Metabolic and Reproductive Parameters in Young Female Rats Subjected to Feed Restriction and/or Ginger Oil Administration

1. INTRODUCTION

The metabolic status of animals affects reproductive performance. Numerous studies demonstrated the effects of nutrition on many aspects of reproduction in several species [1, 2]. Undernutrition reduces body weight and body condition scores [3]. Such effects of undernutrition are manifested in reduced gonadotropin secretion, delayed puberty, reduced estrus expression, impaired follicular development, and delayed postpartum return to estrus. These effects of nutrition are to ensure that reproduction is supported by a plentiful food supply that will meet the high nutritional demands of gestation and lactation [4].

More research addresses the nutrition-reproduction interaction in females than in males. This is primarily because the consequences of undernutrition not only affect the female herself but also her offspring’s growth and development. Thus, the female’s “nutritional investment in reproduction” is much greater than that of the male [4]. This can be seen when maternal malnutrition during gestation influences the prenatal development of her offspring, resulting in lower fetal weights and delayed ossification [5]. In addition to the effects above, undernutrition can affect the level of tissue oxidation. Feed supplements (or additives) can be used to counteract the oxidative effects. A study by Guo et al. [6] reported that feed restriction during the luteal phase of the estrous cycle altered energy metabolism and increased oxidative stress of ovarian tissues in sheep. In the same study, arginine supplementation was effective in reducing the negative effects of feed restriction through altering gene expression, increasing resistance to oxidative stress, and reducing apoptosis.

Ginger (Zingiber officinale Roscoe), a medicinal plant anciently used in Asia, Europe, and the Middle East, is known to have anti-oxidative effects [7]. Ginger has been shown to protect tissues and organs against oxidative stress. It was able to reduce the induced oxidative effects of several stressors on various tissues [8-10]. Besides acting as an antioxidant, ginger supplementation appears to improve male reproductive parameters; rats [11] and mice [12] supplemented with ginger experienced increased sperm concentration, viability, motility, and serum total testosterone. Herbal medicines with antioxidant properties, such as ginger, can neutralize intermediate free radicals, halt oxidation chain reactions, and ultimately enhance specific sperm fertility indicators, thereby improving the fertility potential of sperm in roosters [13, 14]. Male fertility can be improved by using medicinal herbs with antioxidant properties. These herbs help reduce oxidative stress, enhance gonadal hormone levels, boost spermatogenesis, and ultimately increase male reproductive efficiency [14]. In terms of direct effects on reproduction, we could not find any literature on the effects of ginger on pubertal female rats. For this reason, this study was conducted to evaluate whether ginger oil supplementation can reduce the negative effects of feed restriction on metabolic and reproductive parameters in young female rats.

2. MATERIALS AND METHODS

3. RESULTS

3.1. Body Weight and Size

Fig. (1A) shows body weight change in all groups. There was a significant sampling week effect (P < 0.05) whereby rats gained weight as the experiment advanced. However, rats in the feed-restricted group showed a modest increase in body weight during the first two weeks before reaching a plateau; they gained less weight (P < 0.05) than those in the remaining groups. There was a treatment x sampling day interaction (P < 0.05) with respect to body size. Feed-restricted rats (G2) started out numerically longer but had reduced growth in size (Fig. 1B) as the experiment advanced, accompanying the decline in body weight.

3.2. Cortisol and Blood Metabolites

Cortisol concentration was not affected by treatment (Table 1). Similarly, serum cholesterol and triglycerides did not differ among groups (Table 1). Serum glucose (Fig. 2A) and urea nitrogen (Fig. 2B) were significantly influenced (P < 0.05) by feed restriction but not by ginger supplementation. Feed restriction resulted in increased serum glucose and reduced urea nitrogen in rats.

Table 1.

Blood Parameter	Treatment
	Control (n=6)	Feed Restriction (n=6)	Ginger (n=6)	Ginger Plus feed Restriction (n=6)
Cholesterol (mg/dL)	55.3±5.2	56.9±4.8	57.5±4.8	61.5±4.8
Triglycerides (mg/dL)	117.4±18.6	97.0±16.6	98.7±16.6	101.6±16.6
Cortisol (µg/dL)	4.25±0.87	5.06±0.87	4.37±0.87	4.92±0.87

Note: ¹Ginger oil was supplemented at the rate of 0.2mL/rat/day.

