Somatostatin 1-28

Somatostatin 1-28 circulates in human plasma.[Pubmed:6191365]

Regul Pept. 1983 Apr;6(1):63-9.

The gel filtration profile of immunoreactive somatostatin in human plasma in the fasting state is not well established as a consequence of insufficient sensitivity of the combined chromatography and radioimmunoassay procedures usually employed. We here report the gel filtration profiles of plasma samples after somatostatin concentration by batchwise immunoaffinity chromatography. The results clearly and reliably document the presence of a circulating peptide in human plasma with a gel permeation chromatography profile identical to the one of synthetic Somatostatin 1-28. Approximately 46% of the total somatostatin-like immunoreactivity in plasma is due to this component.

Different effects of three kinds of somatostatin (15-28, 1-14, 1-28) on rabbit's platelet aggregation.[Pubmed:2860550]

Life Sci. 1985 May 27;36(21):2047-52.

We studied the different effects of three kinds of somatostatin (somatostatin 1-14, somatostatin 15-28, Somatostatin 1-28) on the aggregation of rabbit's platelets. It was clarified that somatostatin 15-28 had inhibitory effects on rabbit's platelet aggregation stronger than somatostatin 1-14 did, and that Somatostatin 1-28 did not have any such effects. These anti-aggregatory effects of somatostatin were stronger when induced by collagen than induced by ADP.

Effect of somatostatin-28 on growth hormone response to growth hormone-releasing hormone--impact of aging and lifelong dietary restriction.[Pubmed:9158069]

Neuroendocrinology. 1997 May;65(5):369-76.

The present study was designed to investigate the modulating effect of aging and lifelong dietary restriction (DR), a powerful anti-aging intervention in laboratory rodents, on growth hormone (GH) secretion from pituitary cells in response to GH-releasing hormone (GHRH) in the presence of somatostatin (SS)-28. Dispersed pituitary cells from 6- and 24-month-old rats fed ad libitum (AL-Y, AL-O, respectively) and 24-month-old rats dietary restricted from 6 weeks of age (DR-O) were subjected to a reverse hemolytic plaque assay under variable conditions including GHRH (0, 1, 10 nM) and SS-28 (0, 10 nM). The proportion of GH plaque-forming cells in dispersed pituitary cells increased by GHRH and decreased by SS-28. The proportion of these cells was lowest in AL-O rats; it was lower in DR-O than in AL-Y rats, particularly in the presence of SS-28. The reduction in these cells by SS-28 was greatest in Group AL-O. The mean area of these plaques, reflecting the amount of GH released from individual cells, was not different among the three rat groups in the absence of SS-28. In contrast, SS-28 produced a significantly higher reduction in the plaque area in Group AL-O compared with AL-Y and DR-O rats. Our results indicated that: (1) aging did not alter the responsiveness of GH-secreting cells to GHRH for GH secretion, while increased sensitivity of GH-secreting cells to SS-28 was noted in aged rats; (2) lifelong dietary restriction did not modulate the responsiveness to GHRH but partially inhibited the age-related increase in the sensitivity to SS-28 of GH-secreting cells, and (3) the major impact of the dietary regimen may include modulation of the number of pituitary cells, which leads to a high proportion of GH-secreting cells compared with that in AL rats at the same chronological age.

Molecular cloning, functional characterization, and chromosomal localization of a human somatostatin receptor (somatostatin receptor type 5) with preferential affinity for somatostatin-28.[Pubmed:7908405]

Mol Pharmacol. 1994 Mar;45(3):417-27.

