Priming-like effect and successful desensitization after anaphylactic shock by latex sublingual immunotherapy.

The present report deals with some unusual events observed restarting allergy vaccine in a case of anaphylactic shock which occurred giving the maximum scheduled dose (25 drops) of rush sublingual immunotherapy (SLIT) to latex. Restarting SLIT by usual (not rush) scheme we observed long-lasting fall of reactivity threshold. The maximum tolerable dose was reduced to 2 drops, a dose fivefold smaller than the one well tolerated during previous rush phase (10 drops). We have excluded a possible nocebo effect and proved that the reduced tolerance was real by double blind placebo-controlled challenge test. We have considered this effect in some ways similar to priming effect. SLIT was continued with two drops every day. After about twenty months we could demostrate a significant reduction of skin reactivity by end-point technique and an improved response to the controlled exposition to latex by use-tests. In the same time the tolerance to vaccine was improved to three drops. The better safety profile allowed us to restart and continue with SLIT also in the reported case of anaphlicatic shock by latex vaccine and, after about two years, to induce valuable hyposensitization. Latex SLIT is confirmed as a safe and effective method.

Interaction between phenytoin and valproic acid: plasma protein binding and metabolic effects.

The effect of sodium valproate (400 mg three times daily) on the disposition kinetics of intravenous phenytoin (250 mg) was investigated in seven normal subjects. After valproate, the free (unbound) fraction of phenytoin in serum rose from 9.6 +/- 0.9% (SD) to 15.6 +/- 1.4% on average (p < 0.001). The effect was associated with an increase in systemic clearance and apparent volume of distribution of total drug. There was a strong positive correlation between percent increment in each of these parameters and percent increment in unbound drug in serum. Free phenytoin concentration in serum and phenytoin concentration in saliva increased during valproate administration. As a result, both the clearance and the apparent volume of distribution of free drug were reduced. There was an increase in the renal excretion of unchanged phenytoin during valproate administration, but the effect was too small to have an appreciable influence on the overall clearance of the drug. There were no consistent changes in the excretion of the major metabolite 5, p-hydroxyphenyl, 5-phenyl, hydantoin (pHPPH), in the urine. These results suggest that valproic acid may have two separate and opposing effects on phenytoin disposition: (1) displacing phenytoin from plasma protein binding sites, thereby enhancing the systemic clearance of total drug, and (2) inhibiting phenytoin metabolism, thereby increasing the concentration of free drug in the serum.

DNA methylases separated through the HeLa cell cycle methodology show allosteric properties.

Two DNA methylases (DNAmets) can be separated through the cell cycle. The first appears as a minor peak in G1, the second as a major peak in S. Both enzymes protect from HpaII a plasmid (H31), constructed with the pBR322 vector (4.3 kbp) and the inverted A gamma fragment of the human globin gene (3.5 kbp), inserted at its HindIII site (the vector carries several HpaII sites, the insert only one HpaII site). DNAmets G1 and S show distinct Km values and different kinetics vs the ionic strength of the medium, while their Michaelis-Menten and Lineweaver-Burk plots are sigmoidal and hyperbolical curves, respectively. This is the first suggestion about the allosteric nature of the eukaryotic DNAmet system.

Plasma protein binding of drugs in pregnancy.

The degree of binding to plasma proteins is an important determinant of drug disposition and response. Normal human pregnancy is associated with concentration of plasma proteins, free fatty acids and possibly other endogenous substances interfering with drug binding. The possibility of an associated change in plasma binding capacity therefore needs to be taken into consideration. Experimental studies conducted mostly in vitro have shown that the plasma protein binding of many (but not all) drugs is decreased during pregnancy, particularly during the last trimester. This phenomenon should be taken into account when interpreting serum concentrations of total (free + protein-bound) drug in clinical practice. Notable examples of drugs whose unbound fraction increases during pregnancy include diazepam, valproic acid, phenytoin, phenobarbitone, salicylic acid, pethidine, lignocaine, dexamethasone, sulphafurazole and propranolol. For many drugs, important differences have been demonstrated in the degree of protein binding between maternal and cord plasma. In some cases, this may provide an explanation for the finding of marked differences in total drug concentration between maternal and fetal plasma at the time of delivery.

