Galanin, galantide and galanin (1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I: structure dependent effects on the rat isolated gastric fundus.

The study was undertaken using selected pharmacodynamic parameters to describe the effects of porcine galanin(1-29)-NH2; porcine galanin fragments; galantide; porcine galanin(1-14)-[alpha-aminobutyric acid8]scyliorhinin-I and the analogues of the latter peptides on rat isolated gastric fundus muscle. All tested peptides, apart from galanin(16-29)-NH2 evoked reproducible concentration-dependent contractions with significantly decreased activities in comparison to the potency of the native galanin(1-29)-NH2 molecule. The order of the contractile ability in the group of galanin(1-29)-NH2 short fragments was as follows: [lysine14]galanin(1-15)-NH2 > galanin(1-15)-OH > galanin(1-15)-NH2 > [glycine5] galanin(1-15)-NH2 > galanin(2-15)-NH2 > [glycine5,lysine14]galanin(1-15)-NH2. Aside from [lysine14]galanin(1-15)-NH2 which had a lower efficacy, none of the peptides showed significant changes in this respect in comparison to the intact galanin(1-29)-NH2 molecule. The concentration-response curves of the tested peptides were to the right and their slopes besides from: galanin(1-15)-OH; galanin(2-15)-NH2; [glycine5]galanin(1-15)-NH2 remained not significantly different from galanin(1-29)-NH2. Hill's coefficient for galanin(1-29)-NH2 is 1.03 indicating an interaction of one galanin(1-29)-NH2 molecule with one receptor, fulfilling criteria of classical receptor theory. For galanin fragments Hill's coefficients are < 1 implying that the rules of classical theory may not apply. Galantide and analogues exhibited a subsequent decrease in potency: [cycloleucine4] galantide > galantide > [homoserine6]galantide > [phenylalnine(4fluor)17] galantide. Galanin(1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I and its analogues contracted the gastric fundus with a decline in strength: galanin(1-13)-[norleucine10]-scyliorhinin-I(3-10) > galanin(1-13)-[phenylalanine(4fluor)7]-scyliorhinin-I > galanin(1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I > galanin(1-13)-[alpha-aminobutyric acid8, norleucine10]-scyliorhinin-I(3-10). They all displayed a greater efficacy than galanin(1-29)-NH2, and the concentration-response curves were slightly to the right, almost parallel to that of galanin(1-29)-NH2. Slopes of the curves were not significantly different from galanin(1-29)-NH2. Hill's coefficient for the galantide, [cycloleucine4]galantide; [homoserine6]galantide; [phenylalanine(4fluor)17]galantide and galanin(1-13)-[phenylalanine(4fluor)7]-scyliorhinin-I are < 1. Hill's coefficients for galanin(1-13)-[norleucine10]-scyliorhinin-I(3-10); galanin(1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I; galanin(1-14)-[alpha-aminobutyric acid8, norleucine10]-scyliorhinin-I(3-10) are > 1. A Hill's coefficient markedly different from 1 might indicate that an activation of more than one type of receptors, negative or positive receptor cooperativity or multiple-step agonist-receptor reaction.

Pharmacological characterization of the contractile effects of galanin (1-29)-NH2, galantide and galanin (1-14)-(alpha-aminobutyric acid8)scyliorhinin-I in the rat gastric fundus.

Porcine galanin (1-29)-NH2, galantide (M15) and galanin (1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I used in concentrations of 300, 1,000 and 3,000 nM respectively caused contractions of rat fundus strips. The contractile responses to galanin(1-29)-NH2 were not modified by atropine (10 microM), guanethidine (10 microM), naloxone (1 microM), a mixture of propranolol (10 microM) and phentolamine (10 microM), indomethacin (10 microM), a mixture of mepyramine (10 microM) and cimetidine (10 microM), saralasin (10 microM), and spantide (100 microM). The effects of M15 and galanin(1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I were significantly decreased by atropine for 36 and 18% and by spantide for 37 and 26% respectively. Indomethacin inhibited the muscle response to M15 without influence on the galanin (1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I-induced action. These results support findings that galanin (1-29)-NH2 contracts rat gastric fundus strips by stimulating specific receptors localized on the surface of smooth muscle cells. M15 and galanin(1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I seem to contract smooth muscles not only by acting at galanin receptors, but by interacting with muscarinic or tachykinin receptors or modulating the release of acetylcholine and substance P. Diltiazem (EC50 825 nM), dantrolene (EC50 30.2 microM) and the phospholipase C inhibitors U-73122 (EC50 549 microM) and U-73343 (EC50 751 microM) lowered the contraction to galanin(1-29)-NH2 in a concentration-dependent manner. These observations imply that though the extracellular Ca2+ influx plays a major role in the action of galanin(1-29)-NH2, the release of Ca2+ ions from the intracellular stores contributes to the response of smooth muscles of galanin(1-29) NH2. Norepinephrine (30, 60, 100 and 300 nM) concentration-dependently reduced the Emax to galanin (1-29)-NH2 and reduced the slopes of the concentration-contraction curves, without a notable change in EC50. Pertussis toxin pre-treatment (10 and 30 mg/kg intravenous [i.v.]), 120 h before the experiment, notably increased the maximal response of the rat gastric fundus to galanin(1-29)-NH2, without a significant change in the properties of the concentration-contraction curves (EC50, slopes). The observations may suggest that pertussis toxin-sensitive GTP-binding proteins are involved in the modulation of the excitatory effects of galanin(1-29)-NH2 in the rat gastric fundus.