Residual Inhibition Research Articles

Recognition of specific patterns of amino acid inhibition of growth in higher plants, uncomplicated by glutamine-reversible `general amino acid inhibition'

The complexity of the regulatory mechanisms that govern amino acid biosynthesis, particularly in multibranched pathways, frequently results in sensitivity to growth inhibition by exogenous amino acids. Usually the inhibition caused by a given amino acid(s) is relieved by another amino acid(s), thus indicating the cause of inhibition to be a specific interference with endogenous formation of the latter amino acid(s). We recently summarized the evidence that Nicotiana silvestris (and probably most higher plants), in suspension culture, exhibits a separate phenomenon of amino acid mediated growth inhibition called general amino acid inhibition. Every amino acid provokes general amino acid inhibition except for l-glutamine. In fact, l-glutamine completely overcomes general amino acid inhibition. We have now demonstrated that specific amino acid inhibition can be recognized and characterized at the level of growth inhibition without interference caused by general amino acid inhibition by the simple provision of exogenous l-glutamine. Several examples of specific amino acid inhibition of growth were demonstrated in N. silvestris. In one case, l-threonine inhibits growth partially in the presence of l-glutamine. The residual amino acid inhibition was overcome by the additional presence of l-lysine and l-methionine, indicating that exogenous l-threonine specifically inhibits the biosynthesis of both l-lysine and l-methionine. As a second example, the l-valine-mediated inhibition of growth that persisted in the presence of l-glutamine was overcome by l-isoleucine, indicating that exogenous l-valine inhibits l-isoleucine biosynthesis. The use of amino acid analogs as experimental tools for biochemical-genetic studies in higher plants is also complicated by general amino acid inhibition. Conditions were demonstrated under which p-fluorophenylalanine and m-fluorotyrosine could be used as specific antimetabolites of l-phenylalanine and l-tyrosine biosynthesis without interference from general amino acid inhibition. We thus present a rigorous basis for recognition of specific relationships between metabolic branches that can guide detailed enzymological analyses.

Selectivity of hemicholinium mustard, an affinity ligand, for the high-affinity choline transport system

The selectivity of the irreversible inhibition of high-affinity choline uptake (HACU) by hemicholinium mustard (HCM; 2,2′-(4,4′-biphenylene)bis[2-hydroxy-4-(2-bromoethyl)-morpholine] hydrochloride) with respect to other cholinergic proteins and other sodium-dependent transport systems was examined. Preincubation of rat forebrain membranes with HCM, followed by washing and measurement of [ 3H]-hemicholinium-3 binding to the high-affinity choline transporter, was shown to decrease binding capacity (B max) by 70% without affecting the apparent affinity of the ligand. However, a similar preincubation, wash and binding experiment using [ 3H]-NMS as a ligand for muscarinic receptors showed no HCM effect on binding parameters. To measure the effects of HCM on choline acetyltransferase (ChAT), synaptosomes were incubated in HCM, then washed. The synaptosomes were lysed and ChAT activity was measured. Treatment with 50 μM. HCM, a concentration that inhibits 100% of synaptosomal HACU, results in a 24% decrease in ChAT activity. HCM demonstrates little residual inhibition of other sodium-dependent neurotransmitter transporter transporters: preincubation with 50 μM HCM results in a decrease of 12% in transport of [ 3H]-dopamine and a decrease of 6% in the transport of [ 3H]-GABA. The binding of HCM, like that of hemicholinium-3 is sodium-dependent. HCM preincubation in the presence of sodium results in inhibition of HACU to 32% of control; in the absence of sodium HACU is 65% of control. This represents a loss of 51% of the observed irreversible inhibition produced by HCM. Irreversible inhibition by HCM can also be prevented by co-incubation with hemicholinium-3. Co-incubation with hemicholinium-3 results in residual HACU inhibition that decreases from 51% (HCM alone) to 28% (HCM + hemicholinium-3). When atropine instead of hemicholinium-3 is co-incubated with HCM, HCM still inhibits 40% of transport, demonstrating the pharmacological specificity of the protective effect of hemicholinium-3. Experiments in the guinea-pig myenteric plexus preparation demonstrate a gradual recovery from the residual effects of HCM. Evoked ACh release decreases to 24% immediately following treatment with 1 μM HCM. After 2 hr of recovery, tissues have recovered to about 50% of control levels, after which recovery continues at a slower rate.

