Effect of the gadolinium ion on body fluid regulation.

Both osmoreception and baroreception are thought to involve ion channels that are sensitive to changes in membrane stretch. We investigated the effect of a blocker of stretch-activated ion channels, the Gd3+ ion, on osmoregulatory and cardiovascular responses in the intact rat. Intracerebroventricular injection of 50-100 nmol Gd3+ reduced thirst induced by various treatments. Similar doses also reduced intake of saline induced by various treatments. Intracerebroventricular injection of 100 nmol Gd3+ transiently increased arterial pressure and reduced the pressor response to intracerebroventricular angiotensin II (Ang II). Systemic administration of Gd3+ failed to alter thirst, except for a high dose (270 micromol/kg) that induced illness. This high dose failed to prevent urinary hypertonicity and excretion of a load of hypertonic NaCl. Intravenous infusion of 270 micromol/kg of Gd3+ reduced blood pressure and pressure responses to intravenous phenylephrine, but did not reduce the baroreceptor reflex control of heart rate. We conclude that the effects of Gd3+ on thirst and on the cardiovascular system are probably not due to a direct effect of the drug on stretch-sensitive ion channels. Instead, many of the effects of Gd3+ were compatible with blockade of voltage-gated Ca2+ channels.