Effect of Insulin on the Myocardium of Active, Hibernating, and Awakened Ground Squirrel Citellus undulatus

摘要

The effect of insulin (from 0.1 to 100 nM) on the papillary muscle of the right ventricle of the heart taken from the ground squirrel Citellus undulatus was studied. In active animals of the spring-summer, autumn, and winter groups, the muscle contractility was reduced in response to the following hormone concentrations: 1 nM, from 0.1 to 0.5 nM, and 10 nM, respectively. A decrease in the amplitude of the papillary muscle contraction was initiated 9 to 12 min after insulin application and reached a maximum in 20 min. The largest negative inotropic effect (about 30% of the control level) observed at the insulin concentration of 50 nM was similar in all groups of active animals. In several cases (predominantly in the spring-summer animal group), insulin added at low concentrations (from 0.1 to 0.5 nM) caused a short-term increase in the muscle contractile activity (by 10-15% over the control level, for 5 to 15 min), which declined to the control level in 20 min after the hormone application. During deep animal hibernation, and during arousal from hibernation (at 3 to 20 ℃ heart temperature) insulin had no significant effect on the heart contractility. At a heart temperature from 26 to 31 ℃, insulin produced only a positive inotropic effect at all concentrations studied. The threshold hormone doses ranged from 0.1 to 0.5 nM; 10 nM insulin caused the maximal effect (about 20% over the control level), whereas at higher concentration (up to 50 nM) the amplitude of contraction either remained unchanged or was gradually reduced to the control level. At a heart temperature from 32 to 36 ℃, the papillary muscle response to insulin was similar to that observed in active animals, who exhibited predominantly the negative inotropic effect. The mechanisms of the insulin effect on the myocardium of the hibernants and those underlying the changes in cell sensitivity to the hormone are discussed.