Evidence against prostaglandin modulation of cardioaccelerator nerve activity in the anesthetized dog

The hypothesis that prostaglandins have a modulatory role in adrenergic neurotransmitter release was tested in the anesthetized dog. Inhibition of prostaglandin synthesis with indomethacin (10 mg/kg, i.v.) did not alter positive chronotropic responses to cardioaccelerator nerve stimulation or blood pressure responses to exogenous norepinephrine. In the presence of indomethacin, infusions of PGE₂ (0.01 and 0.1 μg kg⁻¹ min⁻¹) also failed to influence the responses to cardioaccelerator nerve stimulation although the blood pressure responses to exogenous norepinephrine were reduced in a dose-related manner. It was concluded that endogenous prostaglandins and exogenous PGE₂, the purported physiological inhibitor of neurotransmitter release in cardiac tissue, do not play a role in modulating chronotropic responses during cardioaccelerator nerve stimulation in the anesthetized dog.