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Biomedical subjects

R H Lenox

Publications and source records attributed to R H Lenox.

At least 73 records · Page 4Linked to original sources
PubMed1986

Proteolysis of the platelet surface: dissociation of shape change from aggregation.

Stimulation of intact platelets by ADP results in a shape change followed by aggregation in the presence of fibrinogen. ADP was found to induce a shape change in chymotrypsin-treated platelets that was similar in extent and initial velocity to that of intact (untreated) platelets. Scanning-electron microscopy verified an ADP-induced shape change in chymotrypsin-treated platelets. This shape change could be completely blocked by stimulators of platelet adenylate cyclase (forskolin, prostaglandin E1, and prostacyclin). On the other hand, the aggregation of chymotrypsin-treated platelets by fibrinogen was not dependent on the presence of ADP and could not be blocked by forskolin, prostaglandin E1, or prostacyclin, even though the levels of cyclic AMP (cAMP) formed in chymotrypsin-treated platelets were comparable to levels that completely inhibited the ADP-induced aggregation of intact platelets. This lack of inhibition of platelet aggregation was not due to degradation of the adenylate cyclase or prostaglandin receptors, since chymotrypsin-treated platelets were found to have a functional adenylate cyclase system that could be stimulated by forskolin, prostaglandin E1, and prostacyclin and inhibited by ADP and epinephrine, similar to that of intact platelets. These results provide direct evidence that cAMP does not interact with fibrinogen binding sites once they have become permanently exposed on the surface of platelets. Pretreatment of platelets with chymotrypsin therefore appears to be a useful tool that allows for the dissociation of platelet shape change from aggregation, without inhibiting either response.

Adenosine Diphosphate↗
PubMed1986

Exposure of fibrinogen receptors in human platelets by surface proteolysis with elastase.

Human platelets that were preincubated with porcine elastase aggregated spontaneously upon the addition of fibrinogen. Maximal aggregation to fibrinogen was observed with platelets pretreated with an elastase concentration of 111 micrograms/ml, and half-maximal aggregation occurred after treatment with 11 micrograms/ml elastase. Binding of radiolabeled fibrinogen to elastase-treated platelets was specific, saturable, and showed a single class of 48,400 +/- 9,697 fibrinogen-binding sites per platelet with a dissociation constant of 6.30 +/- 1.48 X 10(-7) M. ATP, apyrase, and the stimulators of platelet adenylate cyclase forskolin, prostaglandin E1, prostacyclin, and N6, 2'-O-dibutyryl cyclic AMP did not inhibit the fibrinogen-induced aggregation of elastase-treated platelets. EDTA completely blocked the initiation of aggregation and reversed the fibrinogen-induced aggregation of elastase-treated platelets. Monoclonal and polyclonal antibodies directed against glycoproteins (GP) IIb and IIIa completely blocked the fibrinogen-induced aggregation of elastase-treated platelets. Immunoprecipitates with these antibodies obtained from detergent extracts of surface-radiolabeled, intact, and elastase-treated platelets contained the glycoproteins IIb and IIIa. We conclude that surface proteolysis by low concentrations of elastase can expose fibrinogen-binding sites associated with GPIIb and GPIIIa on the platelet surface, resulting in spontaneous aggregation upon the addition of fibrinogen. These findings may be relevant to hemostatic changes observed in patients with increased levels of circulating elastase.

Adenosine Triphosphate↗
PubMed1985

Quaternary forms of classical muscarinic antagonists distinguish subpopulations of muscarinic receptors: correlation with gallamine-defined subpopulations.

Atropine and scopolamine inhibit the binding of [3H] quinuclidinyl benzilate (QNB) to muscarinic receptors of rat forebrain in a manner that suggests homogeneity of the binding sites. Under the same conditions, the inhibition by N-methylatropine (NMA) and N-methylscopolamine (NMS) of the binding of [3H]QNB is consistent with the presence of subpopulations of receptors that differ greatly in affinities toward these quaternary ligands. The subpopulations that are defined according to the affinities of NMA and NMS correlate very well with those that are defined by the use of gallamine. It is suggested that the heterogeneity in the binding of NMS explains some of the anomalous interactions between NMS and gallamine that have been reported previously.

Allosteric Site↗
PubMed1985

Inpatient clinical trial of lorazepam for the management of manic agitation.

