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Biomedical subjects

V Levine

Publications and source records attributed to V Levine.

At least 19 recordsLinked to original sources
PubMed2001

Dynamics of nuclear localization sites for COX-2 in vascular endothelial cells.

We investigated the relationships among expression, activity, and spatial organization of cyclooxygenase (COX-1 and COX-2) in endothelial cells from porcine and human cerebral microvessels and from human umbilical vein. In quiescent cells, COX-1 was detected in the perinuclear zone and the cytoplasm, while COX-2 was mainly a nuclear resident possibly connected with the nuclear matrix. COX-2 immunogold labeling was situated in the nuclear envelope, at the nuclear pores, and in connection with the perichromatin regions of the nucleus, considered to be the sites of active transcription. In human endothelial cells transcriptionally activated by interleukin (IL)-1beta, the nucleus remained a major COX-2 localization site during the first 12 h of stimulation, when COX-2 expression was maximally induced. The continuous rise in prostanoid synthesis at 17-23 h of stimulation was associated with COX-2 relocation from the nucleus to the nuclear envelope and the cytoplasm. IL-1beta did not affect COX-1 expression, activity, and localization. COX-2 nuclear localization sites and trafficking between the nucleus and the cytoplasm in endothelial cells may indicate a novel function of COX-2 in regulating gene expression.

Animals↗
PubMed2000

Preservation of cerebrovascular tone and reactivity by sodium channel inhibition in experimental prolonged asphyxia in piglets.

Sodium channels using cAMP as a second messenger play a role in the regulation of cerebral circulation and metabolism. Cerebrospinal fluid (CSF) cAMP levels have been shown to correlate with the degree and duration of hypoxic injury and outcome and to be an indicator of cerebral vascular reactivity. We hypothesize that sodium channel inhibition either before or at termination of experimental asphyxia will attenuate cerebrovascular alterations and maintain CSF cAMP levels. Three groups of piglets with closed cranial windows were studied: asphyxia or group 1 (n = 5) and two treatment groups. Pigs were treated with 50 mg/kg of sodium channel blocker before asphyxia (group 2, n = 6) and after the termination of asphyxia and start of reventilation (group 3, n = 6). Asphyxia was sustained over 60 min by ventilating piglets with 10% O2 gas mixture and decreasing minute ventilation followed by 60 min of reventilation with room air. Every 10 min, pial arterial diameters were measured, and CSF samples were collected for cAMP determination. Vascular reactivity to topically applied isoproterenol (10(-4) M) was evaluated 60 min after recovery. During asphyxia, cAMP levels in group 2 peaked and declined at a later time with mean values remaining significantly higher than those of groups 1 and 3. During reventilation, CSF cAMP concentrations were highest in group 3 and lowest in group 1. Pial arteriolar dilation occurred during asphyxia in all three groups but to a lesser degree in the pretreated group compared with groups 1 and 3. Pial arteriolar reactivity to isoproterenol postasphyxia was preserved in both groups 2 and 3. In summary, in newborn pigs, pretreatment with sodium channel blocker resulted in higher CSF cAMP levels and a lesser degree of pial arteriolar dilation during prolonged asphyxia. Pretreatment or treatment at reventilation restored vascular tone and reactivity.

Animals↗
PubMed1999

Use of point-of-care test in identification of patients who can benefit from desmopressin during cardiac surgery: a randomised controlled trial.

