In absence of physiologic or pathologic conditions altering PRL secretion, hyperprolactinemia with PRL levels mildly or moderately above the normal range (25 -100 ng/ml) has been proposed to represent a physiological response to an increase in metabolic demand, as in case of hypoglycaemia, stress, sexual arousal, and intense physical exercise [42]. This evidence concerns the gene PRL and hyperprolactinemia.