Ontogeny of Myocardial α(1)-Adrenergic Receptor in the Rat

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Abstract
The ai-adrenergic specific radioligand [3H]-prazosin and the ß-adrenergic radioligand (-)-[3H]-dihydroalprenolol [(-)-[3H]-DHA] were used to describe the postnatal ontogeny of α(1)- and β-adrenergic receptors in particulate fractions of rat ventricular myocardium. The number of [3H]-prazosin binding sites increased 4- to 5-fold during the first 15 days of age from 35 ± 9 to 163 ± 5 fmol • mg^-1 protein (p < 0.01), and thereafter decreased progressively with age, reaching 83 ± 5 fmol • mg^-1 protein in the adult myocardium. (-)-[3H]-DHA binding to the same tissue decreased progressively at 1 day of age from 61 ± 6 in the newborn to 37 ± 4 fmol • mg-1 protein in the adult (p < 0.01). Affinities (K(D)) for [3H]-prazosin or (-)-[3H]-DHA were approximately 0.13 and 1.8 nM, respectively, and did not change with advancing age. We conclude that the postnatal development of the α(1)-adrenergic receptors is distinct from that of the β-adrenergic receptor in the rat ventricular myocardium. Possible explanations for this difference are discussed in relation to cardiac sympathetic innervation and cardiac growth.