Crcadian patterns of melatonin, corticosterone, and progesterone in male rats subjected to chronic stress: Effect of constant illumination

Abstract

Plasma and pineal melatonin and plasma corticosterone and progesterone concentrations have been shown to be altered by several types of stressors. This study was designed to define the circadian patterns of the hormones mentioned above in rats subjected to chronic stress and to investigate the influence of constant illumination. The results revealed that melatonin and corticosterone circadian patterns deteriorated and their plasma concentrations were significantly elevated. The constant illumination (2,500 lux) during the dark period (from 2000 to 0600) was not able to suppress melatonin production in stressed animals, while the plasma content of corticosterone was decreased at the end of experimental period compared to control rats. Plasma levels of progesterone were increased in stressed animals as well. Constant illumination, however, provoked also an increase of progesterone secretion in controls. Statistical comparisons between hormonal secretory patterns showed that melatonin and corticosterone correlated negatively in controls (r = -0.58, P less than 0.05) during the nighttime. However, in stressed animals correlation was observed only between melatonin and progesterone secretion during the light and dark period (r = -0.43, P less than 0.05). Surprisingly, the correlation during the nighttime in rats subjected to constant illumination was negative (r = -0.60, P less than 0.02) compared to positive correlation (r = 0.60, P less than 0.02) in rats kept under normal lighting regimen. These results suggest that melatonin release is affected by stress and, possibly, under these circumstances, interacts with adrenal steroid secretion.

Adolescence: A central event in shaping stress reactivity

“…For instance, stressinduced progesterone secretion has been observed in adult males (Andersen, Bignotto, Machado, & Tufik, 2004;Andersen, Martins, D'Almedia, Bignotto, & Tufik, 2005;Persengiev, Kanchev, & Vezenkova, 1991;Schaeffer & Aron, 1987). We have demonstrated that prepubertal males and females show a greater and more prolonged stress-induced progesterone response compared to adults (Romeo, Bellani, & McEwen, 2005;Fig.…”

Sexually Dimorphic Modulation of GABAA Receptor Currents by Melatonin in Rat Gonadotropin-Releasing Hormone Neurons

“…The next question is how this sort of regulation is involved in reproductive physiology. In female rats, LH surge occurs at the late afternoon of proestrus through the early morning of estrus [47], whereas melatonin level in the blood increases from 2-3 h after the onset of the dark period and remains high throughout the period [39]. This increase in melatonin level coincides with the falling phase of LH surge.…”

“…The maximum concentrations of melatonin in the cerebrospinal fluid are 400 pM in rats [33], 20 nM in ewes [34,35], 200 pM in rhesus monkeys (see [36] for review), and 1-10 nM in humans [37,38]. The melatonin concentration is higher in the cerebrospinal fluid than in the blood [39,40], suggesting that melatonin acts on central neurons through the cerebrospinal fluid.…”

Corticosterone and Testosterone Levels after Chronic Stress in an Animal Model of Depression

“…In the present study, the levels of corticosterone are similar to those reported in the literature for the dark phase of the cycle. Dunn et al [24] reported 20 Ìg/dl, Torrelas et al [25] reported 30.7 Ìg/dl, Persengiev et al [26] reported 24 Ìg/dl and Ottenweller et al [27] reported 20 Ìg/dl. Thus, it seems that the high levels of cortisol observed in depressed humans are not reproduced in this suggested animal model of depression.…”