Hill's Sign

Hill's sign (l. e. Hill, 1866-1952, English physiologist) is a set of signs that describe the presence and nature of physiological effects during the interaction of a ligand with a receptor. These signs were proposed by British physiologist Archibald Hill in 1910 to evaluate the interaction between agonists and receptors.

Hill's sign includes:

1. Binding stringency is how quickly and over what concentration range the ligand binds to the receptor.

2. Specificity is how selectively a ligand interacts with a particular receptor compared to other receptors.

3. Reversibility - whether the interaction between the ligand and the receptor can be broken.

4. Saturation effect—whether the response limit is reached as the ligand dose increases.

5. Interchangeability - whether different ligands can produce the same effect through the same receptor.

Hill's sign is widely used in pharmacology to characterize drugs and their interaction with receptors.