The association of haemopoietic dysplasia (pre-leukaemia) and abnormal cell clone with connective tissue disease

A 68-year-old man with haemotological features consistent with haemopoietic dysplasia (pre-leukaemia) and an abnormal cell clone in the marrow, 46, XY, -18, +t(13;18) (q11;123), developed acute connective tissue disease characterised by vasculitis, dermal changes, marked muscular weakness and serological features suggesting an auto-immune disturbance. Although four other cases of haemopoietic dysplasia ("pre-leukaemia") with unusual connective tissue disease had been reported since the recognition of haemopoietic dysplasia as a distinct entity, a definite association between these two disease states still awaits confirmation by further reports and investigations.

In vitro platelet abnormality in adenosine deaminase deficiency and severe combined immunodeficiency

The platelets of an infant with severe combined immune deficiency and adenosine deaminase deficiency showed markedly diminished responses to ADP-induced aggregation in vitro. This abnormality was corrected by the addition of purified adenosine deaminase in vitro. Exogenous adenosine added to platelet-rich plasma caused markedly prolonged inhibition of ADP-induced aggregation. This was shown by isotopic studies to be due to slow clearance of adenosine and hence persistence of this nucleoside. Direct assay for adenosine deaminiase in plasma and platelet lysates of the patient confirmed the very low activity of this enzyme. Raised cAMP levels were demonstrated in his platelets. The deranged adenosine metabolism and raised cAMP in the platelets of this child with severe combined immunodeficiency may explain the altered response to ADP. Despite the in vitro platelet aggregation abnormality, the patient had no clinical evidence of impaired hemostasis.

Metabolism of cyclic AMP in non-pathogenic Mycobacterium smegmatis

The intracellular concentration of cyclic AMP reached a maximum in 3.5-day old cultures of Mycobacterium smegmatis grown in the presence of glycerol as the main source of carbon. Glucose-grown cells exhibited decreased cyclic AMP levels at all stages of growth. When M. smegmatis cells were incubated with various metabolites, pyruvate increased whereas glucose, ctric acid, succinic acid and lactic acid decreased intracellular cyclic AMP levels. No cyclic AMP was detected in the incubation medium. The presence of a cyclic AMP-binding protein was demonstrated in cell-free extracts of M. smegmatis.

Vascular relaxation, aging and thyroid hormones

Previous work indicates vascular can be studied in vitro and that there is a marked age-associated decrease in the ability of rat aortic strips to relax in response to beta-adrenergic agonists. The present studies were aimed at better understanding the role of thyroid hormones in vascular relaxation and aging. Removal of the thyroid gland from young rats resulted in a decrease in the ability of isoproterenol to relax the aorta. Relaxation caused by nitroglycerin, a non-specific relaxant, was not impaired by thyroidectomy. In 22-month-old rats, isoproterenol caused no relaxation unless exogenous thyroid hormones were administered. Hypophysectomy seven months prior to testing improved the ability of thyroid hormones to restore isoproterenol relaxation of the aorta. The loss of relaxation with age could be due in part to a pituitary mediated loss of responsiveness of aortic tissue to thyroid hormones. The data provide new evidence for the importance of thyroid hormones in beta-adrenergic receptor mediated vascular relaxation and demonstrate that the loss of aortic relaxation with aging can be reversed.

Detection and significance of occult axillary node metastases in patients with invasive breast cancer

Blocks of axillary lymph nodes from 78 patients with invasive breast cancer, which after "routine" pathological examination were regarded as negative for metastases, were step-sectioned at 20 u intervals. Occult metastases were detected in 24% of the cases. A significant association between such metastases and a lack of or slight degree of an intraductal carcinomatous component of the dominant cancer was noted. There was no relationship between occult metastases and 15 other histopathological and 3 clinical features investigated, including an average 5 year survival rate. Similarly there was no correlation between any of the possible discriminants investigated in the 24% of patients who have died of their diseases or are living with recurrence regardless of the presence of occult metastases. Factors accounting for the lack of universal survival in patients with Stage I (and those with occult metastases that might be designated as stage 11/2) remain enigmatic. It is concluded that attempts to detect occult metastases by extending histopathological methods may be more academic than practical or therapeutically significant.