BACKGROUND: Platelet dysfunction is a major cause of excessive microvascular bleeding after cardiac surgery. A new point-of-care test (hemoSTATUS) can identify patients at risk of excessive bleeding. We aimed to find out whether patients who can benefit from desmopressin during cardiac surgery can be identified by this test. METHODS: We enrolled 203 patients scheduled for elective cardiac surgery in a prospective, double-blind, placebo-controlled trial. Patients with abnormal hemoSTATUS clot-ratio results (<60% of maximum in channel 5) after discontinuation of cardiopulmonary bypass were randomly assigned desmopressin (n=50) or placebo (n=51). Patients with normal clot ratios were included in an untreated control group (n=72). FINDINGS: Intraoperative platelet counts and clot ratios were significantly higher in the untreated control group than in the study-drug groups. In intensive care, clot ratios in patients who received desmopressin were similar to those in the untreated control group, despite significantly lower platelet counts, but were lower in the placebo group than in the other two groups (p=0.0001). Compared with the placebo group, patients who received desmopressin had less blood loss in 24 h (mean 624 [SD 209] vs 1028 mL [682] p=0.0004) and required less transfusion of red blood cells (1.1 [022] vs 2.2 U [0.32] p=0.009), platelets (0.1 [0.04] vs 1.9 U [4.5] p=0.0001), and fresh-frozen plasma (0.1 [0.07] vs 0.75 U [0.21] p=0.0008), and had less total blood-donor exposures (1.56 [0.31] vs 5.2 [0.8] p=0.0001). Placebo patients also had substantially higher blood loss and transfusion requirements than untreated control patients. INTERPRETATION: Patients identified with hemoSTATUS as being at increased risk of excessive bleeding after cardiac surgery can benefit from administration of desmopressin. Further studies are, however, needed to confirm these findings as well as to identify the mechanism of action and safety of desmopressin in the clinical setting.

Aged↗
PubMed1998

Short-pulse carbon dioxide laser resurfacing in the treatment of rhytides and scars. A clinical and histopathological study.

BACKGROUND: Previous studies have shown the efficacy of short-pulse carbon dioxide (CO2) lasers in the treatment of rhytides and scars. To date, there have been few studies examining the histological aspects of these treatments. OBJECTIVE: The purpose of this study was to perform a prospective clinical and histopathological study of CO2 laser resurfacing for improvement of facial rhytides and scars. METHODS: A total of 23 patients were studied. Clinical improvement was evaluated both pre- and postoperatively using photographs and optical profilometry. Skin biopsies of rhytides were also obtained. RESULTS: Postoperatively, rhytides and scars both demonstrated significant increases in clinical improvement scores. Results from optical profilometry studies reflected these results. Skin biopsies from rhytides posttreatment demonstrated increases in collagen layer thickness. Improvement was sustained as late as 1 year following treatment. CONCLUSIONS: Histopathological studies suggest improvement of rhytides and scars by CO2 laser resurfacing may be attributed to new collagen formation following treatment.

Cicatrix↗
PubMed1997

Effects of platelets and white blood cells and antiplatelet agent C7E3 (Reopro) on a new test of PAF procoagulant activity of whole blood.

This study was designed to evaluate the effects of varying concentrations of platelets, white blood cells (WBC) and Fab fragments of a monoclonal antibody (c7E3, Reopro) directed at the platelet GpIIb-IIIa receptor complex on ACT-based clot ratio values (hemoSTATUS assay) in healthy volunteers. These measurements were made in heparinized whole blood from 10 normal volunteers in which either platelet or WBC concentrations had been varied by differential centrifugation. In addition, blood collected in either heparin or argatroban was incubated with varying concentrations of c7E3 (Reopro). Clot ratio values (%Maximal) in normal blood did not decrease until average platelet counts were less than 50,000. A marked reduction in clot ratios was observed when WBC concentration increased above or decreased below baseline clot ratios within each patient. Strong linear relationships were observed between white cell concentration and clot ratio values when white cell concentrations were either less or greater than baseline values. When argatroban was used as an anticoagulant, inverse relationships were demonstrated between clot ratio values and increasing c7E3 concentration (Ch 3: r = -0.33, Ch4: r = -0.84, Ch5: r = -0.87, Ch 6: r = -0.71). ACT-based clot ratio values determined in heparinized whole blood presumably reflecting PAF inducible platelet procoagulant activity, are affected by platelet concentration when counts are less than 50,000/microliter. The hemoSTATUS test was also found to be affected by WBC concentration since clot ratio values decreased when WBC counts were below 4,000/microliter or above 9,000/microliter. A dose-dependent reduction in clot ratio values was also observed with increasing concentrations of c7E3. This test can reliably detect platelet dysfunction only if the platelet count is > 50,000 and the WBC is normal.

