Characterization of alpha-1 adrenergic receptors linked to [3H]inositol metabolism in rat cerebral cortex.
The properties of alpha-1 adrenergic receptors in rat cerebral cortex were examined by measuring increases in [3H]inositol metabolism in brain slices. Slices of rat cerebral cortex were incubated in the presence of 0.23 microM [3H]inositol in Krebs-Ringer-bicarbonate buffer containing 10 mM lithium chloride, and the production of water-soluble [3H]inositol phosphates was monitored after extraction and anion-exchange chromatography. Norepinephrine caused a 4- to 6-fold increase in [3H]inositol metabolism in cerebral cortical slices, and this response was blocked much more potently by the alpha-1-selective antagonist prazosin than by the alpha-2-selective antagonist yohimbine. Epinephrine and norepinephrine were both full agonists and stimulated [3H]inositol metabolism to the same extent in this system. The synthetic drugs phenylephrine and methoxamine were both partial agonists at these receptors, with intrinsic activities only 56 to 58% of epinephrine and norepinephrine. A variety of imidazoline and other partial agonists caused no measurable stimulation of [3H]inositol metabolism in this preparation. The response to norepinephrine was completely blocked by alpha adrenergic receptor antagonists with the potency order prazosin greater than BE 2254 greater than indoramin = phentolamine greater than azapetine greater than piperoxan greater than yohimbine. In the absence of calcium, basal [3H]inositol metabolism was increased, but norepinephrine caused the same 5-fold stimulation as in the presence of 2.5 mM CaCl2. The potencies of both antagonists and agonists in inhibiting or activating [3H]inositol metabolism in slices of rat cerebral cortex were highly correlated with their ability to displace the alpha-1 adrenergic receptor selective radioligand [125I]BE 2254 from specific binding sites in membrane preparations of rat cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism*; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D013997:Time Factors; D014018:Tissue Distribution
D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D007294:Inositol; D008729:Methoxamine; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine