Hypothalamic monoamines in cold stress on the background of changes in the activity of the nitric oxide system.

The effects of the NO donor sodium nitroprusside and the NO synthase blocker L-omega-N-nitroarginine (LNA) on body temperature, hypothalamic monoamines, and plasma corticosterone in conditions of cooling were studied in Male Wistar rats. Reductions in body temperature on cooling, both after administration of sodium nitroprusside and LNA, were no different from those seen without treatment. The basal corticosterone level after treatment with sodium nitroprusside increased from 5.3 +/- 2.2 to 29.1 +/- 1.8 microg%. Cooling led to a multiple increase in corticosterone levels in all animals, both in control conditions and after treatment with sodium nitroprusside and LNA. Sodium nitroprusside significantly decreased the basal hypothalamic noradrenaline level, by 37%. Cooling of the animals in these conditions led to an additional drop in the noradrenaline level. Noradrenaline levels 48 h after cold stress applied to animals cooled after treatment with LNA or sodium nitroprusside were significantly higher than in those cooled without treatment. No changes in serotonin and 5-hydroxyindoleacetic acid levels were seen in these experiments. The basal dihydroxyphenylacetic acid and dopamine levels increased after treatment with sodium nitroprusside, by 379% and 239% respectively. No dopamine response to cold was observed, though the dihydroxyphenylacetic acid level in the control group and animals treated with LNA increased. Thus, cold stress did not reveal differently directed directions for the actions of the NO donor and the NO synthase blocker, as seen with other types of stress.