REPETITIVE INJECTIONS OF GROWTH-HORMONE RELEASING HORMONE (GHRH1-44) TO NORMAL VOLUNTEERS AND PATIENTS WITH GROWTH-HORMONE DEFICIENCY

The present study was designed to answer the following three questions: Is there any difference between the growth hormone (GH) response to i.v. injections of GHRH 1-44 by a slowly injecting hormone pump or to a s.s. or rapid i.v. injection by syringe? Do nocturnal injections of GHRH 1-44 i.v. elicit different GH levels than during daytime? Can repetitive administration of GHRH 1-44 in patient with GH deficiency induce a physiological GH pattern and thereby normalize the condition resulting from a hypothalamic defect? A rapid i.v. bolus injection of 50 μg GHRH 1-44 by syringe with an injection time of one second elicited in the same subject at the same time of the day a twofold greater response than a slowly injecting (60 seconds) hormone pump. In six male adult volunteers each GHRH i.v. bolus was followed by a GH secretory pulse. The GH response at night (area under the curve and peak plasma GH levels) was significantly greater than at daytime (P < 0.05) and greater than the GH pulses measured during a spontaneous nocturnal profile (P < 0.05). Out of six GH deficient young adult patients who had been receiving extractive GH until two years prior to the study, three responded much like the controls, the other three patients - those who lacked any spontaneous nocturnal GH peaks - had markedly lower GH levels after GHRH (P < 0.05). However, there was a clear-cut GH release after GHRH injection in each patient. No influence of repetitive GHRH administration was seen on cortisol, prolactin and glucose levels and their profiles. It is concluded that it may indeed be possible to induce an almost normal circadian GH pattern by repetitive i.v. injections of GHRH in GH deficient patients.