Metabolic and reproductive consequences of the serotonin transporter promoter polymorphism (5-HTTLPR) in adult female rhesus monkeys (Macaca mulatta)

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The serotonin (5HT) reuptake transporter (SERT) plays a key role in 5HT homeostasis by recycling 5HT into the presynaptic neurons. Recently, polymorphisms in the length of the promoter region of the gene that encodes SERT have been linked to functional differences in reactivity to psychosocial stress, as the short (s) promoter length allele shows reduced transcriptionally activity in vitro and is associated with reduced 5HT activity and increased vulnerability to affective disorders. Given 5HT's important role in appetite regulation, polymorphisms in the SERT gene could also affect metabolic parameters. In addition, since reduced 5HT activity may also predispose females to reproductive deficits, polymorphisms in the SERT gene may help explain individual differences in ovulatory function. The present study, using a rhesus monkey model, tested the hypothesis that the presence of the s-variant allele would be associated with altered metabolic regulation and impaired ovulatory cycles compared with the l/l genotype. Females homozygous for the long allele in the SERT gene (l/l, n = 19) were compared to those with the s-variant allele (l/s or s/s, n = 20). All females had similar social histories. Body weights (P = 0.026) but not heights (P = 0.618) were significantly lower in s-variant compared to l/l females. In addition, both BMI (P = 0.032) and sagittal abdominal diameters (SAD) (P = 0.031), as indices of adiposity, were significantly lower in s-variant females. Consistent with these differences, fasting and non-fasting levels of leptin were significantly lower in s-variant females (P = 0.002). While there were no genotype differences in non-fasting levels of insulin, s-variant females had significantly lower concentrations of insulin during a fast than did l/l females (P = 0.052). Neither glucose, T 3, T 4, nor ghrelin varied significantly between groups during either the fasted or non-fasted condition (P > 0.05). Analysis of a subset of females indicated that significantly fewer s-variant females (62.5%) exhibited ovulatory cycles than l/l females (100%, P < 0.05). However, there were no differences in serum estradiol or progesterone in l/l females and those s-variant females that did ovulate (P > 0.05). In addition, females with the s-variant genotype also had reduced 5HT activity (P = 0.030), assessed from the acute increase in serum prolactin following the administration of the 5HT reuptake inhibitor, citalopram. Finally, s-variant females were significantly less responsive to glucocorticoid negative feedback (P = 0.030) yet more responsive to corticotropin releasing hormone (CRH, P = 0.016) in terms of plasma cortisol than were l/l females. These data indicate that adult female rhesus monkeys with the s-variant polymorphism in the SERT gene exhibit metabolic and reproductive alterations in conjunction with reduced serotonergic responsivity and increased LHPA activity and suggest the possibility that this genotype may predispose females exposed to psychosocial stressors to further metabolic and reproductive deficits.