Presynaptic neural projections are thought to participate in the maturation of postsynaptic sensitivity to neurotransmitters. In the current study, the effects of sympathectomy with 6-hydroxydopamine on the ontogeny of the linkage of beta-adrenergic receptors to cardiac growth and heart rate control in the rat have been examined. Destruction of sympathetic projections at birth compromised the ability of beta-receptor stimulation to evoke cardiac hypertrophy, a defect which persisted into young adulthood. The chronotropic response to beta-receptor activation, assessed by acute challenge with a submaximally-effective dose of isoproterenol, also exhibited a slowed development, but did eventually achieve normal sensitivity. In contrast, neonatal sympathectomy had only minor effects on resting heart rate, basal heart rate (the intrinsic rate in the absence of autonomic input) or maximal heart rate; these animals also showed beta-receptor desensitization of chronotropic action in response to chronic isoproterenol treatment. (Copyright (c) Oxford University Press 1989.)