatin-like immunoactivity (SRIF-LI) by dispersed cells of fetal rat brain maintained in long term culture. Phorbol-12-myristate-13-acetate (PMA) and phorbol 12, 13-dibutyrate stimulate SRIF-LI secretion in a dose-dependent fashion. 4-O-Methyl-PMA is approximately 100 times less potent than phorbol 12, 13-dibutyrate. 4-beta-Phorbol was inactive. Treatment with a nonphorbol irritant, teleocidin, also was associated with significantly augmented release of SRIF-LI. Significant stimulation is seen within 7.5 min of treatment and response is linear over 1 h. Administration of phorbol diesters in low calcium buffer (0.1 mM) with or without cobalt or pretreatment with verapamil are associated with significantly diminished secretion. Substitution for sodium ion by choline or pretreatment with tetrodotoxin (10(-7) M) also inhibits response to PMA. gamma-Aminobutyric acid (50 microM) or the gamma-aminobutyric acid agonist muscimol (5 microM) decrease response to PMA as does sodium pentobarbital (IC50 approximately 30 microM). Phenobarbital is less potent as an inhibitor; significant suppression is not seen until approximately 300 microM. The data are consistent with an action for phorbol diesters mediated at least in part by voltage dependent sodium channels and calcium influx into excitable cells. Inhibition by hyperpolarizing agents is compatible with this mechanism. Phorbol diesters may thus mimic endogenous modulator substances active at the nerve cell membrane.

Alkaloids↗
PubMedDate not supplied

Release of the predicted calcitonin gene-related peptide from cultured rat trigeminal ganglion cells.

Calcitonin gene-related peptide (CGRP) is a putative novel neuropeptide predicted on the basis of alternative RNA processing events of primary transcripts of the calcitonin gene. Distinct mRNAs encoding either calcitonin or CGRP are generated from the calcitonin gene RNA transcript in what appears to be a tissue-specific manner. The predicted peptide has now been detected immunocytochemically in discrete regions of the central and peripheral nervous systems and potent in vivo actions have been reported for centrally and peripherally administered synthetic CGRP. However, so far there is no evidence that CGRP is secreted or released by intact cells. The present experiments investigated the possible secretion of CGRP in vitro using primary dispersed cell cultures of the adult rat trigeminal ganglion, which previously has been found to contain large amounts of CGRP mRNA (ref. 2). We report here that immunoreactive CGRP is spontaneously released by cultured trigeminal ganglion cells and that secretion is stimulated by incubation in high potassium medium in a calcium-dependent fashion. Chromatographic characterization of the secreted CGRP-like immunoreactivity (CGRP-LI) isolated only one molecular form which appears to be similar or identical to the predicted rat CGRP (1-37).

Animals↗
PubMedDate not supplied

Alkalinization and precipitation characteristics of 0.2% ropivacaine.

BACKGROUND AND OBJECTIVES: Alkalinization of local anesthetics has been used to increase the speed of onset of nerve blocks. However, alkalinization of local anesthetic solutions may cause precipitation, thereby decreasing bioavailability and anesthetic activity. Alkalinization of ropivacaine has not been described. This laboratory study assessed the alkalinization and precipitation characteristics of ropivacaine. METHODS: Aliquots (2 mL) of commercially available ropivacaine (Naropin, 0.2%; Astra Pharmaceutical, Westborough, MA) were alkalinized with increasing amounts (0.01, 0.02, 0.04 mL) of sodium bicarbonate (8.4%) and immediately monitored for pH change and onset of visible precipitation at room temperature. We then alkalinized ropivacaine with sodium bicarbonate and measured the amount of precipitate that accumulated after various incubation times. RESULTS: The pH of ropivacaine increases with the addition of small amounts of bicarbonate. The calculated percentage of nonionized ropivacaine increased from 0.3% to greater than 30% with alkalinization from pH of 5.51 to 7.63. Drug loss to precipitation increased with higher doses of bicarbonate, reaching 25% to 30% of the total ropivacaine. Even with a low dose of bicarbonate (0.1 mL bicarbonate/20 mL ropivacaine), precipitation increased with time of incubation, reaching a plateau at 20 minutes. CONCLUSIONS: A laboratory evaluation that establishes the alkalinization characteristics of ropivacaine is a prerequisite for designing a clinical study of alkalinized ropivacaine. In our experiment, low doses of bicarbonate produced significant increases in the proportion of nonionized ropivacaine with only modest precipitation. There would be a low likelihood of substantial drug precipitation if the mixture was administered within 5 to 10 minutes after alkalinization. These results indicate that alkalinized ropivacaine should not be used for infusions and that ropivacaine should not be alkalinized until just before use.

Amides↗
PubMedDate not supplied

pH adjustment of local anesthetic solutions with sodium bicarbonate: laboratory evaluation of alkalinization and precipitation.

pH adjustment of several commonly administered local anesthetic solutions was evaluated in the laboratory. The pH achieved after the addition of sodium bicarbonate and the onset of precipitation for alkalinized solutions were recorded. Solutions of 2-chloroprocaine and lidocaine readily alkalinized to near physiological pH without precipitation. Mepivacaine solutions exhibited a tendency for delayed precipitation (18-20-minute latency for 1.5% mepivacaine) above neutral pH. Bupivacaine and etidocaine solutions precipitated after the addition of small amounts of sodium bicarbonate and could not be alkalinized to physiologic pH. Two commercially available sodium bicarbonate preparations, 4% (wt/vol) and 8.4% (wt/vol), were compared and produced similar pH changes and precipitation behavior. The data obtained for pH and time to precipitation for local anesthetic solutions alkalinized with sodium bicarbonate may be useful for practical application in the clinical setting.

Anesthetics, Local↗