Separate mechanisms for central osmotically-induced drinking and vasopressin release in minipigs

Operant drinking and lysine vasopressin (LVP) release were investigated in minipigs following intracerebroventricular (ICV) injections of hypertonic equiosmolar (1.4 osM) solutions of NaCl and of sucrose and mannitol dissolved in 0.15 M NaCl or water, and of urea dissolved in 0.15 M NaCl. Hypertonic (0.74 M) NaCl produced significant drinking and LVP release in all minipigs tested whereas hypertonic equiosmolar (1.4 osM) solutions of sucrose and mannitol induced only drinking. Mannitol, both with and without NaCl, was more effective than sucrose. Hypertonic urea was ineffective both as an osmotic dipsogen and at stimulating the release of LVP. These results suggest that two independent mechanisms could be involved in drinking and LVP responses to ICV administration of hypertonic solutions in minipigs.