Acute infusion of lithium chloride raises blood pressure in the conscious rat

The effects of acute infusion of lithium chloride (LiCl) were studied on mean arterial pressure (MAP) and magnocellular activity as shown by the concentrations of vasopressin-associated neurophysin ([VP-RNP]) and concentrations of oxytocin-associated neurophysin ([OT-RNP]) in plasma in conscious Long-Evans rats. Chronically-cannulated rats were infused intravenously at 10 μ1/100 g body wt/min with 13% LiCl for 20 min (total dose = 6.16 mequiv./kg body wt) or 0.65% LiCl for 60 min (total dose = 0.92 mequiv./kg body wt). Effects of 13% LiCl on mean arterial pressure were also examined in vasopressin-deficient homozygous Brattleboro rats. For Long-Evans rats, infusion of 13% Lid produced rapid and significant ( P < 0.001) increases in mean arterial pressure, the concentration of lithium in plasma ([Li +]), plasma osmolality ( P osmol). [VP-RNP], [OT-RNP] and significant decreases in heart rate and sodium concentration in plasma ([Na +]). For similar changes in plasma osmolality, lithium had a greater effect than sodium on mean arterial pressure, [VP-RNP], [OT-RNP]. For the 20 min infusion of 13% LiCl, there was a significant relationship ( P < 0.033) between ΔMAP and log Δ[VP-RNP] with a slope of 11.9 mmHg fmol −1 ml −1 ( r = 0.5678). Unlike that of Long-Evans rats, infusion of 13% LiCl only did not produce significant changes of mean arterial pressure in Brattleboro rats. For Long-Evans rats, infusion of 0.65% LiCl resulted in more gradual and smaller elevations of blood pressure, [Li +] and smaller decreases in heart rate with no significant changes in plasma osmolality, [Na +], [VP-RNP] and [OT-RNP]. The relationship between ΔMAP and log [Li +] over the 60 min of infusion of 0.65% LiCl was highly significant ( P < 0.001) with a slope of 15.0 mmHg mequiv. −1 1 −1 ( r = 0.6815). The data show that acute intravenous infusion of LiCl raised the blood pressure in the conscious Long-Evans rat and this effect of Li may involve mechanisms that are independent as well as dependent of the activity of vasopressin-containing neurons.