Adrenocortical sensitivity to ACTH in neonatal rats: correlation of corticosterone responses and adrenal cAMP content

Abstract

A coordinated hypothalamic-pituitary-adrenal axis response is important for the survival of newborns during stress. We have previously shown that prior to postnatal day (PD) 5, neonatal rats exposed to hypoxia (one of the most common stressors effecting premature neonates) exhibit a large corticosterone response with a minimal increase in immunoassayable plasma ACTH and without a detectable increase in adrenal cAMP content (the critical second messenger). To explore the phenomenon of ACTH-stimulated steroidogenesis in the neonate, we investigated the adrenal response to exogenous ACTH in the normoxic neonatal rat. Rat pups at PD2 and PD8 were injected intraperitoneally with porcine ACTH at low, moderate, or high doses (1, 4, or 20 μg/kg body wt). Trunk blood and whole adrenal glands were collected at baseline (before injection) and 15, 30, or 60 min after the injection. ACTH stimulated corticosterone release in PD2 and PD8 pups. In PD2 pups, plasma corticosterone at baseline and during the response to ACTH injection was greater than values measured in PD8 pups, despite lower adrenal cAMP content in PD2 pups. Specifically, the low and moderate physiological ACTH doses produced a large corticosterone response in PD2 pups without a change in adrenal cAMP content. At extremely high, pharmacological levels of plasma ACTH in PD2 pups (exceeding 3,000 pg/ml), an increase in adrenal cAMP was measured. We conclude that physiological increases in plasma ACTH may stimulate adrenal steroidogenesis in PD2 pups through a non-cAMP-mediated pathway.

The effects of flutamide on the neonatal rat hypothalamic–pituitary–adrenal and gonadal axes in response to hypoxia

“…Our study confirmed that the adrenal stress hyporesponsive period occurs in PD7 and PD14 pups, which is most likely a result of decreased adrenal sensitivity to ACTH (Arai & Widmaier, 1993;Brake, Arai, As-Sanie, Jefcoate, & Widmaier, 1999;Lee & Widmaier, 2005;Nagaya, Arai, & Widmaier, 1995;Zilz et al, 1999) and not explained by a change in corticosteroid-binding globulin (CBG) (Johnson et al, 2013). We confirmed that the corticosterone hyporesponsive period in the neonatal rat occurs despite a large increase in ACTH, as we have shown previously (Bodager et al, 2014;Bruder et al, 2008;Chintamaneni et al, 2013). Other studies have also suggested that the stress hyporesponsive period is the result of a decrease in critical adrenal genes and factors in the neonatal steroidogenic pathway (Brake et al, 1999;Lee & Widmaier, 2005;Zilz et al, 1999).…”

“…Figure 1 shows the effect of the standard dose of flutamide (10 mg/kg) on the plasma ACTH and corticosterone responses to hypoxia. Because of heteroscedasticity of the data, we are only presenting the within age comparisons since that is the focus of the hypothesis addressed in this study and because the between age differences have been described previously (Bodager, Gessert, Bruder, Gehrand, & Raff, 2014;Wood & Walker, 2015). Note: Data are shown as mean (SEM).…”

“…However, PD7 corticosterone plasma concentrations were not significantly different between high and standard dose flutamide treatments. It is important to note that PD7 adrenal glands are stress and ACTH hyporesponsive (Bodager et al, 2014;Bruder et al, 2008;Chintamaneni, Bruder, & Raff, 2013;Zilz, Li, Castello, Papadopoulos, & Widmaier, 1999). High-dose flutamide in PD14 pups showed a significant increase in the plasma corticosterone response to hypoxia; however, this effect was not present in the PD21 pups.…”

“…more mature) state earlier than the female. PD21 pups had an "adult-like" augmentation of the ACTH response to hypoxia with standard dose flutamide that was not reflected in the corticosterone response, likely because the adrenal was already at its maximum secretory rate (Arai & Widmaier, 1993;Bodager et al, 2014;Wood & Walker, 2015;Zilz et al, 1999). These high concentrations in plasma corticosterone may be due to a near maximal rate of release of corticosterone into the blood, which is dependent on rat age, adrenal mass, and capillary blood flow (Stockham, 1964).…”

Insulin sensitivity, leptin, adiponectin, resistin, and testosterone in adult male and female rats after maternal-neonatal separation and environmental stress

“…In fact, there are striking differences in acute stress responses and hypothalamic-pituitaryadrenal axis control in the PD7-10 pup compared to earlier and later in development suggesting that PD9 may be a unique moment in development in the neonatal rat (6,10,36,82,83,86). Our approach is designed to model human prematurity, hence why we performed daily maternal-neonatal separation in the youngest rat pups feasible.…”