Effects of acute increases in plasma osmolality on plasma vasopressin-associated neurophysin in conscious rats: implications for osmoregulation.
We studied the responses of the hypothalamo-neurohypophysial system to intravenous infusions of 18% saline, 25% mannitol and a combination of 15% mannitol and 1.35% saline in conscious, chronically catheterized Long-Evans rats. Infusions of 18% saline and 25% mannitol produced similar increases in plasma osmolality (Posm) and plasma vasopressin-associated neurophysin concentration [( VP-RNP]). As expected, plasma sodium concentration [( Na+]) for the 18% saline-treated animals was significantly elevated while that for the 25% mannitol-treated animals was significantly reduced. Mannitol infusion caused a significantly greater loss of body weight. The slopes of the relationship between delta [VP-RNP] and delta Posm were almost identical for the two groups. Infusion of a combination of 15% mannitol and 1.35% saline produced a rise in Posm comparable to that observed for the other two infusion regimens, but caused smaller increases in [VP-RNP], the slope of the relationship between delta [VP-RNP] and delta Posm being about half of those for the infusion with 18% saline or 25% mannitol. This combination also maintained [Na+] close to normal levels and in these animals there was a loss of body weight that was significantly smaller than that for those rats receiving 25% mannitol. The results of this study imply that factors other than osmoreceptors and/or sodium receptors are involved in causing a release of neurohypophysial principles during acute infusion of hypertonic solutions.
D000818:Animals; D007700:Kinetics; D008297:Male; D008353:Mannitol / Q000008:administration & dosage; D009481:Neurophysins / Q000097:blood*; D051381:Rats; D012462:Saline Solution, Hypertonic; D014667:Vasopressins / Q000097:blood*; D014882:Water-Electrolyte Balance / Q000187:drug effects
D009481:Neurophysins; D012462:Saline Solution, Hypertonic; D014667:Vasopressins; D008353:Mannitol