Suppression of brown adipose tissue metabolism following intraventricular bombesin in rats.

The effects of intraventricular bombesin (BS) at doses of 0.1, 1.0, and 10.0 micrograms on thermoregulatory and cardiovascular functions were studied in conscious rats with a direct calorimeter at ambient temperatures (Ta) of 18, 23, and 28 degrees C. At two lower TaS, the central BS produced a profound decrease in colonic temperature (Tcol) with a reduction of the temperature difference between the interscapular brown adipose tissue (BAT) and the colon (TBAT-Tcol). Increases in nonevaporative and evaporative heat losses and mean arterial blood pressure (BP) were consistent following the central BS at any dose tested at any Ta. In the sinoaortic deafferentated rats, a 0.1 microgram of BS produced hypothermia with a significant decrease in (TBAT-Tcol) and heat production (M). Changes in Tcol, (TBAT-Tcol), and M in the denervated rats, however, were not different from those in the sham-operated rats. These results suggest that the central BS suppresses BAT thermogenesis and facilitates heat loss mechanisms. The baroreflex-mediated metabolic reduction is not the case in the BS-induced hypothermia in rats.