title: An extension of pA principle to the potentiation of drug effects, and its application to the biological assay of some anticholinesterases and cardenolides.
abstract: A new scale for the potentiation was introduced and was termed pA1/2. The value can be calculated by using an equation; (Formula: see text), which is similar to that which is used for the calculation of pA2. For the use of the equation, the parallel shift of the dose-response curve and the unchanged maximum response are prerequisites. This experiment showed the validity and the usefulness of calculating the pA1/2 values, in the biological assay. In the assay of anticholinesterases, the potentiating effects of neostigmine or physostigmine on the acetylcholine-induced contraction were examined, by using frog's rectus abdominis. The pA1/2 values obtained in the presence of two different concentrations of anticholinesterases were the same, indicating that pA1/2 is a parameter which is specific to the potentiator. The potentiating effects of some cardenolides on the K-induced contracture were examined, by using the frog's ventricular muscles. The relative potencies of four cardenolides obtained from the pA1/2 values well agreed with those reported earlier. The amount of the cardenolides required for this assay was smaller than required for other methods.
mesh_terms: D000818:Animals; D001001:Anura; D001681:Biological Assay; D002298:Cardenolides / Q000032:analysis* / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000032:analysis* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D066298:In Vitro Techniques; D008962:Models, Theoretical; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009388:Neostigmine / Q000494:pharmacology; D010830:Physostigmine / Q000494:pharmacology; D011898:Ranidae
chemical_list: D002298:Cardenolides; D002800:Cholinesterase Inhibitors; D009388:Neostigmine; D010830:Physostigmine