Cyclic guanosine monophosphate

Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a second messenger much like cyclic AMP, most notably by activating intracellular protein kinases in response to the binding of membrane-impermeable peptide hormones to the external cell surface.

Structure and synthesis

cGMP is synthesized from GTP by the enzyme guanylate cyclase, and is degraded back into GTP by phosphodiesterase. The synthesis and degradation of cGMP are regulated by multiple factors, including the levels of GTP and the activity of guanylate cyclase and phosphodiesterase.

Function

cGMP serves as a regulator of several biological processes, including vasodilation, insulin secretion, and peristalsis. It also plays a crucial role in the phototransduction pathway in the retina, and in the regulation of cardiac contractility.

In the vascular system, cGMP acts as a potent vasodilator by activating protein kinase G (PKG), which in turn phosphorylates various proteins, leading to relaxation of smooth muscle cells in blood vessels.

In the endocrine system, cGMP is involved in the regulation of insulin secretion by pancreatic beta cells.

In the gastrointestinal system, cGMP is believed to regulate smooth muscle contraction and thus influence peristalsis.

Clinical significance

Alterations in cGMP levels have been implicated in a variety of disease states, including heart failure, diabetes, and erectile dysfunction. Drugs that increase the levels of cGMP within the body are currently used to treat these and other conditions.

See also

• Cyclic AMP
• Guanylate cyclase
• Phosphodiesterase
• Protein kinase G