Nursing Pharmacology Chapter 23: Ergot Alkaloids
Peripheral (5 HT2) serotonin receptor peripheral antagonist
Behavioral effects: agonist presynaptic or postsynaptic 5 HT2 effects.
Bromocriptine (Parlodel) and pergolide (Permax) exhibits specificity for pituitary dopamine receptors
Suppression of pituitary prolactin secretion occurs by activating regulatory dopamine receptors
Bromocriptine (Parlodel) and pergolide (Permax) are competitive with dopamine and other dopamine agonists (apomorphine) for these binding sites
Ergotamine (unrelated compounds) are mainly vasoconstricting.
Vasoconstriction: partially blocked by α-adrenergic receptor blocking drugs.
Suggesting vasoconstriction by ergot alkaloids may be due to partial agonist effects at α-adrenergic receptors
α-adrenergic receptor effects
5 HT receptor-mediated effects
Vasoconstriction: differential vascular sensitivity to ergot alkaloids
Most sensitive: cerebral arteriovenous anastomotic vessels to:
Overdosage (ergotamine and related agents)
Severe, long-lasting vasospasm may occur and these vasospasms are:
Not reversible by α-adrenergic receptor blockers (antagonists)
Not reversible by serotonin antagonists
Stimulant action: involves serotonergic, α-adrenergic, and other effects
Uterine sensitivity changes during pregnancy (possibly due to progressively increasing numbers of α1 receptors
Small doses: rhythmic uterine contraction and relaxation
Larger doses: substantial, prolonged contractions
Ergonovine: more uterine selective (agent of choice for obstetric uses)
Bronchiolar smooth muscle: no effect
Gastrointestinal smooth muscle: variable sensitivity exhibiting as nausea, diarrhea, and vomiting which occur with variability associated in part with dosing.
Mechanism of Action:
Activation of gastrointestinal serotonin receptors
CNS emetic centers
Burkhalter, A, Julius, D.J. and Katzung, B. Histamine, Serotonin and the Ergot Alkaloids (Section IV. Drugs with Important Actions on Smooth Muscle), in Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 261-286.; New "Triptans" and Other Drugs for Migraine, The Medical Letter, Vol. 40 (Issue 1037); October 9, 1998