Acid-secretory response and parietal cell sensitivity in patients with duodenal ulcer before and after treatment with sucralfate or ranitidine

Patients with endoscopically proved duodenal ulcer were randomly assigned to treatment with either ranitidine 300 mg at bedtime or sucralfate 2 g twice daily for six weeks. Acid-secretory studies were performed before commencement and 60 to 84 hours after cessation of treatment and endoscopic healing was confirmed. Patients were randomly assigned to receive a constant infusion of secretory stimulant: either pentagastrin 0.1 and 6.0 micrograms/kg/hour or histamine acid phosphate 4.0 and 40 micrograms/kg/hour. Acid output in mmol/hour was measured for basal, low dose, and high dose output. Parietal cell sensitivity (PCS) was calculated as the ratio of low-dose acid output: high-dose acid output and expressed as a percentage. Values before and after treatment were compared and significance of differences was determined using the Student paired t test. There was an apparent decrease in basal acid output, low-dose acid output, high-dose acid output, and PCS with ulcer healing, regardless of treatment or stimulant used. Basal acid output, low-dose acid output, high-dose acid output, and PCS were significantly lower in the sucralfate-treated group, but only high-dose acid output decreased significantly in the ranitidine-treated group. These differences may be relevant to early duodenal ulcer relapse in ranitidine-treated patients.

Monooxygenation of N-acetylhistamine mediated by L-ascorbate

In the presence of molecular oxygen and a catalytic amount of copper(II) ion, ascorbate almost completely degraded histamine (approx. 72%). The reaction was shown to occur at the imidazole group but not at the primary amino group in histamine. 4-[2-(Acetylamino)ethyl]-2,3-dihydroimidazol-2-one, a monooxygenated form of N-acetylhistamine, was first isolated as the primary product.

Pharmacological properties of the hydroxylated histamine, (+/-)-4(5)-(2-amino-1-hydroxyethyl)-imidazole

The pharmacological effects of the beta-hydroxylated histamine, 4(5)-(2-amino-1-hydroxyethyl)-imidazole, on smooth muscle contraction of the ileum (H1-receptor activity) and gastric acid secretion (H2-receptor activity) of the guinea-pig were investigated and compared with those of histamine. Although beta-hydroxy histamine contracted the ileum with the same maximal response as histamine, the concentration response curve was shifted to the right by approximately three orders of magnitude. At submaximal concentrations, co-administration of beta-hydroxy histamine with histamine revealed only additive effects. This H1-activity was competitively inhibited by diphenhydramine. Similarly, the hydroxylated analogue also increased intracellular cyclic AMP level and [14C] aminopyrine accumulation as a marker of acid secretion in the parietal cells. However, the EC50 was approximately ten fold that of histamine. This H2-receptor activity was inhibited completely by cimetidine. These results suggest that beta-hydroxy histamine possesses nearly full intrinsic activities at both H1 and H2-receptors and that the introduction of a hydroxyl group at the beta-carbon reduces and dissociates these activities.

Neurophysiological and endocrine consequences of immune activity

The studies presented herein demonstrate the potency with which activity of the immune system is able to influence the central nervous system. Electrophysiological recordings have demonstrated significant changes in preoptic area/anterior hypothalamic (PO/AH) multiunit electrical activity (MUA) following sensitization with sheep red blood cells. The peak of activity occurred on the fifth day after immunization, the same day that serum antibodies were first detected. A significant increase in paraventricular nucleus MUA was also demonstrated, but this appeared to be delayed with respect to that in the PO/AH, occurring on the sixth day. Further changes thought to be associated with the immune response also were found: Serum corticosterone levels were elevated on the eighth day of the response, and PO/AH tissue levels of norepinephrine were reduced between the sixth and tenth days. During induction of a secondary response, PO/AH MUA showed a different profile of activity from that recorded during the first response. Chronic administration of the immunosuppressive drug, cyclophosphamide, prevented the recorded changes in PO/AH MUA. These results suggest that some secretory product(s) of the activated immune system may be able to exert effects on the central nervous system. Various immunoactive substances therefore were administered intra-cerebroventricularly in order to examine their effects upon PO/AH MUA, cortical EEG and adrenocortical hormone secretory activity. alpha-Interferon and thymic humoral factor were both found to decrease PO/AH MUA, increase EEG synchronization, and decrease basal levels of circulating corticosterone. In contrast, histamine and interleukin-1 did not alter PO/AH MUA but did cause decreased EEG synchronization and increased serum corticosterone levels. With another preparation, a specific activating effect of interleukin-1 upon putative corticotropin-releasing factor-secreting neurones has also been found, identified vasopressinergic neurones not being affected.

