Circadian Regulation of Growth Hormone Secretion After Treatment in Acromegaly*

Abstract

In eight patients who underwent transsphenoidal adenomectomy for acromegaly,baselineplasma GH levels were consistently less than 8 ng/ml during 1–4 yr postoperatively. Plasma GH was measured every 20 min for 24 h, and the responses to oral glucose, iv TRH, and oral bromocriptine were examined during the follow—up. The 2-h mean (±SD) GH value varied from 1.1 ± 0.9 to 10.8 ± 4.9 ng/ml. Statistical analysis of these mean values allowed identification of two groups of patients. In each group I patient (five cases), the mean 24-h GH level was less than or equal to 2.0 ng/ml. One to four daytime GH secretion peakswith intervening periods oflow secretory activity were observed. In all five cases, a significant nocturnal GH rise was found; this rise coincided with the onset of deep sleep in only two patients. Responses to dynamic tests returned t o normal after surgery in this group. In group II patients (three cases), the mean (±SD) 24-h GH levels varied from 46 ± 1.0 to 10.8 ± 4.9 ng/ml. Two patients presented marked diurnal bursts of GH, while the third had stable GH levels throughout the 24-h period. Low levels of daytime secretory activity and nocturnal GH secretion were absent in all three cases and abnormal responses to dynamic tests persisted postoperatively. After 3 months of bromocriptine therapy (15 mg daily), plasma GH levels were significantly lowered in two of three group II patients, but abnormal 24-h GH patterns persisted in all threecases. Results of this study indicate that 1) physiological regulation of baseline and dynamic GH secretion can be achieved after transsphenoidal surgery, and 2) bromocriptine therapy does not induce the resumption of physiological GH secretion patterns, although hormonelevels are significantly reduced. {J. Clin En-docrinol Metab50: 322,1980)