Sustained effect of glucose-insulin-potassium on myocardial performance during regional ischemia. Role of free fatty acid and osmolality

To evaluate the influence of glucose infusate administered with insulin and potassium on left ventricular function during 4 h of ischemia, as well as mechanism of action, four groups of intact anesthetized dogs were studied. Acute regional ischemia was induced with a balloon tip catheter in the left anterior descending artery and infusates were begun after 20 min of ischemia. A threefold increase of plasma glucose concentration was associated with improved left ventricular function during ischemia, compared to animals receiving isovolumic saline. There was a significant decline of left ventricular end-diastolic pressure associated with elevation of stroke volume and ejection fraction to control levels, as determined by indicator dilution. In a separate subgroup studied by cineangiography, shortening of the ischemic anterior wall, after an initial decline, was increased in response to glucose but there was no evidence of extension of injury. Ischemic tissue exhibited a smaller gain of water as well as Na+ per gram dry weight as compared to ischemic controls. On precordial electrocardiogram mapping there was a significant decrease in the sigmaST (sum of ST elevation) as well as NST (number of ST segment elevations), but the reduction of R wave amplitude was not different from controls. To further evaluate long-term effects, eight controls and six treated animals underwent myocardial ischemia and were sacrificed after 4 mo. Calculated area and weight of scar, as well as degree of wall thinning, were similar in both groups. The glucose-treated animals had a significant decrease of plasma FFA in contrast to controls which manifested a significant rise. To examine the postulate that the decrease in FFA was important to therapeutic action, a third group was infused with Intralipid (Cutter Laboratories, Inc., Berkeley, Calif.) and heparin, simultaneously with the glucose infusate, to effect an elevation of plasma FFA during ischemia. Changes in myocardial function and electrolyte composition, as well as precordial electrocardiogram mapping, were similar to that of animals receiving glucose alone. Because serum osmolality was increased approximately 40 mosmol during the glucose infusion, the potential role of hyperosmolality was assessed by infusion of 20% mannitol during acute ischemia in a fourth group. After a transient small increase, there was a moderate decline in function by 4 h, suggesting that the response to glucose is not dependent upon extracellular osmolality. Thus, it is concluded that during the initial hours after the onset of myocardial ischemia the glucose infusate improves ventricular performance without evidence of arrhythmia induction or intensification of ischemic injury. Evolution of irreversible necrosis appears to be delayed rather than prevented under the circumstances of this study.

Studies of the conformation of modified dinucleoside phosphates containing 1,N6-ethenoadenosine and 2'-O-methylcytidine by 360-MHz 1H nuclear magnetic resonance spectroscopy. Investigation of the solution conformations of dinucleoside phosphates

Seven dinucleoside monophosphates containing epsilonA (1,N6-ethenoadenosine) and 2'-O-methylcytidine were studied by 360-MHz proton magnetic resonance and compared with unmodified dimers and component monomers at 4, 20, 45, and 75 degrees C. These studies show that the dimers exhibit preference for the gg and g'g' conformations for the C-4'-C-5' and C-5'-O-5' bonds, respectively, and that dimerization induces an increase of the population and inflexibility of the 3'-endo conformations for the ribose ring. Three stacked (or stable) conformations for dimers, I, II, and III, in equilibrium with an unstacked (or open) form in solution, are suggested by dimerization shifts of ribose protons. Conformation I exhibits anti, gg, 3'-endo, phi' = 203 to approximately 211 degrees, omega' = 300 degrees, omega = 290 degrees, g'g', gg, 3'-endo, and anti conformation from the 5' end to the 3' end of the dimer. Conformation II shows anti, gg, 3'-endo, phi' = 203-211 degrees, omega = 30 degrees, omega = 100 degrees, g'g', gg, 3'-endo, and anti conformation. Conformation III is anti, gg, 2'-endo, phi' = 260 degrees, omega' = 50 degrees, omega = 220 degrees g'g', gg, 3'-endo, and anti (x approximately 100 degrees) conformation. The dimers, PupPu and PupPy, prefer conformations I and II, while PypPu and PypPy prefer conformation II. Introduction of epsilonA for the base of -pN induces an increase of conformations II and III, while the epsilonA substitution for the Np- residue induces an increase of conformation I. 2'-O-methylation of the Cp- residue of CpC decreases conformation I and increases conformation II. Based on the stable solution conformations of these dimers, a possible conformation of the anticodon loop is proposed, which is an alternative to the one observed in the crystal of tRNAPhe.

