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

Abstract

Hypoxia is common with preterm birth and may lead to long‐term effects on the adult hypothalamic–pituitary–adrenal (HPA) axis that are sexually dimorphic due to neonatal androgens. Although the adult rat adrenal does not express appreciable CYP17 activity, the neonatal rat adrenal may synthesize androgens that could be a critical local factor in the development of adrenal function. We evaluated these phenomena by pretreating the neonatal rats on postnatal days (PD) 1, 6, 13, 20 with flutamide (a nonsteroidal androgen receptor antagonist) at a standard or a high dose (10 mg/kg or 50 mg/kg) compared to vehicle control. One day later, neonatal rats were exposed to acute hypoxia and blood was sampled. We found that (a) in PD2 pups, flutamide augmented corticosterone responses in a sexually dimorphic pattern and without an increase in ACTH, (b) PD7 and PD14 pups had the smallest corticosterone response to hypoxia (c) PD21 pups had an adult‐like corticosterone response to hypoxia that was sexually dimorphic, (d) flutamide attenuated ACTH responses in PD7 hypoxic pups, and (e) high‐dose flutamide suppressed the HPA axis, FSH, and estradiol. Flutamide demonstrated mixed antagonist and agonist effects that changed during the first three weeks of neonatal life. We conclude that the use of flutamide in neonatal rats to evaluate androgen‐induced programming of subsequent adult behavior is not optimal. However, our studies suggest neonatal androgens play a role in regulation of adrenal function that is sexually dimorphic and changes during early development.

Insulin and glucose responses to hypoxia in male and female neonatal rats: Effects of the androgen receptor antagonist flutamide

“…For the purposes of clarity and communication, and following our previous approach (Rolon et al., 2019), we have presented the data as follows: We first describe the results from the vehicle injections compared to the standard dose of flutamide (10 mg/kg) used in our previous study chosen because it does not have long‐term feminizing effects (Gray et al., 2006; McCormick & Mahoney, 1999). The second section of the Results presents the data from the standard dose of flutamide compared to the higher dose (50 mg/kg) as described in the Methods section.…”

“…Flutamide has been used as an agent for androgen receptor modulation in the neonatal rat (Gray et al., 2006; McCormick & Mahoney, 1999). We have previously used flutamide in our neonatal rat model that involves separation (fasting) and hypoxia and mimics human prematurity and clinical intensive care (Rolon et al., 2019). We have now continued our previous study using flutamide in this model to evaluate plasma glucose and insulin dynamics.…”

“…This is a follow‐up study of a cohort of neonatal rats treated with flutamide and subsequently exposed to hypoxic stress as described in detail previously (Rolon et al., 2019) and briefly summarized here. Timed‐pregnant Sprague Dawley rats ( N = 75) were obtained from Envigo and kept in a standardized environment with food (Envigo, product #8604 which contains corn, soy, and wheat) ad libitum (Gehrand et al., 2016; Gehrand et al., 2019).…”

“…Male and female pups were studied on four postnatal days (PD) to determine age‐dependent changes before weaning on fasting plasma glucose and insulin. Flutamide and vehicle injections were randomized to PD1, PD6, PD13, or PD20 pups that were then studied 24 hr later (at PD2, PD7, PD14, PD21) (Rolon et al., 2019).…”

“…The long‐term goal is to determine if flutamide is a consistently effective androgen receptor antagonist in the neonatal rat to utilize it to evaluate the effect of neonatal androgens on long‐term, sexually dimorphic phenotypes. We previously established the dynamics of flutamide action on the HPA‐axis in our neonatal rat model of hypoxia and suggested that flutamide may not have consistent, developmental AR antagonist activity at different ages from birth to weaning (Rolon et al., 2019). Here, we extend these studies by evaluating the effects of standard and high dose flutamide pretreatment on the neonatal insulin and glucose response to hypoxia—a common stressor in prematurity.…”