Droxidopa is a medication used to treat symptomatic neurogenic orthostatic hypotension (nOH) caused by dopamine beta-hydroxylase deficiency, non-diabetic autonomic neuropathy and primary autonomic failure caused by conditions such as Parkinson's disease. Droxidopa is a precursor of noradrenaline that is used in the treatment of Parkinsonism. Droxidopa is an orally active synthetic precursor of norepinephrine that increases the deficient supply of norepinephrine in patients with NOH, thereby improving orthostatic blood pressure and alleviating associated symptoms of lightheadedness, dizziness, blurred vision, and syncope through the induction of tachycardia (increased heart rate) and hypertension. Through the beta-1 adrenergic receptor, the heart is stimulated by norepinephrine. Droxidopa crosses the blood-brain barrier where it is converted to norepinephrine via decarboxylation by L-aromatic-amino-acid decarboxylase. Norepinephrine is stored in synaptic storage sites where norepinephrine was already being stored. When the neuron is depolarized, this accumulation of norepinephrine is released into the synapse. The norepinephrine activates Beta-1 adrenergic receptor which is coupled to the G-protein signalling cascade. Activation of the receptor activates the cascade which leads to activated protein kinase through activation of adenylate cyclase. Protein kinase activates calcium channels in the membrane, causing the channels to open and allow Ca2+ into the cell. This causes a high concentration of Ca2+ to be present in the cardiomyocyte which activates activates the ryanodine receptor on the sarcoplasmic reticulum. This transports more Ca2+ into the cytosol. The high concentration of Ca2+ binds to troponin to cause cardiac muscle contractions and therefore, an increased heart rate. Some side effects of using droxidopa may include headache, dizziness, nausea, high blood pressure, and fainting.

Droxidopa B1-Adrenergic Cardiac Muscle Contraction Pathway References