Stimulation of Growth Hormone by Vasoactive Intestinal Polypeptide in Acromegaly*

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Abstract
Vasoactive intestinal polypeptide (VIP) was administered as aniv bolus of 1µg/kg BW to 8 acromegalic patients and in doses of 0.5 and 1 µg/kg BW to 15 normal volunteers. Both systolic and diastolic blood pressures decreased, and pulse rate increased transiently after VIP injection. VIP stimulated PRL release from the anterior pituitary in normal subjects. Plasma PRL responses to VIP in women were dose dependent and larger than those in men. Onthe other hand, plasma GH levels rose markedly after VIP injection in all 6 patients with untreated acromegaly. In 2 patients studied after transsphenoidal microadenomectomy, there was no plasma GH response to VIP. In 2 other patients with inactive acromegaly as well as in normal subjects,VIPfailedto affect plasma GH levels. In all 6 patients with active acromegaly, LRH (1-2 µg/kgBW, iv) did not increase plasma GH levels, but TRH (5-10 µg/kg BW, iv) caused significant increases in plasma GH, the magnitude of which was not similar to that of increases seen after VIP injection. Paradoxical GH responses to TRH were not observed in patients in the inactive phase aftertranssphenoidol surgery. These findings suggest that VIP stimulates GH release in vivo in acromegalic patients. A VIP test as well as a TRH test offer promise as simple and reliabletechniques to evaluate the activity of acromegaly, particularly after transsphenoidal surgery.