Opioid inhibition of Ca2+ channel subtypes in bovine chromaffin cells: selectivity of action and voltage-dependence.

Bovine chromaffin cells possess a mixture of high-voltage-activated Ca2+ channel subtypes: L-type, dihydropyridine-sensitive channels, and N-, P- and Q-types, omega-conotoxin MVIIC-sensitive channels. In these cells, we studied the reversible, naloxone-antagonized inhibition of Ba2+ currents by the opioid agonist met-enkephalin (IC50 = 272 nM). This inhibition could be resolved into a voltage-dependent and a voltage-independent component. The first was revealed by its slow Ba2+ current activation kinetics at 0 mV and by the current facilitation induced by short prepulses to +90 mV. The second was estimated as the residual inhibition persisting after the facilitation protocol. The two inhibitory components varied markedly from cell to cell and each contributed to about half of the total inhibition. Replacement of internal GTP by GDP-beta-S or cell pretreatment with pertussis toxin completely abolished the voltage-dependent inhibition by opioids, partially preserving the voltage-independent component. The opioid-induced inhibition was not selective for any Ca2+ channel subtype, being not prevented after the addition of specific Ca2+ channel antagonists. However, when separately analysing the contribution of each channel type to the voltage-dependent and voltage-independent modulation, a clear-cut distinction could be achieved. The voltage-independent inhibition was effective on all Ca2+ channel subtypes but predominantly on L-type Ca2+ channels. The voltage-dependent process was abolished by omega-conotoxin-MVIIC, but unaffected by nifedipine, and was thus sharply restricted to non-L-type channels (N-, P- and Q-types). Our data suggest a functionally distinct opioid receptor-mediated modulation of L- and non-L-type channels, i.e. of the two channel classes sharing major control of catecholamine secretion from bovine chromaffin cells.

Slow dissociation of long-acting Ca2+ antagonist amlodipine from 3H-PN200-110 binding sites in membranes of rat hearts and brains.

The dissociation rate of amlodipine ((+/-)-3-ethyl 5-methyl 2-[(2-aminoethoxy)methyl]-4-(o-chlorophenyl)-1,4-dihydro-6-methyl- 3,5- pyridinedicarboxylate benzenesulfonate) from rat heart and brain membranes preincubated with drugs and washed out with buffer was assessed by radioligand binding assay using 3H-PN200-110 as a radioligand. The remaining KCl-induced contraction in rat aortic strips washed out after treatment with this drug and the pKi (inhibition constant) values of the drug were compared with those of nisoldipine, nifedipine, manidipine and benidipine. The inhibition of 3H-PN200-110 binding induced by nifedipine was reversed by washing, whereas that induced by amlodipine, manidipine, and benidipine was not readily reversed under these conditions. When rat aortic strips were pretreated with Ca2+ antagonists, the rank order of the inhibition of contractions induced by 50 mM KCl was manidipine = benidipine > amlodipine > nisoldipine > nifedipine, even though Ca2+ antagonists were not present in the extracellular medium. The pKi values of amlodipine in the heart and brain were 6.86 and 7.41, respectively, and these values were lower than those of the other Ca2+ antagonists. There was a good correlation between the potency of the inhibition of 3H-PN200-110 binding by drugs after the washout of membranes and the inhibition exerted by the drugs in contractions induced by 50 mM KCl after the washout of tissues, although this residual inhibition was not correlated with pKi values. Thus, these results suggest that amlodipine has a very slow rate of dissociation from 3H-PN200-110 binding sites, as do manidipine and benidipine, and this property may explain its long-lasting antihypertensive effect.

