HEMORRHAGE-INDUCED VASOPRESSIN RELEASE IN THE PARAVENTRICULAR NUCLEUSMEASURED BY IN-VIVO MICRODIALYSIS

Experiments were carried out, using the technique of in vivo microdial ysis in conscious rats, to determine whether hemorrhage, a potent stim ulus for the release of vasopressin from the posterior pituitary into the circulation, would also result in a local release of vasopressin f rom the paraventricular nucleus (PVN), and whether this release is aff ected by gender. Male and non-estrous female rats were prepared with a microdialysis probe adjacent to the PVN and femoral arterial and veno us catheters the day before the experiment. On the day of the experime nt, rats was bled either 20% or 30% of blood volume. The concentration of vasopressin in the dialysate increased significantly in the males following both hemorrhages and in the females following the 30% hemorr hage. There were no statistically significant differences in the post- hemorrhage dialysate vasopressin concentration with respect to either gender or magnitude of the hemorrhage. The plasma vasopressin concentr ation increased markedly in response to the hemorrhage and this respon se was greater in females following the 30% hemorrhage. There were no gender differences in the reduction in arterial pressure following eit her hemorrhage. It is concluded that physiological stimuli for the rel ease of vasopressin into the circulation also result in intrahypothala mic release of this hormone.