Effects of intraventricular neurotensin on blood pressure and heat balance in rats.

The effects of intraventricular neurotensin (NT) at doses of 0.1, 1.0, and 10.0 micrograms on blood pressure (BP), heart rate (HR), heat production (M), heat loss (H), and colonic temperature (T co1) were investigated in conscious rats in a direct calorimeter at 18 and 28 degrees C. At 18 degrees C, a 10.0 micrograms of NT significantly increased BP for several minutes after injection with prolonged bradycardia. The larger two doses (1.0 and 10.0 micrograms) significantly reduced M and T co1. In sinoaortic denervated rats, a 1.0 microgram of NT elevated BP and decreased HR. The decrease in HR was significantly smaller than that in nerve intact rats, which indicates the occurrence of baroreflex with intraventricular NT. The changes in M and T co1 in the denervated rats were, however, not statistically different from the intact rats. The baroreflexive suppression of metabolism seems to play a minimum role in the NT-induced hypothermia. H slightly increased for several minutes after central NT (1.0 and 10.0 micrograms) and significantly decreased thereafter. Thermal conductance significantly increased for a longer period of time after NT injection. At 28 degrees C, 1.0 microgram of NT increased H and M. It is concluded that central NT produced hypothermia by reducing M and enhancing H in the cool environment, but not at 28 degrees C.