Receptor mechanisms for 5-hydroxytryptamine in rabbit arteries

Area of Science:

• Pharmacology
• Vascular Biology
• Neuroscience

Background:

• Vascular actions of biogenic amines like 5-hydroxytryptamine (5-HT) and noradrenaline (NA) are implicated in migraine.
• Previous studies indicated 5-HT and NA act on distinct receptors in rabbit aorta, but ear arteries primarily show alpha-adrenoceptor-mediated responses to 5-HT.

Purpose of the Study:

• To investigate if the lack of specific 5-HT receptors in rabbit ear arteries is unique or common to other distributing arteries.
• To characterize the distribution of 5-HT and alpha-adrenoceptors in various rabbit arterial preparations.

Main Methods:

• Studied agonist-antagonist interactions using pizotifen and phentolamine in rabbit common carotid, external carotid, femoral arteries, and perfused ear arteries.
• Determined pA(2) values to assess receptor pharmacology and competitive antagonism.
• Investigated the mechanism of 5-HT action in external carotid arteries, including the role of alpha-adrenoceptors and cocaine's effect.

Main Results:

• Common carotid and femoral arteries possess both D-type 5-HT receptors and alpha-adrenoceptors, similar to the aorta.
• External carotid and ear arteries lack specific 5-HT receptors; 5-HT's action is mediated via alpha-adrenoceptors.
• 5-HT and NA showed similar potency in common carotid and femoral arteries, but NA was more potent than 5-HT in external carotid and ear arteries.

Conclusions:

• Rabbit common carotid and femoral arteries exhibit distinct 5-HT receptor populations, unlike the ear and external carotid arteries.
• The absence of specific 5-HT receptors in the rabbit extracranial circulation, including the external carotid artery, may limit its utility as a migraine model.