Endotoxin and prostaglandin fever of newborn guinea pigs at different ambient temperatures.

At an ambient temperature (Ta) of 30 degrees C, injection of 0.2 micrograms E. coli endotoxin into the lateral cerebral ventricle (icv) of three-day-old or younger guinea pigs was followed by a biphasic febrile rise in body temperature (Tc) and oxygen consumption (VO2), interrupted by a transient fall. At Ta 20 degrees C the change in Tc and VO2 was still biphasic, the first rise was similar as that seen at Ta 30 degrees C, but the subsequent fall was more pronounced. Thus, Tc became lower than before endotoxin and remained below the pre-injection level during and after the second rise. Injection of 10 ng PGE1 icv caused sustained monophasic hyperthermia at both Ta-s. Icv injection of 0.9% NaCl did not affect Tc and VO2 at either Ta. Accordingly, prostaglandins might contribute to, but cannot account for, the whole febrile response to endotoxin.     

The central effect of 5-hydroxytryptamine, gamma-amino-butyric acid and carbachol on thermoregulation in the neonatal guinea pig.

5-Hydroxytryptamine (10 microgram), gamma-amino-butyric acid (20 microgram) and carbachol (1 microgram) were injected through the soft skull into the lateral cerebral ventricle of guinea pigs aged 2 to 12 days, at the slightly subneutral ambient temperature of 30 degrees C. 5-Hydroxytryptamine (5-HT) produced no immediate change in oxygen consumption, whereas colonic temperature fell rapidly. One hour after injecting 5-HT, when colonic temperature had decreased by about 0.5 degrees C, oxygen consumption increased and after a lag of 30--40 min was followed by an increase in colonic temperature. Gamma-amino-butyric acid (GABA) increased oxygen consumption and colonic temperature after a latency of 30--60 min. Carbachol was followed by an immediate decrease in colonic temperature and oxygen consumption. Colonic temperature was below the pre-injection level throughout the five-hour period of observation.     

The central effect of noradrenaline on thermoregulation in the neonatal guinea pig.

Noradrenaline (10 microgram) injected into the lateral cerebral ventricle of guinea pigs aged 2 to 12 days produced a rapid increase in oxygen consumption and in colonic temperature at an ambient temperature of 30 degrees C. The increase was most pronounced in the youngest animals and decreased with advancing age, but was still significant at 12 days of age. Species differences and the role of ambient temperature in the responses are discussed.