Characteristics of Basic Parameters of the Hormonal Function of the Adrenal Cortex and Its Modification in Rat Ontogenesis

Abstract

The stress-reactivity of the pituitary-adrenocortical system (PAS) as assessed by the dynamics of the blood corticosterone level changes was studied in rats administered with cortisol at different periods of their pre- and postnatal ontogenesis. The participation of the activation and deactivation mechanisms in this process was estimated by means of a mathematical modeling, using the basic parameters of hormonal wave. It is established that in the one-month old rat pups born from mothers injected with cortisol from the day 14 to 18 of pregnancy, the basal and stress-evoked PAS activity was not essentially changed, whereas the adult animals demonstrated a faster decrease of the stress-induced corticosterone level. Injection of cortisol at the early neonatal ontogenesis (1–5 day of life) decreased the basal and stress-induced corticosterone levels at the morning hours in one-month old rats, whereas in adult rats it increased the PAS stress-reactivity. Injection of cortisol in the late neonatal ontogenesis, i.e., during the period of formation of the sensory systems (opening of the ears, eyes, maximal motor activity) resulted predominantly in changing the time of completion of the stress-induced hormonal response that became longer than in control animals of the same age. With the aid of mathematical modeling, we have found that at the early neonatal period of development the hormonal exposure mainly increases the rate of PAS activation, whereas injection of glucocorticoids at the late neonatal period changes PAS regulation by a feedback mechanism, thus decreasing the rate of system inactivation and increasing the time of completion of PAS stress-induced reaction. It is concluded that the phenotypic reorganization of PAS stress-reactivity by exogenous corticosteroids depends on the time of their action on development of the excitatory and inhibitory mechanisms during the critical periods of their formation.