Characterization of Pituitary Membrane Receptors for Somatostatin in the Rat*

Publisher Website
Google Scholar
Abstract
We have demonstrated the presence of specific receptors for somatostatin (SRIF) in normal rat pituitary membranes using ([125I-Tyru11]SRIF) as the radioligand. These receptors bind SRIF with high affinity (Ka ∼0.47 × 1010 M-1) and have a maximal binding capacity of 0.095 pmol/mg membrane protein. Two other radioiodinated SRIF analogs which contain N-terminally situated radiolabel, [125I-Tyr1]SRIF and [125I-N-Tyr] SRIF, were found unsuitable for receptor binding studies due to loss of the radiolabel from the ligand molecule under the experimental conditions employed. Binding of [125I-Tyr11SRIF tothese receptors was specific and was not influenced by a variety of other neuropeptides. The specificity of SRIF receptors was also examined using 10 synthetic SRIF analogs as well as catfish somatostatin I. Catfish somatostatin I was 8.3 times less potent than SRIF in binding to SRIF recepto s, alth ugh it has been reported to be equipotent in terms of in vitro GH inhibition. Analogs which exhibit greater potency for GH inhibition in vitro bound to these receptors with greater affinities than SRIF, whereas biologically inactive analogs showed markedly reduced binding, suggesting that the in vitro GH inhibitory actions of SRIF analogs are related to their ability to interact with SRIF receptors.

This publication has 0 references indexed in Scilit: