Genistein during Development Alters Differentially the Expression of POMC in Male and Female Rats

Abstract

Phytoestrogens are considered beneficial for health, but some studies have shown that they may cause adverse effects. This study investigated the effects of genistein administration during the second week of life on energy metabolism and on the circuits regulating food intake. Two different genistein doses, 10 or 50 µg/g, were administered to male and female rats from postnatal day (P) 6 to P13. Physiological parameters, such as body weight and caloric intake, were then analyzed at P90. Moreover, proopiomelanocortin (POMC) expression in the arcuate nucleus (Arc) and orexin expression in the dorsomedial hypothalamus (DMH), perifornical area (PF) and lateral hypothalamus (LH) were studied. Our results showed a delay in the emergence of sex differences in the body weight in the groups with higher genistein doses. Furthermore, a significant decrease in the number of POMC-immunoreactive (POMC-ir) cells in the Arc in the two groups of females treated with genistein was observed. In contrast, no alteration in orexin expression was detected in any of the structures analyzed in either males or females. In conclusion, genistein can modulate estradiol's programming actions on the hypothalamic feeding circuits differentially in male and female rats during development.

Keywords: arcuate nucleus; genistein; proopiomelanocortin; rats; sex differences.

Figure 1

(A) Body weight evolution in all groups. (B) Weekly food intake in all groups (repeated measured ANOVA). Statistically significant differences (p < 0.05) are labelled as follows: a = sex differences in C and G10 groups; b = sex differences in G50 groups. # = sex differences in all groups studied. All values are expressed as means ± S.D. CM: control males: CF: control females; G10M: genistein treated males, dose 10 µg/g; G10F: genistein treated females, dose 10 µg/g; G50M: genistein treated males, dose 50 µg/g; G50F: genistein treated females, dose 50 µg/g.

Figure 2

(A) Schematic representation of the procedure used from treatment to immunostaining. From P6 to P13, daily injections of synthetic genistein (10 or 50 µg/g) or vehicle according to experimental group were administered. From weaning on P21 to P34, an acclimatization period was implemented. Food intake and body weight were measured weekly from P34 until P89. Animals were sacrificed on P90. (B,C) Photomicrographs showing the distribution of immunostaining of POMC-ir positive cells in Arc nucleus. (D,E) Orexin-ir positive cells in the PF and LH. Arrows show orexin-ir and POMC-ir positive cells counted. ArcM: arcuate medial subdivision, ArcL: arcuate lateral subdivision; LH: lateral nucleus of the hypothalamus; DMH-PF: dorsomedial-perifornical nucleus B Bar = 200 μm; C Bar = 50 μm ; D Bar = 300 μm; E Bar = 75 μm [44].

Figure 3

Graph (A) showing the number of POMC-ir neurons in ArcM in all experimental groups (two-way ANOVA) * indicates differences between groups (p < 0.05 in all cases). The error bars indicate standard error of the mean. CM: control males; CF: control females; G10M: genistein treated males, dose 10 µg/g; G10F: genistein treated females, dose 10 µg/g; G50M: genistein treated males, dose 50 µg/g; G50F: genistein treated females, dose 50 µg/g. n = 6 in all groups. All treatments, either injection of genistein or vehicle, were administered from P6 to P13. (B–D) photomicrographs showing the distribution of POMC-ir positive cells in Arc nucleus. B = control female, C = G10 female, D = G50 female. Bar = 200 μm [44].