Abciximab↗
PubMed1997

Hemofiltration during cardiopulmonary bypass: the effect on anti-Xa and anti-IIa heparin activity.

Previous studies have demonstrated that heparin concentrations during cardiopulmonary bypass (CPB) may vary considerably, which may be related to variability in redistribution, cellular and plasma protein binding, and clearance of heparin. The purpose of this study was to determine whether hemofiltration removes lower molecular weight fractions of heparin from plasma and thus contributes to variability of blood levels of heparin. Twenty patients undergoing cardiac surgery with CPB were enrolled in this study after informed consent was obtained. The study was subdivided into two phases. The first 10 patients were enrolled in Phase I, which was designed to determine whether hemofiltration removes lower molecular weight fractions of heparin from blood. Blood specimens obtained from the inflow line and outflow lines of the hemofiltration unit were used to measure complete blood counts (CBC) and plasma heparin activity by anti-Xa and anti-IIa assays. Phase II was designed to evaluate the effect of hemofiltration on circulating plasma heparin activity. In Phase II, blood specimens were obtained from 10 patients via the arterial cannula of the extracorporeal circuit prior to and after hemofiltration for measurements of CBCs, anti-Xa plasma heparin, as well as whole blood heparin concentration using an automated protamine titration assay (Hepcon instrument, Medtronic Inc., Parker, CO). Ultrafiltrate and reservoir volumes were measured in both phases of the study. Hemofiltration did not remove lower (anti-Xa measurable) molecular weight heparin, but it resulted in a considerable increase in heparin activity in the outflow line, as measured by both anti-Xa and anti-IIa assays. The plasma anti-Xa heparin activity obtained after hemofiltration (5 +/- 1.8 U/mL) was substantially (P = 0.003) greater than heparin activity obtained prior to hemofiltration (3.9 +/- 1.7 U/mL). The increase in heparin activity with hemofiltration was directly related to ultrafiltrate volume (r = 0.63, P < 0.0001) and hematocrit (r = 0.73, P < 0.0001). Hemofiltration increases heparin concentration and may contribute to variability in heparin activity during CPB. Point-of-care heparin concentration methods would allow identification of the anticipated rise in heparin concentration, with the apparent clinical implication of a reduced need for supplemental heparin to maintain a target whole blood heparin concentration.

Cardiopulmonary Bypass↗
PubMed1997

Antithrombin III during cardiac surgery: effect on response of activated clotting time to heparin and relationship to markers of hemostatic activation.

UNLABELLED: This study was designed to determine if, and to what extent, antithrombin III (AT) levels affect the response of the activated clotting time (ACT) to heparin in concentrations used during cardiac surgery, and to characterize the relationship between AT levels and markers of activation of coagulation during cardiopulmonary bypass (CPB). After informed consent, blood specimens obtained from eight normal volunteers (Phase I) were used to measure the response of the kaolin and celite ACT to heparin after in vitro addition of AT (200 U/dL) and after dilution with AT-deficient plasma to yield AT concentrations of 20, 40, 60, 80, and 100 U/dL. In Phase II, blood specimens collected before the administration of heparin and prior to discontinuation of CPB, were used to measure the response of the kaolin ACT to heparin (preheparin only), AT concentration, and a battery of coagulation assays in 31 patients undergoing repeat or combined cardiac surgical procedures. In Phase I, strong linear relationships were observed between kaolin (slope = 1.04 AT - 2, r2 = 0.78) and celite (slope = 1.36 AT + 6, r2 = 0.77) ACT slopes and AT concentrations below 100 U/dL. In the pre-CPB period of Phase II, only factors V (partial r = -0.49) and VIII (partial r = -0.63) were independently associated with heparin-derived slope using multivariate analysis; an inverse relationship was observed between AT and fibrinopeptide A levels (r = -0.41) at the end of CPB. Our findings indicate that the responsiveness of whole blood (ACT) to heparin at the high concentrations used with CPB is progressively reduced when the AT concentration decreases below 80 U/dL. Because AT is variably, and sometimes extensively, reduced in many patients before and during CPB, AT supplementation in these patients might be useful in reducing excessive thrombin-mediated consumption of labile hemostatic blood components, excessive microvascular bleeding, and transfusion of blood products. IMPLICATIONS: Heparin, a drug with anticoagulant properties, is routinely given to patients undergoing cardiac surgery to prevent clot formation within the cardiopulmonary bypass circuit. However, when levels are reduced, heparin is not as effective. Findings within this study indicate that administration of antithrombin III may help to preserve the hemostatic system during cardiopulmonary bypass.

