Daily rhythms in the somatotropic axis of Senegalese sole (Solea senegalensis): The time of day influences the response to GH administration

ABSTRACT

Growth factors in vertebrates display daily rhythms, which, while widely described in mammals, are still poorly understood in teleost fish. Here, we investigated the existence of daily rhythms in the somatotropic axis of the flatfish Solea senegalensis. In a first experiment, daily rhythms of the expression of pituitary adenylate cyclase–activating polypeptide (pacap), growth hormone (gh), insulin-like growth factor 1 (igf1) and its receptor (igf1r) were analyzed under a 12:12 h light:dark cycle. All genes displayed daily rhythms with the acrophases of pacap, gh and igf1 located in the second half of the dark phase (ZT 20:28–0:04 h), whereas the acrophase of igf1r was located around mid-light (ZT 5:33 h). In a second experiment, the influence of the time of day (mid-light, ML, versus mid-darkness, MD) of GH administration on the expression of these factors and on plasma glucose levels was tested. The response observed depended on the time of injection: the strongest effects were observed at MD, when GH administration significantly reduced pituitary gh and enhanced liver igf1 expression. These results provide the first evidence of daily rhythms and differential day/night effects in growth factors in S. senegalensis, suggesting new insights for investigating the physiology of growth and possible applications to improve fish aquaculture.

KEYWORDS:

• Flatfish
• GH chronopharmacology
• growth hormone
• insulin-like growth factor
• pituitary adenylate cyclase-activating polypeptide

Acknowledgements

The authors thank Jose Antonio Oliver for his help with fish maintenance and sampling; Borja Blanco-Vives for his help with sampling; the personnel of the Molecular Biology Section from the Research Support Service (SAI) of the University of Murcia for their help with qPCR assays; and the Spanish Ministry of Defense for providing their facilities at the Naval Base of Algameca (ENA).

Funding

This research was funded by projects AGL2010-22139-C03-01 and AGL2013-49027-C3-1-R granted by the Spanish Ministry of Economy and Competitiveness (MINECO) to F.J. Sánchez-Vázquez, and by project AGL2013-48835-C2-1-R granted by MINECO to J.M. Mancera. J.F. López-Olmeda was funded through a research fellowship granted by MINECO (Juan de la Cierva Program).

Declaration of interest

The authors report no conflict of interest. The authors alone are responsible for the content and writing of the article. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the article.

Additional information

Funding

This research was funded by projects AGL2010-22139-C03-01 and AGL2013-49027-C3-1-R granted by the Spanish Ministry of Economy and Competitiveness (MINECO) to F.J. Sánchez-Vázquez, and by project AGL2013-48835-C2-1-R granted by MINECO to J.M. Mancera. J.F. López-Olmeda was funded through a research fellowship granted by MINECO (Juan de la Cierva Program).