Definition:
Agonist binds to receptors => receptor cells release enzymes
Ex: Tyrosine kinase inhibitors

Pharmacology examples:
- Insulin:

The insulin receptor (IR) is a transmembrane receptor that is activated by insulin.
The insulin receptor mediates their activity by causing the addition of a phosphate group to particular tyrosines on certain proteins within a cell. The "substrate" proteins that are phosphorylated by the Insulin Receptor leads to an increase in the high affinity glucose transporter (Glut4) molecules on the outer membrane of insulin-responsive tissues, including muscle cells and adipose tissue, and therefore to an increase in the uptake of glucose from blood into these tissues. In other words, the glucose transporter Glut4 is transported from cellular vesicles to the cell surface, where it then can mediate the transport of glucose into the cell. (3)

- Tyrosine kinase inhibitors:

Phosphorylation of proteins by kinases is an important mechanism in communicating signals within a cell (signal transduction) and regulating cellular activity, such as cell division. Protein kinases can become mutated, stuck in the "on" position, and cause unregulated growth of the cell, which is a necessary step for the development of cancer. Therefore, kinase inhibitors, such as imatinib, are often effective cancer treatments. (1)

- Peptide growth hormones:

Binding of growth hormone to the receptor leads to receptor activating of intra- and intercellular signal transduction pathway leading to growth.(2)

insulin

References:
(1): https://en.wikipedia.org/wiki/Tyrosine_kinase
(2): https://en.wikipedia.org/wiki/Growth_hormone_receptor
(3): https://en.wikipedia.org/wiki/Insulin_receptor