Histidine abolishes the inhibition by zinc of naloxone binding to opioid receptors in rat brain

Zinc ions inhibited the specific binding of [3H]naloxone to opioid receptors in the hippocampus, cortex, midbrain and striatum of the rat in a dose-dependent manner. Scatchard analysis performed by using a concentration of zinc close to its IC50 (about 30 microM) revealed that inhibition was due to a decrease in receptor affinity, without change in the number of binding sites. Of several compounds tested, only histidine was capable of reversing the inhibition by zinc in these areas of the brain so preventing the zinc-induced increase in the KD of opioid receptors for naloxone. Histidine alone did not affect the KD or Bmax of opioid receptors for [3H] naloxone in the areas of brain studied. The fact that histidine prevented the zinc-induced increase in the KD but had no effect on receptor affinity or the number of binding sites for [3H] naloxone suggests that histidine exerts its effects by complexing with zinc ions and acting as a chelator. In addition to Zn2+, Cu2+, Cd2+ and Hg2+ inhibited the binding of [3H] naloxone to opioid receptors in the cerebral cortex of the rat in a dose-dependent manner. However, histidine was not capable of abolishing the inhibition to the same extent as that of zinc. Thus, among all of the metal ions studied, the most dramatic effect of histidine was observed with zinc ions.

Immunoanalysis of histamine through a novel chemical derivatization

The immunoanalysis of histamine was carried out with the powerful approach of chemical derivatization. A novel acylating reagent, succinyl glycinamide N-hydroxysuccinimide ester, was synthesized, and monoclonal antibodies were raised to acylated histamine. The monoclonal antibodies had 5 X 10(5) greater affinity for acylated histamine than for native histamine. In agreement with theoretical prediction, no interference was generated, even with closely related amines. An immunoassay of exceptional selectivity and sensitivity was designed that can be used to quantify histamine in any biologic fluid or cell extract.

Differential effects of histamine mediated by histamine H1- and H2-receptors on contractility, spontaneous rate and cyclic nucleotides in the rabbit heart

The effects of histamine on the contractile force, spontaneous rate of contraction, and cyclic AMP and cyclic GMP content were investigated in isolated rabbit cardiac preparations. Histamine had a positive inotropic effect in the left atrium and papillary muscle, and a positive chronotropic effect in the right atrium. Both effects were produced in a concentration-dependent manner. Impromidine also induced the same effect in the left and right atrium as histamine did. The effects produced by histamine and impromidine were antagonized by cimetidine and tiotidine. On the other hand, the positive inotropic response of papillary muscle to histamine was antagonized by mepyramine and chlorpheniramine and was mimicked by 2-(2-pyridyl)ethylamine. Impromidine at a high concentration induced a small increase in the contractile force, an effect which was antagonized by cimetidine. Histamine significantly increased the cyclic AMP levels in both atria but not in papillary muscles. The increase in cyclic AMP was abolished by cimetidine. Histamine also increased cyclic GMP levels in all of the preparations. The increase in cyclic GMP was abolished by chlorpheniramine. The results suggest that both H1- and H2-receptors exist in all parts of the rabbit heart. However, the positive inotropic and chronotropic effects induced by histamine in left and right atrium are mediated predominantly via H2-receptors, whereas the positive inotropic effect in papillary muscle is predominantly mediated via H1 receptors.

