Direct agonist, definition

Within each group evidence that members associate with the same receptor and/or exhibit similar modes of binding may be advanced in greater or lesser extent on the basis of comparative structure-activity relationships and direct assessments of receptor affinities by these means it may also prove possible to classify more specifically some members of the miscellaneous group. Factors governing the spectrum of activity of individual compounds and the definition of pure or mixed agonists-antagonists add a further dimension to the structure-activity analyses. 

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