No abstract

A heterologous RIA method for pituitary adenylate cyclase activating polypeptide with 38 residues (PACAP38) and a homologous RIA method for a shorter form of PACAP with 27 residues (PACAP27) were established to determine PACAP content in central and peripheral tissues in rats. The highest concentration of radioimmunoassayable PACAP38 was found in the hypothalamus, but other brain regions also contained considerable amounts of PACAP38. PACAP38 concentration in the posterior pituitary was comparable with that in the extrahypothalamic brain, but its concentration in the anterior pituitary was very low. Unexpectedly, the testis contained a high abundance of PACAP38, and the total amount of PACAP in both testes exceeded its content in the whole brain. Reverse phase HPLC suggested that the major testicular PACAP38 immunoreactivity represents PACAP38. Among peripheral tissues, adrenal gland contained the second highest concentration of PACAP. Smaller amounts of PACAP were widely distributed in the digestive tract and other peripheral tissues. The concentration of PACAP in stomach, duodenum and jejunum appeared to be greater than in other portions of the gut. In all tissues, PACAP27 represented only a minor portion of total PACAP immunoreactivity.

An orphan receptor discovered in 1993 was called bombesin receptor subtype 3 (BRS-3) because of 47-51% amino acid identity with bombesin (Bn) receptors. Its pharmacology is unknown, because no naturally occurring tissues have sufficient receptors to allow studies. ]Bn-(6 -14) bound to both cell lines with high affinity. Neither Bn nor 14 other naturally occurring Bn peptides bound to hBRS-3 with a K d <1000 nM. Twenty-six synthetic peptides that are high affinity agonists or antagonists at other bombesin receptors had an affinity >1000 nM. Guanosine 5-(␤,␥-imido)triphosphate inhibited binding to both cells due to a change in receptor affinity. These results demonstrate hBRS-3 has a unique pharmacology. It does not interact with high affinity with any known natural agonist or high affinity antagonist of the Bn receptor family, suggesting the natural ligand is either an undiscovered member of the Bn peptide family or an unrelated peptide. The availability of these cell lines and the hBRS-3 ligand should facilitate identification of the natural ligand for BRS-3, its pharmacology, and cell biology. We made two cell lines stably expressing the human BRS-3 (hBRS-3). hBRS-3 was overexpressed in the huRecently, an orphan receptor that is a member of the heptahelical superfamily of receptors was described in both human small cell lung cancer cells (1) and guinea pig uterus (2). Because this orphan receptor had a high degree of homology to mammalian bombesin receptors (i.e. 51-52% for the gastrinreleasing peptide receptor (GRP-R) 1 and 47% for the neuromedin B receptor (NMB-R) (1, 2)), it was named the BRS-3 for bombesin receptor subtype-3 in one study (1). Studies of the distribution of the receptor mRNA show that BRS-3 has a pattern of expression limited to rat secondary spermatocytes (1), guinea pig brain and pregnant uterus (2), and some tumor cell lines (various human small cell and non-small cell lung cancer cell lines (1), the human ductal breast cancer cell line T47D (3), and the human epidermal cancer cell line A431 (3)). However, the natural ligand that interacts with the BRS-3 is unknown, and its pharmacology is largely unknown because of the lack of a radioligand. In addition, little is known about the cellular basis of action of BRS-3 except that it is coupled to phospholipase C when expressed in Xenopus oocytes (1) or when transfected into Balb 3T3 cells (4). The ability to elucidate the pharmacology of the BRS-3 is not only limited by the lack of a radioligand but also by the lack of a cell containing native BRS-3 receptors in sufficient numbers to allow binding studies to identify a possible radioligand.To deal with this latter issue, in the present study we have used two different strategies to produce cell lines stably expressing the human BRS-3 (hBRS-3) receptor whose pharmacology and coupling will probably closely resemble that of the native hBRS-3. Furthermore, we have discovered a unique ligand that is a synthetic analogue of bombesin-(6 -14), which interacts with high affinity with the hBRS-3. With ...

No abstract

No abstract

Aims/hypothesis The glucose-lowering effect of glucagonlike peptide-1 (GLP-1) is based not only upon its potent insulinotropic actions but also on its ability to restrain glucagon secretion. Surprisingly, the closely related glucose-dependent insulinotropic peptide (GIP) stimulates glucagon release. We examined whether the islet hormone somatostatin, which strongly inhibits glucagon secretion, is involved in this divergent behaviour. Methods At 1.5 mmol/l glucose and therefore minimal insulin secretion, the glucagon, insulin and somatostatin responses to 20 mmol/l glucose, GLP-1, GIP and somatostatin were studied in the presence of a high-affinity monoclonal somatostatin antibody and of a highly specific somatostatin receptor subtype 2 (SSTR2) antagonist (PRL-2903) in the isolated perfused rat pancreas. Results In control experiments, GLP-1 at 1 and 10 nmol/l reduced glucagon secretion significantly to 59.0±6.3% (p<0.004; n=5; SSTR2 series; each vs pre-infusion level) and to 48.0±2.6% (p<0.001; n=6; somatostatin antibody series) respectively. During somatostatin antibody administration, GLP-1 still inhibited glucagon secretion significantly, but the effect was less pronounced than in control experiments (p<0.018). Co-infusion of the SSTR2 antagonist completely abolished the GLP-1-induced suppression of glucagon secretion. In contrast, neither the GIP-induced stimulation of glucagon release nor its inhibition by 20 mmol/l glucose was altered by somatostatin antibody or SSTR2 antagonist administration. Conclusions/interpretationWe conclude that GLP-1 is capable of inhibiting glucagon secretion even in the absence of secretory products from the beta cell. It is highly likely that this is mediated via somatostatin interacting with SSTR2 on rat alpha cells. In contrast, GIP and glucose seem to influence the alpha cell independently of somatostatin secretion.

No abstract

This following article is written for Prof. Abba Kastin’s Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (Bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on Bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in the Prof Kastin’s Handbook of Biological Active Peptides [137,138,331].