Interpretation of drug levels in acute and chronic disease states.

Serum drug concentration monitoring can be an invaluable aid to patient management, particularly in certain pathological conditions when individualisation of dosage is particularly critical. To be clinically useful, however, drug levels must be interpreted in the context of all factors that could influence the correlation between the concentration of the drug in plasma and the intensity of action. Several such factors may be operating in acute and chronic disease states. For example, a number of pathological conditions are associated with marked changes in the fraction of free, pharmacologically active drug in plasma and this will result in disruption of the normal relationship between total serum drug level and effect, as seen for phenytoin in uraemia. An altered response to a given serum drug level in disease states may also be caused by changes in tissue distribution, by abnormal accumulation of pharmacologically active metabolites in plasma or by changes in end-organ responsiveness. The latter are best illustrated by the altered sensitivity to digoxin in patients with various conditions, including hypokalaemia and thyroid disease. In addition to the factors listed above, consideration should also be given to potential interactions with concomitantly used drugs and to the possibility of analytical errors, especially in view of the evidence that the performance of otherwise reliable drug assays may be grossly impaired in certain diseases (e.g. uraemia), due to abnormal plasma composition and/or accumulation of interfering metabolites. In view of these complexities, a correct interpretation of serum drug levels requires a good knowledge of clinical pharmacology and a close collaboration between physician and laboratory. In any case, serum drug concentrations, like other laboratory tests, are not a substitute for careful patient observation, and any decision about drug treatment should be primarily based upon evaluation of the clinical state and, whenever possible, direct measurement of drug effects.

The effect of catecholamines and sympathetic stimulation on the release of acetylcholine from the guinea-pig colon.

1. In isolated guinea-pig terminal colon, the effect of sympathetic stimulation on contraction and acetylcholine release elicited by pelvic and transmural stimulation was investigated.2. Sympathetic stimulation reduced the nerve-mediated contractile responses more than those produced by added acetylcholine.3. Sympathetic stimulation also reduced the acetylcholine released during pelvic and transmural stimulation at low frequency. The inhibitory effect on acetylcholine released from resting colons is concealed by the simultaneous release of acetylcholine in considerable amounts from stimulated periarterial nerves which probably contain parasympathetic fibres.4. The inhibitory effect of endogenous and exogenous catecholamines prevails when cholinergic neurones fire at low rates. It was confirmed that adrenaline is more active than noradrenaline.5. The release of acetylcholine from unstimulated colons was for the most part maintained by nerve-conducted activity, because tetrodotoxin was able to reduce it to about one-tenth.6. It is suggested that the sympathetic control of gastrointestinal tone and motility is exerted through two different routes: inhibition of intramural cholinergic plexuses and direct relaxation of smooth muscle cells.7. The possible site and mechanism of action of catecholamines on intramural cholinergic structures is briefly discussed.

A pharmacological analysis of the peristaltic reflex in the isolated colon of the guinea-pig or cat.

1. The peristaltic reflex in the colon was elicited by a localized intraluminal stimulus. The contractile response of the longitudinal coat, which consists of two phases, begins before the start of propulsion. Although the contractions of the longitudinal and circular musculature are usually associated, they may be independent of each other. In particular, the longitudinal contraction does not seem to be necessary for propulsion.2. Both the longitudinal reflex contraction and the segmental responses of the circular muscle to distension, namely a contraction above and a relaxation below the bolus, are abolished by tetrodotoxin and ganglion blocking agents.3. In the guinea-pig, longitudinal and circular reflex contractions are usually resistant to antimuscarine, antihistamine and antitryptamine drugs but in the cat they are abolished by antimuscarine drugs. In both species, however, atropine and hyoscine can impair propulsion by blocking selectively the descending inhibition. In the cat, it is possible to find doses which abolish the descending inhibition without affecting the contractile responses of the longitudinal and circular muscle.4. Sympathetic denervation and pretreatment with reserpine do not affect the propulsive activity. The maintenance of the descending inhibition in denervated organs suggests that the inhibitory neurones to the circular muscle are not adrenergic.5. On the basis of the effects of drugs, the possible nervous mechanism subserving the polarity of propulsion has been examined. Such a mechanism seems to require an inhibitory pathway involving muscarinic receptors at some point.6. Pelvic nerve stimulation facilitates propulsive activity. The effect of transmural stimulation is different at low and at high frequencies of stimulation. The inhibitory effect of sympathetic stimulation on the reflex responses seems to be due mainly to an action on intrinsic nervous structures.