The combined effects of histamine and methacholine on the maximal degree of airway narrowing in normal humans in vivo

In normal subjects in vivo the dose-response curve to inhaled nonsensitizing stimuli reaches a plateau at mild degrees of airway narrowing. We investigated whether the limitation of the response is due to non-optimal smooth muscle activation, by administering high doses of histamine and methacholine together. In fifteen normal subjects a complete dose-response curve to methacholine was recorded by a tidal breathing method on three randomized days. On a separate day a complete histamine inhalation test was carried out. Each methacholine test was directly followed by double blind inhalation of the highest dose of either histamine or methacholine, or a dose of saline. The response was measured by flows from partial flow-volume curves (V 40p), and was expressed in % fall from baseline. Twelve subjects reached a maximal response plateau to methacholine which was reproducible. The addition of saline or extra methacholine did not change the response from its methacholine plateau value. Histamine caused a small increase in the response on top of the methacholine plateau (+ 9.0% fall; p less than 0.001). However, the response to the combined histamine and methacholine was not significantly larger than the maximal response to histamine alone. We conclude that there is no interaction between histamine and methacholine on the maximal degree of airway narrowing. This suggests that the plateau of the dose-response curve in normal subjects in vivo is due to other factors than limited smooth muscle activation.

Histamine turnover in the brain of morphine-dependent mice

The turnover of brain histamine was examined in mice implanted subcutaneously with a morphine pellet (50 mg free base). The numbers of naloxone-precipitated jumpings and body shakes were maximum 2 and 3 days after implantation, respectively. The brain tele-methylhistamine level significantly increased (50% to 115%) during 12 h-3 days after implantation of a morphine pellet, whereas the histamine level remained unchanged. The accumulation of tele-methylhistamine by pargyline treatment was significantly enhanced when pargyline was administered 12 h after implantation, suggesting an enhancement of histamine turnover. However, a similar degree of the tele-methylhistamine accumulation was induced by pargyline during 1-5 days after implantation, as compared with the accumulation in the control mice implanted with a placebo pellet. In mice undergoing morphine withdrawal by either the removal of morphine pellet or the treatment with naloxone 3 days after implantation, the degree of the pargyline-induced tele-methylhistamine accumulation or the (S)-alpha-fluoromethylhistidine (alpha-FMH)-induced histamine decrease was similar to that observed in the placebo pellet-control mice. The numbers of naloxone-precipitated jumpings and body shakes occurring in mice 3 days after implantation were not significantly affected by any of L-histidine, alpha-FMH or metoprine. These results suggest that turnover of histamine in the brain is enhanced by acute morphine treatment and returns to the normal rate in the stage of chronic treatment and remains unchanged during the state of withdrawal.

Inhibitors of histidine decarboxylase decrease basal gastric acid secretion in the rat

We examined the ability of two specific inhibitors of histidine decarboxylase, (s)-alpha-fluoromethylhistidine (FMHd) and (s)-alpha-fluoromethylhistamine (FMHm), to inhibit basal gastric acid secretion. The two highest doses of FMHd administered, 50 and 100 mg/kg, decreased basal gastric acid secretion and total secretion volume but did not affect intraluminal pH. FMHm decreased gastric acid secretion, raised intraluminal pH, and to a lesser degree decreased total secretion volume. Neither compound changed the severity of gastric ulcers produced by cold restraint stress.

