Shape Change of Blood Platelets—a Model for Cerebral 5‐hydroxytryptamine Receptors?

Abstract

In blood platelets of rabbits isolated by a stractan gradient and incubated in a protein‐poor medium, tryptamine, 5‐hydroxytryptamine (5‐HT) and derivatives, quipazine and mescaline caused a shape change. This shape change was inhibited by low concentrations of methysergide. The most potent antagonists of the 5‐HT‐induced shape change included ergoline derivatives and neuroleptic drugs, which showed high stereoselectivity. (‐f)‐Lysergic acid diethylamide ((+)‐LSD), psilocine and some N',N′‐dimethylated tryptamines acted as mixed agonist‐antagonists. The compounds found to be agonists or mixed agonist‐antagonists on platelets have previously been shown to act also as 5‐HT agonists in the central nervous system (CNS). With regard to 5‐HT antagonists, the 5‐HT receptors of platelets reacted differently from those described earlier in brain areas with dense 5‐hydroxytryptaminergic innervation, but showed similarities to 5‐HT receptors investigated previously in spinal cord, cerebral cortex and possibly reticular formation. It is concluded that platelets may be considered with caution as models for some, but not for all, 5‐HT receptors in the CNS.

Rapid intracellular release of calcium in human platelets by stimulation of 5‐HT2‐receptors

“…However, this increase was rather slow (maximum attained after 30 min) and was only seen in the presence of extracellular Ca2+ (Affoter et al, 1984). In contrast, the 5-HT-induced shape change reaction is a rapid event which also occurs in a Ca2+-poor medium containing disodium edetate (EDTA) (Born et at., 1978;Graf & Pletscher, 1979;Affolter et al, 1984). Using a slightly modified quin-2-method we have shown in the present experiments that in platelets, stimulation of the 5-HT2-receptor causes an elevation of intracellular free Ca2+ as rapid as the shape change reaction, even in a Ca2+-poor medium.…”

Serotonin-Induced Platelet Intracellular Ca2+ Response in Patients with Anorexia Nervosa

“…Other 5-HT receptors are mediated by adenylyl cyclase [23,46] or ion channels or the mediating effector system is still unknown. Graf and Pletscher [20] found that the 5-HT receptor of platelets resembles that of nerve cells. Further studies characterized the 5-HT 2A receptor binding in platelets [18,38,43] .…”

Platelet release reaction and aggregation induced by canatoxin, a convulsant protein: evidence for the involvement of the platelet lipoxygenase pathway

“…Among several other similarities, it has been demonstrated that the platelet's release reaction is physiologically equivalent to the synaptosome's secretion of neurotransmitters (Stormorken, 1969). In addition, both preparations share common agonists and receptor properties (Boullin & Glenton, 1978;Graf & Pletscher, 1979;Brodde, et al, 1983).…”