Ontogeny of mammalian cardiac alpha 1-adrenergic receptors.

We find a similar number of alpha 1-adrenergic receptors in fetal mouse hearts of 15--20 day gestational age as compared to adult mouse hearts, and a significantly greater number of alpha 1-adrenoceptors in the early neonate (7--21 days) hearts. Cardiac norepinephrine (NE) concentrations were extremely low in the fetus and increased continuously after birth to reach adult levels at about 21 days of age. The cardiac alpha 1-adrenergic receptors mature prior to the development of a presynaptic component (NE) and show a dramatic increase in density without a change in affinity in the early neonate which then decreases with innervation.