Drinking and renal responses to peripherally administered osmotic stimuli in the pigeon (Columbia livia).

Pigeons drank copiously in response to intravenous (I.V.) infusion of approximately equi-osmolar hypertonic solutions of NaCl (0.5 M), sucrose (1.0 M) or mannitol (1.0 M). I.V. infusions of hypertonic glucose (1.0 M) or urea (1.0 M) were less effective in causing drinking. The calculated percentage change in plasma osmolality at the onset of drinking was similar for the three hypertonic solutions, NaCl, sucrose and mannitol, irrespective of the concentration of the solution infused. A greater volume of water was drunk in response to I.V. infusion of 7 ml of 1.0 M-sucrose than in response to a similar volume of 1.0 M-NaCl or mannitol. This appeared to be in response to the large diuresis caused by sucrose infusions. Excretion of the osmotic load was more rapid following I.V. hypertonic sucrose and mannitol than following hypertonic NaCl, glucose or urea in the 10 h of the experiment. In anaesthetized pigeons, I.V. infusion of hypertonic NaCl (0.5 M), sucrose (1.0 M) or urea (1.0 M) caused similar increases in plasma osmolality. The haematocrit was significantly reduced after NaCl or sucrose but not after urea. Plasma Na+ concentration was significantly increased after NaCl, and decreased after sucrose, whereas urea produced little change. Following I.V. hypertonic NaCl or urea, the Na+ concentration of the cerebrospinal fluid (c.s.f.) was increased and its flow reduced compared with isotonic NaCl infusions. Hypertonic sucrose stopped the flow of c.s.f. almost completely during the course of the experiment. These experiments suggest that the drinking and renal responses of pigeons following osmotic stimuli are similar to those of mammals and that they appear to retain Na+.