title: Hydro-osmotic activity of "carba' analogues of oxytocin and [8-arginine] vasopressin on frog (Rana esculenta) bladder.
abstract: The biological potency of neurohypophysial hormone analogues in stimulating water transport across the frog bladder (Rana esculenta) was estimated from the pD2 (negative logarithm of the peptide concentration eliciting 50% of its maximal hydroosmotic effect) and from the maximal response. Most analogues elicited maximal responses similar to those of the natural hormones. Both replacement of sulfur by a methylene group in the disulfide bridge and omission of the terminal amino group in oxytocin reduced hydroosmotic activity; carba substitution in oxytocin led to a greater drop in pD2 than the same substitution in deamino-oxytocin. On the contrary, the effects of substituting phenylalanine for tyrosine and of omitting the amino group were almost additive. Elimination of the carboxyl-terminal tripeptide sequence considerably reduced hydroosmotic potency; pressinamide was inactive up to 3 mug/ml. The highly potent antidiuretic peptides, deamino-[D-Arg8]vasopressin and deamino-6-carba-]D-Arg8]vasopressin, were weakly active in the hydroosmotic assay.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001127:Arginine Vasopressin / Q000031:analogs & derivatives / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects*; D066298:In Vitro Techniques; D010121:Oxytocin / Q000031:analogs & derivatives / Q000494:pharmacology*; D010443:Peptide Chain Termination, Translational; D011893:Rana esculenta; D001743:Urinary Bladder / Q000187:drug effects*; D014667:Vasopressins / Q000031:analogs & derivatives*
chemical_list: D014667:Vasopressins; D001127:Arginine Vasopressin; D010121:Oxytocin