Chen X, Green AS, Macko AR, Yates DT, Kelly AC, Limesand SW. Enhanced insulin secretion responsiveness and islet adrenergic desensitization after chronic norepinephrine suppression is discontinued in fetal sheep. Am J Physiol Endocrinol Metab 306: E58 -E64, 2014. First published November 19, 2013 doi:10.1152/ajpendo.00517.2013.-Intrauterine growth-restricted (IUGR) fetuses experience prolonged hypoxemia, hypoglycemia, and elevated norepinephrine (NE) concentrations, resulting in hypoinsulinemia and -cell dysfunction. Previously, we showed that acute adrenergic blockade revealed enhanced insulin secretion responsiveness in the IUGR fetus. To determine whether chronic exposure to NE alone enhances -cell responsiveness afterward, we continuously infused NE into fetal sheep for 7 days and, after terminating the infusion, evaluated glucose-stimulated insulin secretion (GSIS) and glucose-potentiated arginine-induced insulin secretion (GPAIS). During treatment, NE-infused fetuses had greater (P Ͻ 0.05) plasma NE concentrations and exhibited hyperglycemia (P Ͻ 0.01) and hypoinsulinemia (P Ͻ 0.01) compared with controls. GSIS during the NE infusion was also reduced (P Ͻ 0.05) compared with pretreatment values. GSIS and GPAIS were approximately fourfold greater (P Ͻ 0.01) in NE fetuses 3 h after the 7 days that NE infusion was discontinued compared with age-matched controls or pretreatment GSIS and GPAIS values of NE fetuses. In isolated pancreatic islets from NE fetuses, mRNA concentrations of adrenergic receptor isoforms (␣1D, ␣2A, ␣2C, and 1), G protein subunit-␣i-2, and uncoupling protein 2 were lower (P Ͻ 0.05) compared with controls, but -cell regulatory genes were not different. Our findings indicate that chronic exposure to elevated NE persistently suppresses insulin secretion. After removal, NE fetuses demonstrated a compensatory enhancement in insulin secretion that was associated with adrenergic desensitization and greater stimulus-secretion coupling in pancreatic islets. adrenergic receptor; -cell; intrauterine growth restriction; uncoupling protein 2; catecholamines SMALL-FOR-GESTATIONAL AGE or intrauterine growth-restricted (IUGR) infants are at greater risk for developing metabolic diseases such as type 2 diabetes mellitus (29,40,54). Impaired insulin secretion is associated with a diabetic phenotype indicating that in utero complications can permanently compromise -cell development and function (27,28). A fetal sheep model with placental insufficiency-induced intruterine growth restriction shares many similarities with human IUGR fetuses, such as asymmetric growth, hypoxemia, hypoglycemia, hypoinsulinemia, and hypercatecholaminemia [epinephrine and norepinephrine (NE)] (4, 16,18,22,23,32,41,47). Furthermore, glucose-stimulated insulin secretion (GSIS) and -cell mass are lower in IUGR sheep fetuses, which also replicate features in human IUGR fetuses (34 -36, 41, 53). Several characteristics of the fetal IUGR environment, including hypoglycemia, hypoxemia, and hypercatecholaminemia, are proposed to ...