Effect of Dietary Protein Levels on Sex Hormones in Growing Male Rats Kept under Constant Darkness

Abstract

Abstract:The purpose of this experiment was to clarify the effects of dietary protein levels on the gonadal development and sex hormones in male rats kept under constant darkness as a model of disturbed daily rhythm. Four-week-old male rats (Fischer 344 strain) were kept under constant darkness or normal lighting (12-h light/dark cycle). Two kinds of experimental diet were prepared, one with low dietary protein levels (9% casein) and one with normal levels (18% casein). Harper mineral mixture and Panvitan were used as mineral and vitamin sources, respectively. After 4 weeks, gonadal weight, serum testosterone, and other hormone contents were evaluated. The gonadal weight in the constant darkness groups (D-groups) was lower than that in the normal lighting groups (N-groups). Although the low-protein diet in the D-groups significantly reduced gonadal weight, the normal-protein diet mitigated the reduction of gonadal weight in rats kept under constant darkness. Serum testosterone and androstenedione concentrations were lower in D-group rats fed the lowprotein diet. There were no effects of lighting condition or protein levels on serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), or progesterone concentrations. These results indicate that the suppression of gonadal development in D-group rats fed the low-protein diet was caused by low testosterone, which we attribute to the inhibition of synthesized androstenedione, a precursor of testosterone. The present study showed that constant darkness and the low-protein diet inhibited the synthetic pathway from progesterone to androstenedione.

Comparison of the Effects of Dietary Protein on the Sexual Organ Development of Male Mice and Rats Kept under Constant Darkness

“…We have been investigating the effects of various nutrients on sexual organ development in rats kept under constant darkness (5)(6)(7)(8)(9)(10)(11)(12). The present study used a model in which the daily rhythm was free-running rather than a 24-h rhythm.…”

Environment-wide association study to comprehensively test and validate associations between nutrition and lifestyle factors and testosterone deficiency: NHANES 1988–1994 and 1999–2004

“…Yet, the direction of this influence remains unclear due to contradicting results found in the literature. A few experimental studies have reported that a low-protein diet can lead to low levels of T in male rat models [39,40], but an inverse association was found between protein and T levels in a number of population-based studies [25,41]. Interestingly, more recent literature has focused mainly trying to compare and assess the effects on T levels by different types of proteins (e.g.…”

The Effects of Prolonged Darkness Phase of Photoperiodic Cycle on Serum Levels of Creatine Kinase and Alkaline Phosphatase in Female Rats

“…For example several studies show that prolonged darkness phase in photoperiodic cycle causes decreased serum level of T3 [16], [17], whereas there is a study indicating that prolonged darkness phase has no effect on secretion of T3 hormone [18]. The probable mechanism of action could be referred to the effect of prolonged darkness phase on systems such as immunity and gonadal system [19]- [21], which in turn, may result in increased serum level of creatine kinase and alkaline phosphatase. On the other hand experiences show that prolonged darkness phase causes increased melatonin secretion and pineal activity [16] and this may also lead to increased serum level of creatine kinase and alkaline phosphatase.…”