AIM Oxytocin produces concentration-dependent relaxation of isolated isthmus and ampulla of human oviduct precontracted by histamine. The aim of our study was to investigate whether this oxytocin effect was specific and by which receptors it was mediated. METHODS We investigated effects of oxytocin and its antagonists on isolated isthmus and ampulla of the uterine tubes from 20 women who underwent surgery for uterine fibroids. Selective vasopressin and oxytocin antagonists were used to treat isolated preparations of the tubes. RESULTS In a concentration-dependent manner, oxytocin enhanced spontaneous relaxation of both isthmus (EC50=1.23+/-0.03 x 10(-7) mol/L) and ampulla (EC50=1.04+/-0.26 x 10(-7) mol/L) precontracted by histamine. Neither predominantly selective vasopressin V1 receptor antagonist, [beta-mercapto-beta,beta-cyclopentamethylene-propionyl1,0-metyr2,arg8]-vasopressin (1.0 x 10(-9)-1.0 x 10(-7) mol/L), nor predominantly selective vasopressin V2 antagonist, [1-(beta-mercapto-beta,beta-cyclopentamethylene-propionic acid), 2-D-isoleucine, 4-D-isoleucine]-arginine-vasopressin (1.0 x 10(-9)-1.0 x 10(-7) mol/L) affected significantly the relaxation of isolated ampulla and isthmus produced by oxytocin. On the other hand, [Deamino-Cys1,D-Tyr (Et)2, Thr4, Orn8]-oxytocin, a selective blocker of oxytocin receptors, produced in a concentration-dependent manner (6.7 x 10(-9) mol/L, 2.0 x 10(-8) mol/L, and 6.7 x 10(-7) mol/L) significant shifts of the concentration-response curves of relaxation for oxytocin to the right in isolated preparations of both the ampulla and the isthmus. The values of pA2 for [Deamino-Cys1,D-Tyr (Et)2, Thr4, Orn8]-oxytocin calculated from constrained Schilds plot were 8.08+/-1.53 for ampulla and 7.94+/-0.67 for isthmus. CONCLUSION Oxytocin relaxes smooth muscles in human oviduct through a specific effect on oxytocin receptors.

Both excitatory and inhibitory intrinsic neurons could be found within the gastric wall, both of them receiving innervation from vagal fibres and being sensitive to nicotine. The effects of three nicotine receptor agonists, nicotine, tetramethylammonium (TMA) and 1,1-dimethyl-4-phenylpiperazinium (DMPP), on contractile activity of preparations isolated from feline and human gastric corpus wall were investigated. While DMPP (3.5x10(-8) to 5.9x10(-4)m) did not affect either spontaneous contractions or basal tension of isolated preparations from both species, TMA produced concentration-dependent tonic contractions of both circular and longitudinal isolated preparations from human (3.66x10(-5) to 5.10x10(-3)m) and feline (6. 1x10(-7) to 2.1x10(-3)m) stomach. On the other hand, nicotine (4. 1x10(-8) to 7.0x10(-4)m) produced concentration-dependent relaxation of only circular isolated preparations from feline gastric corpus. The effect of nicotine was sensitive to mecamylamine, and not to pancuronium, while the effect of TMA was sensitive to both mecamylamine and pancuronium. Although in our experiments DMPP had no effect, its excitatory action on gastric intrinsic neurons through the hexamethonium-insensitive pathway had already been described. The results of our study suggest that two different types of ganglion nicotine receptor exist together within the wall of feline stomach: (1) type N(N1)which is involved in relaxation and is sensitive only to nicotine and mecamylamine, and not to DMPP, TMA and pancuronium; (2) and type N(N2)which is involved in contraction of gastric muscle and sensitive to DMPP, TMA, mecamylamine and pancuronium, and not to nicotine.