Changes in vasoactive intestinal Peptide binding site densities in the female rat central nervous system and pituitary during lactation

Using quantitative autoradiography, vasoactive intestinal peptide (VIP) binding site densities were investigated in the female rat during lactation. Plasma prolactin levels were significantly (P<0.01) elevated on days 3 and 10 of lactation. In the brain, there was a significant (P<0.05) increase in VIP binding sites during lactation in the striatum, thalamus, anterior portion of the paraventricular nucleus of the hypothalamus, and several cortical areas compared to virgin female diestrous rats. VIP binding density in the anterior pituitary was significantly higher (P<0.01) when measured on day 3 of lactation, and decreased to diestrous levels by day 10. Pup removal resulted in a significant reversal of the lactation-induced increase in VIP binding density in the thalamus, parietal and insular cortices, and the anterior portion of the paraventricular nucleus. Taken together, modifications in VIP binding site density in the pituitary and in several central areas are associated with changes in the level of prolactin secretion. Moreover, the pattern of VIP receptor induction during lactation suggests a role for VIP in the brain that extends beyond the regulation of prolactin secretion.