Identification of adenosine 3',5'-monophosphate in Mycobacterium smegmatis

Cyclic adenosine 3',5'-monophosphate isolated from Mycobacterium smegmatis cells was identified by thin-layer chromatography, stepwise conversion to adenosine 5'-monophosphate and adenosine, ultraviolet absorption spectrum, phosphate analysis, and detection by two relatively specific radioisotopic methods.

Calcium antagonist activity of methadone, l-acetylmethadol and l-pentazocine in the rat aortic strip

These studies described physiologic evidence that methadone and related compounds can function as calcium antagonists. Methadone (1 X 10(-5)-1 X 10(-4) M) inhibited the contraction of the isolated rat aortic strip preparation produced by potassium chloride, norepinephrine, l-pentazocine or morphine. Methadone was most effective in diminishing aortic contractions which were highly dependent on the concentration of extracellular calcium. The d- and l-isomers of methadone were equipotent inhibitors of aortic contraction. l-Acetylmethadol (1 X 10(-6)-1 X 10(-5) M) was a potent inhibitor of vascular contraction. l-Pentazocine inhibited its own ability to contract the aorta as the dose was raised 3 X 10(-5) M. The inhibition of aortic contraction produced by methadone, l-acetylmethadol and l-pentazocine was overcome by raising the concentration of calcium in the tissue baths. The inhibition of contraction and the apparent calcium-antagonist activity of these drugs best correlates with their lipid solubility. Since calcium is a critical regulator of cellular function, the calcium-antagonist action of methadone and l-acetylmethadol may prove to be important in mediating some of their pharmacologic and toxicologic effects.

Conformational properties of purine-pyrimidine and pyrimidine-purine dinucleoside monophosphates

The detailed conformational features and dynamics of heterodinucleoside monophosphates ApU, ApC, GpU, GpC, UpA, CpA, UpG, and CpG have been studied in aqueous solution by high field nuclear magnetic resonance (NMR) spectroscopy. Analysis of the resultant NMR parameters leads to a number of discernible trends throughout the series. Thus the ribose rings of the dimers exist as equilibrium mixtures of C(2')-endo(2E) in equilibrium C(3')-endo(3E) conformers with a proclivity for the 3E pucker in most cases; the C(4')-C(5') bonds of both nucleotidyl units show significant preference (74-96%) for a gg conformation and the dominant conformer (85-89%) about C(5')-O(5') is g'g'. Orientation about the C(3')-O(3') bond is coupled to the ribose conformational equilibrium and the system exists with a bias for the 3Eg- coupled conformation in which the H(3')-C(3')-O(3')-P dihedral angle occupies the narrow range of 33-35 degrees. Dimerization, on the average, causes about 10% increase in gg and g'g' populations and the g-domain becomes increasingly populated about the C(3')-O(3') bond. The ribose equilibrium 2E in equilibrium 3E shifts in favor of 3E upon dimerization, the effect being very conspicuous for the pu-py series (similar to 40 yields 60%) and less noticeable for the py-pu systems (similar to 47 yields 58%), clearly suggesting a correlation between sequence and ribose conformational equilibrium. The temperature and dimerization data for the heterodinucleoside monophosphates show that the transition 2E yields 3E is directly related to XCN changes induced by dimerization and stacking. Analysis of the ribose coupling data shows that the percentage populations of stacked species vary from dimer to dimer with GpC displaying a maximum of 45% stacked population and UpG about 10%. However, in general, the pu-py dimers show a higher preference (27-45%) for stacked conformations than py-pu dimers (10-25%). It is proposed that the pronounced deshielding of H(5') of the 5'-nucleotidyl units upon dimerization is associated with the presence of right-handed stacks (g-g-), whereas the chemical shift trends of H(5') and H(5') of 3'-nucleotidyl units are due to the presence of left-handed stacks (g+g+) in all the dimers. In pu-py dimers, the population of the g-g- species is found to be greater than that of g+g+. Also the population of g-g- stacks in pu-py dimers is generally greater than in their corresponding matched py-pu dimers. Thus the base sequence has not only an explicit effect on the overall populations of stacked species, but also on the handedness of the stacks. The present results further confirm the interdependence of conformational bonds throughout the nucleotidyl framework.

