Central Administration of Corticotropin-Releasing Factor Modulates Oxytocin Secretion in the Rat*

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Abstract
Recently, it has been reported that oxytocin (OT), classically known for its function during parturition and lactation, is secreted in response to stressful stimuli in male rats. In these and in the present report it was found that swimming stress, restraint stress, ether stress, and footshock stress elevate OT secretion without affecting arginine-vasopressin (AVP) secretion. In the present studies, we investigated the possible modulation of OT secretion by CRF which is known to be released during stress. Male and female rats received intraventricular (icv) injections of 0.75 nmol (5 .mu.g) rat CRF and were killed 5 min after the treatment. CRF significantly elevated OT secretion in male and female rats 3.4- and 4-fold, respectively. Plasma AVP levels were not affected by the treatment. The effect of CRF on OT release was structure specific since rat CRF, ovine CRF, and suagvagine were equipotent releasers of OT while an inactive analog to CRF, ovine CRF7-41 did not change plasma OT levels. In another set of experiments rats were pretreated with either CRF-antiserum (0.5 ml i.v) or dexamethsone (20 .mu.g/rat ip) and then injected with icv CRF. Both CRF-antiserum and dexamethasone blocked the rise in ACTH release after icv CRF completely but did not influence the OT response. This suggests CRF may be acting centrally but not at the level of the neurohypophysis to change OT secretion. Since parvocelluar but not magnocellular neurons of the paraventricular nucleus have been demonstrated to be steroid sensitive in immunohistochemical studies, we suggest CRF may act directly or indirectly upon magnocellular neurons to increase OT release. Intravenous administration of 0.75 nmol CRF increased both OT and AVP levels in peripheral blood. The magnitude of this increase was similar (2- to 4-fold stimulation) to responses after icv administration of CRF. Intravenous administration of CRF results in hypotension and may therefore cause a baroreceptor mediated release of AVP and OT. From the above evidence we conclude: 1) physical and mental stresses which do not result in changes in blood volume or osmolality evoke an increase in OT secretion while AVP secretion remains unchanged; 2) CRF administered icv mimics OT responses observed after ether stress or footshock stress: 3) CRF may play a role in regulating stress-induced OT secretion in the rat.