Properties of the reversible, K +-competitive inhibitor of the gastric H +/K +)-ATPase, SK&F 97574. II. Pharmacological properties

SK&F 97574 [3-Butryl-4-(2-methylamino)-8-(2-hydroxyethoxy) quinoline] is a potent, reversible inhibitor of the gastric (H +/K +)-ATPase. In an anaesthetised lumen-perfused rat preparation, it inhibited pentagastrin-stimulated gastric acid secretion with intravenous and intraduodenal inhibitory ED 50 values of 2.40 μmol/kg and 4.43 μmol/kg, respectively. In the conscious fistula rat model, doses of 10 μmol/kg IV and 25 μmol/kg PO produced mean peak inhibitions of basal acid output of 91% and 97%, respectively. In these experiments, the duration of action of SK&F 97574 was much shorter than that of the covalent (H +/K +)-ATPase inhibitor, omeprazole. In the conscious Heidenhain pouch dog, SK&F 97574 inhibited histamine-stimulated gastric acid secretion after both intravenous and oral administration with ED 50 values of 0.49 μmol/kg and 0.89 μmol/kg, respectively. In this model, duration of action studies showed that significant residual inhibition of acid secretion remained 8 hours after intravenous dosing with SK&F 97574 (producing peak inhibition of 92%). However, 24 hours after oral dosing of SK&F 97574 (10 μmol/kg), no significant inhibition remained. These data indicate that the duration of action of SK&F 97574 is longer than that of the histamine H 2 receptor antagonists such as cimetidine, but shorter than that of covalent (H +/K +)-inhibitors such as omeprazole. Overall, the pharmacological properties of SK&F 97574 suggest that it could be a potentially useful clinical treatment for acid-related diseases.

Different Inhibitory Effects of the Newly Developed CCK Receptor Antagonists FK480 and KSG-504 on Pancreatic Exocrine and Endocrine Secretion in the Isolated Perfused Rat Pancreas

Cholecystokinin (CCK) receptor antagonists are shown to have therapeutic as well as preventive effects in some types of acute pancreatitis. However, there is a possibility that administration of CCK receptor antagonists with a high inhibitory potency on the endocrine pancreas to patients with acute pancreatitis exacerbates the associated glucose intolerance. In the present study we simultaneously examined the effects of the newly developed benzodiazepine derivative FK480 and proglumide-related antagonist KSG-504 on CCK octapeptide (CCK-8)-stimulated exocrine and endocrine function in the isolated perfused rat pancreas. FK480 and KSG-504 inhibited CCK-8-stimulated pancreatic juice flow, protein output, and insulin release in a dose-dependent manner. FK480 was approximately 10 times more potent than KSG-504 in inhibiting exocrine and endocrine secretion. Both antagonists inhibited CCK-8-stimulated insulin release more potently than exocrine secretion. FK480 caused a dose-dependent residual inhibition of exocrine secretion after its removal from the perfusate, whereas insulin release was only slightly impaired even at the highest dose. In contrast, termination of KSG-504 infusion resulted in an immediate increase in both exocrine and insulin responses without causing any residual inhibition. With regard to the residual inhibition, therefore, KSG-504 had no significant influences on exocrine and insulin release, whereas FK480 inhibited exocrine secretion more potently than insulin response. These results suggest that FK480 might become a useful therapeutic agent for pancreatitis with respect to its long-duration inhibitory effect on exocrine secretion and short-duration inhibitory effect on insulin release.

Characteristics of Tinnitus Induced by Head Injury

To determine if the characteristics of tinnitus produced by head trauma are specific and exclusive when compared with other origins of tinnitus. Retrospective study using clinic test results and data from the Tinnitus Data Registry compiled from questionnaires, interviews, and testing. Tinnitus produced by head injury was compared with tinnitus of mixed origins, including no known origin. A tinnitus referral clinic where all patients must see an otologist or an ear, nose, and throat physician prior to attending the clinic. All patients had severe to moderately severe constant tinnitus and presented with tinnitus as the primary symptom. No exclusive characteristics were found to describe head injury-induced tinnitus. The tinnitus for the group with head injury was statistically significantly (P = .004) louder and occurred with greater incidence of continuing pain in the ears. The group with head injury also had more episodes of dizziness and a more severe form of tinnitus. However, no marked difference was noted in pitch of tinnitus, complexity (number of sounds) of tinnitus, or the minimum masking level. This retrospective study found that tinnitus induced by head injury was significantly (P = .004) louder than tinnitus induced from other causes but, interestingly, did not require higher levels of masking. The patients with head injury-induced tinnitus more frequently (P = .0003) displayed residual inhibition although the duration of residual inhibition was not different from that of the comparison group. Other symptoms associated with the tinnitus onset were more frequently mentioned by the group with head trauma-induced tinnitus, except for the condition of pressure sensation in the ears. Using a severity questionnaire, the group with head trauma-induced tinnitus rated their tinnitus as being more severe than did the comparison group. However, such things as pitch of the tinnitus, masking level, acceptance of wearable maskers, general hearing level, and complexity of the tinnitus did not distinguish the two groups.