Anticoagulants↗
PubMed1997

A comparison between continuous infusion versus standard bolus administration of heparin based on monitoring in cardiac surgery.

This study was designed to determine prospectively if stable heparin concentrations can be maintained during extracorporeal circulation by using a continuous infusion technique, compared with a bolus regimen based on whole blood heparin concentration monitoring. Forty patients were assigned randomly to either an infusion or a monitoring group. The reference heparin concentration was defined as the whole blood heparin concentration associated with a kaolin activated clotting time (ACT) of approximately 480 s prior to institution of cardiopulmonary bypass (CPB) for both cohorts. For infusion patients, doses of heparin were administered using a continuous infusion based on the initial patient-specific heparin dose per unit weight; heparin was also added to solutions administered after the initiation of CPB based on the reference heparin concentration. For monitoring patients, the dose of heparin administered during CPB was calculated by the Hepcon instrument. Blood specimens collected prior to and during the CPB period were used to measure anti-Xa plasma heparin concentration and complete blood counts, kaolin ACT and whole blood heparin concentration. Doses of heparin and protamine administered and transfusion requirements were similar in patient cohorts. The apparent rate of clearance of heparin from plasma was variable among patients in the monitoring group prior to CPB. Stable heparin concentrations were maintained using whole blood heparin measurements, whereas mean heparin concentrations were slightly lower using the continuous infusion technique. Therefore, an optimal approach might involve the combined use of these regimens.

Aged↗
PubMed1997

Relationship between leukocyte count and patient risk for excessive blood loss after cardiac surgery.

OBJECTIVE: To evaluate the relationship between leukocyte counts and risk for excessive blood loss after cardiac surgery when including numerous demographic, operative, and laboratory factors in the comparison. DESIGN: A prospective, clinical evaluation. SETTING: A point-of-care laboratory and the cardiac surgical unit of a university-affiliated tertiary center. PATIENTS: Patient-related and hematologic variables were measured, using blood specimens obtained from 89 hospitalized patients who underwent cardiac surgery involving cardiopulmonary bypass. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Demographic, operative, and transfusion-related data were recorded for each patient. Routinely obtained measurements of laboratory-based prothrombin time, partial thromboplastin time, complete blood count, and bleeding time were recorded. Hemoglobin concentration, platelet count, and red and white blood cell counts were measured with an on-site instrument before initiation (pre-cardiopulmonary bypass) and before discontinuation (end-cardiopulmonary bypass) of cardiopulmonary bypass. Hematocrit was calculated using recorded variables, and white blood cell percent change values were calculated using white blood cell counts from both periods, using the following formula: [(end-cardiopulmonary bypass - pre-cardiopulmonary bypass)/pre-cardiopulmonary bypass] x 100. When we excluded four patients who had a surgical source of post-cardiopulmonary bypass bleeding, significant (p < .0001) relationships were observed between white blood cell count (r2 = .46) and white blood cell percent change values (r2 = .71) and cumulative mediastinal chest tube drainage in the first 4 postoperative hours in 85 patients. Bayes theorem was used to evaluate the predictive ability of hematologic measurements in identifying patients with excessive bleeding (n = 24), defined as >1000 mL of cumulative chest tube drainage in the first 24 postoperative hours, when compared with patients without excessive bleeding (n = 61). Demographic and operative variables were similar between these patients except that patients with excessive bleeding required more red blood cell, platelet, and plasma transfusions during the postoperative interval. Significantly (p < .0001) greater white blood cell percent change values were obtained in the excessive bleeding cohort (119 +/- 93 percent change) when compared with patients without excessive bleeding (28 +/- 36 percent change). CONCLUSIONS: On-site measurements of white blood cell count, as an index of the inflammatory response to extracorporeal circulation, may be useful in identifying patients at increased risk for excessive bleeding. Further studies are needed to examine whether white blood cell counts during multiple cardiopulmonary bypass periods may identify patients with an exaggerated inflammatory response to extracorporeal circulation. By using this information, physicians may be able to intervene with anti-inflammatory medications and blood preservation techniques.

