Abstract
Previously we found intragranular colocalization of immunoreactive endothelin-1 and neurohypophysial hormones in the axon terminals of the rat neural lobe. To investigate the function of endothelin-1 in the rat neural lobe, immunoreactive endothelin-1 in plasma and the neural lobe was measured by enzyme immunoassay in rats subjected to hemorrhage and in other rats who were deprived of water for 2 days to induce dehydration. Changes in plasma arginine vasopressin were determined by radioimmunoassay. In addition, morphometric analysis was performed in the neural lobe of rats exposed to these stresses. Plasma concentrations of immunoreactive endothelin-1 were unchanged following hemorrhage or dehydration, whereas those of immunoreactive vasopressin were remarkably increased. In the neural lobe, immunoreactive endothelin-1 content and the number of neurosecretory granules decreased significantly after dehydration. However, immunoreactive endothelin-1 in tissue increased nearly three-fold in hemorrhaged rats, whereas the endothelin-1-immunolabeling in the axon terminals was unchanged. These results suggest that endothelin-1 in the hypothalamo-hypophysial system may be involved in the local modulation of vasopressin secretion when an animal is exposed to hypovolemic and/or osmotic stress.
