Production of 3-carbon units (as lactate) by granulosa cells (GC) is important in follicular and oocyte development, and may be modulated by metformin. Objective: To examine the action of metformin on GC lactate production and potential mediation via AMP-activated protein kinase (AMPK). Design: GC were prepared from follicular aspirates. After exposure to metformin and other potential modulators of AMPK in culture, aspects of cellular function were examined. Setting: Private fertility clinic/

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... iversity academic centre. Patients: Women undergoing routine in vitro fertilisation. Interventions: All agents added in culture. Main outcome measures: Lactate output of GC was measured. Cell extracts were prepared after culture and phosphorylated forms of AMPK and acetyl CoA carboxylase (ACC) assayed using Western analysis. Results: Metformin led to a rapid increase in lactate production by GC (minimum effective dose, 250µM; maximum dose studied, 1mM (1.22-fold; P<0.01)). This dose range of metformin was similar to that required for stimulation of p-AMPK in GC (minimum effective dose, 250µM; maximum effect, 500µM (2.01-fold; P<0.001)). Increasing p-ACC, as a representative downstream target regulated by AMPK, was apparent over a lower range (minimum effective dose, 31µM; maximum effect, 250µM; P<0.001). A level of metformin (125µM) insufficient for the stimulation of lactate output when used alone, potentiated the effects of sub-optimal doses of insulin on lactate production. Adiponectin (2.5µg/ml) had a small but significant effect on lactate output. Conclusions: Metformin activates AMPK in GC, stimulating lactate production and increasing p-ACC. Metformin also enhances the action of sub-optimal insulin concentrations to stimulate lactate production. _______________________________________________________________ Polycystic ovary syndrome (PCOS) is a common endocrine disorder in women usually characterised by hyperandrogenism and oligomenorrhea (1). Women with PCOS often exhibit insulin resistance, which contributes to an underlying mechanism important in the pathogenesis of PCOS (2). This concept has led to the use of insulin sensitisers, such as metformin, in the treatment of PCOS.