Figure 1. The effect of halothane on the thermogenic response to norepinephrine. (A) A typical recording from a control experiment. The experiment was performed as detailed in Experimental Procedure for Spontaneously Breathing Hamsters, with a cold-acclimated hamster (133 g). It was left undisturbed for about 3 h (the last 40 min are shown here) before it was injected with norepinephrine (NE). When the effect of the first norepinephrine injection had ceased, a second norepinephrine injection was administered. The vertical axis indicates the change in oxygen concentration in the air drawn from the metabolic chamber, RMR-2, NE-1, RMR-3, and NE-2 indicate the intervals during which values for Figure 2were obtained (see Methods for definition). RMR-1 was obtained before the depicted registration. (B) A typical recording from a halothane experiment with a cold-acclimated hamster (118 g). After about 2 h (the last 20 min are shown here), 3% halothane was mixed with the incoming air; after about 15 min, the concentration of halothane was reduced to 1.5%(the shifts in baseline indicated by the shaded area are due to the decrease in the oxygen concentration caused by the introduction of halothane). After about 40 min, the hamster was injected with norepinephrine. After about 80 min, halothane was discontinued. After almost full recovery (50 min is deleted from the recording, where indicated), a second norepinephrine injection was administered.