Effects of galanin, its analogues and fragments on rat isolated fundus strips

Abstract

1 Rat and porcine galanin (rGal and pGal) produced dose-dependent contraction of rat fundus strips in a concentration range of 6 nM-100 nm. 2 The stimulatory effect of rGal on rat fundus strips was not modified in the presence of somatostatin (250nM), naloxone (1 uM), guanethidine (10 CM), a mixture of propranolol (3 #M) and phentolamine (3puM), tetrodotoxin (1 pM), indomethacin (10pM), atropine (1 M), a mixture of methysergide (2.5,UM) and ketanserin (2.5 uM), a mixture of mepyramine (10,UM) and cimetidine (10M), and saralasin (10puM) The order of potency of the galanin peptides, analogues and fragments to contract rat fundus strips was:The data originating from our structure-activity study suggest that the C-terminal portion of Gal contributes mainly to the afflinity of Gal receptors whereas the N-terminal portion of Gal is responsible for the full activation of Gal receptors in this tissue. In particular the amino acids in position 1 and 2 of Gal (Gly-Trp) appear to be essential for binding and intrinsic activity.

Isolation and primary structure of pituitary human galanin, a 30-residue nonamidated neuropeptide.

“…Interestingly, nonamidated and amidated hGals showed no differences in biological activity or high-affinity binding (results not shown). These findings are in agreement with several structure-activity studies for the characterization of Gal and the interaction with its receptor: it has been demonstrated that the N-terminal portion ofGal, which is completely conserved in all species, is important for receptor interaction in rat pancreatic B cells (21,34), central nervous system neurons (35,36), and isolated smooth muscle strips (14,29). In contrast, a number of Gal-specific antisera reacting with the C-terminal part of the peptide show poor cross-reactivity among species and divergent tissue levels of Gal (4, 6).…”

“…In comparison to bovine Gal (bGal) and rGal, 7 and 4 residues are different, respectively. All amino acid substitutions are restricted to the C-terminal part of the molecule (positions [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Table 1 compares the sequences of hGal, rGal, pGal, and bGal.…”

“…Isolated longitudinal muscle strips from rat fundus were prepared, as described (29 (Fig. 2C), characterized by UV-absorption at 214 nm and 280 nm (the latter not shown).…”

Galanin receptors in the rat gastrointestinal tract

“…The effects of galanin are mediated by three distinct G-protein-coupled receptors that involve different signaling pathways: galanin receptor 1 (GalR1) (G i/o ), GalR2 (G q/11 ) and GalR3 (G i/o ) (Smith et al, 1997;Branchek et al, 1998Branchek et al, , 2000Wang et al, 1998). The effect of galanin on gastrointestinal motility varies according to the species and the segment investigated, suggesting activation of multiple receptors (Tamura et al, 1987;Muramatsu and Yanaihara, 1988;Fontaine and Lebrun, 1989;Katsoulis et al, 1990). To better understand which receptor mediates a particular galanin effect, it is critical to determine the tissue specific distribution of individual GalRs.…”

Expression of galanin receptor messenger RNAs in different regions of the rat gastrointestinal tract

“…The effects of galanin on gastrointestinal motility are both stimulatory and inhibitory, and are the result of a direct myogenic and a nerve-mediated effect involving the release of other transmitters. In general, galanin actions vary depending on the tissue, the species and the experimental conditions [8,12,16,25].…”