Diurnal variations in thermoregulatory responses to intrahypothalamic and intravenous injections of noradrenaline in the pigeon.

The differences in responses of Tb, Tf and VO2 both to intrahypothalamic and i.v. administration of NA were measured both at noon and at midnight in the pigeon. Although the Tb and VO2 were at a higher level in the daytime, no differences in the magnitude of the fall in VO2 and Tb were obtained after either intrahypothalamic or i.v. injections of NA, whether it was measured during the day or at night. The only marked difference was the more prominent vasodilatation in the daytime after both routes of injection.