Adult↗
PubMed1996

Aprotinin prolongs activated and nonactivated whole blood clotting time and potentiates the effect of heparin in vitro.

This study was designed to evaluate the effect of aprotinin on activated versus nonactivated whole blood clotting time using two different on-site methods and to quantify these anticoagulant properties when compared to heparin in a controlled, in vitro environment. Blood specimens were obtained prior to heparin administration from 56 patients undergoing cardiac surgery. Specimens obtained from the first consecutive 20 patients were mixed with either normal saline (NS) or aprotinin (400 kallikrein inhibiting units (KIU)/mL), inserted into Hemochron tubes containing either NS or heparin (0.3 or 0.6 U/mL) and then used to measure celite-activated (celite ACT) and nonactivated whole blood clotting time (WBCT1) using four Hemochron instruments. Accordingly, specimens obtained from the second consecutive 20 patients were mixed with either NS or aprotinin, inserted into Automated Clot Timer cartridges containing either NS or heparin (0.06, 0.13, or 0.25 U/mL) and then used to measure kaolin-activated (kaolin ACT) or nonactivated whole blood clotting times (WBCT2) using four Automated Clot Timer instruments. Specimens obtained from the last 16 patients were mixed with either incrementally larger doses of aprotinin (0, 100, 200, 300, or 400 KIU/mL) or heparin (0, 0.12, 0.24, 0.36, 0.48, or 0.72 U/mL) and were then used for measurement of whole blood clotting time (WBCT2) using six Automated Clot Timer instruments. Aprotinin significantly prolonged activated or nonactivated whole blood clotting time and potentiated the prolongation of whole blood clotting time by heparin. The linear relationship between whole blood clotting time and either heparin concentration (WBCT2 = H x 357 + 280, mean adjusted r2 = 0.88) or aprotinin concentration (WBCT2 = A x 0.97 + 300, mean adjusted r2 = 0.94) was variable among patients. On average, 200 KIU/mL of aprotinin prolonged WBCT2 to the same extent as 0.69 +/- 0.28 U/mL of heparin using linear regression models within each patient. Aprotinin significantly prolongs activated or nonactivated whole blood clotting time measurements in a dose-dependent manner. Since prolongation of whole blood clotting time by heparin is potentiated by aprotinin in vitro, aprotinin's anticoagulant properties may in part account for the prolonged celite activated clotting time values observed in the presence of aprotinin.

Adult↗
PubMed1996

Evaluation of a new point-of-care test that measures PAF-mediated acceleration of coagulation in cardiac surgical patients.

