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Somatostatin receptors in the rat adrenal cortex: characterization and comparison with brain and pituitary receptors.

Abstract：

:Specific receptors for tetradecapeptide somatostatin (S-14) in rat adrenal cortical membranes were quantitated by direct binding studies using [125I-Tyr11]S-14. Competitive inhibition of this radioligand by S-14 showed that these receptors constitute a single class of high affinity binding sites [dissociation constant (Kd) = 1.08 nM and maximum binding capacity (Bmax) = 0.35 pmol/mg membrane protein]. Structural analogs of S-14 with halogenated Trp8 moiety exhibited 4- to 46-fold greater binding affinity than S-14, [D-F5-Trp8]S-14 being the most potent. [Tyr11]S-14 and [des-Ala1]S-14 bound to these receptors with reduced affinity whereas [Phe4]S-14 exhibited 1.5-fold greater affinity than S-14. Somatostatin-28 (S-28) and S-14 were equipotent, whereas the N-terminal fragments of S-28 [S-28(1-14) and S-28(1-12)] were inactive. High affinity binding sites were also quantitated using a radioligand prepared from the tyrosinated S-28 analog, [Leu8, D-Trp22, Tyr25]S-28 (Kd = 1.2 nM; Bmax = 0.21 pmol/mg membrane protein). Both S-14 and S-28 exhibited comparable relative potencies for inhibiting the specific binding of this radioligand and [125I-Tyr11]S-14. Extracts of whole adrenal or the adrenal medulla and cortex contained very low levels of S-14-like immunoreactivity (2.4 pg/mg protein). These studies confirm the presence of specific receptors for S-14 in the adrenal cortex and suggest that 1) with respect to S-14 biological activity, Trp8-modified S-14 analogs should be more potent than S-14, S-28 equipotent with S-14, and N-terminal fragments of S-28 inactive in this tissue. 2) Direct binding studies using radioiodinated [Tyr11]S-14 and [Leu8,D-Trp22, Tyr25]S-28 appear to quantitate the same receptor sites in adrenocortical tissue. 3) The ligand specificity of the adrenocortical S-14 receptor differs from that previously reported for the pituitary and brain providing further evidence for the heterogeneity of the S-14 receptor. 4) In view of the very low concentrations of endogenous S-14-like immunoreactivity, the adrenal actions of S-14 and S-28 are probably mediated through an endocrine mechanism.

journal_name

Endocrinology

journal_title

Endocrinology

authors

Srikant CB,Patel YC

doi

10.1210/endo-116-5-1717

subject

Has Abstract

pub_date

1985-05-01 00:00:00

pages

1717-23

issue

eissn

0013-7227

issn

1945-7170

journal_volume

116

pub_type

杂志文章

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Somatostatin receptors in the rat adrenal cortex: characterization and comparison with brain and pituitary receptors.