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

1 Rat and porcine galanin (rGal and pGal) produced dose‐dependent contraction of rat fundus strips in a concentration range of 6 n m –100 n m . 2 The stimulatory effect of rGal on rat fundus strips was not modified in the presence of somatostatin (250 n m ), naloxone (1 μ m ), guanethidine (10 μ m ), a mixture of propranolol (3 μ m ) and phentolamine (3 μ m ), tetrodotoxin (1 μ m ), indomethacin (10 μ m ), atropine (1 μ m ), a mixture of methysergide (2.5 μ m ) and ketanserin (2.5 μ m ), a mixture of mepyramine (10 μ m ) and cimetidine (10 μ m ), and saralasin (10 μ m ) or when strips were desensitized to substance P and neurotensin. 3 These results suggest the localization of specific Gal receptors on the surface of smooth muscle cells of rat fundus. 4 The galanin analogues [ d ‐Trp 2 ]‐rGal, [NLe 4 ]‐rGal, [ d ‐Ala 7 ]‐rGal, [ d ‐Trp 2 ‐NLe 4 ‐ d ‐Ala 7 ]‐rGal and fragments [Cys 23 ]‐Gal (1–23), Gal (1–18) were fully active. In contrast, rGal (3–29) was completely inactive and showed no antagonistic properties to the contractile effect of intact galanin. 5 The order of potency of the galanin peptides, analogues and fragments to contract rat fundus strips was: pGal > rGal > [NLe 4 ]‐rGal > [Cys 23 ]‐Gal (1–23) > Gal (1–18) > [ d ‐Ala 7 ]‐rGal > [Trp 2 ]‐rGal > [ d ‐Trp 2 ‐NLe 4 ‐ d ‐Ala 7 ]‐rGal. 6 The data originating from our structure‐activity study suggest that the C‐terminal portion of Gal contributes mainly to the affinity 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.