Effects of sympathomimetics outside cardiovascular system Domina Petric, MD

Activation of β2-receptors in smooth musculature of bronchi Results in bronchodilatation. That is why are β2-agonists very important in asthma treatment. Healthy Liverpool

In the eye muscle dilator pupillae has α-adrenergic receptors: effect is mydriasis. Alfa-receptors stimulators decrease production and increase drain of occular water from anterior eye chamber which causes decrease in the intraocular pressure.

Base of urinary bladder, sphincter urethrae and prostate have α1-receptors that cause these structures to contract and hold urine. Midodrine (α1-receptor agonist) can cause urine retention. α-receptors are very important for normal ejaculation and for cessation of erection after ejaculation.

Salivary glands Salivary glands have adrenoreceptors that regulate secretion of amilase and water. Klonidin is an example of sympathomimetic that causes dry mouth.

Sweat glands Adrenalin causes increased sweating. Activity of apocrine sweat glands on the palms is associated with psychological stress and those glands do not participate in regulation of body temperature.

Metabolic processes Activation of β-receptors in fat tissue increases lipolysis and release of free fatty acids and glycerol in the blood. Fat cells also contain α2-receptors that inhibit lipolysis (by lowering intracellular cAMP). Sympatomimetics increase glycogenolysis in the liver with increased release of glucose in the circulation. High concentration of catecholamines can cause metabolic acidosis. Activation of β2-receptors with endogenous adrenalin induce potassium ions intracellular uptake wich causes decrease of potassium levels in the circulation. This mechanism is a protection from hyperkalemia during physical stress and excercise.

Metabolic processes Activation of beta-receptors in pancreatic islets causes mild increase in insulin secretion, whilst activation of α2-receptors decreases insulin secretion. Plasma glucose level is the most important insulin secretion regulator.

Other hormones secretion Activation of β1-receptors stimulates renin secretion, whilst activation of α2-receptors inhibits renin secretion. Adrenergic receptors modulate parathyroid hormon, calcitonine, thyroxine and gastrin secretion with moderate significance. In high concentration adrenalin causes leukocytosis.

Central nervous system Catecholamines do not pass blood-brain barrier and do not cause central effects, except in the case of high speed infusion. Amphetamine passes through blood-brain barrier and has stimulative effect on the central nervous system.

Katzung, Masters, Trevor. Clinical pharmacology.