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The vasopressin system in the brain, in concert with other systems, regulates the differential behavioral and physiological re- sponses of the organism to changes in environmental inputs during stress. Recent findings of B. Bohus and co-workers (Institute for Animal Physiology, Groningen) support the hypothesis that the central nucleus of the amygdala, the bed nucleus of the stria termi- nalis and the npv are involved in the fine-tuning of the autonomic, motor and neuroendocrine re- sponses to environmental stimuli, and that vasopressin is closely involved in these processes. Vaso- pressin appears to reinforce

stress-induced parasympathetic activation, to reduce sympathetic activation and often to facilitate immobility and behavioral arrest. According to Bohus, vasopressin is the neuropeptide of the passive coping strategy.

S. Snyder 0ohns Hopkins School of Medicine, Baltimore) discussed recent evidence for a role of nitric oxide (NO) as an intracellular messenger in the brain. NMDA receptor agonists cause an in- crease in cGMP levels in the cer- ebellum; glutamate and other ex- citatory amino acids enhance the formation of NO from arginine. Interestingly, methylarginine, an inhibitor of NO synthetase (which

TiPS - September 1990 [Vol. 11]

converts arginine into citrulline and NO), also inhibits glutamate- induced cGMP formation. Snyder and co-workers have purified NO synthetase to homogeneity; on SDS-PAGE it migrates as a single 150kDa band. The enzyme is most abundant in the cerebellum, but also occurs in the olfactory bulbs, the mammillary bodies and other brain regions, and in the pituitary gland. NO may therefore play an important role in synaptic events in the brain.

DIRK H . G~ V E R S T E E G

Rudolf Magnus Institute for Pharmacology, University of Utrecht, Vondellaan 6, 3521 GD Utrecht, Netherlands.

New drugs for asthma Davos, S~'tzerland lO-lO July 1990

This meeting reflected the increas- ing contribution of the pharma- ceutical industry research to the treatment of asthma which is now a major public health problem in the Western world.

T. Torphy (SmithKline Beecham, King of Prussia) summarized the evidence for different tissue dis- tributions and functions of phos- phodiesterase (PDE) isozymes [see also J. A. Beavo and D. H. Reifsnyder (1990) TiPS 11, 150- 155]. Inhibition of type III (cGMP- inhibited) PDE seems to lead to bronchodilation whereas inhi- bition of type 1V (cAMP-specific) PDE is associated with anti- inflammatory activity (inhibition of pulmonary inflammatory cell infiltration or activation). Two mixed PDE types III/IV inhibitors, zardaverine (Ch. Sch.Jdt, Byk Gulden, Konstanz) and AH21132 (R. Small, University of Man- chester) also have anti-inflam- matory activity in animals but are distinguishable in that AH21132 does not induce PDE-inhibition- associated vomiting. K. Murray (SmithKline Beecham, Welwyn) reported that SK&F96231, a novel selective inhibitor of cGMP-speci- fic PDE, has bronchodilator ac- tivity. The isozyme specificity of a novel xanthine derivative anti-inflammatory bronchodilator SDZMKS492 (J. Morley, Sandoz, Basel) was not revealed.

New leukotriene receptor an- tagonists and 5-1ipoxygenase in-

SCH~CH2CO2Na

o co,.a ~ - N H

- , s , , S K & F 1 0 6 2 0 3 , X = H

I C I 2 0 4 2 1 9 ~ " o / ~ H]C

MK571

Fig. 4. New drugs for asthma.

O H

C H 3

I oH U753G2

hibitors have sufficient potency and efficacy for their therapeutic role in asthma to be assessed. In early clinical trials of the leukotriene receptor antagonist ICI204219 (Fig. 4) it produced a shift of >2 log units in the dose-response curve to inhaled LTD4, and there is evi- dence for attenuation of both early- and late-phase bronchoconstriction following allergen inhalation in volunteers (R. D. KreU, ICI, Wil- mington). Similarly, SK&F104353 (Fig. 4; J. Gleason, SmithKline Beecham, King of Prussia) in- hibited LTD4-inhalation-induced bronchoconstriction, had an addi- tive protective effect with terfen-. adine in allergen challenge and blunted the response to exercise- induced bronchoconstriction in volunteers. The clinical effects of the more potent successor com- pound SK&F106203 are not estab- lished. MK571 (R.N. Young, Merck-

Frosst, Quebec), infused i.v., pro- duced > 40-fold shifts in the LTD4 dose-response and attenuated both early and late asthmatic reactions. M. A. Bray (Ciba-Geigy, Basel) introduced a novel leukotriene antagonist, CGP45715, with a potency at least comparable to ICI204219, but with a duration of action > 24 h in preclinical tests.

Hydroxyurea derivatives (proto- type BWB70C) of earlier aceto- hydroxamic acid 5-1ipoxygenase inhibitors (e.g. BWA4C) are orally active, and have longer duration of action and higher potency (A. N. Payne, Wellcome, Beckenham). Questions still surround the role of thromboxane in asthma: Glaxo's TXA2 antagonist, GR32191, failed to improve asthma symptoms in all clinical parameters assessed (R. Coleman, Glaxo, Ware) but this drug may not be sufficiently po- tent to resolve the dispute.

