Effects Of Dietary Protein Levels On The Onset Of Puberty In Female Rats

Kisspeptin/GPR54 system was proposed as the key component involved in regulating puberty onset and follicular development, however, it remains unclear whether the effects of protein intake on the puberty onset and follicular development, if any, could be explained by the Kisspeptin/GPR 54 system. Eighty 21-day-old SD weanling rats were randomly allocated into four treatment groups to fed four diets containing graded protein content at 8%(CP8,n=20),13%(CP13,n=20),18%(CP18, n=20),23%(CP23, n=20) by increase casein content at the expense of corn starch. Virgin smear was conducted to check the occurrence of virginal opening. Rats were slaughtered on the second occurrence of dioestrus for sample collection of serum, hypothalamus, pituitary, ovary, uterus and liver. Ovarian morphology, serum amino acid composition, IGF-1, Leptin, reproductive hormones and gene expressions at HPG axis were investigated. Results:1 Age at vaginal opening or dioestrus of rats was significantly affected in response to varied dietary protein content (P<0.05). CP8 rats reached vaginal opening at an average age on 40.25d, which was significantly delayed compared with CP13 (36.93d), CP18 (36.13d) and CP23 rats (33.86d). Regression analysis revealed that age at vaginal opening was negatively corrected with dietary protein content (y=-0.3328x+127.5, R2=0.949, P=0.025).2 Bodyweight at vaginal opening was higher in CP18 rats compared with CP8 rats (P<0.05). Relative weight of abdominal fat to bodyweight was the highest in CP8 rats, and lowest in CP23 rats, and that in CP13 and CA18 rats were intermediate and was different from CP8 and CP23 rats.3 Development of reproductive tissues and follicles was significantly affected in response to varied dietary protein content (P<0.05). Relative weight of uterus and ovary to bodyweight of rats fed CP18 and CP23 diets were significantly higher than those fed CP8 or CP13 diets. Number of antral follicles and corpus luteum of rats fed CP8 diet was significantly lower than those in rats fed CP13, CP18 and CP23 diets. In contrast, the number of preantral follicles in rats fed CP8 and CP13 diets was significant higher than those in rats fed CP18 and CP23diets. The average number of atretic follicles did not differ among the four groups.4 Serum leptin, IGF-Ⅰ and LH concentrations were not affected in response to varied protein content. Concentrations of E2, GnRH and FSH were significantly elevated in response to increasing protein content. Serum amino acid composition analysis revealed that concentrations of essential amino acid were decreased, and concentrations of non-essential amino acid were increased as the increasing protein content.5 RT-PCR analysis revealed that mRNA expressions of KiSS-land ERα in CP8 and CP13 rats were significantly decreased compared with CP18 and CP 23 rats (P<0.05) mRNA expressions of FSHR and LHR in CP8 and CP13 rats were significantly decreased compared with CP18 and CP 23 rats (P<0.05)Abouve all, our data ascertain that protein restriction could delay the age at puberty. The compromised hypothalamic KiSS-1 expression and the retarded ovarian follicle development was the leading cause for the late timing of puberty and reproductive maturity.