Chronology of development of serum antispirochete antibody in swine experimentally exposed to swine dysentery: preliminary report

By using an indirect fluorescent antibody test (with immunofluorescence of large spirochetes as positive), serum antispirochete antibodies were detected initially at 4 weeks after onset of diarrhea in swine exposed to infective swine dysentery inoculum. Antibodies continued to be present in serum of swine tested 5 months after onset of diarrhea.

A direct fluorescent antibody test for large spirochetes in swine dysentery using hyperimmunized swine serum

A direct fluorescent antibody test was developed for the identification of large spirochetes which are considered to be the cause of swine dysentery. Sera from swine which had recovered from swine dysentery and had been hyperimmunized by the intravenous and intraperitoneal injection of filtered spirochetes were used for conjugation with fluorescein isothiocyanate. A bright greenish fluorescence of large spirochetes was observed with the conjugated serum from hyperimmunized pig No. 1 when diluted 1:8 and hyperimmunized pig No. 2 when diluted 1:2. Pig No. 1 had developed a serum titer of 1:64 using the indirect fluorescent antibody test for large spirochetes. The conjugated serum from the three swine which had recovered from swine dysentery fluoresced spirochetes only when undiluted. The conjugated serum from the two swine treated while having a hemorrhagic diarrhea did not fluoresce spirochetes. No immunofluorescence of Vibrio spp. was observed.

Influence of medication on development of serum antibody to swine dysentery as detected with indirect fluorescent antibody method

Serums from 119 swine exposed to swine dysentery inoculum, and medicated with various drugs, were tested for antibodies to the large spirochete, using the indirect fluorescent antibody test, and were compared in tests with known positive serums from 18 nonmedicated swine which had recovered naturally. An inverse relationship existed between the efficacy of the drug and the serum antibody titer (highest dilution of the serum producing immunofluorescence of large spirochetes). The more efficacious drugs or doses resulted in lesser development of serum antibody. Diarrhea usually seemed necessary for the development of serum antibody. With the less efficacious drugs, there were more days of diarrhea. Some swine had diarrhea but did not develop an antibody titer, and a few swine had a titer but did not develop diarrhea. Swine which developed a titer were more immune against reexposure with infective inoculum. The medicaments, especially those given at higher concentrations, seemed to resolve the diarrhea or prevent the development of diarrhea, occurrences which were necessary for the development of immunity.

