https://www.cell.com/trends/pharmacological-sciences/pdf/S0165-6147(97)01043-2.pdf

The 5-HT7 receptor: orphan found

Studies on hemorrhagic and endotoxin shock in relation to vasomotor changes and endogenous circulating epinephrine, norepinephrine and serotonin.

1. The responses of individual pial arterioles and small arteries to perivascular injections of 5-hydroxytryptamine were studied in anaesthetized cats.

2. Pial arteriolar calibre was measured by a television image-splitting technique.

3. At normotension, the average response of pial vessels was dilatatory at injected 5-hydroxytryptamine concentrations between 10−10 and 10−4 M.

4. These pial vascular changes were, however, dependent upon the resting vessel calibre: those arterioles < 70 μm dilated universally, whereas small arteries ≥ 200 μm in resting diameter tended to constrict in response to 5-hydroxytryptamine.

5. The 5-hydroxytryptamine-induced dilatation of pial arterioles < 70 μm in resting calibre was directly dependent on mean arterial pressure, although no such relationship was observed with the larger cerebral vessels.

6. It is concluded that the specific cerebrovascular actions of 5-hydroxytryptamine are largely tone-dependent. The greater the resting tone of a pial arteriole, then the greater will be the tendency of that vessel to dilate in response to 5-hydroxytryptamine, and vice versa.

7. The direct vascular actions of 5-hydroxytryptamine are in contradistinction to the observed changes in cerebral tissue perfusion and it would therefore appear that the effects of this amine on cerebral metabolism and neuronal activity outweigh its cerebrovascular actions under physiological conditions.

Effects of 5‐hydrooxytryptamine on pial arteriolar calibre in anaesthetized cats

Analysis of the cardiovascular effects of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (Catapres).

MIGRAINE, A FAMILIAL disorder characterized by recurrent attacks of usually unilateral headache, classically presents itself in two main phases. The initial pre-headache phase comprises of certain non-painful sensory symptoms usually attributed to intracerebral vasoconstriction.1-3 The initial vasoconstriction is followed, during the headache period, by an excessive dilatation of the temporal, occipital and middle meningeal arteries (all of which are the branches of the external carotid artery). The latter phenomenon appears to be the chief source of pain in migraine.2 It is also known that the amplitude of pulsations and the blood flow in these extracranial vessels increases on the affected side during migraine headache.4,5 The exact etiology of the above changes is still uncertain. Nevertheless, certain recent findings implicate the involvement of one or more of the biogenic vasoneuroactive substances, such as 5-HT (serotonin), bradykinin and the similar peptides, histamine, substance P, acetylcholine and catecholamines, in the pathophysiology of the vascular pain.6-10

The effects of antimigraine drugs on the vascular responses by‐5‐hydroxytryptamine and related biogenic substances on the external carotid bed of dogs: possible pharmacological implications to their antimigraine action

Locally injected epinephrine and norepinephrine elevate dog foreleg total vascular resistance primarily through small vessel constriction Serotonin does not significantly change total resistance, constricts large arteries and veins and dilates small vessels

Effect of Epinephrine, Norepinephrine and Serotonin Upon Systemic Small and Large Vessel Resistance

In the dog foreleg, serotonin antagonizes extremes of vascular tone induced by neurogenic means. It produces net dilatation when the bed is constricted and net constriction when the bed is dilated. This bidirectional response derives ultimately from the facts that changes in nervous activity change calibers of small vessels without greatly altering calibers of large vessels, and that serotonin produces small vessel dilatation at the same time that it constricts large vessels. When small vessels are already neurogenically dilated, serotonin cannot dilate them further, but continues to constrict large vessels. Thus, the net effect is constriction. When small vessels are highly constricted, serotonin dilates small vessels more than it constricts large vessels. The net effect is dilatation. The study also indicates why it is more difficult to demonstrate a similar antagonism when tone is varied by humoral means.

The influence of tone upon responses of small and large vessels to serotonin.

Direct resistance measurements in the foreleg of the anesthetized dog show that the rise in total resistance following reduction of air temperature is due predominately to small vessel constriction and is based upon at least three different mechanisms. The large arteries and veins also constrict and evidence is presented which suggests that the venous and possibly the arterial resistance responses are predominately due to changing levels of circulating epinephrine, norepinephrine or both.

Effect of Change in Air Temperature Upon Systemic Small and Large Vessel Resistance

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Effect of Epinephrine, Norepinephrine and Serotonin Upon Systemic Small and Large Vessel Resistance

The influence of tone upon responses of small and large vessels to serotonin.

Effect of Change in Air Temperature Upon Systemic Small and Large Vessel Resistance