BACKGROUND: This study was designed to evaluate a new point-of-care test (HemoSTATUS) that assesses acceleration of kaolin-activated clotting time (ACT) by platelet activating factor (PAF) in patients undergoing cardiac surgery. Our specific objectives were to determine whether HemoSTATUS-derived measurements correlate with postoperative blood loss and identify patients at risk for excessive blood loss and to characterize the effect of desmopressin acetate (DDAVP) and/or platelet transfusion on these measurements. METHODS: Demographic, operative, blood loss and hematologic data were recorded in 150 patients. Two Hepcon instruments were used to analyze ACT values in the absence (channels 1 and 2: Ch1 and Ch2) and in the presence of increasing doses of PAF (1.25, 6.25, 12.5, and 150 nM) in channels 3-6 (Ch3-Ch6). Clot ratio (CR) values were calculated with the following formula for each respective PAF concentration: clot ratio = 1-(ACT/control ACT). These values also were expressed as percent of maximal (%M = clot ratio/0.51 x 100) using the mean CRCh6 (0.51) obtained in a reference population. RESULTS: When compared with baseline clot ratios before anesthetic induction, a marked reduction in clot ratios was observed in both Ch5 and Ch6 after protamine administration, despite average platelet counts greater than 100 K/microliter. There was a high degree of correlation between clot ratio values and postoperative blood loss (cumulative chest tube drainage in the first 4 postoperative hours) with higher concentrations of PAF: CRCh6 (r = -0.80), %M of CRCh6 (r = -0.82), CRCh5 (r = -0.70), and %M of CRCh5 (r = -0.85). A significant (P < 0.01) improvement in clot ratios was observed with time after arrival in the intensive care unit in both Ch5 and Ch6, particularly in patients receiving DDAVP and/or platelets. CONCLUSIONS: Activated clotting time-based clot ratio values correlate significantly with postoperative blood loss and detect recovery of PAF-accelerated coagulation after administration of DDAVP or platelet therapy. The HemoSTATUS assay may be useful in the identification of patients at risk for excessive blood loss and who could benefit from administration of DDAVP and/or platelet transfusion.

Aged↗
PubMed1992

Localized vulvar pemphigoid in a child misdiagnosed as sexual abuse.

BACKGROUND: Various primary dermatoses can affect the vulva of children and be misdiagnosed as child abuse, with devastating social consequences. OBSERVATION: A 3-year-old girl with vulvar erosions was removed from her parent's care after a pediatrician and gynecologist diagnosed child abuse. Histopathologic and immunofluorescence studies were consistent with vulvar pemphigoid. CONCLUSION: Localized pemphigoid should be added to the differential diagnosis of vulvar lesions. Dermatologists, pediatricians, and gynecologists should be familiar with nonvenereal diseases that can exclusively affect this area. The dermatologist's expertise is particularly valuable in differentiating between primary diseases and sexual abuse.

Child Abuse, Sexual↗
PubMed1983

Forskolin activates adenylate cyclase activity and inhibits mitosis in in vitro in pig epidermis.

The novel adenylate cyclase activator forskolin caused rapid and high intracellular accumulation of cyclic AMP in a floating skin (epidermal) slice system. Increased cAMP levels were also detected in the media. Addition of a phosphodiesterase inhibitor to forskolin-containing medium caused only a slight increase in the intracellular cAMP level and forskolin itself did not inhibit phosphodiesterase activity. Ka of forskolin for epidermal adenylate cyclase was about 2-3 X 10(-5) M. This forskolin activation was rapidly reversed after washing. The forskolin stimulation (Ka 5 X 10(-5) M) was also found when tested with an epidermal membrane preparation which contained the catalytic unit of adenylate cyclase but lacked either the GTP or receptor stimulation. With the epidermal slice system, the combination of forskolin and epinephrine (or histamine) stimulated adenylate cyclase synergistically. The data suggest that forskolin activates not only the catalytic unit but also the nucleotide regulatory protein or the receptor-regulatory protein complex of the adenylate cyclase system. The cAMP accumulation caused by forskolin produced a dose-dependent mitotic inhibition of epidermal cells in an in vitro outgrowth system. This inhibitory effect was reversible 48 h after washing out the forskolin.