157 SUITABILITY OF A SHREDDED NEWSPAPER, KITCHEN WASTE COMPOST AS A ROOT SUBSTRATE FOR TOMATO SEEDLINGS

A small, continuous flow compost reactor was employed to produce a compost from a shredded newspaper/kitchen waste mixture. Transit time through the reactor was 4 weeks and the compost was then stockpiled for 5, 7, 8 or 9 weeks prior to evaluation. Cress seed germination was not reduced in graded aqueous compost extracts, however, seedling radicle length was significantly reduced in the nondiluted extract.. Elemental analysis of the compost showed PO4 ond K to be about 20 and 2 times recommended levels and No 5 times the maximum level at 577 mg. liter-1. Electrical conductivity of the compost was 5 dS.m-1 and pH range was 6.2-7.3. Composts were leached with water to E.C.'s of 1-1.5 dS.m-1 before planting tomato seedlings. Dry weights of tomato seedlings grown 5 weeks in the composts were equal to those in a peat vermiculite control, except that dry weights of seedlings in the compost stockpiled for 5 weeks were less than those of control plants. Some residual inhibition of growth may hove remained in the compost for at least 5 weeks after the production dote but by the 7th week, no growth inhibition was apparent.

Characterization of a New Cholecystokinin Receptor Antagonist FK480 in in Vitro Isolated Rat Pancreatic Acini

Biochemical and pharmacologic characteristics of a newly developed benzodiazepine derivative (S)-N-[1-(2-fluorophenyl)-3,4, 6,7-tetrahydro-4-oxo-pyrrolo-[3,2,1-jk] [1,4]benzodiazepine-3-yl]-1H-indole-2-carboxamide (FK480) as a cholecystokinin (CCK) receptor antagonist were examined in the isolated rat pancreatic acini and compared with those of MK-329 and loxiglumide. FK480, MK-329, and loxiglumide inhibited CCK octapeptide (CCK-8)-stimulated amylase release and binding of [125I]CCK-8 in a concentration-dependent manner, with a half-maximal inhibition (ID50) at 1.30 +/- 0.12 nM, 1.33 +/- 0.21 nM, and 1.27 +/- 0.23 microM, respectively, for amylase release, and 0.40 +/- 0.06 nM, 0.68 +/- 0.08 nM, and 0.38 +/- 0.03 microM, respectively, for [125I]CCK-8 binding. The antagonism was competitive in nature because these three compounds caused a parallel rightward shift of the dose-response curve for CCK-8-stimulated amylase secretion, without altering the maximal increase. The antagonism produced by FK480 was specific for CCK in that the effects of other receptor secretagogues or agents bypassing receptors were not altered. FK480 not only prevented but also reversed CCK-8-stimulated amylase release. This compound caused a residual inhibition of the action of CCK-8. When acini were preincubated with 100 nM FK480 for 30 min, the subsequent dose-response curve to CCK-8 was shifted 10-fold toward higher concentration. Similar results were obtained with MK-329 but not with loxiglumide. FK480 appeared to be bound to the receptors on acinar cells in a slowly dissociating state.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymer dissolution. I. On the dissolution behavior of copolymers of methyl methacrylate and methacrylic acid

AbstractCopolymers of methyl methacrylate with methacrylic acid [P(MMA/MA)] are interesting resist materials for microlithography. At moderate baking temperatures, these copolymers undergo an intramolecular cyclization, yielding terpolymers containing anhydride moieties. This process has striking consequences for the dissolution behavior and results in higher ketone solubilities. The dissolution rates in methyl ethyl ketone (MEK) and in mixtures with ethyl glycol (EG) correlate in an Arrhenius‐like manner with the reciprocal baking temperatures. Two distinct temperature ranges with different slopes between 130–180°C and 180–230°C are found. This is in good agreement with other findings, indicating a different mechanism of anhydride formation in these temperature regions. The activation energies for the dissolution of P(MMA/MA) in EG or EG/MEK mixtures are about 17 kcal/mol and those of the thermally treated material in MEK or MEK/EG or mixtures of MEK with methyl isobutyl ketone (MIBK) are in the range of 20–30 kcal/mol. For the investigation of the Mn dependence, γ‐irradiated probes of the copolymer were used. We obtained the usual exponential Mn dependence with an exponent of 0.7–0.8 in MIBK and 0.3–0.4 in EG. Our findings are in agreement with a “relaxation‐controlled” dissolution behavior, especially for the anhydride‐containing terpolymer. No residual layers or pronounced inhibition periods indicative for gel‐layer formation, however, could be found. We suggest a normal dissolution process with a very small gel layer. For the copolymer in an alcohol‐containing solvent, a stress‐driven dissolution behaviour is more likely. © 1994 John Wiley & Sons, Inc.

