Assessment of hypothalamic-pituitary-adrenal axis and sympathetic nervous system activity in pregnant sows through the measurement of glucocorticoidsand catecholamines in urine

We validated the use of urine to monitor changes in the activity of both th e hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous sys tem (SNS) in swine. Ten pregnant sows were fitted with venous catheters 3 w k after mating. In the early (wk 6), middle (wk 9), and late (wk 14) stages of gestation, blood and urine were collected over 24 h to monitor diurnal changes in plasma cortisol, urinary cortisol, and urinary catecholamines (n orepinephrine [NE] and epinephrine [EPI]). Dexamethasone suppression tests (DST) and ovine corticotropin-releasing hormone (CRH) challenge tests were also performed at each stage of gestation. All plasma and urinary values ch anged markedly around the clock. Diurnal variations of urinary cortisol wer e comparable to those in plasma, with a late nocturnal peak and a trough oc curring in the evening. During the dark period, urinary catecholamines were lower than during the light period. Norepinephrine increased sharply after lights came on and peaked after meal time. Epinephrine began to rise at th e end of the dark period and peaked just before meal time. Average plasma c ortisol increased with the stage of gestation, due to higher levels during daylight hours. Dexamethasone at 2000 (20 mu g/kg i.v.) decreased plasma co rtisol at 0830 and nocturnal cortisol excretion. The magnitude of the decre ase in plasma ACTH and urinary cortisol after DST was lower in late than in early and midgestation, indicating increased feedback resistance at that s tage. The CRH (1 mu g/kg i.v.) increased plasma and urinary cortisol. Peak levels occurred 30 min and 2 to 3 h after the injection, respectively. Cate cholamines and cortisol in urine produced during the night (2000 to 0800) a nd the early morning (0400 to 0800 and 0800 to 0900) were highly correlated with their 24-h excretion rate. These results indicate that it is possible to monitor changes in the HPA axis and SNS activity through urinary measur ements in pigs.