The present study examines the relationship of the hypothalamic paraventricular nucleus (PVN) to discrete brain and pituitary pools of immunoreactive (ir) vasopressin (VP), oxytocin (OT) and particular opioid peptides in the rat. Selective, bilateral destruction of the PVN resulted in a parallel depression in levels of ir-VP, ir-OT, ir-dynorphin (DYN), ir-DYN1–8 and ir-α-neo-endorphin (α-NE) in the neurointermediate lobe of the pituitary, whereas in its anterior counterpart no decrease in the content of any of these peptides was seen. In contrast, the content of ir-β-endorphin (β-EP) in the neurointermediate lobe was not significantly altered. Further, a rise in levels of ir-β-EP in the anterior lobe, together with a fall in these in systemic plasma, was found. In the hypothalamus, in distinction to ir-metenkephalin (ME), a diminution in the content of ir-VP, ir-OT, ir-DYN, ir-DYN1–8, ir-α-NE and, in addition, ir-β-EP was observed. In the septum, midbrain and medulla/pons, however, a selective depression in levels of ir-VP (and, as measured in the medulla/pons, of ir-OT) was seen: the content of ir-DYN, ir-DYN1–8, ir-α-NE, ir-β-EP and ir-ME was unchanged in these tissues. These data indicate that: (1) the PVN is an important contributor to neurointermediate lobe, but not anterior lobe, pools of ir-VP, ir-OT, ir-DYN, ir-DYN1–8 and ir-α-NE in contrast to ir-β-EP. (2) the PVN provides a mayor input of ir-VP (and ir-OT), in contrast to ir-DYN, ir-DYN1–8, ir-α-NE, ir-β-EP and ir-ME, to the septum, midbrain and medulla pons. (3) although coexisting with ir-VP in a hypothalamo-neural lobe tract partially derived from the PVN, ir-DYN, ir-DYN1–8 and ir-α-NE exist independently of the PVN-originating VP-containing neurons which innervate extrahypothalamic brain tissue. (4) the PVN may interact with hypothalamic ir-β-EP and plays a facilitatory role in the tonic regulation of adenohypophyseal secretion of ir-β-EP into the systemic circulation.

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