Evaluation of the Hypothalamus-Hypophysis-Adrenal Axis in Male Rats Programmed by Gestational Protein Restriction

Abstract

Diet manipulations during the gestation of animal models, in this case, the lipoprotein diet, mimic the alterations related to low birth weight, providing studies of the mechanisms involved in chronic disease development in later life. Our research group identified in adult male rats submitted to gestational protein restriction, increased anxiety-like behavior, basal plasmatic corticosterone (CORT) and catecholamines elevation, and decrease of hippocampal glucocorticoid receptors (GRs), indicating dysfunction of the stress response, which is related to the sympathetic-adrenomedullary system and the hypothalamic–pituitary–adrenal (HPA) axis alterations. Not only insults during gestation but also maternal care behavior during breastfeeding can modulate the HPA axis of the offspring, influencing its activity in adulthood. Thus, we evaluated maternal care behavior and morphological and functional parameters of the adrenal and pituitary glands in gestational protein-restricted male rats to elucidate mechanisms that can trigger these possible alterations. Mated Wistar rats were submitted to a normal-protein diet (NP group; 17% protein) or a low-protein diet (LP group; 6% protein) throughout pregnancy. From the day of birth until weaning, the maternal care behavior parameters were evaluated, and at the 16th week of age, plasma, adrenal, and pituitary glands were collected for hormonal analysis by LC-MS/MS, western blot, and immunohistochemistry. LP offspring animals showed low birth weight and recovered at weaning, indicating the effect of catch-up growth. No difference in maternal care behavior was found between the groups, suggesting that maternal care may not influence the decrease of hippocampal GR in LP offspring. The plasma levels of 11-dehydrocorticosterone (11-DHC) in 21PND and 16-week-old LP offspring decreased, whereas the plasma levels of CORT and 11-DHC of 8-week-old LP offspring increased. GR and mineralocorticoid receptors, essential to glucocorticoids' practical actions, were increased in the pituitary and adrenal glands in LP 16-week-old animals, indicating possible negative feedback. However, the 98.8% increase in CRH receptor and 63.3% ACTH in the pituitary of the LP offspring indicates failure of this feedback at the pituitary level. The morphometric analysis of the LP 16-week-old animal's adrenal gland showed an increase in medullary area, accompanied by an increase of 39.67% in NeuN, indicating an increase in medullary cellularity and an increase of 168.77% in PCNA, suggesting a cell proliferation under the demand of adrenal hyperactivity. In addition, an increase of 5-HT1A receptor (48.69%) in the LP adrenal gland, which is associated with inhibitory catecholamine secretion, and an increase of immunostaining of 5-HT1A and 5-HT2A receptors differently within the pituitary lobes, suggesting modulation of the HPA axis at the pituitary level through the serotonergic innervation from hypothalamic CRH neurons. Gestation protein restriction results in adult rat offspring, morphological and functional changes in the adrenal glands, and hormonal modulations associated with stress responsively and adrenergic hyperactivity. These alterations could participate in the genesis and maintenance of hypertension in this model.