Studies on mode of antagonism between adrenergic beta-mimetics and beta-blocking agents (I). Beta-blocking action of mescaline and its derivatives

Studies on the mode of antagonism between adrenergic beta-mimetics and beta-blocking agents (IV). Influence of functional antagonism by spasmogens

A new theory is presented to describe the effect of functional antagonism on the competitive antagonism between adrenergic beta-mimetics and beta-blockers. According to this theory the shape of the log (dose ratio-1) vs.--log [B] curve and the apparent pA2 value in competitive antagonism should be affected by functional antagonism when the agonist is taken up by the saturable uptake process, and this was experimentally confirmed. The competitive antagonism between isoproterenol (ISO) and propranolol (Prop) was influenced by the functional antagonism between ISO and spasmogens (histamine and carbachol). The log (dose ratio-1) vs. --log [B] curve is ISO-Prop competitive antagonism was shifted variously depending on the concentration of a spasmogen used. Theoretical predictions and experimental results were in good parallel.

Studies on the mode of antagonism between adrenergic beta-mimetics and beta-blocking agents (III). Functional antagonism between beta-mimetics and spasmogens

New equations which can explain the following characteristic phenomena in the functional antagonism between isoproterenol (ISO) and spasmogens in guinea-pig trachea are proposed: (1) The amplitude of relaxation of the muscle induced by ISO varied depending on the concentration of a spasmogen used (histamine or carbachol). (2) The dose-response curves for the relaxation by ISO shifted to the right in a parallel manner as the concentration of the spasmogen increased, and became stationary at high concentrations of the spasmogen. (3) The slope of the dose-response curve became steeper with increasing concentrations of the spasmogen. When the saturable uptake process of ISO was taken into consideration, a satisfactory parallel was seen between the theoretical dose-response curves and the present experimental results.

Studies on the structure activity relationship of adrenergic beta-mimetic benzylamine derivatives

Appropriately substituted benzylamine (BZA) derivatives, fragmented derivatives of tetrahydroisoquinolines, were found to be directly acting adrenergic beta-stimulants, exhibiting tracheal relaxing, positive chronotropic and free fatty acid (FFA) releasing activities. The chemical structures essential for manifestation of the beta-action were i) 3,4-dihydroxybenzylamine, ii) arylmethyl group at position alpha, iii) lower alkyl group on the N atom. The structure activity relationships of BZA-derivatives were almost similar to, but partly different from those of tetrahydroisoquinoline- and catecholamine-derivatives. The tracheal relaxing, positive chronotropic and FFA-releasing actions of alpha-(3,4,5-trimethoxybenzyl)-N-methyl-3,4-dihydroxybenzylamine, the most active compound in the BZA-derivatives tested, were approximately one-hundred, thirty and fifty times less active than those of ISO, respectively. These results indicate that this compound is beta1-selective, while trimetoquinol is beta2-selective.

Studies on the mode of antagonism between adrenergic beta-mimetics and beta-blocking agents (II). Analysis by the uptake saturation model

Curves of experimentally plotted log (dose ratio-1) vs.-log [B] for the antagonism between adrenergic beta-mimetics, isoproterenol (ISO) and trimetoquinol (TMQ), and various beta-antagonists in relaxation of guinea-pig trachea could not be reasonably fitted to Schild's equation which has been commonly used in the analysis of drug-antagonism. Taking into consideration the saturable uptake process of the drug used herein, the equation presented in this paper fitted fairly well to the experimental curves and explains the following results: 1, TMQ was more strongly antagonized than ISO by all the blocking agents tested, that is, the apparent modes of antagonism were different between ISO and TMQ although they are considered to interact with the same receptor site. 2, The slope of the curve for a given antagonist markedly differed between ISO and TMQ. It is hypothesized that ISO is more easily taken up than TMQ. This was experimentally confirmed: i.e., ISO was potentiated about 8 fold by inhibiting the uptake process with dibenamine while TMQ was not. By pretreatment with dibenamine, the log (dose ratio-1) vs.-log [B] curve for the ISO-propranolol antagonism was shifted upward and superimposed with the theoretical curve of antagonism in which uptake of the agonist was neglected.