Effects of adrenalectomy on daily gene expression rhythms in the rat suprachiasmatic and paraventricular hypothalamic nuclei and in white adipose tissue

Abstract

It is assumed that in mammals the circadian rhythms of peripheral clocks are synchronized to the environment via neural, humoral and/or behavioral outputs of the central pacemaker in the suprachiasmatic nucleus of the hypothalamus (SCN). With regard to the humoral outputs, the daily rhythm of the adrenal hormone corticosterone is considered as an important candidate. To examine whether adrenal hormones are necessary for the maintenance of daily rhythms in gene expression in white adipose tissue (WAT), we used RT-PCR to check rhythmic as well as 24 h mean gene expression in WAT from adrenalectomized (ADX) and sham-operated rats. In addition, we investigated the effect of adrenalectomy on gene expression in the hypothalamic SCN and paraventricular nucleus (PVN). Adrenalectomy hardly affected daily rhythms of clock gene expression in WAT. On the other hand, >80% of the rhythmic metabolic/adipokine genes in WAT lost their daily rhythmicity in ADX rats. Likewise, in the hypothalamus adrenalectomy had no major effects on daily rhythms in gene expression, but it did change the expression level of some of the neuropeptide genes. Together, these data indicate that adrenal hormones are important for the maintenance of daily rhythms in metabolic/adipokine gene expression in WAT, without playing a major role in clock gene expression in either WAT or hypothalamus.

The role of feeding rhythm, adrenal hormones and neuronal inputs in synchronizing daily clock gene rhythms in the liver

“…In the present study we showed that the daily rhythm of clock gene expression in the liver is still intact under 6-meals-a-day feeding conditions, after adrenalectomy, after total hepatic denervation or after total hepatic denervation with adrenalectomy or 6-meals-a-day feeding schedule. These results are similar to previous findings in liver (Cailotto et al 2005;Oishi et al 2005;Pezuk et al 2012;Sujino et al 2012), epididymal white adipose tissue (eWAT) (Su et al 2014(Su et al , 2015, kidney (Pezuk et al 2012;Sujino et al 2012), salivary gland (Pezuk et al 2012) and lung (Pezuk et al 2012). Together these findings demonstrate that feeding rhythm, adrenal hormones (in particular corticosterone) and neuronal inputs are not indispensable for synchronized daily clock gene rhythms.…”

Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

“…Other studies suggest that GC also directly affect clock gene expression in metabolically active tissues, such as liver and kidney, whereas they can trigger rhythmic gene expression in the liver of SCN-lesioned animals (Balsalobre et al, 2000;Oishi et al, 2005;Reddy et al, 2007). By contrast, in the white adipose tissue and liver, adrenalectomy abolishes many daily rhythms in metabolic/adipokine gene expression, but not clock gene expression (Oishi et al, 2005;Su et al, 2014). Moreover, besides clock mechanisms, the GC rhythm is profoundly affected by stress and stressful events occurring during the daily trough of plasma GC (i.e., late night and morning in nocturnal species) will therefore mask the endogenous rhythm of GC.…”

HPA axis and vagus nervous function are involved in impaired insulin secretion of MSG-obese rats

“…Sham-ADX was performed using the same approach, with only localization of the adrenals, leaving the glands intact. ADX rats were maintained on 0.9% NaCl to correct the aldosterone insufficiency throughout the 10 days following the operation (Su et al 2015).…”