Pre‐and Postnatal Developmental Changes of Adrenoceptor Subtypes in Rat Brain

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Abstract
β‐Adrenergic receptor subtypes, β1 and β2, were studied during pre‐and postnatal development in the rat brain. [125I]Iodocyanopindolol (6–300 pmol/L) binding assays in the presence of 5‐hydroxytryptamine (0.6–6 μmol/L) were used to measure exclusively β‐adrenergic receptors. In forebrain tissue, saturable and stereoselective binding was detected on gestational day 13. The amount of β‐adrenergic binding increased until postnatal day 23, when adult values were reached. The dissociation constants of [125I]iodocyanopindolol binding remained the same throughout development, as did the affinity of several β‐adrenergic and non‐β‐adrenergic compounds. The proportion of the β2‐adrenergic receptors was determined using the β1‐selective antagonist ICI‐89406 (7–150 nmol/L) and was found to change from 65% in prenatal forebrain tissue to 28% in adulthood. In cerebellum/medulla pons tissue, however, the proportion of β2‐receptor binding (80%) remained unchanged during the whole developmental period.