1-Methyl-3-isobutylxanthine↗
PubMed1983

"Leaky" epidermal cells contain a complete receptor-mediated adenylate cyclase system with an accessible GTP regulatory protein.

Hormone sensitivity to epinephrine or histamine of the adenylate cyclase system in pig skin is very labile to homogenization. We have developed a new adenylate cyclase receptor-mediated assay system with trypsinized epidermal cells which are treated with hypotonic shock. This new assay system maintained the hormonal sensitivity, as both epinephrine and histamine clearly stimulated cyclic AMP production. Moreover, the Ka for each hormone on this system was similar to that obtained from the floating pig skin slice system. Receptor-adenylate cyclase unit (coupling) in this assay system is therefore preserved as it occurs in intact tissue or cells. Because of the "leaky" nature of our preparation, phosphorylated compounds such as GTP and its analogue and NaF can penetrate the cell membrane and stimulate cyclic AMP production. In this system refractoriness is still maintained to subsequent stimulation by a receptor activator, and cholera toxin can be shown to dramatically increase the activity of GTP on the GTP binding protein, presumably by preventing GTP hydrolysis.

Adenylyl Cyclases↗
PubMed1983

Agents that activate cyclic AMP-dependent protein kinase inhibit explant culture growth and mitotic activity.

Epidermal cells contain 4 separate surface receptors which are linked to adenylate cyclase. Activation of any one of these receptors leads to the accumulation of cAMP within the cell which in turn leads to the activation of cAMP-dependent protein kinase. The levels of cAMP accumulation within the cell caused by the 4 activators are not the same. Epinephrine, histamine, adenosine, and prostaglandins of the "E" series cause easily measurable concentrations of cAMP within 5 min of exposure. Prostaglandin F2 alpha causes only a small nonsignificant increase. Similarly, 2 phosphodiesterase inhibitors, which inhibit the breakdown of cAMP formed within the cell, differ in their ability to accumulate cAMP when cells are exposed to these agents alone. Isobutylmethylxanthine causes a measurable increase in cAMP, while theophylline, a weak inhibitor of phosphodiesterase, gives a nonsignificant increase in cAMP. Recently, experiments have shown that agents that give only slight increases in cAMP by biochemical measurements, that is, prostaglandins F2 alpha and theophylline, are equally able to activate protein kinase within the cell. Since activation of protein kinase is the only mechanism for an increase in cAMP to have a physiologic effect, all of these agents that do activate protein kinase should cause physiologic effects. Using an explant culture system, we show in this paper that this supposition is correct and that all agents that activate protein kinase do result in inhibition of mitotic activity regardless of whether or not they are able to raise cAMP to a level that can be biochemically measured as being significantly different from the baseline value.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Cyclic AMP-dependent protein kinase isozymes of pig skin and human skin from normal and psoriatic subjects.

Cyclic AMP-dependent protein kinase isozymes of pig and human skin (epidermis) were separated by DEAE-cellulose column chromatography after micromodification for small biopsy samples. Clear-cut separations of type I and type II isozymes, which were of about equal amounts, could be obtained only when the ischemia effect was avoided by in vivo freezing of skin and homogenization for less than 10 s. Intradermal injections of epinephrine caused dose-dependent activation of type I isozyme, but not of type II. Injections of other skin adenylate cyclase stimulators such as histamine, adenosine, and prostaglandin E2 elevated the local cyclic AMP levels to not more than 5 pmol/mg protein and also stimulated only the type I isozyme. Incubation of keratome-sliced pig skin under various conditions caused both activation by dissociation and inactivation by reassociation of the subunits, which appeared to be dependent on the cyclic AMP content. Epinephrine added to the incubation medium led to complete activation of both type I and type II isozymes (the intraepidermal cyclic AMP contents ranged from 20-50 pmol/mg protein). The isozymes of normal skin and involved skin of psoriatics showed identical peaks of type I and type II isozymes of equal amounts. The data indicate that protein kinase in the involved skin is not in an activated (by cyclic AMP) state.

Animals↗