Developmental Neuro- and Cardiotoxicity of TerbutalineEPA Grant Number: U916179
Title: Developmental Neuro- and Cardiotoxicity of Terbutaline
Investigators: Garofolo, Melissa C.
Institution: Duke University
EPA Project Officer: Zambrana, Jose
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $92,541
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Academic Fellowships , Fellowship - Toxicology , Health Effects
Beta-2-adrenergic receptor (B2AR) agonists, such as terbutaline, are widely used to arrest preterm labor, despite the fact that this is not on the Food and Drug Administration's list of approved uses. B2AR agonists cross the placenta to stimulate fetal beta-andrenergic receptors (BARs) that control neural and cardiac cell differentiation. The objective of this research is to determine if terbutaline exposure causes developmental damage, which may precondition the organism to enhance the subsequent vulnerability to environmental toxins; in this case, to be tested with the organophosphate insecticide, chlorpyrifos (CPF). The combination of terbutaline and CPF was chosen because of the widespread exposure of the human population to both agents: approximately 20 percent of all U.S. births involve the management of preterm labor, whereas exposure to CPF is virtually ubiquitous. Separately, these two agents ultimately converge on the development of cholinergic neurotransmission, so that the two together may have an augmented, adverse effect.
We conducted experiments using biomarkers that characterize cell proliferation, cell number, and neural cell types in each case examining the impact of terbutaline administered to developing rats in three different exposure periods corresponding to second-to-third trimester human fetal development. Terbutaline given on gestational days 17-20 decreased cell numbers (DNA content) in the fetal brain and liver. Early postnatal exposure (postnatal days 2-5) reduced DNA synthesis in early developing brain regions of females and decreased DNA content in male cerebellum. Later treatment (postnatal days 11-14) still targeted the cerebellum, evoking a decrease in DNA synthesis in both sexes. Many of these effects resemble those reported for CPF in earlier work. In addition, in the developing heart, we examined the specific developmental "crosstalk" between BARs (the target for terbutaline) and M2-acetylcholine receptors, which are stimulated by acetylcholine, the neurotransmitter whose activity is increased by CPF. Both terbutaline and CPF separately reduced the expression of cardiac M2-receptors.
Our current task is to explore the concept that prenatal exposure to commonly used drugs may precondition the organism to enhanced subsequent vulnerability to environmental toxins. We have constructed a model where developing rats are exposed first to terbutaline during the developmental phase (postnatal days 1-4) that mostly closely corresponds to the early third trimester of human development, the period in which terbutaline is most commonly used to arrest preterm labor. On postnatal days 11-14, a period of peak sensitivity of the developing brain to damage caused by CPF, the animals are given a CPF regimen that lies below the threshold for toxicity. We currently are examining biomarkers for brain cell differentiation and development, as well as indices of cholinergic synaptic function in brain areas targeted by CPF, and that are involved in critical functions in learning and memory. This research project will ascertain if the therapy of preterm labor creates a population of individuals who are sensitized to environmental cholinergic insults, such as exposure to pesticides (such as CPF) that act through inhibition of cholinesterase.