Androgen receptor antagonism and an insulin sensitizer block the advancement of vaginal opening by high-fat diet in mice

Abstract

Reduced hypothalamic sensitivity to steroid negative feedback may contribute to the onset of puberty. In high fat-fed rodents, the timing of vaginal opening (VO) is advanced, suggesting that puberty begins earlier. Because obesity can increase androgens, which interfere with normal steroid feedback in adult females, we hypothesized that androgens reduce hypothalamic sensitivity to negative feedback during puberty and that blocking androgen action would prevent advanced VO in high fat-fed mice. Age at VO was examined in mice fed high-fat or low-fat diets from weaning and treated with the androgen receptor antagonist flutamide or vehicle (controls). VO was advanced in high-fat vs. low-fat controls, and flutamide blocked this advancement. VO was also delayed in low fat-fed flutamide-treated females, suggesting involvement of androgens in the timing of normal puberty. We next investigated if high-fat diet-induced insulin resistance contributes to early VO, as elevated insulin can stimulate androgen production. VO was examined in mice on either diet treated with the insulin sensitizer metformin. Metformin blocked high-fat advancement of VO but did not alter the timing of VO in low fat-fed mice. Insulin was elevated in high fat-fed females that had undergone VO compared with age-matched low fat-fed or metformin-treated animals on either diet that had not undergone VO. Together, these data suggest a model in which metabolic changes induced by high-fat diet, including transient increased circulating insulin, act in part by increasing androgen action to influence the timing of puberty in females.

FIG. 1.

Blocking androgen receptors delays puberty in both low fat-fed and high fat-fed female mice. A) Mean ± SEM age at VO. B) Mean ± SEM body mass at VO. C) Mean ± SEM body mass over time. Open bars, low-fat diet; black bars, high-fat diet; con, control; flut, flutamide. *P < 0.05 vs. low fat-fed mice in same treatment and #P < 0.05 vs. vehicle-treated controls on the same diet.

FIG. 2.

An insulin sensitizer, metformin, delays puberty in high fat-fed female mice. A) Mean ± SEM age at VO. *P < 0.05 vs. low fat-fed mice in same treatment and #P < 0.05 vs. high fat-fed vehicle-treated controls. B) Mean ± SEM body mass at VO. C) Mean ± SEM body mass over time. *P < 0.05 body mass of high fat-fed mice vs. low fat-fed mice. Open bars, low-fat diet; black bars, high-fat diet; con, control; met, metformin.

FIG. 3.

Neither diet nor treatment with the insulin sensitizer metformin affected serum parameters examined after puberty as assessed by VO. Mean ± SEM serum insulin (A) and NEFAs (B). Open bars, low-fat diet; black bars, high-fat diet.

FIG. 4.

Serum insulin levels are elevated by high-fat diet during the pubertal process. A) Percentage of animals in each group that had undergone VO at the time of blood sampling. B) Mean ± SEM serum insulin levels. Open bars, low-fat diet; black bars, high-fat diet. *P < 0.05.