Ontogeny of myocardial alpha 1-adrenergic receptor in the rat

The alpha 1-adrenergic specific radioligand [3H]-prazosin and the beta-adrenergic radioligand (-)-[3H]-dihydroalprenolol [(-)-[3H]-DHA] were used to describe the postnatal ontogeny of alpha 1- and beta-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 less than 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 less than 0.01). Affinities (KD) 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 alpha 1-adrenergic receptors is distinct from that of the beta-adrenergic receptor in the rat ventricular myocardium. Possible explanations for this difference are discussed in relation to cardiac sympathetic innervation and cardiac growth.