Effect of Intravenous Infusion of L-DOPA on Plasma Growth Hormone Levels in Man

Abstract

S u m m ar y in high eoneentrations, it is relatively low in eoneen-Effect of intravenous infusion of 100 mg of L-Dopa on plas-tration in the median eminenee (Laverty and Sharman ma human growth hormone (HGH) levels was studied in nor-1965). On the eontrary, it was reported that the eonmal subjects and patients with certain central nervous system tent of dopamine is very high in the median eminence diseases. Intravenous infusion of L-Dopa caused a rise in (Laverty and Sharman 1965). Schneider and McCann plasma HGH in most of the normal subjects tested. with peak HGH levels of 15.5 ± 6.1 mpgJml. Plasma HGH rose (1969) suggested the possible role of dopamine in resignificantly during the infusion of L-Dopa in most of the gulating release of luteinizing hormone-releasing faepatients with Parkinson's disease, other degenerative central tor, from their in vitro experiment. L-Dopa, unlike nervous system diseases and anorexia nervosa, although ap-exogenous dopamine, erosses the blood brain barrier parently less marked than in normal subjects. Oral admin-d istration of glucose did not affect the magnitude of HGH where it is believed to be eonverted to opamine. response to L-Dopa but delayed the peak of plasma HGH The present study is designed to investigate the efslightly. Combined administration 01" propranolol, a beta feet of the intravenous infusion of L-Dopa on plasadrenergic blocking agent, significantly enhanced plasma HGH ma HGH levels. response to L-Dopa, whereas phentolamme, an alpha blocking agent, had no signiticant elleCL Materials and Methods

Suppressive Effect of Cyproheptadine on L-DOPA-induced Growth Hormone Release in Man

“…It has been reported that the plasma hGH response to 1-DOPA, a precursor of dopamine, is enhanced by propranolol, a beta adrenergic blocking agent (Imura et al, 1973a) and inhibited by phentolamine, an alpha adrenergic blocking agent (Kansal et al, 1972). We also observed that propranolol enhances plasma hGH response to 5-hydroxytryptophan (5-HTP), a precursor of serotonin, while phentolamine inhibits it (Nakai and Imura, 1974b).…”

“…Accumulating evidence in recent years suggests that adrenergic, dopaminergic and serotoninergic mechanisms are involved in regulating secretion of human growth hormone (hGH) (Imura et al, 1968(Imura et al, , 1971(Imura et al, , 1973a(Imura et al, , 1973bBlackard and Heidingsfelder, 1968;Boyd et al, 1970;Bivens et al, 1973;Nakai et al, 1974a). However, exact interrelationships between these monoaminergic mechanisms remain unclear.…”

Effect of Adrenergic-blocking Agents on Plasma Growth Hormone Response to L-5-Hydroxytryptophan (5-HTP) in Man

“…It is noteworthy that the plasma hGH rise induced by L-DOPA is also enhanced by propranolol (Imura et al, 1973a) and inhibited by phentolamine (Kansal et al, 1972). However, it is still not clear whether or not 5_14TP exerts its effect by the same mechanism as that of L-DOPA action.…”

“…Evidence has accumulated in recent years suggesting that these amines play an important role in the control of anterior pituitary function. Previous studies by us (Imura et al, 1968(Imura et al, , 1971(Imura et al, , 1973a and others (Blackard and Heidingsfelder 1968;Boyd et al, 1970) revealed that both adrenergic and dopaminergic mechanisms seem to be involved in regulating secretion of human growth hormone (hGH).…”

Interaction of Immobilized Avidin with an Aequorin–Biotin Conjugate: An Aequorin-Linked Assay for Biotin

“…Under certain circumbilization supports. The effect was more pronounced stances, however, biphasic curves in which the dosewhen low concentrations of aequorin-biotin conjuresponse curve has a maximum at low concentrations gate were used, and diminished at a high conjugate of ligand have been observed (14)(15)(16)(17)(18). These ''hook'' anism.…”