Abstract
Availability of radioimmunoassay for growth hormone releasing hormone (GHRH) in plasma has made it possible to measure circulating GHRH concentrations during stimulation of growth hormone (GH) secretion. It has been previously shown that administration of L-dopa increases plasma levels of GHRH, followed by an elevation of plasma GH concentration. Ornithine or clonidine do not seem to affect plasma levels of CHRH. To elucidate the role of GHRH in the stimulation of GH secretion during pharmacological stimulation tests we measured plasma immunoreactive GHRH and GH levels in 8 healthy adult men during insuline induced hypoglycemia (IH) and after oral administration of clonidine of L-dopa. Plasma samples for the determination of GHRH levels were purified with octa-decyl-silica cartridges and assayed by a radioimmunoassay specific for the midportion of human GHRH. Mean GH response (SEM) after administration of L-dopa was 8.67 ug/l (2.9), 2.22ug/l (1.0) in clonidine test and 24.33 ug/l (4.4) during insuline induced hypoglycemia. Mean GHRH responses rospectively were 9.64 ng/l (2.6), 6.65 ng/l (2.3) and 4.25 ng/l (3.4).
The plasma GHRH peaks preceded or coincided with GH peaks in all subjects after L-dopa administration. In the clonidine test and IH no correlation was found between the GHRH and GH peaks. These results confirm that the effect of L-dopa on GH secretion is mediated by GHRH, whereas other factors than GHRH seem to play a major role in GH stimulation by IH and clonidine test.
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Lautala, P., Tapanainen, P., Leppäluoto, J. et al. MECHANISH OF GROWTH HORMONE (GH) SECRETION IN PHARMACOLOGICAL STIMULATION TESTS. Pediatr Res 23, 110 (1988). https://doi.org/10.1203/00006450-198801000-00053
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DOI: https://doi.org/10.1203/00006450-198801000-00053