High-fat-feeding in rats has been reported to enhance stress reactions, as assessed by elevation of blood glucose and corticosterone levels. This study was designed to investigate the relationship between changes in blood glucose and hypothalamic neuronal noradrenaline activity (HNNA), as indexed by the ratio of dihydroxyphenylethyleneglycol (DHPG) to noradrenaline (NA), following physiological stress in high-fat-fed rats. Two groups of adult male Wistar rats were fed isocaloric diets high in fat (59% of calories) or starch (70% of calories). After 3 weeks each of these groups was further subdivided into (a) control, (b) 2 min ambient temperature (20 degrees C) swim or (c) 2 min swim in ice-cold water. Animals were decapitated 20 min after commencing the swim; trunk blood and a sample of medial basal hypothalamus were obtained. Computerized gas chromatography/mass spectrometry was used to measure hypothalamic DHPG and NA concentrations. There were no differences between fat- and starch-fed rats in basal levels of serum glucose, insulin or corticosterone and no differences in DHPG, NA or DHPG/NA ratio. Compared to starch-fed rats, ambient swim stress in the fat-fed group produced significantly larger serum glucose (P less than 0.01), serum corticosterone (P less than 0.05), DHPG (P less than 0.05) and DHPG/NA (P less than 0.01) responses. Following cold swim stress similar differences between fat- and starch-fed animals were observed. In addition, serum insulin was found to be significantly suppressed in the fat-fed group (P less than 0.05) following cold swim.(ABSTRACT TRUNCATED AT 250 WORDS)