Desensitisation of the cardiac response to somatostatin in isolated toad atria but not in whole toads.
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.
Preston
E
E
School of Physiology and Pharmacology, University of New South Wales, Sydney, Australia.
Carlo-Stella
R
R
Courtice
G P
GP
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
D013004:Somatostatin; D001285:Atropine