Chintamaneni K, Bruder ED, Raff H. Effects of age on ACTH, corticosterone, glucose, insulin, and mRNA levels during intermittent hypoxia in the neonatal rat. Am J Physiol Regul Integr Comp Physiol 304: R782-R789, 2013. First published March 13, 2013 doi:10.1152/ajpregu.00073.2013.-Apnea, the temporary cessation of respiratory airflow, is a common cause of intermittent hypoxia (IH) in premature infants. We hypothesized that IH elicits a stress response and alters glucose homeostasis in the neonatal rat. Rat pups were studied on postnatal day (PD) 2, 8, 10, 12, and 14. Pups were exposed to normoxia (control) or six cycles consisting of 30-s exposures to hypoxia (FIO 2 ϭ 3%) over a 60-min period. Blood samples were obtained at baseline, after the third cycle (ϳ30 min), and after the sixth cycle (ϳ60 min). Tissue samples were collected following the sixth cycle. Plasma ACTH, corticosterone, glucose, and insulin were analyzed at all ages. Hypothalamic, pituitary, and adrenal mRNA expression was evaluated by quantitative PCR in PD2, PD8, and PD12 pups. Exposure to IH elicited significant increases in plasma ACTH and corticosterone at all ages studied. The largest increase in corticosterone occurred in PD2 pups, despite only a very small increase in plasma ACTH. This ACTH-independent increase in corticosterone in PD2 pups was associated with increases in adrenal Ldlr and Star mRNA expression. Additionally, IH caused hyperglycemia and hyperinsulinemia at all ages. We conclude that IH elicits a significant pituitary-adrenal response and significantly alters glucose homeostasis. Furthermore, the quantitative and qualitative characteristics of these responses depend on developmental age.hypothalamic-pituitary-adrenal axis; newborn; anoxia; apnea; adrenal cortex APNEA, the cessation of respiratory airflow, causes hypoxemia and bradycardia in the neonate (27). Apnea is the most common cause of hypoxia in neonates, particularly with prematurity, and is usually due to immature respiratory control systems (20). Incomplete respiratory maturation may involve deficits in neural respiratory control, central and peripheral chemoreceptors, or coordination of the upper airway muscles (20). It has previously been shown that about half of babies born prematurely (30 -31 wk of gestational age) may experience bouts of apnea (27).We have shown that acute, continuous hypoxia in the neonatal rat, a model of cardiopulmonary disease of prematurity, is a metabolic challenge that elicits a stress response from the hypothalamic-pituitary-adrenal (HPA) axis (3). This experimental model also results in bradycardia, alterations in glucose homeostasis, and a dramatic decrease in body temperature (3, 4, 11).The current study used intermittent hypoxia (IH) as an established model of apnea-induced hypoxia (21). IH mimics spontaneous, short duration episodes of hypoxia that occur during apnea in the neonate. A widely used definition of apnea specifies a 15-to 20-s cessation of breathing, a decrease in oxygen saturation to Ͻ80%, and a refractory period ...

Intermittent hypoxia (IH) is an animal model of apnea-induced hypoxia, a common stressor in the premature neonate. Neonatal stressors may have long-term programming effects in the adult. We hypothesized that neonatal exposure to IH leads to significant changes in basal and stress-induced hypothalamic-pituitary-adrenal (HPA) axis function in the adult male rat. Rat pups were exposed to normoxia (control) or 6 approximately 30-second cycles of IH (5% or 10% inspired O₂) daily on postnatal days 2-6. At approximately 100 days of age, we assessed the diurnal rhythm of plasma corticosterone and stress-induced plasma ACTH and corticosterone responses, as well as mRNA expression of pertinent genes within the HPA axis. Basal diurnal rhythm of plasma corticosterone concentrations in the adult rat were not affected by prior exposure to neonatal IH. Adults exposed to 10% IH as neonates exhibited an augmented peak ACTH response and a prolonged corticosterone response to restraint stress; however, HPA axis responses to insulin-induced hypoglycemia were not augmented in adults exposed to neonatal IH. Pituitary Pomc, Crhr1, Nr3c1, Nr3c2, Avpr1b, and Hif1a mRNA expression was decreased in adults exposed to neonatal 10% IH. Expression of pertinent hypothalamic and adrenal mRNAs was not affected by neonatal IH. We conclude that exposure to neonatal 10% IH programs the adult HPA axis to hyperrespond to acute stimuli in a stressor-specific manner.

Apnea is the temporary cessation of respiratory airflow and is a common cause of intermittent hypoxia (IH) in the premature infant. We hypothesized that IH elicits a stress response in the neonate and alters mRNA expression for critical proteins involved in adrenocortical function. Postnatal day 2 (PD2), PD8, and PD12 rat pups were exposed to 6 cycles of 30 sec of IH (3% O2) over 60 min, and blood samples were obtained at the 3rd (30 min) and 6th (60 min) cycle. Plasma ACTH and corticosterone increased significantly in PD8 and PD12 pups exposed to IH. Interestingly, plasma corticosterone increased in the PD2 pups even though plasma ACTH remained unchanged. Expression of adrenal StAR and Ldlr mRNA increased in PD2 pups exposed to IH, but were not affected in PD8 or PD12 pups. Expression of adrenal Mc2R mRNA decreased in all age groups exposed to IH. IH resulted in profound bradycardia and a decrease in body temperature. We conclude that IH in PD2 pups elicits an adrenocortical response not mediated by ACTH, but associated with an increase in the expression of specific adrenal mRNAs. In PD8 and PD12 pups, the adrenal response is ACTH dependent like an adult. Using the PD2 rat as a model of extreme prematurity in the human, we suggest the existence of a unique non‐ACTH controller of adrenal function during IH.

Apnea due to immature respiratory control is a common cause of neonatal intermittent hypoxia (IH). We hypothesized that IH disrupts glucose homeostasis and is a metabolic stressor. Rats at postnatal days (PD) 2–3, 7–8, or 11–12 were exposed to 6 @ 30‐sec cycles of IH (3% O2) over 1 hr. An additional group of PD7‐8 pups underwent IH for 3 cycles over 0.5 hr, but were pretreated (on PD3, 5, and 6) with guanethidine (chemical sympathectomy). In PD2‐3 rats, plasma glucose, insulin, and C‐peptide were increased at the 6th cycle of IH. In PD7‐8 rats, plasma glucose, insulin, and C‐peptide increased by the 3rd cycle, but by the 6th cycle, glucose had returned to baseline. PD11‐12 pups experienced a similar increase in plasma glucose, but a much larger increase in insulin and C‐peptide compared to PD7‐8. IH caused bradycardia and a decrease in body temperature. Pretreatment with guanethidine in PD7‐8 rats augmented the increase in insulin and C‐peptide; heart rate at baseline, and heart rate and body temperature at their nadirs during IH were lower after guanethidine pretreatment. We conclude that IH alters glucose homeostasis and induces bradycardia in neonates. The sympathetic nervous system restrains the insulin response and maintains heart rate during IH in the neonate.