Diurnal variation in the concentrations of catecholamines and indoleamines in the median eminence and in the intermediate and posterior lobes of the pituitary gland of the male rat

Abstract

Diurnal changes in monoamine concentrations were studied in the median eminence and in the intermediate and posterior lobes of the pituitary gland of the male rat. The concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NA) and dopamine (DA) were analyzed at 7 time points over a 24-h period. Diurnal variation was analyzed by analysis of variance (ANOVA) with time of day as a class variable as well as by 24 h and 12 h cosine curve fittings. There were marked time-dependent changes in the median eminence concentrations of 5-HT (ANOVA: P = 0.0085), 5-HIAA ( P = 0.003) and NA ( P = 0.0003). Cosine curves with 24-h periods fit the data points with peaks around 13.00 h. DA levels also varied with an apparent 24-h rhythm in the median eminence, but the changes did not reach the level of significance in the ANOVA. In the intermediate lobe of the pituitary gland, the concentrations of DA varied significantly during the course of the 24-h cycle ( P = 0.0011) and were well-fitted to a 24-h cosine wave. The 5-HIAA levels also showed marked dirunal changes ( P = 0.025) with an evident 12-h rhythm. In contrast, NA and 5-HT concentrations did not appear to vary during the 24-h cycle. In the posterior lobe of the pituitary gland, DA had a 24-h rhythm ( P = 0.0005) similar to the intermediate lobe. NA and indoleamine levels did not show any significant variation. The present study provides biochemical evidence that monoamine levels have different diurnal variation in the median eminence and in the intermediate posterior lobes of the pituitary gland of the male rat. These changes may be related to diurnal patterns of release of various pituitary hormones.