Effect of thyrotropin-releasing hormone on growth hormone release in normal subjects pretreated with human pancreatic growth hormone-releasing factor 1-44 pulsatile administration.

Growth hormone (GH) increase after thyrotropin-releasing hormone (TRH) has been documented in many pathological conditions. In order to evaluate whether exposure to growth hormone-releasing factor (GRF) might contribute to this effect in normal subjects, we studied GH responses to placebo, TRH, GRF and GRF plus TRH either in basal condition or after GRF administration. Ten subjects received placebo, TRH, GRF and GRF plus TRH on four separate occasions. GRF induced a clear rise in plasma GH, statistically different from those obtained after placebo or TRH (p less than 0.01). TRH was completely ineffective in both stimulating GH release and amplifying the secretory GH response to GRF. Twenty subjects, subdivided in four groups, received 3 consecutive intravenous GRF boli at two-hour intervals. Two hours later they were given a fourth stimulus: 5 had another 25 micrograms GRF i.v., 5 had 200 micrograms TRH i.v., 5 were tested with simultaneous 25 micrograms GRF and 200 micrograms TRH i.v. injection, and 5 with 1 ml saline. GH secretory responses were quantitated by determining the net incremental area under the curve (nAUC) over 60 min after the administration of each stimulus. The pattern of GH secretion after 1-3 GRF boli was not statistically different among the four groups. Plasma GH nAUC was higher after the first GRF injection than after the following ones (p less than 0.01). The administration of a fourth GRF bolus also caused a GH increase which was significantly smaller than that after the first one (p less than 0.01), but greater than that after placebo (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)