Immunofluorescence of spirochetes with serum from swine recovered from swine dysentery using an indirect fluorescent antibody test

Using an indirect fluorescent antibody test, immunofluorescence of large spirochetes was observed with serum from swine that had recovered from swine dysentery. The spirochetes were obtained from scrapings of the colonic mucosa on the first day of diarrhea which was the time when the spirochete population was observed to be the highest. Of 29 exposed nonmedicated swine which developed and recovered from a diarrhea characteristic of swine dysentery 27 had antispirochete serum titers which ranged from 1:2 to 1:16. None of the 50 nonexposes swine developed a titer. Of 19 swine with a serum titer and reexposed with infective swine dysentery inoculum, 18 did not develop a diarrhea and were presumed to be immune. Considering these findings it is possible that this test could be used to detect antispirochete antibody in unknown swine serum.

Conformational properties of dinucleoside monophosphates in solution: dipurines and dipyrimidines

In order to obtain information about the conformational features in a polyribonucleotide at the nearest neighbor level, detailed nuclear magnetic resonance studies of the dinucleoside monophosphates ApA, ApG, GpA, UpU, CpC, UpC, and CpU were undertaken. Proton spectra were recorded at 100, 220, 270, or 300 MHz for D2O solutions, 0.01-0.03 M, pD 7.4 at 20+/-2 degrees C. Spectra of ApA, ApG, UpU, and UpC were also recorded in the temperature range of 70-90 degrees C. Unambiguous signal assignments of all proton resonances were made with the aid of selectively deuterated dimers. Complete, accurate sets of nuclear magnetic resonance (NMR) parameters were derived for each nucleotidyl unit by simulation-iteration methods. A complete set of chemical shift and coupling constant data was also obtained for all the constituent monomeric units at a concentration and ionization state comparable to that of the dimers. Conformational properties were evaluated quantitatively for most of the bonds in the dinucleoside monophosphates using procedures developed in earlier studies. All of the dimers have a flexible conformational framework in aqueous solution. While flexibility is allowed and alternate conformations are accessible, these molecules nevertheless attempt to achieve conformational identity by showing preferences--sometimes overwhelming preferences--for certain orientations. Thus the ribose rings exist as equilibrium mixtures of C2'-endo in equilibrium C3'-endo conformers with a bias for the C3'-endo pucker in most cases. The C4'-C5' bonds of both nucleotidyl units show significant preference (70-85%) for a gg conformation. Similarly, the dominant conformer (80-90%) about C5'-O5' is g'g'. Even though an unambiguous determination of the orientation about C3'-O3' cannot be made, there is suggestive evidence that the orientation of the 3' phosphate group is coupled to the ribose conformational equilibrium and it is likely that a 3Eg- in equilibrium 2Eg+ equilibrium exists with a bias for the 3Eg- coupled conformation in which the H3'-C3'-O3'-P dihedral angle is about 34-38 degrees. The individual nucleotidyl units in the dimers differ in several key ways from corresponding monomer conformations. Specifically, the ribose equilibrium C2'-endo in equilibrium C3'-endo shifts in favor of C3'-endo upon dimerization, the only exception being UpU. The C4'-C5' and C5'-O5' bonding network in the dimer forms a stable conformational unit and no correlation exists in the dimers between the conformational preference of this fragment and ribose conformer population. The temperature data for the dimers and dimerization data clearly indicate that the transition C2'-endo leads to C3'-endo is directly related to XCN changes brought about by dimerization and stacking...

Stereoselective and calcium-dependent contractile effects of narcotic antagonist analgesics in the vascular smooth muscle of the rat

