MECHANISM FOR CARDIAC STIMULATION DURING HYPOXIA

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.

PARTICIPATION OF SYMPATHOADRENAL SYSTEM IN ENDOTOXIN SHOCK

Experiments have been carried out on dogs, cats, and monkeys to determine the role of the sympathoadrenal system in endotoxin shock. It was found that hepatosplanchnic pooling in the dog after endotoxin is not dependent on an intact nerve supply to the abdominal viscera or the presence of the adrenals. Splanchnic denervation and adrenalectomy did not prevent portal hypertension, systemic hypotension, or intestinal hemorrhagic necrosis after endotoxin in the dog. Increases in foreleg vascular resistance and leg weight were found to be independent of the presence of the adrenals. Humorally induced vasoconstriction after endotoxin in cat and monkey preparations was found to be minimal. Hemoconcentration did not occur and net losses in weight were observed in cat and monkey perfused foreleg preparations. No evidence was obtained assigning detrimental roles to the sympathoadrenal system in the dog, cat, or monkey in this form of shock. Findings underscore the view that the primary mechanisms causing death from endotoxin may vary with the species.