Evaluation of a "shotgun" regimen for sudden hearing loss

One hundred nine patients with idiopathic sudden hearing loss were treated with a "shotgun" regimen that included dextran, histamine, Hypaque, diuretics, steroids, vasodilators, and carbogen inhalation. Thirty-three patients received the entire protocol and 76 patients received most, but not all, of the protocol drugs. Some improvement of hearing (greater than 10 dB in pure-tone average) was seen in 52% of patients treated with the complete protocol and in 54% of patients who received the partial protocol. All patients were analyzed for potential prognostic indicators. Patients with thresholds at 8000 Hz better than at 4000 Hz fared better than the group as a whole. Vertigo at the time of onset of hearing loss was a sign of poor prognosis. There was no correlation between hearing improvement and the age of the patient or the sedimentation rate. Most importantly, there was no statistically significant difference in outcome between patients treated with the complete protocol and those who received only part of the protocol. Furthermore, when the effect of each drug was examined individually, there was no significant difference between those patients receiving and not receiving treatment. The results suggest that this "shotgun" approach for treatment of sudden hearing loss offers no better outcome than is reported in the literature for spontaneous recovery.

Congener derivatives and conjugates of histamine: synthesis and tissue and receptor selectivity of the derivatives

A series of 19 congener derivatives and conjugates of histamine was synthesized and tested to determine whether the ligands would alter the conventional histamine activity in various tissues. The derivatives, which contained either branched or unbranched aliphatic groups, aromatic amide groups, or dipeptides, exhibited affinities for histamine type 1 and/or type 2 receptors that were widely different from the progenitor. The p-trifluoromethyl derivative of histamine with an intermediate chain length of four methylenes (compound 13) was the most potent lymphocytes H2 receptor agonist but was inactive on guinea pig myocardium H2 receptors. The deletion of a single methylene chain (compound 12) from this compound resulted in total loss of its H2 activity on lymphocytes and its H1 activity on aorta. Compound 12 became an exclusive H1 agonist on lymphocytes H1 receptors. The dipeptide conjugate (compound 17) and the aliphatic congener derivative (compound 18), both with four methylenes, retained some of the activity on guinea pig myocardium H2 receptors, but lost their activity on lymphocytes H2 receptors. Therefore, histamine can be modified at sites that are at a distance from the imidazole moiety, resulting in tissue selective histamine receptor agonists.

Fixed ventilation during tidal volume breathing bronchial challenge may improve repeatability

Tidal breathing during bronchial challenge shows both between- and within-subject variation. A challenge protocol permitting controlled ventilation was designed in order to improve repeatability of the method. Twenty-five patients were challenged twice with an interval of 2 h. The 2 min ventilation was kept constant at each concentration administered. During the 2 min inhalation of aerosol all expired air (VE) was led through a dry gas meter and respiratory frequency was counted concomitantly. The patients were instructed to achieve the same 2 min ventilation at each dosage. All patients accomplished the two challenges without problems. A PC20 was determined by interpolation on the log dose-response curve. Repeatability was improved compared to what has been found in previous studies on adults, although statistically non-significant when compared to one study. The 95% confidence interval for PC20 based on a single determination was rather narrow, being the observed value +/- 0.58 two-fold concentration differences.

Effects of histamine and related compounds on the release of immunoreactive thyrotropin-releasing hormone from the rat stomach in vitro

Effects of histamine and related compounds on the release of immunoreactive thyrotropin-releasing hormone (ir-TRH) from the rat stomach in vitro were studied. The rat stomach was incubated in medium 199 with 1.0 mg/ml of bacitracin and 100 micrograms/ml of ascorbic acid (pH 7.4) for 20 min. The amount of TRH release into the medium was measured by radioimmunoassay. The ir-TRH release from the rat stomach was enhanced significantly in a dose-related manner with the addition of histamine and inhibited with the addition of famotidine, but not with mepyramine. The stimulatory effect of histamine on ir-TRH release from the stomach was partially blocked with the addition of famotidine, but not with mepyramine. The elution profile of acid-methanol-extracted rat stomach on Sephadex G-10 was identical to that of synthetic TRH. These findings suggest that histamine stimulated ir-TRH release from the rat stomach in vitro, and that histamine's effects may be mediated via a H2-receptor.

