Dopamine Receptors and Fenoldopam Pharmacology

Vocabulary flashcards covering dopamine receptor subtypes (D1-like and D2-like), their tissue-specific physiological actions, and the pharmacology, clinical use, ADRs, and precautions for Fenoldopam.

D1-like Receptors (Signaling Mechanism)

Coupled to $Gs \rightarrow \text{increased adenylyl cyclase} / \text{increased cAMP}$.

D1-like Receptors: Renal Vasculature Effect

Produces vasodilation, resulting in increased renal blood flow and GFR.

D1-like Receptors: Renal Proximal Tubule Effect

Inhibits $NHE3$ and $\text{Na}^+/\text{K}^+\text{-ATPase}$, leading to natriuresis and diuresis.

D1-like Receptors: Juxtaglomerular Cells Effect

Stimulates renin release.

D1-like Receptors: Vascular Smooth Muscle Effect

Causes vasodilation in renal, mesenteric, coronary, and cerebral beds.

D2-like Receptors (Signaling Mechanism)

Coupled to $Gi/Go \rightarrow \text{decreased adenylyl cyclase} / \text{decreased cAMP}$.

D2-like Receptors: Sympathetic Nerve Terminals Effect

Decreases norepinephrine release, resulting in decreased vasoconstriction and decreased sympathetic tone.

D2-like Receptors: Sympathetic Ganglia Effect

Inhibits ganglionic transmission.

D2-like Receptors: GI Smooth Muscle Effect

Decreases motility, relaxes the lower esophageal sphincter, and delays gastric emptying.

D2-like Receptors: Chemoreceptor Trigger Zone Effect

Triggers nausea and vomiting; located in the area postrema which lies outside the blood-brain barrier (BBB).

D2-like Receptors: Adrenal Cortex Effect

Causes tonic inhibition of aldosterone secretion in the zona glomerulosa.

D2-like Receptors: Pancreatic $\beta$ ext{-cells} Effect

Inhibits insulin secretion.

D2-like Receptors: Anterior Pituitary Effect

Inhibits prolactin secretion in lactotrophs.

D2-like Receptors: Carotid Body Effect

Modulates chemoreceptor and ventilatory response.

Fenoldopam (Pharmacological Class)

Selective peripheral dopamine-1 receptor agonist.

Fenoldopam (Clinical Indications)

Used for short-term, IV in-hospital management of severe hypertension and hypertensive emergencies.

Fenoldopam (Vascular & Renal Hemodynamics)

Causes vasodilation in renal (preferential effects on the afferent arteriole), mesenteric, coronary, and peripheral beds, lowering systemic vascular resistance and improving renal perfusion.

Fenoldopam (Drug-Drug Interaction)

$\beta$ ext{-blockers} may potentiate hypotension; blood pressure should be monitored closely.

Fenoldopam (Adverse Drug Reactions)

Includes headache, flushing, nausea, hypotension, dose-dependent reflex tachycardia, hypokalemia, and increased intraocular pressure in patients with glaucoma or ocular hypertension.

Fenoldopam (Precautions & Contraindications)

Not recommended in patients with sulfite allergies; requires continuous monitoring during infusion for hemodynamic stability.