Using a combination of polymerase chain reaction and genomic library screening we have cloned a human gene for a subtype of the somatostatin (SST) receptor (SSTR) termed human SSTR5 (hSSTR5), which is located on chromosome 16. The predicted amino acid sequence of hSSTR5 displays 75% sequence identity with a recently identified rat SSTR [Mol. Pharmacol. 42:939-946 (1992)], suggesting that it is the human homologue of this receptor. hSSTR5 consists of a 363-residue polypeptide exhibiting a putative seven-transmembrane domain topology typical of G protein-coupled receptors. The receptor displays considerable sequence identity to hSSTR1 (42%), hSSTR2 (48%), hSSTR3 (47%), and hSSTR4 (46%). Membranes prepared from COS-7 cells transiently expressing the hSSTR5 gene bound 125I-Leu8,D-Trp22,Tyr25-SST-28 (125I-LTT-SST-28) with high affinity and in a saturable manner. SST-14, SST-28, and various synthetic SST peptide agonists produced dose-dependent inhibition of radioligand binding with the following rank order of potency: LTT-SST-28 > SST-28 > D-Trp8-SST-14 > SST-14 approximately RC-160 approximately BIM 23014 > MK-678 > SMS 201-995. hSSTR5 bound SST-28 with a 12.6-fold greater affinity (Ki = 0.19 nM), compared with SST-14 (Ki = 2.24 nM), indicating that the receptor is SST-28 selective. Addition of GTP, guanosine-5'-O-(3-thio)triphosphate, Na+ ions, or pertusis toxin greatly reduced 125I-LTT-SST-28 binding, thereby indicating that hSSTR5 is coupled to pertussis toxin-sensitive G proteins. Both SST-14 and SST-28 displayed dose-dependent inhibition of forskolin-stimulated cAMP accumulation, consistent with functional coupling of the receptor to adenylyl cyclase inhibition. Northern blot analysis of SSTR5 mRNA revealed a 2.4-kilobase transcript in normal rat pituitary and GH3 rat pituitary tumor cells and a 4.0-kilobase transcript in normal human pituitary. Reverse transcriptase polymerase chain reaction revealed expression of the hSSTR gene in fetal human pituitary and hypothalamus but not in human cerebral cortex. In situ hybridization of the rat pituitary showed that SSTR5 mRNA is selectively localized in the anterior lobe. SSTR5 mRNA was not expressed in four human pituitary tumors (somatotroph adenoma, prolactinoma, and chromophobe adenomas) or in a human insulinoma. Although hSSTR5 displays approximately 75% sequence identity with rat SSTR5, the two receptors display significantly different pharmacological profiles, especially with respect to their binding affinities for the SST analogue SMS 201-995.

Expression of multiple somatostatin receptor genes in AtT-20 cells. Evidence for a novel somatostatin-28 selective receptor subtype.[Pubmed:7904601]

J Biol Chem. 1994 Jan 14;269(2):1506-9.

The pattern of expression of somatostatin receptor (SSTR) genes and gene products in AtT-20 cells was characterized in an attempt to explain the SST-28 binding selectivity that typifies these cells. AtT-20 cells expressed multiple SSTR mRNAs. Paradoxically, this included mRNA for three of the four SST-14 selective receptors: SSTR2 ( +), SSTR1 (+), SSTR4 (+). The SST-28 selective SSTR5 was expressed as a 3.8-kilobase (kb) transcript of relatively low abundance (+) in contrast to normal mouse pituitary which displayed high levels ( ) of a 2.4-kb SSTR5 mRNA. Immunoblot analysis of solubilized membranes with an antipeptide SSTR2 antibody revealed a single SSTR2 protein of 72 +/- 2 kDa. Preincubation of AtT-20 cell membranes with SSTR2 antibody reduced 125I-[Leu8,D-Trp22,Tyr25]SST-28 binding sites by 38%. Residual binding sites exhibited a 4.9-fold increase in affinity for SST-28, a 2.6-fold decrease in affinity for SST-14, and an SST-28:SST-14 potency ratio of 40:1 compared with a potency ratio of 3.5:1 in control membranes. These results demonstrate the expression of four SSTR genes in AtT-20 cells of which SSTR2 predominates. Blockade of SSTR2 with antibody exposes high affinity SST-28 selective sites with comparable binding characteristics to those reported for cloned SSTR5. These SST-28 binding sites may arise from a SSTR5 variant encoded by a high molecular weight 3.8-kb transcript or more likely from another as yet undiscovered member of the SST-28 selective SSTR subfamily.