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Glucose homeostasis and hypothalamic-pituitary-adrenocortical axis during development in rats
1Department of Biology, Boston University, Massachusetts 02215.
Insights
Young rats exhibit distinct stress responses compared to adults, lacking normal glucose sensing but utilizing alternative fuels. These age-related differences highlight evolving metabolic needs and stress adaptation strategies during development.
Area of Science:
- Neuroendocrinology
- Developmental Biology
- Metabolic Physiology
Background:
- Glucoprivation serves as a model stressor to study age-dependent physiological responses.
- Evidence suggests the rat brain possesses a glucose sensor, but its biochemical basis remains elusive.
- Neonatal rats display unique stress responses, differing significantly from adult patterns.
Purpose of the Study:
- To investigate age-related differences in stress responses to glucoprivation in rats.
- To explore the glucose-sensing capabilities of the young rat hypothalamus.
- To understand the developmental changes in hormonal and metabolic adaptations to stress.
Main Methods:
- In vivo and in vitro monitoring of stress responses.
- Measurement of hormonal secretions (corticotropin-releasing factor, adrenocorticotropic hormone, corticosterone, catecholamines, glucagon).
- Analysis of metabolic fuel utilization and enzyme induction.
Main Results:
- Young rats lack typical hypothalamic glucose-sensing and associated hormonal responses to glucoprivation.
- Neonatal rats exhibit hypersecretion of catecholamines and glucagon compared to adults.
- Alternative fuel sources are utilized by neonatal rats, supported by high early steroid levels.
Conclusions:
- Stress response and compensatory mechanisms in rats evolve significantly from neonatal to adult life.
- Developmental changes in stress response are closely linked to the animal's metabolic requirements.
- The definition of stress and its management strategies adapt throughout an organism's lifespan.
Abstract:
Glucoprivation represents a model stress in which activation of different stress responses at different ages can be monitored both in vivo and in vitro. Physiological data indicate rat brain contains a liver/pancreas-type glucose sensor, yet no biochemical or immunocytochemical evidence exists for such a sensor. Young rats appear to lack normal hypothalamic glucose-sensing ability and do not show typical secretory patterns of corticotropin-releasing factor, adrenocorticotropic hormone, or corticosterone after experimentally induced glucoprivation. However, they hypersecrete catecholamines and glucagon (compared with adults) and thrive on fuel sources other than glucose that are abundant after birth. High steroid levels during the first 24 h after birth may be critical for inducing gluconeogenic enzymes and promoting differentiation of tissues like pancreas. Neonatal rats also have unique control systems to combat the damaging effects of other stresses like hypoxia; these systems may disappear in adults. Thus the definition of stress may change during development, and the compensatory mechanisms employed to combat stress change from neonatal to adult life and are intricately related to the metabolic needs of the animal.