Mechanism for cardiac stimulation during hypoxia

¹ Instituto de Farmacología, Escuela de Medicina, Universidad de Chile, Santiago, Chile

In isolated guinea pig atria, hypoxia was induced by bubbling nitrogen through Tyrode solution. A significant increase in both the amplitude and frequency of the contractions occurred, followed by a decrease. Average rate in 11 control atria was 138 ± 9.2 contractions/min and increased during hypoxia by an average value of 12.7 ± 2.3 contractions/min (P < 0.001). Amplitude of shortening increased by an average of 10.5 ± 2.12% (P <0.001). In 19 preparations pretreatment with reserpine blocked the transient stimulant effect of hypoxia on both amplitude and frequency of contractions. Isometric contractions were recorded from 30 isolated cat papillary muscles. The developed isometric tension increased during hypoxia by an average of 17.3 ± 2.8% (P < 0.001). Later, a decrease in contractile force was observed. Pretreatment of the animals with guanethidine and chronic cardiac sympathectomy blocked and pretreatment with reserpine decreased the stimulant effect of hypoxia on the cat papillary muscle. The transient stimulant effect of hypoxia was compared to the staircase phenomenon. Both chronic cardiac sympathectomy and pretreatment with reserpine blocked the increase in force induced by a change in rate from 60 to 120.

Key Words: myocardial stimulant effects of hypoxia • heart and hypoxia • chronic cardiac sympathectomy and hypoxia • hypoxia in isolated heart preparations • reserpine on myocardial hypoxia • guanethidine on myocardial hypoxia • effect of myocardial cathecholamine depletion on heart hypoxia

Submitted on April 22, 1964