Somatostatin: Likely the most widely effective gastrointestinal hormone in the human body

Table 1 Localization of somatostatin

Organs	Type of Cells	Location
Major sites
Nervous system	Neurons	Hypothalamus
		Cerebral cortex
		Limbic system
		Basal ganglia
		Major sensory systems
		Spinal cord
		Dorsal root ganglia
		Autonomic ganglia
Pancreas	D-cells	Islets
Gut	D-cells	Mucosal glands
	Neurons	Submucous and myenteric plexuses
Minor sites
Adrenal		Scattered medullary cells
Placenta		Cytotrophoblasts in chorionic villi
Reproductive organs		Testis, epididymis, prostate
Submandibular Gland	D-cells	Scattered ductal cells
Thyroid	C-cells	Scattered parafollicular cells, coexisting with calcitonin
Urinary system		Scattered cells in renal glomerulus and collecting ducts
Miscellaneous		Thymus, heart, eyes, erythrocytes

Table 2 The 5 subtypes of human SS receptors

Feature	SS receptors
	Subtype 1	Subtype 2	Subtype 3	Subtype 4	Subtype 5
Amino acid sequence	361	369 (A), 346 (B)	418	388	364
Chromosomal location	14	17	22 20	20 22	16
G protein coupling	Yes	Yes	Yes	Yes	Yes
Effector system
Adenylate cyclase activity	Reduced	Reduced	Reduced	Reduced	Reduced
Tyrosine phosphatase activity	Increased	Increased	Not investigated	Not investigated	Not investigated
Possible binding affinity to receptors
SS-14	++	++	++	++	++
SS-28	++	++	++	++	++
Octreotide	±	++	+	±	++
Vapreotide (RC-100)	±	++	+	+	+++
Lanreotide (BIM-23014)	±	++	+	+	+++
1Distribution in normal human tissue	Brain, lungs, stomach, jejunum, kidneys, liver, pancreas	Brain, kidneys	Brain, pancreas	Brain, lungs	Brain, heart, adrenal glands, placenta, pituitary, small intestine, skeletal muscle

¹Not all human tissues were tested simultaneously. This table was modified from Steven et al.