Antipsychotic medications have traditionally been used for their sedative effects in the management of the behavioral and emotional agitation of mania while awaiting the therapeutic effect of lithium. On the premise that a nonantipsychotic sedative might satisfactorily and more specifically control this agitation without neuroleptic or hypotensive side effects and without prolongation of the acute illness, the authors conducted an open trial with four acutely manic patients in which only the benzodiazepine lorazepam was administered along with lithium; no antipsychotic medications were used. Lorazepam, administered in oral and parenteral form on an as-needed basis to maintain patient cooperation with the treatment plan and milieu, was found to be rapid and effective in controlling the manic agitation of these patients, with few troublesome side effects, and with no obvious prolongation of the acute illness.

Adult↗
PubMed1985

Tardive dyskinesia: clinical and neuroendocrine response to low dose bromocriptine.

Twelve patients with a long-standing history of moderate to severe symptoms of tardive dyskinesia, which had remained stable for several months, participated in a 6-week trial with bromocriptine. All patients were receiving a concomitant neuroleptic medication and were treated with a low dose of bromocriptine (0.75 to 7.5 mg). Patients showed a modest overall improvement of 16.6%, with a trend for greater improvement in male patients (23.6%). Baseline prolactin levels in the female patients showed a positive correlation with age and duration of tardive dyskinesia symptomatology. Plasma prolactin levels 4 hours following administration of bromocriptine were negatively correlated with the dose of bromocriptine. There appears to be a differential sensitivity for prolactin and growth hormone response to bromocriptine at these low doses in the presence of chronic neuroleptic treatment.

Bromocriptine↗
PubMed1985

Muscarinic receptors on intact human fibroblasts. Absence of receptor activity in adult skin cells.

The intact human fibroblast has been used in clinical and basic research studies of receptor-mediated control of cell function, however there is little information about the relationship between muscarinic receptor density and the regulation of cyclic AMP (cAMP) accumulation. We have compared the muscarinic receptor characteristics of both lung and skin intact fibroblasts at fetal and adult stages of development using carbachol-mediated inhibition of cAMP accumulation and the binding of [3H]quinuclidinyl benzilate (QNB). Prostaglandin E1 (PGE1) stimulated cAMP accumulation in all four cell lines, while carbachol inhibited cAMP accumulation only in the fetal lung, adult lung, and to a lesser extent, the fetal skin. Adult skin fibroblasts did not display significant evidence of inhibitory muscarinic receptor activity. [3H]QNB binding was saturable for the fetal and adult lung, and the fetal skin, yielding Kd values of approximately 0.5 nM for these cell lines. Bmax values were 360 fmol/mg for fetal skin, 600 fmol/mg for adult lung, and 876 fmol/mg for the fetal lung. Specific binding of [3H]QNB to adult skin fibroblasts was found to be low and variable. Comparisons of the Bmax values and maximal inhibitory capacities showed that the receptor density paralleled receptor activity in all cell lines. The lack of muscarinic receptor activity in the adult skin fibroblast was confirmed in several different adult skin cell lines, indicating that the adult skin fibroblast may not be an appropriate model for muscarinic receptor activity in clinical investigations.

Adult↗
PubMed1985

Alpha 2-adrenergic receptor-mediated regulation of adenylate cyclase in the intact human platelet. Evidence for a receptor reserve.

The alpha 2-adrenergic receptor on the human platelet is known to mediate the inhibition of adenylate cyclase activity. A comparison of the binding and response properties of intact cells revealed that the full agonists norepinephrine and epinephrine inhibit cyclic AMP accumulation with apparently higher affinity than they exhibit in inhibiting the binding of [3H]yohimbine. Additionally, Hill coefficients of the occupancy curves of the agonists were less than unity, suggesting the presence of a heterogeneous receptor population in intact platelets under conditions that permit robust inhibition of cyclic AMP accumulation. The partial agonist clonidine was found to possess the same affinity in the binding assay as in the response assay. These data are consistent with the presence of a receptor reserve in this system, a suggestion that was confirmed in experiments utilizing the irreversible alpha 2 antagonist phenoxybenzamine. The IC50 (100 nM) derived from the blockade of [3H]yohimbine binding by phenoxybenzamine was significantly less than the IC50 (550 nM) for the corresponding reversal by phenoxybenzamine of the effects of norepinephrine on cyclic AMP accumulation. Further studies demonstrated a rightward shift in the dose-response curves for the inhibition by norepinephrine of cyclic AMP accumulation following pretreatment with increasing phenoxybenzamine concentration. These data consistently indicated that occupancy of approximately 10% of the alpha 2-adrenergic receptors by norepinephrine elicits a half-maximal adenylate cyclase response. The relationship of these findings to current models of receptor-effector coupling is discussed.

Adenylyl Cyclases↗
PubMed1984

Platelet-activating factor-induced aggregation of human platelets specifically inhibited by triazolobenzodiazepines.

