PRL and hyperprolactinemia: Indeed, hyperprolactinemia has been related to the pathogenesis of impaired glucose tolerance and hyperinsulinemia up to overt insulin resistance (8–14), as demonstrated by the evidence that high PRL levels promote the increase of the surrogate index of insulin resistance (HOMA-IR, 11–13) and the reduction of the surrogate index of insulin sensitivity (14), either in obese and lean patients.