Studies on plasma corticosteroids in the rhesus monkey (Macaca mulatta)

Area of Science:

• Endocrinology
• Neuroscience
• Primate Physiology

Background:

• Plasma corticosteroid regulation is crucial for physiological homeostasis.
• Understanding the hypothalamic-pituitary-adrenal (HPA) axis in non-human primates offers insights into human physiology.
• Previous studies reported higher basal corticosteroid levels in rhesus monkeys.

Purpose of the Study:

• To investigate the physiological regulation of plasma corticosteroid concentration in female rhesus monkeys.
• To characterize the circadian rhythm and response to stimuli of the HPA axis in this species.
• To compare the HPA axis function in rhesus monkeys to that of humans.

Main Methods:

• Measurement of plasma corticosteroid concentration using competitive protein-binding assays.
• Administration of phencyclidine hydrochloride for sedation.
• Intravenous administration of synthetic alpha1-24 adrenocorticotrophic hormone (ACTH).
• Administration of lysine-vasopressin and induction of hypoglycemia via insulin.
• Administration of metyrapone to assess corticosteroid precursor levels.

Main Results:

• Established morning basal plasma corticosteroid levels (8.0-25.2 mug/100 ml), lower than previously reported.
• Demonstrated a circadian rhythm in plasma cortisol concentration.
• Observed increased plasma cortisol during prolonged phencyclidine sedation.
• Confirmed rapid plasma cortisol increase following synthetic ACTH administration, with dose-dependent responses.
• Showed increased corticosteroid levels after lysine-vasopressin administration and insulin-induced hypoglycemia.
• Metyrapone administration resulted in decreased 11-hydroxycorticosteroids and increased total corticosteroids.

Conclusions:

• The hypothalamic-pituitary-adrenal axis in rhesus monkeys exhibits a qualitatively and quantitatively similar function to that of humans.
• Rhesus monkeys serve as a valuable model for studying human HPA axis regulation.
• Further research can explore specific regulatory mechanisms and responses within this primate model.