Comparison of maximal gastric secretion in smokers and non-smokers with and without duodenal ulcer

Maximal gastric secretion was induced in 122 control subjects (without peptic ulcer) and 201 preoperative duodenal ulcer patients by intravenous histamine acid phosphate (130 nmol/kg/h), and measured as Vg (ml/h) and MAO (mmol/h). In both groups, men secreted more than women, and smokers secreted more than non-smokers. Significant correlations were found between maximal gastric secretion on the one hand, and height, age, and chronic smoking on the other. After standardisation for these factors, including standardisation to zero smoking, the subgroups of the controls no longer differed significantly, as was also the case for the duodenal ulcer patients. Thus, differences in height, age, and smoking habit were sufficient to account for the variation in maximal secretion between individuals in either the control or duodenal ulcer groups. Even after standardisation, however, the duodenal ulcer patients still secreted significantly more than the controls, and therefore, although chronic smoking has been shown to affect maximal gastric secretion, it does not appear to be the sole reason for hypersecretion in duodenal ulcer patients.

Molecular determinants for recognition of triazole and tetrazole analogs of histamine at H2-receptors

Calculations of molecular structures, relative stabilities of the various tautomers, and molecular electrostatic potentials (MEPs) were used to examine the molecular properties that determine the actions at H2-receptors of histamine analogs in which the imidazole ring was replaced by triazole or tetrazole. The analysis indicates that the most stable tautomer of 3-ethylamine-1,2,4-triazole (EATRI), is also the most similar to the assumed active form of histamine. Differences in the MEP of EATRI and histamine are observed mainly near the N(2) nitrogen of EATRI which is the steric equivalent of the C(4) position of histamine. Because EATRI is recognized at the receptor in spite of these differences, we conclude that the H2-receptor has no selectivity with respect to the electrostatic or steric properties near this position, in agreement with previous observations from structure-activity relations. This conclusion contrasts with the apparent selectivity of the receptor for the reactivity properties of the position equivalent to C(2) in histamine. Thus, the analysis of the tautomeric forms and MEP of the 5-ethylamine-1,2,3,4-tetrazole, which is not recognized by the H2-histamine receptor, suggests that the negative potential near the N(3) nitrogen, which corresponds to C(2) in histamine, is responsible for the inactivity of this molecule. The mechanism of receptor activation by EATRI is analyzed in relation to results from a theoretical simulation of a proposed activation mechanism of H2-histamine receptors. We find that the discriminant property for receptor activation by EATRI should be the relative energy of the ring protonated tautomers, and our results indicate that only the cation in which the ring protonation is on N(1) and N(4) and the side chain is anchored at the negative receptor site can be recognized at the histamine H2-receptor, and can participate in the proposed activation process.

H3 receptor assay in electrically-stimulated superfused slices of rat brain cortex; effects of N alpha-alkylated histamines and impromidine analogues

The release of the putative neurotransmitter histamine (HA) from rat brain cortex slices is under negative feedback control by an HA autoreceptor. This autoreceptor has been postulated to belong to a new class of HA receptors, H3. To verify this hypothesis we have developed an assay using superfused rat brain cortex slices. The HA transmitter pool is labelled by incubation of the slices with the precursor 3H-histidine; 3H-HA is estimated after separation by column chromatography. Release of HA was found both after K+-induced depolarization and electrical field stimulation. The latter resulted in higher and more reproducible HA release. Electrically induced HA release could be fully inhibited in a concentration dependent way by exogenous HA in the superfusion buffer. N alpha-alkylated histamines also showed agonistic activity. The action of exogenous HA was totally blocked by the potent H2 agonist impromidine and some of its analogues.

The effect of inhaled bronchoconstrictors on transcutaneous gas tensions in normal adult subjects

The administration of histamine and leukotriene D4 (LTD4) by nebulised aerosol in logarithmically increasing doses to normal subjects resulted in significant bronchoconstriction. Transcutaneous oxygen tension (tcPO2) was monitored during and after the bronchial challenge tests. Following histamine challenge there was significant hypoxaemia in all subjects (mean fall in tcPO2, 20 mmHg). However, following LTD4 administration, there was a small and insignificant fall in tcPO2. Transcutaneous carbon dioxide tension (tcPCO2) was also monitored throughout bronchial challenge, but showed no significant change. We suggest that the hypoxaemia following histamine challenge was due to increased ventilation/perfusion (V/Q) mismatching in the lung induced by histamine deposition.

