Effect of prostaglandin, pyrogen and noradrenaline, injected into the hypothalamus, on thermoregulation in newborn lambs.

Thirteen newborn lambs were implanted stereotaxically with an array of 4 guide tubes positioned bilaterally so that their tips lay above various hypothalamic loci. At postnatal ages 50-70 h, rectal temperature was monitored, and bilateral 1 microliter injections were made into the hypothalamus. Prostaglandin E1 (0.2 microgram) and prostaglandin E2 (0.2-2.0 microgram) did not cause fever on any occasion though injections were made into 44 sites throughout the hypothalamus. Nevertheless, lambs that did not develop fever following central injection were often, if sensitized by bacterial pyrogen given earlier able to develop fever after intravenous injection of bacterial pyrogen. Infusion of a bacterial pyrogen (S. abortus equi, 0.2 microgram) into these same sites caused fever only when injections were made into the anterior hypothalamic/preoptic area (AH/POA). Eight lambs were placed in a 10 degrees C environment and noradrenaline was injected. Rectal temperature fell by 0.5-1.4 degrees C after 7 bilateral injections into the AH/POA, but 9 injections into other hypothalamic areas caused little temperature change. When 6 lambs were placed at a temperature of 30 degrees C and noradrenaline was injected, no consistent temperature changes were observed after microinjection into the AH/POA or other parts of the hypothalamus.