TiPS - September 1990 [Vol. 11]

I. Richards (Upjohn, Kalamazoo) described L T B 4 antagonists (U75302 and LY255283) and a non- glucocorticoid 21-aminosteroid (U75412E) which represent ad- vances in the pharmacological in- hibition of airway eosinophil ac- cumulation that may be of benefit

in asthma. A prototype inhibitor of total and allergen-specific lgE synthesis, IPD1151T, h~s shown clinical benefit in preliminary studies (A. Koda, Gifu University). The effect of IPD1151T is IgE- isotype specific but the relatively small reduction in IgE levels ob-

349

served clinically suggests that other mechanisms of action con- tribute to the clinical improvement of asthma and allergy symptoms.

GARY ANDERSON

Pharmaceutical Research Division, Ciba- Geigy, CH-4002, Basel, Switzerland.

Dopamine 90 Como, Italy 8-11 July 1990

Molecular biological and pharma- cological evidence reported at this meeting has placed proposals that there are subtypes of both Dt and D2 receptors on a -much firmer footing.

D. R. Sibley (NIH, Bethesda) isolated a Dt receptor cDNA using the polymerase chain reaction to amplify RNA hybridizing with a pair of highly degenerate primers derived from the third and sixth transmembrane regions, followed by screening of a rat brain cDNA library. The longest open reading frame of this cDNA encodes a 487 amino acid residue protein (Mr

54000). COS-7 cells transiently transfected with the cDNA showed saturable and specific [3H]SCH- 23390 binding, and Dl-receptor- mediated stimulation of cAMP production. Screening of a human retina cDNA library with a 72 base oligonucleotide probe based on the sequence of rat D2 receptor cDNA allowed M. G. Caron (Duke University Medical Center, Dur- ham) to isolate a single clone; this was used to isolate a clone with an open reading frame encoding a 447 residue protein from a human gen3mic library. Although ex- pression of this DNA in COS-7 cells also confers to these cells the ability to bind [3H]SCH23390 specifically and to elevate cAMP concentration in response to dop- amine, the sequence of this D1 receptor is not the same as that isolated by Sibley.

D 2 receptors activate different second messenger systems in dif- ferent tissues, and it has been proposed that this reflects the existence of two subtypes of D2 receptor: one coupled to inhi- bition of adenylyl cyclase activity, which leads to increased per- meability of Ca2+-activated K + channels; and one directly coupled

to a voltage-sensitive K + channel [see P. H. Andersen et al. (1990) TiPS 11, 231-236]. Pharmacological evidence for the existence of struc- turally different receptor mol- ecules was presented by P. F. Spano (Brescia University Medical School); the azepine derivative talipexole (BHT920) and the new D 2 receptor agonist Ro419067 (a substituted octahydrobenzoquin- oline derivative) behave as selec- tive agonists of the D2B receptor in both lactotroph and striatal synap- tosome preparations.

The sequence of a novel dopa- mine receptor gene ('D3') was reported by P. Sokoloff (INSERM, Paris). This receptor molecule con- tains seven putative transmem- brane domains and a deduced amino acid sequence of 446 resi- dues. The gene contains only one

intron (in the third intracyto- plasmic loop), suggesting that generation of isoforms via alterna- tive splicing does not occur. In situ hybridization of rat brain sections revealed that D 3 receptor mRNA is most abundant in the limbic areas. When expressed in CHO cells, D3 receptors do not affect adenylyl cyclase activity and display a pharmacological profile similar but not identical to the D 2 receptors.

In the light of the increasing evidence for receptor heterogen- eity, a nomenclature committee has been set up by the newly founded International Dopamine Club.

PIERFRANCO SPANO

Institute of Pharmacology and Experimental Therapeutics, School of Medicine, University of Brescia, Via Valsabbina t9,1-23124 Brescia, Italy.

Endogenous digitalis- like factors: purification, properties, physiological functions Giessen, FRU 8-10 July 1990

The search for an endogenous ligand of the cardiac glycoside binding site of the Na+/K+-trans - porting ATPase has been under way since it was discovered, in 1979, that hypothalamic extracts inhibit this transport.

The bufadienolide resibufo- genin is an endogenous digitalis- like substance in toad plasma. F. J. Haddy (Uniformed Services University, Bethesda) observed that bufalin has all the physiologi- cal characteristics of a digitalis- like substance. It can raise blood pressure and produce postinfu- sion diuresis. However, it does this at concentrations where oua- bain and ouabagenin do not affect these parameters, although they are equipotent with bufalin in

i~hibiting Na+/K+-ATPase; this suggests that an additional mech- anism is involved.

Endogenous Na+/K+-ATPase - inhibiting digitalis-like substances from different sources are chemi- cally distinct. From rat hypo- thalamic cells in culture, M. A. Mir (University of Wales, Cardiff) has purified a 13 amino acid residue peptide with :t blocked N termi- nus. By contrast, a low molecular weight (< 1000) inhibitor purified from bovine hypothalamus and hypophysis (J. M. Sancho, Centro Ramon y Cajal, Madrid) is neither a peptide nor a lipid, and does not cross-react immunologically with digoxin antibodies. This fac- tor is a nontoxic vasoconstrictor and has a positive inotropic effect (G. T. Haupert, Massachusetts General Hospital, Boston). Using the inhibition of 86Rb+ uptake into erythrocytes as an assay, J. H. Ludens and colleagues (UpJohn, Kalamazoo) have purified a low molecular weight factor (< 1000) from human plasma, which is dis- tinct from those reported from