Inspiratory impedance during histamine-induced bronchoconstriction in patients with bronchial asthma

Histamine inhalation provocation tests were performed in 18 asymptomatic asthmatic patients with progressively increasing doses of a pressurized aerosol of histamine phosphate. Forced expiratory volume in 1 s (FEV1), total neuromuscular output, assessed by mouth occlusion pressure (P0.1), mean inspiratory flow (VT/Ti), and the P0.1/(VT/Ti) ratio, which represents an index of effective inspiratory impedance of the respiratory system, were measured. With histamine, compared to control, FEV1 decreased and P0.1/(VT/Ti) increased (p less than 0.01 for both). After bronchoconstriction was reversed by administration of a beta 2-agonist bronchodilator (fenoterol), a significant decrease in P0.1/(VT/Ti) (p less than 0.001) and a significant increase in FEV1 (p less than 0.01) were noted as compared to histamine. With histamine, change in P0.1/(VT/Ti) was found to be related to its pre-histamine value (p less than 0.01). Furthermore, with histamine and fenoterol, changes in P0.1/(VT/Ti) and concurrent changes in FEV1 were found to be significantly related (p less than 0.001). From these data we calculated that the P0.1/(VT/Ti) ratio provides a useful tool in the clinical assessment of histamine-induced bronchospasm.

Pharmacological investigation into the effects of histamine and histamine analogues on guinea-pig and rat colon in vitro

The effects of histamine and specific histamine agonists has been examined on isolated longitudinal colon strips of guinea-pig and rat. Histamine and 2-pyridyl-ethylamine but not 4 methylhistamine produced a concentration-related contractile response in the guinea-pig colon. The H1-antagonist clemizole antagonized competitively the effect of histamine but the H2-antagonist ranitidine did not modify the dose-response curve to histamine in the guinea-pig colon. Atropine, hexamethonium, prazosin and propranolol failed to modify the contractile response to histamine. Tone induced with KCl in guinea-pig isolated colon was not modified by histamine agonists even in tissues pretreated with clemizole or ranitidine. Histamine and histamine analogues were without effect on the isolated longitudinal strip of the rat colon. It is concluded that histamine produced dose-dependent contractions of the guinea-pig colon due to direct activation of H1-histamine receptors. There is no evidence in favour of the existence of H2-histamine receptors in this preparation. The lack of effect of histamine agonists in rat colon strip argues against the existence of histamine receptors in this preparation.

The effects of derivatives of histamine on natural suppressor cells

Histamine is an impressive modulator of immune functions at least via its effects on lymphoid cells. Its in vivo effects will not be used practically as long as they produce the profound cardiovascular and pulmonary effects for which the drug is known. A series of 13 congener derivatives and conjugates of histamine was constructed and was tested to investigate whether chemical alterations would result in pharmacologic actions on leukocytes that were more potent and effect specific than histamine. The new compounds, which contained spacer groups of varying lengths between ligand and carrier and with various aromatic modifying groups, showed potencies widely different from histamine when tested in natural suppressor cells. Some compounds showed selective effects on natural suppressor cells in that they were inactive on myocardial tissue, whereas other compounds were selectively active on the myocardium. Some compounds augmented the suppressive capacity of natural suppressor cells in mixed leukocyte reactions via H1 receptors. Our scheme might be more widely extrapolated to other low m.w. immune modulators in an attempt to make them lymphocyte specific. The data also encourage the in vivo testing of selected histamine analogues as selective modulators of immunity. Some of these modulators might be experimentally useful in vivo because they may lack actions in other tissues.