In patients, pentazocine administered i.v. can have an unusual action for a strong analgesic-an elevation of blood pressure. The objective of this study in rats was to better quantify and explain the molecular mechanism for the vascular action of l-pentazocine and compare it with other analgesics and narcotic antagonists. In anesthetized rats, l-pentazocine (0.3-3 mg/kg i.v.) elevated blood pressure and this effect was potentiated in pithed rats. The contraction appeared to be nonadrenergic as it was not blocked by the alpha blocker, phenoxybenzamine. In vitro, morphine (ED50 = 4 X 10(-5) M) and the l-isomers of pentazocine (ED50 = 8 X 10(-6) M) contracted the spirally cut aortic strip. The l-isomers were approximately 5 times more potent than their d-enantiomers. Contraction of the aorta by l-pentazocine was not inhibited by dibenamine, atropine, diphenhydramine, pyrilamine or indomethacin nor potentiated by propranolol. On the other hand, not only was the contraction highly dependent on the concentration of calcium in the bath but it was also blocked by verapamil and SKF-525A, drugs known to inhibit transmembrane calcium influx. Naloxone (3 X 10(-4) to 1 X 10(-3) M), which produced no contractile effect by itself, reduced aortic contraction of l-pentazocine to the greatest extent, that of potassium moderately and that of norepinephrine only slightly. The naloxone blockade of l-pentazocine vascular contraction was reversed by increasing Ca++ concentration in the media, suggesting the action of naloxone may resemble a calcium blocker. It is proposed that a direct, stereoselective and calcium dependent vascular action of l-pentazocine contributes to its ability to raise blood pressure. The possibility that in high doses narcotic antagonists may decrease calcium influx should also be considered.

Activity of L-cysteinesulfinate carboxy-lyase and persulfurase in livers of rats fed different levels of sulfate and cysteine

Activity of L-cysteinesulfinate carboxy-lyase (CSC) and persulfurase was measured in livers of rats fed 15% casein diets supplemented with (1) 0.53% cysteine, (2) 0.40% cysteine, (3) 0.40% cysteine + 0.10% sulfate, (4) 0.42% sulfate, or (5) 0.42% sulfate + 0.40% cysteine. The diets were fed to adult rats for 1 week and to weanling rats for periods of 1 and 4 weeks. At the end of each feeding period, the highest CSC activity was detected in livers from animals fed diet 4, but no differences in CSC activity were detected among livers from the other four groups. Persulfurase activity did not differ significantly among those weanling or adult rats fed the diets for 1 week but was lower among those fed diet 4 than diet 5 for 4 weeks. The acitivity patterns did not parallel those of taurine excretion or conjugation observed previously among rats fed the same diets, and may indicate that factors other than taurine synthesis and ingestion control those processes.

Nuclear magnetic resonance studies of the solution conformation of nucleoside diphosphohexoses and their components

The solution conformations of UDPG, UDPGN, UDPGal, UDPM, UDPGluc, UDPGalc, ADPG, ADPM, GDPG, GDPM, and CDPG and their components Glu-1-P, Gal-1-P, Man-1-P, Gluc-1-P, Galc-1-P, ADP, GDP, UDP, and CDP are studied by high resolution fast Fourier transform nuclear magnetic resonance spectroscopy with iterative computer line shape simulation. The following results were observed. (1) The six-membered ring is in 4C1 chair form with the C(5')-C(6') bond in gg equilibrium tg equilibrium for the derivatives of glucose and mannose and gt equilibrium tg for those of galactose. (2) No conformational preference can be detected for C(1')-O(1') bond in hexose-1'-P moiety. (3) Chemical shift dependencies for the pyranoid ring protons and their structural and conformational relations are: (a) axial proton is at higher field than equatorial: (b) the shielding effect of a gauche vicinal hydroxyl group is stronger than a trans vicinal; (c) the vicinity of a hydroxyl group located more than three bonds away tends to shift the proton downfield. (4) The conformation of the nucleoside 5'-diphosphate part is [anti, 2E equilibrium 3E, g'g' equilibrium g't', g'g' equilibrium g''/t''], with slight variation of each conformation occuring for individual compounds. (5) No significant interactions are detected between the hexose and nucleoside parts in the nucleoside diphosphohexoses, and the hexose and nucleoside components display the same conformational preference as they become integrated to form nucleoside diphosphohexoses.

The cathartic colon: pathological findings and radiological/pathological correlation

Cathartic colon has been described radiologically, but the pathological characteristics have not been reported. The authors describe a case in which radiological/pathological correlation was possible, with emphasis on the pathology of the colon. The disease simulates chronic ulcerative colitis radiologically and pathologically.

