Influence of gestonorone caproate on rat prostate

Possible involvement of lipoxygenase pathway of arachidonic acid in rat pituitary hormone release in vitro

The roles of arachidonic acid (AA) and its lipoxygenase products in control of secretion of anterior pituitary hormones were studied in vitro using cultured cells. AA (10(-4)M) and 5-hydroxy-eicosatetraenoic acid (5HETE) (5 x 10(-6)M) significantly (p less than 0.05) stimulated the releases of LH, TSH, GH, PRL, ACTH and beta-endorphin (beta-E). Added leukotriene B4 (LTB4) (5 x 10(-6)M) also caused significant increases in the secretions of LH, GH, ACTH and beta-E. The other lipoxygenase metabolites tested, 12HETE, 15HETE, LTA4, LTC4 and LTD4, had no effect on the releases of anterior pituitary hormones. These results suggest that AA and 5-lipoxygenase metabolites may be involved in the control of the releases of anterior pituitary hormones.

Dopamine decreases release of luteinizing hormone releasing hormone from superfused rat mediobasal hypothalamus

The effects of dopamine hydrochloride (DA) on the releases of LHRH and LH were examined in a serial sequential double chamber perifusion system by perifusing the mediobasal hypothalamus including the preoptic area and/or pituitaries excised from diestrus female rats. DA, perifused at a dose of 4.2 X 10(-4) M, significantly (p less than 0.05) lowered LH secretion from the pituitary in series with the hypothalamus 40-80% below the preinfusion level, but it had no effect on LH efflux from the pituitary perifused alone. DA also significantly (p less than 0.05) reduced the LHRH level 20-40% below the initial level. Perifusion with the DA receptor blocker haloperidol at a concentration of 10(-6) M abolished the suppressive effect of DA on LH secretion. These findings indicate that DA suppressed hypothalamic LHRH release, resulting in decrease in LH secretion from the pituitary in diestrus rats.

Effect of pituitary transplants on the LH-RH concentrations in the medial basal hypothalamus and hypophyseal portal blood

The effects of hyperprolactinemia on catecholamine turnover in the medial basal hypothalamus (MBH) and on the luteinizing hormone-releasing hormone (LH-RH) concentrations in MBH and hypophyseal portal blood were investigated in female Wistar rats. Chronic endogenous hyperprolactinemia was produced by implantation of anterior pituitary glands under the kidney capsule. Catecholamine turnover in the MBH was studied by inhibiting monoamine oxidase and then measuring the accumulation of catecholamines by high-performance liquid chromatography with electrochemical detection. Rats bearing pituitary transplants exhibited: (1) persistent vaginal diestrus within 3-6 days of the implantation; (2) increased serum concentrations of prolactin (PRL); (3) decreased serum concentrations of luteinizing hormone (LH); (4) increased pituitary concentrations of LH and follicle-stimulating hormone (FSH); (5) increased turnovers of dopamine in the MBH; and (6) decreased concentrations of LH-RH in the MBH and in plasma of hypophyseal portal blood. These findings suggest that chronic hyperprolactinemia may increase dopaminergic tone in the MBH that may inhibit LH-RH secretion from the MBH, and LH release from the pituitary. These processes may be responsible for disturbances of cyclic pituitary-ovarian activity.

Effects of clomiphene citrate on the pituitary gland in chronically estrogenized rat

Effects of clomiphene citrate (clomiphene) on the pituitary gland of chronically estrogenized ovariectomized rats were investigated. Estradiol-17 beta (E2) pellet implanted subcutaneously in castrated rats for 7 days caused significant increases in pituitary weight and serum prolactin (PRL) level but suppressed serum luteinizing hormone (LH) level. In the estrogenized rats about 40% of estrogen receptor (ER) found in whole pituitary cells (65 +/- 7 fmol/10 mg tissue) was observed in the nucleus, while 60% of ER was present in the cytosol fraction. A single injection of 5 micrograms E2 translocated cytosol ER immediately to nuclear compartment; amounts of ER found in cytosol and nuclear fractions were 16 +/- 1 and 37 +/- 4 fmol/10 mg tissue, respectively, at 1 h. However, the distribution of ER returned to the pre-injection level within 4 h. In the non-estrogenized castrated rats, the nuclear retention of ER was significantly longer than that in the estrogenized rats. A single administration of 200 micrograms clomiphene in the estrogenized rats, on the other hand, increased nuclear ER gradually. Nuclear ER reached the peak level at 4 h (62 +/- 5 fmol/10 mg tissue) and the level remained almost unchanged for 24 h. Cytosol ER decreased and reached a nadir at 4 h (4.3 +/- 0.3 fmol), and the replenishment of cytosol ER could not be detected for 24 h. Similar patterns of cytosol and nuclear ER following the clomiphene injection were also found in the castrated rats. The clomiphene administration in the estrogenized rats resulted in a significant reduction of the pituitary weight 48 h after the administration. The present results seem to show the antiestrogenic action of clomiphene in the pituitary gland.