The psychogenic effects of prolactin.

Prolactin modulates maternal functions and is involved in behaviour. Binding sites have been identified in the hypothalamus and substantia nigra. Hyperprolactinaemia stimulates dopamine turnover in several areas of the brain, including the nucleus accumbens, and reduces turnover in other regions, e.g. the substantia nigra. Hyperprolactinaemia stimulates the opioidergic system. The portal concentration of dopamine and oxytocin (a prolactin stimulatory substance) may be increased in hyperprolactinaemia. In mammals, prolactin is associated with learning, stimulation of the immune response, reduction of body temperature and increased corticosterone secretion. It is involved in the behavioural aspect of reproduction. Secretion is strongly stimulated in the female rat on exposure to pups. Hyperprolactinaemia in male rats reduces sexual behaviour. Hyperprolactinaemia reduces libido in both men and women but in men it is also associated with low testosterone levels. There is evidence that in families characterized by an absent or alcoholic father young girls may be predisposed to develop hyperprolactinaemia later in life as a reaction to losses. The underlying mechanism of such a psychosomatic reaction, a typical example of which is pseudopregnancy, may be an extemporaneous activation of a neuroendocrine "maternal subroutine" characteristic of pregnancy. Prolactinomas may result from somatic changes occurring in activated lactotrophs.