3.3. Organ Weights

Several organs were collected and weighed. The right and left ovaries and kidneys for each animal were weighed separately. There was no feed restriction by ginger supplementation interactions with respect to any of the organs measured. Kidneys, heart, liver, spleen, and pituitary gland were unaffected by treatment (Table 2). Right ovaries were affected (P < 0.05) by feed restriction and tended to be influenced (P < 0.10) by ginger supplementation but not their interaction (Fig. 3A and C). Left ovaries, however, were not significantly affected by either treatment (Fig. 3B and D), although they were numerically heavier in the ad libitum-fed rats and in rats receiving ginger oil. The right ovaries of rats in the feed-restricted groups weighed less than those of animals receiving ad libitum feeding. Similarly, ginger supplementation tended to increase right ovarian weights compared to animals not receiving ginger regardless of feed restriction (Fig. 3B). Reproductive tract weights were also influenced by ginger supplementation (P < 0.05). Rats in the ginger-supplemented groups had heavier reproductive tracts than their non-supplemented counterparts (Fig. 4).

Table 2.

Organ Weights	Treatment
	Control (n=6)	Feed Restriction (n=6)	Ginger (n=6)	Ginger Plus Feed Restriction (n=6)
Left kidney (g)	0.85±0.05	0.83±0.05	0.84±0.05	0.90±0.05
Right kidney (g)	0.89±0.06	0.93±0.06	0.85±0.06	0.98±0.06
Heart (g)	0.77±0.04	0.78±0.04	0.83±0.04	0.74±0.04
Liver (g)	8.29±0.36	7.65±0.36	8.49±0.36	8.29±0.36
Spleen (g)	0.61±0.03	0.65±0.03	0.57±0.03	0.61±0.03
Pituitary gland (mg)	9.9±6	19.6±6	19.4±6	10.5±6

Note: ¹Ginger oil was supplemented at the rate of 0.2mL/rat/day.

Table 3.

Parameter	Treatment
	Control (n=6)	Feed Restriction (n=6)	Ginger (n=6)	Ginger Plus Feed Restriction (n=6)
Dam birth weight (g)	237.3±6.6	234.6±6.6	235.4±7.4	224.6±6.1
Rats giving birth (Ratio)	5/6	5/6	4/6	6/6
Litter size (No.)	11.5±0.7	11.8±0.7	12.8±0.7	12.2±0.7
Litter weight (g)	61.7±9.1	78.5±9.1	75.2±9.1	70.5±9.1
Individual pup weight (g)	6.3±0.6	6.6±0.6	6.0±0.6	5.8±0.6
Days from male introduction to birth (d)	24.2±0.7	25.4±0.8	24.0±0.7	24.6±0.8

Note: ¹Ginger oil was supplemented at the rate of 0.2mL/rat/day.

4. DISCUSSION

The strong link between nutrition and reproduction ensures that the female is able to sustain her own body before supporting another life (or lives). A low plane of nutrition can negatively influence reproduction; however, the magnitude of this depends on severity and duration. Feed restriction can increase the level of tissue oxidation, leading to apoptosis [6]. Ginger, an antioxidant, has been shown to protect against oxidative stress induced by many factors [16, 17]. This study evaluated the effects of supplementing ginger oil to feed-restricted female rats on metabolic and reproductive parameters.

Rats in the feed restriction group (G2) experienced a reduction in growth (body weight and size). This was expected as these animals received 75% of the estimated intake for 30 days. The other feed restriction group (G4) did not experience any effects on body weight and size. Rats receiving a lower plane of nutrition experience reduced body weights. Chapin et al. [18] reported lower body weights in Sprague-Dawley male and female rats exposed to feed restriction. Ginger oil supplementation to G4 rats appears to be the main factor preventing the effects of the low plane of nutrition on growth. This may be due to the energy content in ginger oil; various varieties of ginger oil provide from 375 to 396 kcal/100g [19].

Rats receiving ginger oil appeared to be more docile and less stressed during the daily handling for treatment administration. Ginger supplementation has been reported to modulate stress response in fish [20]. The authors observed a lesser increase in cortisol concentrations following exposure to hypoxic conditions in the ginger-supplemented group compared with the controls. In this study, however, we detected similar cortisol concentrations among the four treatment groups.