Platelet-activating factor (PAF), a naturally occurring phospholipid, is a potent activator of various biological processes, including platelet aggregation. The mechanisms by which PAF acts are largely unknown, partly because of the lack of specific inhibitors for PAF-elicited responses. It was found that in washed human platelets the psychotropic triazolobenzodiazepine drugs alprazolam and triazolam potently inhibited PAF-induced changes in shape, aggregation, and secretion. The effects were specific for PAF activation, since the responses of human platelets to adenosine diphosphate, thrombin, epinephrine, collagen, arachidonate, and the calcium ionophore A23187 were not inhibited by the triazolobenzodiazepines. These psychotropic drugs should be useful in investigating the possibility that PAF or PAF-like phospholipids play a role in neuronal function and in elucidating biochemical mechanisms activated specifically by PAF in a variety of cells.

Adenosine Diphosphate↗
PubMed1984

Activation of adenylyl cyclase by preincubation of rat cerebral-cortical membranes under phosphorylating conditions: role of ATP, GTP, and divalent cations.

The effects of preincubation under phosphorylating conditions on adenylyl cyclase activity were studied in preparations containing synaptic membranes from rat cerebral cortex. Preincubation of the membranes with 2 mM ATP and 10 mM MgCl2 resulted in a 50% increase of adenylyl cyclase activity which withstood sedimentation and washing. This activation was maximal after 5 min of preincubation, was reversed after longer preincubations, and paralleled the time course of endogenous phosphorylation-dephosphorylation of proteins observed under these conditions. The activation showed a critical requirement for Mg2+ ions and was dependent on ATP concentration. Similar activation was observed after preincubation of cerebral-cortical membranes with adenosine-5'-O-(3-thiophosphate) (ATP gamma S), but this activation was not reversed by prolonged preincubation times. The activation by ATP gamma S was potentiated severalfold by including synaptoplasm in the preincubation. Further experiments indicated that the activity of nucleoside diphosphokinase, which converts ATP gamma S to guanosine-5'-O-(3-thiophosphate) (GTP gamma S), could account for this potentiation. Preincubation of washed membranes for 5 min with 10 microM GTP and 10 mM MgCl2 also produced a 50% activation of adenylyl cyclase which withstood sedimentation and washing and was reversed by longer preincubations. Endogenous phosphorylation of specific protein components in the membranes during the preincubation was examined by including radioactively labeled nucleoside thiophosphates in the preincubation medium. Incorporation of 35S from [35S]ATP gamma S into a protein component with apparent Mr of 54,000 daltons ( 54K ) correlated significantly with the activation of adenylyl cyclase by ATP gamma S. Thiophosphorylation of the 54K protein was potentiated by addition of GDP to reactions carried out with [35S]ATP gamma S. Endogenous activity utilizing [gamma-32P]GTP as a phosphate donor also preferentially phosphorylated the 54K protein band. These results support previous suggestions that protein phosphorylation plays a role in the regulation of adenylyl cyclase activity. Among the numerous membrane-bound phosphoproteins in rat brain, we have identified a specific protein component with an apparent Mr of 54,000 daltons as the most likely candidate for involvement in this mode of regulation. This 54K protein, which is a principal substrate for a GTP-preferring protein kinase activity in brain membranes, can now be at the focus of investigations attempting to demonstrate a direct role for protein phosphorylation in adenylyl cyclase regulation.

Adenosine Triphosphate↗
PubMed1984

Regional brain and pituitary cyclic nucleotide response following central cholinergic stimulation in rats chronically exposed to lead.

Long Evans rats were exposed continuously to lead (1,000 ppm of lead acetate in the drinking water of dam or weanling) throughout gestation, lactation and until sacrifice at 60 days of age. A matched group of control animals was exposed to distilled water. On the day of sacrifice, control and lead treated animals were administered methylatropine 40 min. and oxotremorine (a muscarinic agonist) 10 min. prior to sacrifice by microwave irradiation. Locomotor activity was monitored during the 10 min. immediately preceding sacrifice. Levels of cyclic AMP and cyclic GMP were determined in 21 brain regions by radioimmunoassay. Locomotor activity following oxotremorine was significantly reduced in both lead treated and control animals. Levels of cyclic GMP were increased in septal region and frontal cortex and reduced in cerebellum and inferior colliculus of both groups of animals. The level of cyclic AMP in the pituitary increased 20-25 fold with a greater response noted in lead treated rats. Elevations of cyclic AMP were also noted in the interpeduncular nucleus, corpus striatum and substantia nigra in both groups. These data suggest that the cellular response to a muscarinic agonist was significantly affected by chronic exposure to lead in the pituitary but not in the remainder of the central nervous system.

Animals↗