Somatic afferent regulation of plasma prolactin in anesthetized rats

The effects of noxious and non-noxious mechanical stimulation of various segmental skin areas (face, forelimb, abdomen, and hindlimb) on the plasma concentrations of prolactin (PRL) were examined in anesthetized rats. The experiments were performed on urethane-anesthetized female Wistar rats, ventilated artificially, on the day of estrus. Blood samples (0.5 ml) were collected from the femoral artery every 20 min. Plasma concentrations of PRL were determined by radioimmunoassay. Noxious mechanical stimulation was delivered by pinching the skin with a surgical clamp, while non-noxious mechanical stimulation was delivered by brushing the skin with a toothbrush. Pinching the hindpaw for 6 min significantly increased plasma PRL concentration during stimulation to about 280% of the prestimulation value (p < 0.05). Pinching the face, the forepaw or the abdomen had no significant effect. Brushing of any skin area for 6 min did not significantly change plasma PRL concentrations. These results indicate that cutaneous, nociceptive sensory information contributes to the reflex regulation of PRL secretion from the anterior pituitary when emotional factors are eliminated by anesthesia, and this effect is highly dependent on the site of stimulation.