Immunoreactive growth hormone-releasing hormone (IR-GHRH) in the feto-placental circulation and differential effects of L-dopa, L-arginine and somatostatin-14 on the plasma levels of IR-GHRH in normal adults.
The relation of the physiological releases of growth hormone-releasing hormone (GHRH) and growth hormone (GH) into the circulation in various conditions was investigated using a sensitive and specific radioimmunoassay for plasma GHRH. The mean fasting plasma level of immunoreactive (IR)-GHRH in 72 normal adults was 10.3 +/- 0.5 (mean +/- SEM) pg/ml and there was no significant sex difference in the level. The concentrations of IR-GHRH in plasma from the umbilical artery and umbilical vein were 107.3 +/- 20.5 pg/ml and 33.6 +/- 3.8 pg/ml, respectively, and a marked arterio-venous gradient was observed in all 12 individuals examined. The plasma level of IR-GHRH in the maternal vein was significantly lower than that in the cord blood, but was similar to that in non-pregnant women. In normal adults, although there was no apparent fluctuation in the level of plasma IR-GHRH or of plasma GH during bed rest, a significant increase of plasma IR-GHRH was detected followed by, or synchronized with the surge of plasma GH after oral administration of L-dopa. In contrast, on L-arginine infusion, no proportional elevation of plasma IR-GHRH with increase in plasma GH was observed. During and after intravenous infusion of somatostatin, the circulating IR-GHRH level did not increase, but on stopping the infusion there was an immediate and marked rebound surge of GH. We conclude that 1) the elevated IR-GHRH in the cord blood plasma originates from the fetus and may have a primary role in enhancing secretion of GH which promotes growth in early human life, and 2) the participations of GHRH in the mechanisms of GH secretion seen after administrations of L-dopa, L-arginine and somatostatin are different.
Saito
H
H
Department of Internal Medicine, Tokushima Teishin (Posts and Telecommunications) Hospital, Japan.
Hosoi
E
E
Yamasaki
R
R
Kameyama
K
K
Irahara
M
M
Ohno
Y
Y
Saito
S
S
D000328:Adult; D001120:Arginine / Q000494:pharmacology*; D005260:Female; D005312:Fetal Blood / Q000737:chemistry / Q000502:physiology*; D013007:Growth Hormone-Releasing Hormone / Q000097:blood* / Q000378:metabolism; D019382:Human Growth Hormone / Q000097:blood* / Q000378:metabolism; D006801:Humans; D007231:Infant, Newborn; D007980:Levodopa / Q000494:pharmacology*; D008431:Maternal-Fetal Exchange; D011247:Pregnancy; D011863:Radioimmunoassay; D012016:Reference Values; D013004:Somatostatin / Q000494:pharmacology*; D013997:Time Factors
D019382:Human Growth Hormone; D007980:Levodopa; D013004:Somatostatin; D013007:Growth Hormone-Releasing Hormone; D001120:Arginine