If you wanted to design an artificial hormone who's action on a target cell required the least amount of interaction with that cell, what type of hormone would you want to use and explain why. *

The water soluble hormones affect the target cells with least amount of interaction.

Explanation:

Hormones are the chemical messengers. These are the substances secreted by the endocrine glands. The hormones are secreted directly into the bloodstream and are carried to the target cells within the blood only.  

Based on their structure, hormones are water-soluble or lipid-soluble. The lipid-soluble hormones are steroid hormones and thyroid hormones. These hormones can easily pass through the lipid bilayer of the cell membrane of the target cell. Therefore, the lipid-soluble hormones have intracellular receptors that are present in either cytoplasm or the nucleus of the target cells.  

On the other hand, the water-soluble hormones can not pass through the lipid bilayer of the target cells. Therefore, these hormones have extracellular receptors on the surface of the target cells. Binding of the water-soluble hormones to their cell surface receptors triggers the production of the intracellular second messengers that finally carry the signal to the target protein or any other target molecule.

Therefore, a water-soluble hormone exhibits the least amount of interaction with the target cell. Amine hormones such as epinephrine and melatonin, peptide hormones such as oxytocin are some examples of the water-soluble hormones.