Vasoactive intestinal polypeptide (VIP) selectively stimulates prolactin release in healthy women

The neuropeptide, vasoactive intestinal polypeptide (VIP), is released from the hypothalamus to the portal circulation, and experiments on animals provide evidence that it might modulate hormone secretion from the pituitary. Here we report the effects of VIP on the release of different pituitary hormones, including prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyrotropin-releasing hormone (TSH), in normal women. Seven healthy women (aged 27-32; body weight 53-60 kg), with normal menses and receiving no medication, were tested on days 20-23 of their cycle. Porcine VIP was injected i.v. as a bolus dose of 1 mcg/kg body weight. Blood samples were collected 10 minutes prior to VIP administration and 5, 15, 30, 45, 60 and 90 minutes after VIP injection. Blood pressure and heart rate were continuously monitored. Hormone levels were determined by RIA. Stress, which can stimulate PRL release, was assayed by measuring the effect of placebo on hormone release (5 controls). VIP injection induced a significant (p less than 0.01) increase in plasma PRL levels. Basal PRL was 20.25 +/- 9.14 ng/ml; 5 minutes after VIP injection PRL levels rose to 45.0 +/- 14.9 ng/ml (p less than 0.01). At 15 minutes a plateau was reached (46.0 +/- 14.5 ng/ml), then the levels slowly decreased. VIP administration did not modify the plasma concentration of LH, FSH or TSH at any time during the observation period. The present study indicates that VIP might play a physiological role as a RPL-releasing factor in human beings.