Vasoactive intestinal polypeptide stimulation of prolactin release and renin activity in normal man and patients with hyperprolactinaemia: effects of pretreatment with bromocriptine and dexamethazone

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Abstract
Vasoactive intestinal polypeptide (VIP) was infused into normal volunteers and patients with hyperprolactinaemia. Heart rate increased from 62 pL 3 to 75 pL 3 beats min‐1 (P= 0·001) in controls and from 70 pL 2 to 78 pL 3 beats min‐1 (P= 0·001) in hyperprolactinaemics. Similarly, haematocrit increased from 38 pL 2 to 44 pL 1% (P= 0·001) and from 40 pL 1 to 43 pL 2% (P= 0·002) and plasma renin activity from 910 pL 59 to a peak of 3344 pL 282 pg ml‐1 h‐1 (P= 0·001) and from 1577 pL 671 to a peak of 4954 pL 1364 pg ml‐1 h‐1 (P= 0·001) in the two groups, respectively. Prolactin concentrations rose in the control group only, from 134 pL 11 to a peak of 377 pL 35 mU l‐1 (P= 0·001), whilst in the hyperprolactinaemics little change occurred from the pre‐infusion concentration of 3873 pL 2179 reaching a peak of 3998 pL 2347 mU l‐1 (P > 0·07).In separate studies, the normal subjects were pretreated with either bromocriptine or dexamethazone. Dexamethazone did not alter any parameter of the response to VIP. Bromocriptine did not affect the heart rate, haematocrit or renin response to VIP but clearly inhibited the rise in prolactin which remained at unmeasurable concentrations throughout the infusion.