Elsevier

Life Sciences

Volume 76, Issue 7, 31 December 2004, Pages 763-774
Life Sciences

Endurance treadmill training in rats alters CRH activity in the hypothalamic paraventricular nucleus at rest and during acute running according to its period

https://doi.org/10.1016/j.lfs.2004.09.014Get rights and content

Abstract

Running training on the treadmill increases the resting hypothalamic corticotropin-releasing hormone (CRH) content in rats, though is still unknown whether and how it occurs in the parvocellular region of the hypothalamic paraventricular nucleus (PVN) where is a predominant region of pituitary-adrenal activity and where CRH and arginine vasopressin (AVP) are colocalized. We thus aimed at examining whether treadmill training would alter the CRH and AVP mRNA levels in the PVN at rest and during acute running with different lengths of a training regime. Male Wistar rats were subjected to treadmill running (∼25 m/min, 60 minutes/day, 5 times/week) for training regimes of 0, 1, 2 or 4 weeks. All training regimes induced an adrenal hypertrophy. Plasma corticosterone levels before acute running increased with lengthening the training period. Four weeks of training produced a significant increase in the resting CRH, but not AVP, mRNA levels in the PVN though relatively shorter training regimes did not. Acute responses of lactate and ACTH release were reduced after 2 and 4 weeks of training, respectively. The responsive PVN CRH mRNA level to acute running decreased with 4 weeks of training but increased with relatively shorter training regimes. These results indicate that running training changes the PVN CRH biosynthetic activity with the regime lasting for 4 weeks, which follows adaptive changes in adrenal functions. Thus, running training-induced changes in hypothalamic CRH activity would originate from the PVN and be induced according to the training period.

Introduction

Acute exercise activates the hypothalamic-pituitary-adrenal (HPA) axis depending on the intensity (Soya, 2001). During intense exercise training, chronic HPA activation such as elevated resting glucocorticoid levels in runners (Luger et al., 1987), cyclists (Silverman and Mazzeo, 1996), and rowers (Snegovskaya and Viru, 1993) is induced and the HPA activation to the same intensity of the acute exercise challenge is reduced (Buono et al., 1987, Luger et al., 1987, White-Welkley et al., 1995). In a previous study, Luger et al. (Luger et al., 1987) inferred that an elevated resting ACTH and glucocorticoid level during intense training may be involved in the hypersecretion of the corticotropin-releasing hormone (CRH) in the hypothalamus. Indeed, the chronic increase in hypothalamic CRH content by running training has been reported in rats (Chennaoui et al., 2002). However, the hypothalamus includes several CRH-containing nuclei (Owens and Nemeroff, 1991) and thus whether CRH synthetic activity increases in the hypothalamic paraventricular nucleus (PVN) is unclear, a predominant region for pituitary-adrenal activation (Bruhn et al., 1984), during exercise training. Although CRH activation of the PVN with the acute running challenge has been reported in previous studies (Richard et al., 1996, Timofeeva et al., 2003), how that effect is modified by running training is currently unknown. Also hypothalamic arginine vasopressin (AVP) is colocalized with the CRH in the PVN (Whitnall et al., 1985) and is presumed to be a factor inducing chronic HPA activation during intense exercise training (Keizer, 1998), though its activity during running training is currently unknown.

We aimed to investigate whether running training would lead to adaptive changes in CRH and/or AVP activity in the parvocellular region of the PVN in the resting condition and responsiveness to an acute running challenge. We report here that running training results in the up-regulated resting CRH mRNA expression and down-regulated running-induced acute response in CRH mRNA when training was done for 4 weeks, where acute running-induced lactate/ACTH responses reduce and pituitary-adrenal activity increase in the resting condition just before running.

Section snippets

Animals

Male Wistar rats aged 4, 6, and 7 weeks were purchased from SLC (Hamamatsu, Japan). The rats were kept in the animal room for 1 week before the experiment. All rats were housed 3 or 4 per cage in a room with a controlled temperature (22 ± 2 °C), humidity (60 ± 10%), and light cycle (lights on from 7:00 A.M. until 7:00 P.M.). Food and water was available ad libitum. The University of Tsukuba's Experimental Animal Use Committee approved the following protocol.

Experimental procedure

As summarized in Fig. 1, rats aged 5,

Results

As shown in Table 1, the relative adrenal weight (mg/100 g body weight) significantly increased with all training independent of the regime length, while the relative thymus weight (mg/100 g body weight) significantly decreased in rats that trained for 2 and 4 weeks, compared with the naive control group.

ANOVA showed significant acute running by training interaction effect on the lactate, glucose, ACTH, and corticosterone levels (Fig. 3). Acute running at 25 meters/minutes for 60 minutes in

Discussion

We aimed at examining whether running training would induce adaptive changes in the CRH and AVP activities in the parvocellular region of the PVN and whether they vary according to the length of the training regime. The results show that running training results in up-regulated resting CRH mRNA in the PVN and down-regulated running-induced acute response in the CRH mRNA with the regime lasting for 4 weeks, with peaked adaptive changes in acute running-induced lactate/ACTH releases (lowered) and

Acknowledgements

We would like to thank Dr. Shinji Nakase (Matsusaka City Hospital), Dr. Masatoshi Takita (National Institute of Advanced Industrial Science and Technology) and our colleagues at the University of Tsukuba's Soya Laboratory, for their kind technical assistance and helpful advice.

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