A sensitive method for the assay of oxytocin in the circulating blood

Different responses of the isolated canine coronary artery superfused with blood or Krebs-Henseleit solution

Responses of ring segments of the isolated canine coronary artery superfused with arterial blood from a donor dog were compared with responses of segments superfused with Krebs-Henseleit (K-H) solution. KC1 (1 - 30 mg) caused contraction in a dose-dependent manner both in K-H solution- and in blood-superfused preparation. However, CaCl2 (1 - 100 mg) and nifedipine (0.1 - 30 micrograms) contracted and relaxed, respectively, only blood-superfused preparation but not K-H solution-superfused one. These results show that even in the same region of the coronary artery, different superfusates result in different responses to contracting or relaxing agents. This difference may be explained by the idea that Ca2+-channels are activated and endow basal tension in blood-superfused preparations, but not in K-H solution-superfused ones.