Activation of 'silent' vasoconstrictive 5-HT1A receptors as a possible mechanism of synergism in angiotensin II and serotonin effect on vascular tone.

It has been shown that the agonist of 5HT1A-receptors 8-OH-DPAT induces contraction of aortic rings in the presence of angiotensin II. This effect is not associated with activation of α-adrenoceptors by 8-OH-DPAT as it is reproduced in the presence of prazosin which completely suppresses the nonspecific vasoconstrictive effect of 8-OH-DPAT via α-adrenoceptors on the aorta incubated without angiotensin II. Synergism in the action of angiotensin II and 8-OH-DPAT is completely preserved after partial desensitization of the receptors of angiotensin II. It has been found that 8-OH-DPAT increases the free cytoplasmic calcium concentration in cultured smooth muscle cells from the rat aorta. The data obtained support the hypothesis about the existence of 'silent' vasoconstrictive 5HT1A-receptors. It has been suggested that activation of these receptors underlies synergism in vasoconstrictive action of serotonin and angiotensin II. [ABSTRACT FROM AUTHOR]

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