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Prolactin secretory rhythm of mated rats induced by a single injection of oxytocin

Departments of ¹Biological Science and ³Mathematics, Institute of Molecular Biophysics, and ⁵School of Computational Science and Information Technology, Florida State University, Tallahassee, Florida; ²Space Biology Group, Swiss Federal Institute of Technology, Zurich, Switzerland; and ⁴Department of Biology and Center for Biological Timing, University of Virginia, Charlottesville, Virginia

Submitted 7 September 2005 ; accepted in final form 6 October 2005

Mating or vaginocervical stimulation [copulatory stimulus (CS)] induces two daily surges of the hormone prolactin (PRL) in rats. This unique secretory pattern of PRL surges is characteristic for the first half of pregnancy and is also present in ovariectomized (OVX) rats. Studies have shown that CS additionally provokes an acute release of the hormone oxytocin (OT). In this study, we tested whether a single injection of OT (iv) is sufficient to initiate the PRL secretion pattern of OVX/CS rats. Furthermore, we measured the 24-h profile of dopamine (DA) content in the anterior lobe of the pituitary gland, because DA is the major inhibitory factor of PRL secretion. The results indicated that a single injection of OT induces a PRL secretory rhythm and a DA release pattern similar to that initiated by CS. Immunocytochemical investigation showed that particular OTergic neurons in the hypothalamus express receptors for PRL, as well as for vasoactive intestinal polypeptide, which indicates an involvement in generating the PRL rhythm and entraining it to the ambient photoperiod. On the basis of this study, we suggest that the PRL-DA inhibitory feedback loop between lactotrophs and DAergic neurons plays a crucial role in generating the oscillatory PRL secretion pattern in CS rats. A timing signal, likely provided by the hypothalamic suprachiasmatic nucleus, entrains the autonomous PRL oscillation to a particular time of day. Mathematical modeling was used to illustrate the proposed network function. The experimental results further suggest an additional feedback mechanism in which certain hypothalamic OTergic neurons are influenced by PRL.

dopamine; suprachiasmatic nucleus; mathematical modeling; lactotrophs

This article has been cited by other articles:

				R. Bertram, M. Egli, N. Toporikova, and M. E. Freeman A mathematical model for the mating-induced prolactin rhythm of female rats Am J Physiol Endocrinol Metab, March 1, 2006; 290(3): E573 - E582. [Abstract] [Full Text] [PDF]