Alzheimers disease and the muscarinic receptor

What exactly is meant by efficacy For the cortical muscarinic receptor, the 

Values were determined by displacement of tritiated ligand from rat cortical homogenates, expressed as affinity constants corrected for ligand occupancy. 

On theoretical grounds, inhibition of the R-A cascade at either the renin or A-II level should be even more therapeutically beneficial. Renin being the rate-limiting enzyme in the RAS, it is considered to be the better target over ACE since inhibition of the latter may be surmountable through build up of 

Direct vasoconstriction NoradrenaliDe rdease AMosterone rdease Increased sotfoim reabsorption 

Inhibition of human renin IC50 (nM) (structural class) 

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