Pharmacokinetics and Pharmacodynamics of Trandolapril After Repeated Administration of 2 mg to Young and Elderly Patients with Mild-to-Moderate Hypertension

The new angiotensin-converting enzyme (ACE) inhibitor trandolapril 2 mg was administered daily for 10 consecutive days to young (mean age +/- SEM 44.1 +/- 2.3 years; n = 10) and elderly (mean age +/- SEM 69.3 +/- 0.9 years; n = 14) patients with mild-to-moderate hypertension. All groups had similar baseline blood pressures: mean 164/100 mm Hg. Maximal plasma ACE inhibition on day 10 and residual inhibition 24 h after the last dose was the same, irrespective of age: young, 85.2 and 57.4%; elderly 89.1 and 59.8%, respectively. There was no difference between the results on day 1 for the young and elderly groups. The absorption of trandolapril was rapid (< 1 h in all groups). The peak plasma concentration (Cmax) and the area under the plasma concentration-time curve (AUC) were slightly higher in the older group, but the elimination half-life (t1/2) was the same, with no accumulation after repeat dosing. A steady-state plasma concentration of the active metabolite of trandolapril, trandolaprilat, was reached after 4 days in the two groups, with similar accumulation ratios (young, 1.48; elderly, 1.49). At steady state, the Cmax and AUC 0-24 h for trandolaprilat were similar in the two groups: young, 7.49 +/- 0.98 ng/ml and 82.27 +/- 6.95 ng/ml/h; elderly, 8.35 +/- 0.67 ng/ml/h and 96.75 +/- 5.67 ng/ml/h. Maximal reductions in systolic/diastolic blood pressures (at 6 h postdose) were -14.1%/-16.1% in young patients and -14.6%/-17.5% for the elderly. Significant blood pressure reduction persisted for 48 h after the last dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a new diphenylpyrazolidinone cholecystokinin antagonist in vitro isolated rat pancreatic acini.

The effects of a newly developed diphenylpyrazolidinone cholecystokinin (CCK) antagonist LY219,057 were examined in the isolated rat pancreatic acini and compared with those of devazepide (previously designated L364,718 or MK-329). LY219,057 caused a concentration-dependent inhibition of 100 pM CCK octapeptide (CCK-8)-stimulated amylase release, with a half-maximal inhibition (ID50) at 287.5 +/- 28.4 nM and was 200 times less potent than devazepide (ID50 = 1.4 +/- 0.2 nM). The antagonism was competitive in nature because LY219,057 caused a parallel rightward shift of the dose-response curve for CCK-8-stimulated amylase secretion without altering the maximal increase. LY219,057 significantly inhibited amylase release in response to CCK-8 and cerulein but had no effect on amylase release stimulated by other receptor secretagogs or agent bypassing receptors. LY219,057, whether added at the beginning or 20 min after the CCK-8 stimulation, inhibited amylase release. This compound caused a residual inhibition of the action of CCK-8. Acini preincubated with 1.0 microM LY219,057 for 30 min at 37 degrees C were threefold less sensitive to CCK-8 than the acini preincubated without LY219,057. These results indicate that LY219,057 acts as a potent, competitive, and specific CCK receptor antagonist of the action of CCK on the exocrine pancreas.

Opposite, phase-dependent effects of 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester or tetracaine on islet function during three phases of glucose-stimulated insulin secretion.

