title: Desensitisation of the cardiac response to somatostatin in isolated toad atria but not in whole toads.
abstract: The cardiac slowing measured in response to repeated application of somatostatin (SOM) was compared in an isolated toad sinus venosus/atrial preparation and in a whole, anaesthetised toad, Bufo marinus. Repeated doses of 0.5-1 x 10(-7) M SOM in the organ bath progressively reduced the cardiac response to 25% or less of the response to the first dose given. When preparations were allowed a recovery period of 50-80 min, the response recovered to 51.0 +/- 3.7% of the control. In contrast, the cardiac chronotropic response in anaesthetised toads to repeated intravenous injections of 2 micrograms or 1.2 nmol SOM over 3 h was not changed. Prolonged exposure to SOM (0.1-0.25 mumol/kg/h infusion), for up to 4 h in anaesthetised toads caused no significant reduction either in the cardiac responses to a bolus dose of SOM (0.6 nmol) or nerve released SOM (3 Hz for 2 min) in the presence of atropine. These opposing results suggest that the half-life of a peptide and the method of exposing receptors to a peptide are important factors in receptor desensitisation.
authors.affiliation: School of Physiology and Pharmacology, University of New South Wales, Sydney, Australia.
authors.forename: E
authors.initials: E
authors.lastname: Preston
authors.forename: R
authors.initials: R
authors.lastname: Carlo-Stella
authors.forename: G P
authors.initials: GP
authors.lastname: Courtice
mesh_terms: D000758:Anesthesia; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002024:Bufo marinus; D004558:Electric Stimulation; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D013004:Somatostatin / Q000494:pharmacology*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology
chemical_list: D013004:Somatostatin; D001285:Atropine