Changes in brown adipose tissue metabolism following intraventricular vasoactive intestinal peptide and other gastrointestinal peptides in rats.

The effects of intracerebroventricular (icv) vasoactive intestinal polypeptide (VIP), secretin, glucagon, and cholecystokinin-octapeptide (CCK-8) on the thermoregulatory and cardiovascular systems were studied in conscious rats. The icv injection of VIP at a dose of 10 micrograms produced hyperthermia with an increase in the positive difference between the interscapular brown adipose tissue (BAT) and colonic temperatures (TBAT-Tco), but had little effect on nonevaporative heat loss. Mean arterial blood pressure and heart rate increased following the icv VIP. The results were consistent at ambient temperatures (Ta) of 18, 23, and 28 degrees C. The icv injection of secretin at doses of 1 and 10 micrograms at Ta of 23 degrees C produced hypothermia with a decrease in (TBAT-Tco) and elevated blood pressure without any change in heart rate. The 10 micrograms of icv glucagon had no effect on the thermoregulatory and cardiovascular systems. The large dose of icv CCK-8 (10 micrograms) induced persistent hyperthermia. Nonsulfated-form CCK-8 and CCK-tetrapeptide, however, were ineffective on all variables measured. These results indicate that the central VIP activates BAT thermogenesis and induces hyperthermia, but has a minimum effect on nonevaporative heat loss. Although VIP, secretin, and glucagon have similarities in terms of chemical structure, their effects on body temperature, BAT thermogenesis, and the cardiovascular system are quite different.