The spontaneous decline of insulin secretion which occurs under a variety of secretory conditions is well documented and suggests a general desensitization of the secretory process distal to signal recognition. Accordingly, we have investigated the effects of agents thought to mobilize intracellular Ca++ on insulin secretion over 24 h, which includes periods of rising secretory activity (second phase) and desensitized secretory activity (third phase). During the first 3 h of glucose stimulation of freshly isolated rat islets, insulin secretion was strongly inhibited by 30 microM 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester (TMB) or 300 microM tetracaine hydrochloride (TC). However, when either of these agents was added for the first time to islets at h 20 when insulin secretion was at a low steady rate (third phase), insulin secretion was greatly enhanced. Both these inhibitory and stimulatory effects declined with continued administration. Removal of TMB and rechallenge with high glucose plus forskolin uncovered a residual inhibition in both chronically and acutely treated islets. Coadministration of forskolin with either TMB or TC blunted both inhibitory and stimulatory effects. Pertussis toxin pretreatment, however, did not alter subsequent response of islets to either agent. Thus TMB or TC have opposite, phase-dependent effects on glucose-stimulated insulin secretion. We postulate that potentiators of glucose-stimulated insulin secretion, which are increased during second phase, are most sensitive to inhibitory effects of TMB or TC, and that the low steady rate of third phase permits their stimulatory component(s) to become apparent.

The cellular basis of conditional bursting in mesencephalic dopamine-containing neurons

Antisaccades produce longer reaction times (RT) than their prosaccade counterparts and this latency increase has been linked to an oculomotor ‘pre-setting’ that prevents the evocation of a stimulus-driven prosaccade. Moreover, a consequence of oculomotor pre-setting is a lengthening of the RTs associated with a subsequent prosaccade. The goal of the present study was to determine whether the constituent elements associated with planning a correct antisaccade (i.e., response suppression and vector inversion) imparts a residual delay that inhibits the planning of a subsequent prosaccade. To that end, participants alternated between pro- and antisaccades in a pseudo-randomized task-switching schedule (e.g., AABBAAB…) and responses were cued via a paradigm that was designed to evoke frequent error antisaccades (i.e., a saccade initially, and incorrectly, planned to the target stimulus). Results showed that RTs for correct antisaccades were longer than error antisaccades and that prosaccades preceded by the former, but not the latter, trial-type were associated with a reliable increase in RT (i.e., prosaccade switch-cost). In other words, error antisaccades were associated with a failure to withhold a stimulus-driven prosaccade and did not delay the planning of a subsequent prosaccade. Based on these findings we propose that the prosaccade switch-cost is not related to an explicit awareness of task goals; rather, our results are consistent with the assertion that a consequence of response suppression and vector inversion is a residual inhibition of stimulus-driven oculomotor planning networks.

Organophosphate polyneuropathy in chicks

Young animals are resistant to organophosphate-induced delayed neuropathy (OPIDP), although biochemical changes on Neuropathy Target Esterase (NTE) caused by neuropathic organophosphorus esters (OP) are similar to those observed in the sensitive hen. We report here that the resistance of chicks to single doses of neuropathic OPs is not absolute because ataxia was produced in 40-day-old chicks by 2,2-dichlorovinyl dibutyl phosphate (DBDCVP, 5.0 or 10.0 mg/kg s.c.) and by diisopropyl phosphorofluoridate (DFP, 2.0 mg/kg s.c.). However, the clinical picture was different from that usually seen in hens; spasticity and complete recovery being the main features. α-Tolyl sulphonyl fluoride (PMSF, 300 mg/kg s.c.) promoted both DBDCVP neuropathy (5.0 or 10.0 mg/kg s.c.) and non-neuropathic doses of DFP (1.5 mg/kg s.c.) or DBDCVP (1.0 mg/kg s.c.). The lowest promoting dose of PMSF given 24 hr after 1.5 mg/kg of DFP was 30 mg/kg. Higher doses had a more severe effect but no further increase of OPIDP severity was obtained with doses ranging from 90 to 300 mg/kg. PMSF (30 mg/kg) protected 40-day-old chicks from subsequent doses of neuropathic OPs even when a promoting dose of PMSF followed. At 60 days of age, chicks' resistance to OPIDP decreased because lower doses of neuropathic OPs became effective and, similarly to hens, PMSF did not fully protect from subsequent promotion. In 40-day-old chicks the threshold of NTE inhibition for OPIDP development was 95–97% (DBDCVP 5.0 mg/kg). When promotion followed initiation, the minimal effective inhibition of NTE for initiation by neuropathic OPs was about 90%. In 36-day-old chicks, PMSF (300 mg/kg) promoted OPIDP when given up to 5 days after DFP (1.5 mg/kg) when residual NTE inhibition in brain and sciatic nerve was about 40%. We conclude that chicks' resistance to OPIDP might reflect either a less effective initiation by phosphorylated NTE or a more efficient repair mechanism or both, and also that promotion is likely to involve a target other than NTE.

