[The inotropic and bathmotropic effects of beta stimulation: a study comparing dobutamine and dopamine on the guinea-pig papillary muscle in isotonic contraction].

The study was aimed at comparing the effects of dobutamine (dob) and dopamine (dop) on isotonic contraction and rhythmicity of isolated guinea-pig papillary muscles (in oxygenated Tyrode at 37 degrees C), by taking into account: 1) the rate of stimulation (50% above the diastolic threshold) at 5 fixed periods: (RR: 1600, 1200, 1000, 800 and 400 ms); 2) 7 log concentrations (logC) of the index amine (from 10(-9) to 10(-3) M). To this end, a dose-relation protocol which explored the effects of all 5 RR and 7 logC was designed and 15 adult female Guinea-pigs (250 to 350 g) were randomized to either the dob (n = 8) or the dop (n = 7) arm. This enabled a total of 525 sets of data to be analyzed: in 38 sets (7.2%) premature contractions (CP) were coded. CP were sustained (freq: > 3) in 25 of these latter 38 sets (4.8%). Compared to the basal state, the amplitude (AMP%) and the log of percent amplitude (logAMP%) and time to peak (TP%) changes of the isotonic (Gould transducer) twitch were calculated along with the log of this latter variable (logTP%). AMP%, log AMP%, TP% and logTP% were linearly correlated with logC at all RR. In the range 1600-400 RR, for both amines, significant linear correlations (magnitude of 0.15 > r < magnitude of 0.70, 0.001 > p < 0.022) were seen for plots of AMP%, logAMP% and TP%:steeper correlations were observed for dop. This was confirmed in multivariate analysis (BMDP-9R) whereby AMP%, logAMP%, TP%, logTP%, CP, and freqCP were dependent variables and coded variables were included to either define the type of treatment (dop versus dob) or logC. In these analyses, logC (t > 11) and dop (t > magnitude of 3) might be used to explain (0.28 > r2 < 0.42, 0.00001 > p < 0.0025) AMP% and logAMP%, meaning that a different inotropic (isotonic) efficacy exists between these 2 amines, at all logC. On the other hand, when CP and freqCP were coded, explanatory variables were AMP% and logAMP% (4.86 > t < 6.95, 0.06 > r2 < 0.09, p < 0.00001), but not the variable used to code the type of treatment (dob versus dop).(ABSTRACT TRUNCATED AT 400 WORDS)