Intracerebroventricular injection of RFRP-3 delays puberty onset and stimulates growth hormone secretion in female rats

Abstract

Background: Puberty onset is a complex, organized biological process with multilevel regulation, and its physiopathological mechanisms are yet to be elucidated. RFRP-3, the mammalian ortholog to gonadotropin-inhibitory hormone, is implicated in inhibiting the synthesis and release of gonadotropin in mammals. However, it is unclear whether RFRP-3 participates in regulating pubertal development.

Methods: This study investigated the functional significance and regulatory mechanism of hypothalamic RFRP-3 neuropeptide in the onset of puberty in young female rats. On postnatal day 22, we implanted cannulas into the lateral ventricles of female rat pups. From postnatal day 28 to postnatal day 36, the intracerebroventricular injection of RFRP-3, or vehicle, was conducted twice a day. To investigate whether puberty onset was affected, we examined the body weight, age of vaginal opening, serum hormone levels, uterus and ovary development, and hypothalamic Kiss-1 mRNA expression.

Results: Intracerebroventricular injection of RFRP-3 significantly decreased the serum concentrations of luteinizing hormone and estradiol, delayed uterine maturation, and postponed the time of vaginal opening. This study suggests that RFRP-3 can delay the onset of puberty in young female rats; the expression of Kiss-1 mRNA is potently inhibited in the RFRP-3 group. Moreover, our data show that RFRP-3 elevates serum growth hormone levels.

Conclusions: These data suggest that intracerebroventricular injection of RFRP-3 significantly delays the onset of puberty in female rats. Additionally, RFRP-3 may be associated with prepubertal rise in the secretion of growth hormone.

Keywords: GH; Kiss-1; Puberty onset; RFRP-3.

Fig. 1

Effects of ICV injection of RFRP-3 on the body weight of female rats. No statistical significance was observed in the body weight among the three groups

Fig. 2

Effects of ICV injection of RFRP-3 on the age at vaginal opening. a The age at VO of the females in the different groups. Data represent means ± SEM. **P < 0.01 versus Vehicle. b The proportion of the females displaying VO at different postnatal ages for the different groups

Fig. 3

Effects of ICV injection of RFRP-3 on the wet weight of the uterus and ovary, and their organ coefficients. a Uterus wet weight. b Ovary wet weight. c Uterus coefficient. d Ovary coefficient. Data represent means ± SEM. *P < 0.05 versus Vehicle

Fig. 4

a, b, c Effects of ICV injection of RFRP-3 on uterine morphology. Compared with the Vehicle group, endometrial thickness (black arrows) of the RFRP-3 group was distinctly thinner. d, e, f Effects of ICV injection of RFRP-3 on ovarian morphology. Ovarian morphology was distinctly similar across groups. Numerous corpora lutea (yellow arrows) were observed in all three groups. Bar 500 μm

Fig. 5

Effects of ICV injection of RFRP-3 on the endometrial thickness. Data represent means ± SEM. *P < 0.05 versus Vehicle

Fig. 6

Effects of ICV injection of RFRP-3 on serum hormone levels. a Serum GH levels. b Serum LH levels. c Serum E2 levels. d Serum FSH levels. Data represent means ± SEM. **P < 0.01 versus Vehicle

Fig. 7

Effects of ICV injection of RFRP-3 on the expression of hypothalamic Kiss-1 and GnRH. a Kiss-1 mRNA level. b GnRH mRNA level. Data represent means ± SEM. **P < 0.01 versus Vehicle