Tinnitus Suppression by Electrical Promontory Stimulation in Sensorineural Deaf Patients

In 62 patients, whose hearing acuity was normal or profoundly impaired, tinnitus suppression was attempted through electrical promontory stimulation (EPS) with a Promontory Stimulator (Cochlear Co.). The causes of tinnitus were idiopathic sudden deafness, ototoxicity, noise induced hearing loss, labyrinthitis, Meniere's disease, acoustic neuroma and unknown origin. Reduction of tinnitus was achieved in 46 of 68 ears (67.6%). Of these, EPS was most effective in cases of noise induced hearing loss (100.0%; 3/3), followed by those of idiopathic sudden deafness (87.5%; 14/16), Meniere's disease (83.3%; 5/6), labyrinthitis (75.0%; 6/8), ototoxicity (66.6%; 4/6) and unknown origin (76.4%; 13/17). The treatment had hardly any effect on patients with acoustic neuroma (8.3%; 1/12). Twenty patients reported residual inhibition with a duration ranging from several hours to one week. Our results suggest that tinnitus due to cochlear lesions can be suppressed by EPS. This technique may also be useful for differentiation between tinnitus resulting from cochlear lesions and from retrocochlear lesions.

Tinnitus suppression following cochlear implantation. A multifactorial investigation.

The effects of cochlear implant on loudness, annoyance, daily duration, location, and residual inhibition of tinnitus were evaluated by a closed-ended, quantifiable questionnaire in 33 postlingually deafened patients who had received implants at the University of Michigan, Ann Arbor, between 1986 and 1990. Preoperative tinnitus was present in 85% of patients. A statistical comparison of preoperative vs postoperative loudness and annoyance indicated a significant reduction in both of these complaints postoperatively. Loudness and annoyance were significantly correlated, both preoperatively and postoperatively. Fifteen patients (54%) with preoperative tinnitus demonstrated a loudness decrease of 30% or more; 43% demonstrated an annoyance decrease of 30% or more; and 48% demonstrated a decrease of 30% or more in daily tinnitus duration. Patients who experienced a loudness or annoyance decrease of 30% or more after implantation demonstrated significantly higher preoperative levels of these complaints, suggesting that degree of tinnitus reduction after implantation may be related to preoperative loudness and annoyance levels. Contralateral tinnitus suppression was reported by 42% of patients. Residual inhibition ranging from 60 seconds to several hours was reported by 50% of patients, predominantly in the ear with the implant. Age, gender, cause of hearing loss, duration of tinnitus, cochlear implant usage, and time after implantation were not predictive of tinnitus suppression. Overall, the majority of the patients (74%) thought that their cochlear implant was helpful in tinnitus suppression, especially in the ear with the implant. Contralateral residual inhibition and tinnitus suppression suggest a central mechanism contributing to these phenomena.

Involvement of C3 exotoxin-sensitive G proteins (rho/rac) in PTH signal transduction in OK cells.

Parathyroid hormone (PTH) in opossum kidney (OK) cells leads to inhibition of Na-Pi cotransport, to the generation of inositol trisphosphate (IP3) and adenosine 3',5'-cyclic monophosphate (cAMP) and to a phosphorylation of proteins present in an enriched apical membrane fraction (27, 28; for review see Ref. 23). In the present report we have identified two of these phosphoproteins with molecular weights of approximately 22,000 and approximately 24,000, respectively, as guanosine 5'-triphosphate (GTP)-binding proteins, ADP-ribosylated by the Clostridium botulinum exotoxin C3 and recognized by an anti-rho polyclonal antibody but not by pan-ras monoclonal antibody; as suggested by Western-blot analysis the content of the proteins recognized by the anti-rho antibody did not alter in the membrane fraction as a function of treatment with PTH. Transient permeabilization of OK cells using streptolysin O and including the C3 exotoxin attenuated PTH-dependent inhibition of Na-Pi cotransport at hormone concentrations higher than 10(-10) M; residual PTH-dependent inhibition is equal to that observed after pharmacological activation of protein kinase A and protein kinase C, respectively. C3 exotoxin did not alter PTH-dependent generation of cAMP but modified production of IP3; it was increased at 10(-11) M and reduced at 10(-8) M PTH, respectively. It is suggested that protein kinase A may be involved in the phosphorylation of C3 exotoxin-sensitive G proteins (rho/rac). These proteins could be involved in PTH signal transduction.

