Changes in sodium appetite in cattle induced by changes in CSF sodium concentration and osmolality

Abstract

Alteration of the sodium concentration in the cerebrospinal fluid (CSF) of sheep induces reciprocal changes in sodium appetite. Similar studies have now been performed in cattle. Heifers were prepared with a unilateral parotid fistula and guide tubes were implanted in the skull for the introduction of probes into the lateral ventricles in order to sample CSF and infuse artificial CSF solutions. The cows were Na depleted by loss of saliva for 46 hr and then given free access for 2 hr to 300 mM NaCl NaHCO 3 solution. Artificial CFS influtions at 1.9 ml/hr were begun one hour before Na access. In control experiments, the cows drank 26.4±1.2 l of Na solution in 2 hr, 1.2±0.2 l of water in the preceding hour, and 0.3±0.1 l of water during Na access. Sham or standard isotonic CSF infusions did not alter these values. CSF [Na +] rose from ∼142 to ∼148 mmol/l, attributable to the effects of drinking the large volume of hypertonic Na solution. Infusion of 500 mM NaCl CSF increased CSF [Na +] and reduced Na intake and increased water intake. Infusion of 700 mM mannitol: 150 mM NaCl CSF reduced CSF [Na +] and increased both Na and water intake. Infusion of a mixture of these solutions had no effect on CSF [Na +] and increased water intake only. Infusion of 270 mM mannitol CSF reduced CSF [Na +] and slightly reduced Na intake. Standard isotonic CSF containing 0.5 or 2.0 μg/ml of angiotensin II increased water intake only. The change in CSF [Na +] and osmolality, induced by these infusions, had much the same effects on Na appetite and thirst as have been observed in Na depleted sheep. The different response to isotonic mannitol infusion might be due to the relatively smaller periventricular area affected in the larger cow brain.