Glucagon exerts a direct positive chronotropic effect on the SA node that is more pronounced than its inotropic effect and is independent of beta-adrenergic receptors.
Caution against clinical extrapolation in humans; leaves open direct SA node effects for translational studies.
Effects of glucagon on SA node pacemaker activity and atrial contractility were investigated in isolated canine atrium preparations which were perfused with blood led from a support dog and suspended in a bath. Glucagon at a dose from 0.1 to 10 mug was injected into the sinus node artery, which caused a marked positive chronotropic but a less inotropic effect. The positive inotropic response was simulated by atrial acceleration produced by atrial pacing. Glucagon effects were not influenced by treatment with an adrenergic beta-blocking agent, alprenolol to SQ 11725, which blocked effects of norepinephrine. It was concluded that glucagon is more effective on pacemaker activity than on atrial contractile force, and glucagon effects may not be mediated by an adrenergic beta-mechanism.
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Shigetoshi Chiba (1975) studied this question.
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