Circadian Profile of Peripheral Hormone Levels in Sprague- Dawley Rats and in Common Marmosets (Callithrix jacchus)

Aim: In the present study, we report the circadian profiles of a wide panel of hormones measured in rats and common marmosets (Callithrix jacchus), under physiological conditions, paying special attention to minimising the stress imposed on the animals. Materials and Methods: Blood collections were performed over a 24-hour period for the analysis of stress and pituitary hormones, metabolic markers and cytokines from male cannulated rats connected to a fully automatic system, and healthy marmosets in which gender differences were also evaluated. Results: In rats, a significant time effect was observed for corticosterone, prolactin (PRL), thyroid stimulating hormone (TSH), growth hormone, follicle-stimulating hormone, brain-derived neurotrophic factor, total ghrelin, insulin, leptin, insulin-like growth factor-1, adiponectin and interleukin-10. In marmosets, a significant time effect for cortisol, adrenocorticotropic hormone (ACTH), PRL and TSH, with gender effect for ACTH and PRL only, was observed. On the contrary, luteinizing hormone in the rat and active ghrelin, peptide YY, pancreatic polypeptide and gastric inhibitory polypeptide in the marmoset did not show any significant circadian variation. Conclusion: The present work confirmed that, due to time-of-day dependent modulation of hormones, circadian rhythmicity is relevant in physiological studies and should also be taken into consideration when performing pharmacological studies.