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Evidence for adenosine A2b receptors in the rat pineal gland

https://doi.org/10.1016/0922-4106(92)90113-AGet rights and content

Abstract

We describe the effects of 5′-N-ethylcarboxamidoadenosine (NECA), a mixed A2a/A2b adenosine receptor agonist and 2-[p-(carboxyethyl)-phenylethylamino]-5′-N-ethylcarboxamidoadenosine (CGS 21680), a selective A2a agonist, on cyclic AMP and N-acetylserotonin synthesis in rat pineal gland. NECA, 1 and 10 μM, increased cyclic AMP by 5- and 25-fold and N-acetylserotonin by 40- and 60-fold respectively, whereas CGS 21680 at the same concentrations was ineffective. These results argue for the presence of adenosine A2b receptors in rat pinealocytes.

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    Citation Excerpt :

    NECA has also been shown to stimulate cyclicAMP production and melatonin secretion in cultured chicken pineal cells (Falcon et al., 1995). The actions of NECA to stimulate N-acetylserotonin and melatonin production in rat pinealocytes has more recently been attributed to activation of adenosine A2B receptors based on the pharmacologic profile of adenosine analogs (Nicholls et al., 1997; Gharib et al., 1992), thus rendering ambiguous evidence for adenosine A2A receptor expression and function in mammalian pineal. Autoradiographic labeling of adenosine A2A receptors in the CNS has typically employed radiolabeled versions of agonists such as 5′-N-ethycarboxamidoadenosine ([3H]NECA) (Alexander and Reddington, 1989), 2-[4-(2-carboxyethy)phenothylamino]-5′-N-ethylcarboxamidoadenosine [3H]CGS21680) (Jarvis et al., 1989; Parkinson and Fredholm, 1990; Johansson and Fredholm, 1995) and 4-aminobenzyl-5′-N-methylcarboxamidoadenosine ([125I]AB-MECA) (Shearman and Weaver, 1997).

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