Differential ontogeny of alpha 1-adrenergic and cholinergic receptor sites in the atria and ventricles of the inbred Dahl hypertension-sensitive (S/JR) and -resistant (R/JR) rat

The ontogeny of atrial and ventricular alpha 1-adrenergic and muscarinic cholinergic receptor sites was investigated in inbred Dahl hypertension-sensitive (S/JR) and -resistant (R/JR) rats between 5 and 150 days of age. The density of sites in both cardiac regions was generally greater in the neonate than mature rat. A marked proliferation of sites was observed in neonatal and young adult rats that occurred in the following order: ventricular cholinoceptors----ventricular adrenoceptors----atrial cholinoceptors----atrial adrenoceptors. The density of ventricular adrenoceptors was greater in the S/JR rat than the R/JR rat at 5 days of age. At 150 days of age, the density of sites was less in the S/JR rat than the age-matched R/JR rat or the normotensive 50-day-old S/JR rat. The development of atrial adrenoceptors was similar between the strains, regardless of the blood pressure. The density of ventricular cholinergic receptors was greater in the S/JR strain at 5 and 15 days of age. However, the density of atrial cholinergic sites was consistently greater in the S/JR strain throughout development. The results of this study suggest that: (1) significant prenatal receptor development occurs in the heart; (2) receptor development may precede the functional maturation of postganglionic autonomic efferents; and (3) distinguishing differences in the regional density of alpha 1-adrenergic and muscarinic cholinergic binding sites are present between S/JR and R/JR rats at much earlier points in development than previously shown.