Differential Mechanisms of Dopamine and Somatostatin Inhibition of Prolactin Secretion from Anterior Pituitary Cells

Abstract The relative potencies of dopamine and somatostatin to inhibit prolactin secretion by pituitary cells in primary culture were compared. Hormone secretion was evaluated under basal conditions as well as after challenging it with thyrotropin-releasing hormone, vasoactive intestinal peptide or with drugs affecting either the activity of adenylate cyclase (forskolin), and protein kinase C (phorbol 12 myristate 13 acetate), or eliciting Ca(2) (+) fluxes in the cell by various ways (A23187, a Ca(2+) ionophore, the dihydropyridine agonist BAY-K-8644, or K(+) depolarization which activates voltage-sensitive Ca(2+) channels). In order to test whether all effects of dopamine and somatostatin were mediated by inhibitory guanosine triphosphate binding proteins, the experiments were systematically carried out in the presence or absence of pertussis toxin, an agent which selectively uncouples given subsets of G proteins from corresponding receptors. Dopamine markedly inhibited basal as well as thyrotropin-releasing hormone-, vasoactive intestinal peptide-, forskolin- and BAY-K-8644-stimulated release of prolactin. In contrast, dopamine was only able to induce partial inhibition of hormone release when secretion was triggered by tumour-promoting activator, A23187 or K(+) depolarization. Under all conditions tested, inhibition by somatostatin was significant, but of limited amplitude. Pertussis toxin completely reversed the effects of somatostatin. In contrast, complete reversal of dopamine effects by pertussis toxin was only achieved after hormone stimulation by tumour-promoting activator, alone or with A23187. Under all other conditions a residual dopamine inhibition was maintained in the presence of the toxin. The amplitude of this residual toxin resistant inhibition was comparable in all other cases to that observed for unstimulated (basal) prolactin release. It is concluded that: 1) As expected, dopamine is a potent inhibitor of secretory processes involving cyclic AMP accumulation or voltage-sensitive Ca(2+) channel activation. In contrast, the amine is only a partial inhibitor of exocytosis resulting from non-voltage-sensitive Ca(2+) channel-gated increase in Ca(2+) or direct activation of protein kinase C. 2) Somatostatin is a partial inhibitor of prolactin under all conditions tested. Dopamine and all somatostatin effects are mediated by pertussis toxin-sensitive G proteins. However, a small, but significant, proportion of dopamine inhibition is resistant to pertussis toxin and can thus be assumed to involve a distinct mode of action. This alternate mechanism of dopamine inhibition operates under all conditions except after treatment with tumour-promoting activator, suggesting that it can be inactivated by protein kinase C stimulation.

Tinnitus diagnosis and therapy in the aged

We report on a study of tinnitus in more than 400 patients 20 to 80 years old who had suffered from tinnitus for more than one year. Quality of tinnitus, localization, frequency range, severity, masking and residual inhibition effects show no age dependence. The possible causes of tinnitus, is onset and duration and factors that increase or reduce tinnitus also show no age dependence. Regarding the grade of annoyance judged from a subjective scaling, younger patients seen to suffer more from tinnitus than do older subjects, who seem to compensate their tinnitus more often. With regard to the different therapeutic methods used in this study (transtympanal electrostimulation, iontophoresis, biofeedback, tinnitus masker, hearing aid), the stable benefit over more than one year experienced by those patients fitted with a hearing aid was encouraging for young and old subjects. In both groups, about 3% of the patients could be successfully equipped with a tinnitus masker. Independent of age, the improvement by the other methods is less than 1%. Our results show that sufficient prognostic data on the efficiency of a therapeutic method cannot be perceived from the different tinnitus measurements for either the young or the old subjects.