Somatostatin system: molecular mechanisms regulating anterior pituitary hormones

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   Somatostatin system: hypothalamus–anterior pituitary lobe axis. Somatostatinergic neuron bodies located at the hypothalamic periventricular (80%) and paraventricular (20%) nuclei travel through the median eminence and pituitary stalk and secrete SRIF into the pituitary portal circulation, reaching the cells of the anterior pituitary gland. Receptor subtype distribution is represented by subtype numbers (1–5) inside the specific cell type and is based on receptor profile in cell-respective human tumors, i.e. GH-, ACTH-, PRL, TSH-secreting adenomas and non-functioning pituitary tumors that also include gonadotroph FSH/LH secreting tumors. Large size red letter indicates that ∼90% of selective tumor type are positive for that receptor subtype, medium size blue letter indicate that ∼70% of selective tumor types are positive for that receptor subtype, small size black letters that ∼50% of selective tumor type are positive for that receptor subtype. Lower percentages are not presented. Receptor profile data is based on Ben-Shlomo & Melmed (2010).
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   Selected SRIF-dependent pituitary signaling pathways. SRIF and SRIF analogs activate multiple molecular signaling pathways depicted here, which control pituitary hormone secretion as well as cell growth. These include Ca²⁺ and K⁺ channels, phosphatases such as SHP1 and PP2A, cyclic nucleotide synthases such as guanylyl and adenylyl cyclase, nitric oxide, NFκB, MAPK/ERK, PKC, as well as BMPs.

• © 2014 Society for Endocrinology