In previous studies, ginger extract administration lowered blood cholesterol and triglycerides in rats [21] and humans [22]. In the present study, serum cholesterol and triglycerides were unaffected by ginger oil administration. Similar results were reported by Jeena et al. [23], whereby ginger oil administration did not induce a significant decrease in blood cholesterol and triglycerides. The discrepancy in findings may be due to the type of supplement (extract vs oil) and dose of ginger used in the studies.

Ginger supplementation had no effect on serum urea nitrogen and glucose. Serum urea nitrogen was lower in the feed-restricted groups, while serum glucose was greater in the feed-restricted groups compared to those receiving ad-lib feeding. The lower feed intake is the primary reason for such a decrease. Reduced total feed intake is associated with lower crude protein intake, which partially accounts for the decline in urea nitrogen. Additionally, the body’s requirement for glucose may have activated gluco- neogenesis, resulting in the utilization of amino acids for the production of glucose. This can also explain the greater glucose concentration in the feed-restricted rats. One additional factor contributing to this justification is the numerical increase in cortisol concentration in the feed-restricted groups (Table 1). Cortisol is a metabolic hormone known to induce glucose production through gluco- neogenesis. Despite its effects on body weight, feed restriction did not affect organ weights, with the exception of the right ovaries, which weighed less in the feed-restricted rats than in those receiving ad libitum feeding. The lower plane of nutrition is probably the cause of reduced ovarian weights in feed-restricted rats, which also relates to the retarded growth observed in these animals. The current study might not have shown that a reduction in body weight has been severe enough to yield a measurable reduction in organ weight. Chapin et al. [18] reported lower liver, kidneys, and right ovarian weights in Sprague-Dawley female rats subjected to feed restriction, especially when those animals reached 70% of the control rats’ body weights. The severity and duration of feed restriction in our project did not match that of the aforementioned study. Similar to feed restriction, ginger supplementation did not affect the non-reproductive organ weights. Similar findings were reported when ginger powder [22] or oil [23] was supplemented in rats. In either of the previous studies, organ weights were comparable among control and ginger-treated rats regardless of form or the administered dose.

The current study found positive effects of ginger oil supplementation on reproductive development without affecting litter data (litter size, pup weight, etc.). Ginger oil-supplemented rats had heavier reproductive tracts and tended to have heavier right ovaries than their non-supplemented counterparts did. Left ovaries, although numerically heavier, were unaffected by treatment. To our knowledge, no previous studies investigated the effects of ginger oil supplementation on reproductive development in feed-restricted female rats. Our results are similar to previous studies that found that ginger supplementation increased ovarian weight in rabbits [24]. The notable increase in ovarian weight observed in the experimental group compared to the control group suggests that the dose might be an optimal level for enhancing ovarian function [24]. Feed restriction has recently been reported to alter energy metabolism and increase oxidative stress of ovarian tissue in sheep [6]. The positive effects of ginger oil reported in the current study may be due to its anti-oxidative properties. In previous studies, rats exposed to oxidative stress (treated with isoproterenol) expressed reduced tissue antioxidant levels [namely catalase, superoxide dismutase (SOD) and glutathione (GSH) [10]. Treating these rats with ginger extract reversed the oxidative effects and returned the aforementioned antioxidants to their normal (catalase and SOD) or above-normal (GSH) levels. Devine et al. [25] reviewed the effects of oxidative stress on ovarian function. They concluded that depletion of GSH stimulates apoptosis in antral follicles and granulosa cells, while antioxidant supplementation inhibits such effects.

CONCLUSION

In summary, the current study evaluated the effects of feed restriction and ginger oil supplementation on growth, blood metabolites, and reproductive development in young female rats. There was no interaction between the two treatments with respect to any of the measured variables. Feed restriction resulted in a significant reduction in body weight accompanied by a reduction in the weight of the right ovary. On the other hand, ginger oil supplementation resulted in increased reproductive tract and right ovarian weights. Such effects may have occurred due to the anti-oxidative properties of ginger oil. Future research should address longer-term, more severe feed restrictions with ginger oil supplementation. Additionally, histological assessment of ovaries should shed some light on the impact of supplementation on follicular development.

REFERENCES