The medial preoptic area modulates the increase in plasma glucose and freefatty acid mobilization induced by acute cold exposure

The effect of cold exposure (0 degrees C, 1 h) on free fatty acid (FFA) mob ilization and plasma glucose was studied in freely moving male rats injecte d with adrenergic blockers (phentolamine or propranolol) into the medial pr eoptic area (MPOA). The rats were implanted with chronic jugular catheters for blood sampling and with unilateral intracerebral cannulas placed just a bove the MPOA. Blood samples were taken 2 min before and 10, 20, 40 and 60 min after cold exposure. After cold exposure plasma glucose and plasma FFA levels rose rapidly, reaching a peak at 20 min post-stimulus. Previous admi nistration of phentolamine (50 nmol), but not propranolol (100 nmol), into the MPOA blocked the glycemic response to cold exposure. On the other hand, previous administration of propranolol, but not phentolamine, into the MPO A blocked the increased FFA mobilization in response to cold exposure. On t he basis of these results, we propose that MPOA alpha-adrenergic synapses r elay impulses activating the sympathetic outflow expressed by neurally medi ated hyperglycemia, and beta-adrenergic synapses relay impulses activating the sympathetic outflow to the adipose tissue, increasing FFA acid mobiliza tion. (C) 1999 Elsevier Science Inc.