PRECONTRACTION WITH HISTAMINE AND U46619 UNMASKS A 5-HT1-LIKE RECEPTOR IN RABBIT RENAL-ARTERY

Rabbit renal arteries were virtually unresponsive to 5-hydroxytryptamine (5-HT) and 5-carboxamidotryptamine (5-CT) under control conditions (including the presence of ketanserin 10(-6) M). However, both agents produced prominent contractions over the range 10(-9)-10(-5) M in tissues pre-contracted with threshold concentrations of either histamine or U46619. These responses were considered to be mediated by activation of 5-HT1-like receptors based on the potency order 5-CT less-than-or-equal-to 5-HT and the sensitivity of agonist responses to antagonism by methiothepin (10(-7) M). Pre-contraction with different types of vasoconstrictor can therefore unmask functional 5-HT1-like receptors in rabbit renal artery.