Interrelation between glycosidic torsion, sugar pucker, and backbone conformation in 5'-beta-nucleotides. A 1H and 31P fast Fourier transform nuclear magnetic resonance investigation of the conformation of 8-aza-5'-beta-adenosine monophosphate and 8-aza-5'-beta-guanosine monophosphate

Hydrogen-1 and phosphorus-31 nuclear magnetic resonance spectra of 5'-AMP, 5'-GMP, 8-aza-5'-GMP, adenosine, 8-aza-adenosine, and guanosine were obtained at biological pH values at a concentration sufficiently low to obtain information regarding their intramolecular solution conformation. The spectra were analyzed by computer simulation. It is shown that all of the above nucleosides and nucleotides have a flexible molecular framework in aqueous solution, 5'-AMP and 5'-GMP showing preference for anti(2-E in equilibrium 3-E)gg-g'g' conformations and the 8-aza analogs showing preference for (syn in equilibrium anti)-(2E in equilibrium 3-E) - g/t-g'g' conformations. In addition, aza substitution causes increase in 3-E sugar populations and in the populations of g'/t' conformers. It is argued that in the 8-aza analogs repulsive electrostatic interactions would prevail between --N (see article) at the 8 position and the negatively charged phosphate group, if the molecule existed in the anti-gg orientation. Such electrostatic repulsions can be relieved by rotating the C(4')--C(5') bond from gg to g/t orientations as well as by torsional variation about the glycosidic linkage from anti to syn conformation. Rotation from anti to syn orientation, for steric and electrostatic reasons, necessitates a simultaneous rotation about the C(4')--C(5') bond from gg to g/t conformation. The observation that the 8-aza substitution in 5'-beta-purine nucleotides cause a depopulation of gg and anti conformers with corresponding increase in the population of g/t and syn orientation seems to support the above thesis. The finding that rotational variation about a bond such as C(4')--C(5') is accompanied by torsional variation about C(5')--O(5') and the glycosidic bonds, as well as changes in the endocyclic torsion angles of the ribose moiety, gives important insight into the engineering of nucleic acid components: even though they in general prefer certain conformations, there is enough flexibility present in their molecular framework, that the entire system can undergo conformational adjustment in response to a perturbation. A conformational basis for the antileukemic effects of 8-aza purines is proposed.

Pharmacological characterization of cardiac histamine receptors: sensitivity to H1-and H2-receptor agonists and antagonists

In the isolated guinea pig heart, histamine H1-receptor antagonists inhibit the histamine-induced negative dromotropic effect, but not the positive inotropic and chronotropic effects (Levi and Kuye, 1974, European J. Pharmacol. 27, 330). Burimamide, the H2-receptor antagonist, inhibits the positive chronotropic effect of histamine (Black et al., 1972, Nature 236, 385). In this study, the hypothesis that H1- and H2-receptors selectively mediate the various cardiac effects of histamine was tested: (a) by investigating the inhibition of cardiac histamine effects by burimamide; (b) by studying the cardiac effects of 2-methylhistamine (an H1-agonist) and 4-methylhistamine (an H2-agonist). Burimamide, as a function of concentration, inhibited the positive inotropic and chronotropic effects of histamine, whereas it attenuated the negative dromotropic effect of histamine at the higher concentration only. 4-Methylhistamine caused dose-dependent positive inotropic and chronotropic but not negative dromotropic effects; conversely, with 2-methylhistamine the negative dromotropic effect prevailed. Sinus tachycardia and slowing of atrioventricular conduction were also obtained in the guinea pig in vivo by the i.v. administration of histamine. Burimamide selectively antagonized the positive chronotropic effect, whereas promethazine (an H1-antagonist) selectively inhibited the negative dromotropic effect. These results substantiate the hypothesis that H2-receptors mediate the histamine-induced increase in rate and contractility, whereas H1-receptors mediate the slowing of atrioventricular conduction.