The role of GABAA receptor function in peristaltic activity of the guinea-pig ileum: a comparative study with bicuculline, SR 95531 and picrotoxinin.

1. The peristaltic activity of the guinea-pig ileum was studied in the absence and in the presence of the blockade of GABAA receptors. 2. Bicuculline (1-30 microM), improved at the highest concentrations the efficiency of peristalsis by enhancing the frequency of propulsive contractions and the amount of fluid ejected per unit of time. 3. Neither SR 95531 (0.3-10 microM), a novel GABAA receptor antagonist, which competitively antagonized 3-aminopropane sulphonic acid induced contractions in myenteric plexus-longitudinal muscle preparations (pA2 value: 6.47), nor picrotoxinin (1-30 microM) modified peristaltic parameters or influenced the potentiating effect of bicuculline on peristaltic activity. 4. In myenteric plexus-longitudinal muscle preparations, bicuculline (1-30 microM) enhanced the amplitude of electrically-induced cholinergic contractions without modifying submaximal contractions to applied acetylcholine. SR 95531 and picrotoxinin had no effect on twitch amplitude. In the presence of each of these compounds, bicuculline retained its potentiating effect. 5. The results obtained with SR 95531 and picrotoxinin question the view that GABAA receptors may exert a critical role in intestinal propulsion by modulating the activity of nerve pathways subserving peristalsis. Bicuculline potentiates the peristaltic activity of the ileum probably via a facilitatory effect on enteric cholinergic transmission that is independent of GABAA receptor blockade.

Effects of desensitization to adenosine 5'-triphosphate and adenosine on non-adrenergic inhibitory responses in the circular muscle of rabbit colon.

An approximate eight fold desensitization of the circular coat of the distal rabbit colon to adenosine 5'-triphosphate (ATP) and adenosine could be achieved by repeatedly exposing the organ to relatively low concentrations (10-100 microM) of these compounds. The desensitization was specific and reversible after prolonged washing. It could be overcome by increasing the concentrations of the purine agonists. Dipyridamole potentiated the non-adrenergic inhibition in response to transmural stimulation but failed to influence the caudad relaxation evoked by radial distension. Desensitization to ATP and adenosine (and to ATP + adenosine simultaneously) did not affect the non-adrenergic inhibition in response to radial distension or transmural stimulation. These results suggest that neither ATP nor adenosine are the final transmitters mediating the non-adrenergic inhibitory responses in the distal colon of the rabbit.

Purine receptors in the guinea-pig internal anal sphincter.

1 In the isolated internal anal sphincter of the guinea-pig, adenosine 5'-triphosphate (ATP) and adenosine induced a concentration-dependent and tetrodotoxin-insensitive relaxation. 2 Pretreatment with theophylline (25-50 microM) had no significant effect on the concentration-response curves obtained with either purine compound. 3 Reactive blue 2 (25-100 microM) shifted the curve to ATP to the right in a dose-dependent fashion leaving that to adenosine unaltered. The antagonism appeared to be non-competitive. 4 Neither reactive blue 2 nor purine receptor occupation by ATP or adenosine altered the electrically-induced non-adrenergic, non-cholinergic inhibitory response. 5 The actions of ATP and adenosine in the guinea-pig internal anal sphincter appear to be mediated by separate receptors. These receptors are not involved in the nerve-mediated relaxation.