A dose of 2.5 g of gamma-hydroxybutyric acid (GHB) was administered intravenously to 6 healthy male volunteers. A significant increase in plasma GH was observed at 30, 45, 60 and 90 min after injection. The plasma prolactin level increased significantly at 45 and 60 min after GHB injection. These responses were not found after the saline vehicle injection in the same subjects. It is conceivable that GHB could modify the release of serotonin from the nerve terminals and then stimulate the release of GH and prolactin.

gamma-Aminobutyric acid (GABA; 50 or 500 microgram/10 microliter) was injected into the right lateral ventricle of urethane- or pentobarbital-anesthetized male rats. The animals were decapitated 15 min after injection. Serum GH and hypothalamic somatostatin (SRIF) concentration were measured by specific RIAs. Intraventricular GABA caused a dose-related increase in GH and SRIF. In another study, aminooxyacetic acid (5 or 20 mg) was injected ip into urethane-anesthetized rats. Aminooxyacetic acid at 20 mg produced a significant increase in both serum GH and hypothalamic SRIF. Furthermore, 12.5 mg gamma-hydroxybutyric acid (GHB) injected ip into urethane- or pentobarbital-anesthetized rats elicited a significant increase in both serum GH and hypothalamic SRIF. Pretreatment with 20 mg L-dopa produced decreases in the GHB-induced serum GH increase and in hypothalamic SRIF in pentobarbital-anesthetized rats. These results show that GABA and GHB stimulated GH secretion, which was accompanied by increased hypothalamic SRIF. Thus, the GH release induced by GABA or GHB may be partly involved in inhibiting the release of hypothalamic SRIF. As the GHB-induced GH release was inhibited by L-dopa, the stimulatory effect of GHB on GH secretion might be mediated by inhibition of the dopaminergic mechanism.

No abstract

gamma-oryzanol (gamma-OZ), a ferulic acid ester of triterpene alcohol, was investigated with regard to its effect on pituitary LH, GH, prolactin and TSH secretion in normal male (M) and ovariectomized female (OVX) rats. gamma-OZ showed a suppressive tendency of LH by a single intravenous injection and also markedly reduced the LH release induced by LHRH when compared with only vehicle-dosed control groups in M and OVX rats. Serum prolactin release induced by TRH was markedly suppressed by 6 days pretreatment with gamma-OZ in OVX rats. These data suggest that gamma-OZ is a potent inhibitor of LH release and may be a weak inhibitor of prolactin in rats.

It is well known that Ca2+ plays an important role in hormone release from the anterior pituitary (1-8); however, the mechanism of Ca2+ action on the anterior pituitary cells remains to be clarified. Douglas et al. (9,10) proposed that hormone release from the neurohypophysis and adrenal medulla is initiated by depolarization of the cell plasma membrane. Depolarization induces a permeability change in the plasma membrane resulting in an influx of Ca2+ into the cells, and this influx may then initiate the intracellular hormone-releasing mechanism.In the present study, we investigated the effects of nifedipine, a Ca2+ blocker, on in vitro release of prolactin, GH, and LH from the anterior pituitary.Materials and methods. Male Sprague-Dawley rats, weighing 180-200 g, were used. The animals were decapitated, and the anterior pituitary was immediately removed and bisected to equal halves. The two halves of each pituitary were placed in a beaker with 1 ml of Krebs-Ringer bicarbonate medium containing 0.25% bovine serum albumin (KRBG-BSA). After two I-hr preincubation periods in a metabolic incubator at 37" under 95% O2 and 5% CO2 gas, the medium was replaced with fresh KRBG-BSA (1 ml) and incubated for 1 hr (first incubation). The incubation medium was collected. Then 1 ml of KRBG-BSA containing the test material was added to the beaker and incubated for another I hr (second incubation), and the incubation medium was collected. The amount of pituitary hormone released during the second 1-hr incubation was compared with that released during the first 1-hr incubation period and expressed as a percentage of that released in the first hour.Nifedipine (Adalat, Bayer Pharmacol. Co.) was dissolved in a vehicle of 15% polyethyl-31