Quantitative correlation between histamine and 35S release from isolated rat mast cells due to the beta-adrenergic blocking drug Kö 1124

Vasoconstrictor reaction to prostaglandins E1 and E2 in the isolated rat hindlimb mediated through serotonin release

The vasoconstrictor effects of prostaglandins E (PGEs) were studied in the isolated perfused hindlimbs of the rat. Doses of PGE1 in the range of 0.01-10 micrograms caused dose-dependent increases in perfusion pressure with rapid development of tachyphylaxis. The pressure increases were inversely temperature-dependent, being 4.8 +/- 1.2 mm Hg at 37 degrees C and 22.2 +/- 1.8 mm Hg at 27 degrees C. The vasoconstriction was limited to PGE1 and PGE2. Other prostaglandins tested, PGF2 alpha, PGD2, PGA1, 7-oxo-PGI2 and arachidonic acid, were without any effect at 27 degrees C. Increased serotonin concentrations were found in the effluent after the administration of 1 microgram of PGE1. The pressor response to PGE1 was blocked by 5-HT2 antagonists, ketanserin (2 micrograms) and naftidrofuryl (100 micrograms), while the alpha-adrenoceptor antagonist phentolamine (6.7 micrograms) was without effect. Rapid tachyphylaxis of the development of vasoconstriction was observed after the repeated administration of PGE1 and PGE2. PGE1 (1 microgram) induced desensitization with more than 60 min duration. All the findings suggest that serotonin was liberated in the rat hindlimbs by PGEs.

Histamine liberation as a result of nonreceptor interaction

The highly lipophilic drug exaprolol liberates histamine from isolated mast cells and decreases the uptake of extracellular histamine in a dose-dependent manner. Intracellular histamine depletion was confirmed by electron microscopy and was accompanied by calcium displacement from intracellular storage sites. The significant decrease in membrane fluidity due to exaprolol was temperature-dependent and was most probably a result of its high membrane affinity and intracellular penetration. Membrane perturbation by exaprolol may account for this nonreceptor interaction. This could contribute to the understanding of adverse reactions to beta-adrenoceptor blocking drugs.

Amine transport in isolated rat mast cells treated with betaadrenoceptor blocking drugs

Histamine and serotonin uptake in isolated rat mast cells is decreased in the presence of betaadrenoceptor blocking (BAB) drugs. Such inhibition is dose-dependent and is evidently higher for the inhibition of serotonin uptake. The most potent drugs were the highly lipophilic compounds Kö 1124 and propranolol. No difference was found among the various BAB drugs in their ability to decrease histamine uptake. It is evident from the ratio between histamine and serotonin liberation on one side, to the uptake of both amines in mast cells on the other side, that with the exception of Kö 1124, all investigated BAB drugs possesses higher inhibition of extracellular amine uptake in comparison with histamine and serotonin liberation. Such an effect might be a result of a primary interaction of BAB drugs with mast cells at the plasma membrane.

On the interaction of beta-adrenoceptor-blocking drugs with isolated mast cells

The interaction of beta-adrenoceptor blocking drugs (BAB drugs) with isolated mast cells resulted, according to the compound, in either a liberation of biogenic amines or an inhibition of stimulated amine release. The liberatory drugs exaprolol and Kö 1124 decreased the level of cAMP, stimulated the activity of cyclic nucleotide-phosphodiesterase, decreased the incorporation of orthophosphate into membrane phospholipids and rapidly displaced calcium from binding sites in mast cells. The inhibitory drugs alprenolol, metipranolol, oxprenolol, practolol and propranolol, possessing lower liposolubility, produced opposite effects. Drugs from both groups displaced histamine from binding sites in isolated mast cell granules. The interaction of BAB drugs with mast cells is a result of non-specific rather than specific receptor interactions. Inhibitory drugs interfere with mast cells at membrane sites while liberatory drugs penetrate the membrane, thus acting both at the level of membrane and intracellularly.

Evidence for intracellular histamine liberation in isolated rat mast cells

The beta-adrenoceptor blocking drug exaprolol liberated histamine from isolated rat mast cells in a dose- and time-dependent way. Histamine was liberated within seconds and was not followed by a parallel granule liberation. The inhibition of histamine liberation was induced with low temperature, low pH, high concentration of Ca2+, TTD, suramin and EDTA. Subcellular distribution of 3H-exaprolol demonstrated a quantitative relationship between histamine depletion against exaprolol uptake in isolated rat mast cell granules. A nonspecific mechanism of action in the effect of exaprolol on mast cells is discussed. It is proposed that the drug acts on mast cells due to the direct and indirect ion exchange mechanism resulted in disproportion between histamine and granule liberation.

Immunohistochemical identification of mastocytes

Antibodies to mastocytes were localized in cells and tissues following formaldehyde or paraformaldehyde fixation and embedding into paraffin or Durcupan ACM, and after chymotrypsin treatment of the sections. Immunomicroscopic examination yielded a more distinct picture of the amount and localization of mastocytes in different tissues.