Biological messengers are compounds which can deliver medicine in predicted place. Globular proteins act as biological messengers in the form of peptide hormones. Peptide hormones play an important role in metabolism, growth and development. Some peptide hormones of note are prolactin and insulin. Prolactin is a hormone secreted by the pituitary gland that triggers the production of breast milk in a nursing mother. Insulin is a hormone that is produced by the pancreas that aids in the body's ability to regulate energy and metabolize sugars.