Pressor responses to centrally-administered prostaglandin E2 in spontaneously hypertensive rats

Blood pressure (BP) and heart rate became elevated when prostaglandin E2, (PGE2) was infused into the cerebral ventricles of awake and anesthetized rats. Frequency of sympathetic neural firing was also increased. While the magnitude of the pressor responses was larger in spontaneously hypertensive rats (SHRs) than in normotensive ones (NTRs), the accompanying increases in sympathetic nerve firing were not significantly different. Pressor effects were appreciable within 2 minutes after the start of th PGE2 infusion did not become maximal until 15 minutes later. By contrast, acceleration in sympathetic nerve firing was maximal within 2 minutes and then dwindled or remained stationary thereafter. Removal of sympathetic vasomotor tone by cervical section of the spinal cord abolished early phases without affecting subsequent peaks of the pressor response. The overall height of the pressor responses in hypophysectomized NTRs was half that in sham-operated controls. These results suggest that GPE2 acts centrally to elevate BP by increasing not only the sympathetic discharge but perhaps also the secretion of hypophysial hormones, such a vasopressin. In light of previous studies showing that SHRs secrete mor vasopressin, it was considered possible that their enhanced pressor responsiveness to PGEs could result from a greater release o endogenous vasopressin.