Noradrenergic control of central oxytocin release during lactation
in rats.
Bealer, Steven L., and William R. Crowley.
Departments of Physiology and Pharmacology, University of
Tennessee, Memphis, TN 38163
APStracts 4:0264E, 1997.
Noradrenergic systems regulate the systemic release of oxytocin (OT)
in lactating rats. However, a role for norepinephrine (NE) in release
of OT within the magnocellular nuclei during suckling has not been
established. These studies were designed to determine 1) if suckling
induces NE release in the supraoptic (SON) and paraventricular (PVN)
nuclei of conscious rats, and 2) the role of NE in the central,
intranuclear release of OT within these nuclei. Female Holtzman rats
were implanted with microdialysis probes adjacent to the PVN or SON
on lactation days 8-12. The following day, the pups were isolated
from the dams for 4 hrs. Microdialysis probes were perfused with
artificial cerebrospinal fluid (ACSF) or with ACSF containing an a-
or a (-adrenergic receptor antagonist. Dialysate was collected
before, during, and following suckling, and analyzed for NE or OT. In
an additional experiment, an a- or -adrenergic agonist was
administered via the microdialysis probes into the PVN in non
-suckled, lactating rats. Extracellular NE increased in the PVN during
suckling, but was not detectable in the SON. OT concentrations in
dialysates from the PVN and SON significantly increased during
suckling. Blockade of either a- (in both PVN and SON) or (- (PVN)
adrenergic receptors prevented the suckling-induced increase in
central OT release. OT release was increased in non-suckled,
lactating rats by central application of either an a- or -adrenergic
agonist. These data demonstrate that intranuclear NE release is
increased in the PVN by suckling, and that subsequent stimulation of
both a- and -noradrenergic receptors mediates intranuclear OT
release.
Received 23 June 1997; accepted in final form 13 November 1997.
APS Manuscript Number E293-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997