Publications (2)6.99 Total impact
-
Article: Epoxygenase products of arachidonic acid are endogenous constituents of the hypothalamus involved in D2 receptor-mediated, dopamine-induced release of somatostatin.
[show abstract] [hide abstract]
ABSTRACT: The epoxyeicosatrienoic acids (EETs) were discovered as products of a cyclooxygenase/lipoxygenase-independent, cytochrome P-450 catalyzed metabolism of arachidonic acid (AA) termed the "epoxygenase" pathway. The rat hypothalamus is able to synthesize EETs from exogenous AA, and 5,6-EET has been found to release the neuropeptide somatostatin (SRIF) from hypothalamic nerve terminals of the median eminence (ME). In the present study, hypothalami from male rats were examined for the presence of endogenous EETs, using chemical, chromatographic, and mass spectral analysis procedures. The samples were initially separated in a C18 Sepralyte column, fractionated on TLC plates, and purified by reverse phase HPLC. Thereafter, they were esterified (pentafluorobenzyl esters) and subjected to negative ion chemical ionization/gas chromatography (GC)/mass spectral (MS) analysis. The GC retention time and the MS fragmentation patterns revealed the presence of a mixture of 8,9-, 11,12- and 14,15-EETs; instability of 5,6-EET during the isolation protocol precluded its identification. Total hypothalamic EET concentration was estimated to be 120 ng/g wet tissue. The 8,9-regiosomer released SRIF from ME nerve terminals with an ED50 of 5 x 10(-12) M; Dopamine (DA) and the D2 receptor agonist PPHT, but not the D1 receptor agonist SKF-38393, induced SRIF release from the ME. This effect was blocked by clotrimazole and ketoconazole, two inhibitors of microsomal cytochrome P-450 function and AA epoxygenase in particular. In contrast, the inhibitors failed to affect the increase in SRIF release induced by 8,9-EET. These results indicate that: 1) in addition to cyclooxygenase and lipoxygenase products, epoxygenase metabolites of AA are endogenous compounds of the hypothalamus, and 2) EETs may mediate the increase in SRIF release from hypothalamic neurons induced by the interaction of DA with D2 receptors.Endocrinology 04/1990; 126(3):1534-40. · 4.46 Impact Factor -
Article: Contribution of arachidonate metabolites to basal and thyrotropin releasing-hormone-stimulated release of prolactin from purified lactotrophs in primary culture.
[show abstract] [hide abstract]
ABSTRACT: Among the different biochemical pathways which have been suggested to play a role in the control of prolactin (Prl) release from anterior pituitaries, arachidonate and its metabolites have been proposed to be involved in the process of Prl release. In this study we investigated the contribution of arachidonate metabolites to both basal and TRH-stimulated Prl release from perifused lactotrophs in culture (derived from pituitary glands of lactating female rats), which exhibit a high sustained release of Prl in absence of inhibitory input. Inhibition of the general oxidative metabolism of arachidonate by 10(-5) M ETYA or of the arachidonate lipoxygenase metabolism by 10(-5) M NDGA decreased basal Prl release to 45 +/- 10% (n = 3) and 36 +/- 4% (n = 6) of the control release, respectively. Indomethacin, an inhibitor of the cyclooxygenase pathway, was without effect. Of the lipoxygenase metabolites tested at 10(-6) M only 15-HPETE and 15-HETE induced Prl release. 15-HETE elicited prolactin release in a concentration dependent manner with a maximal effect at 10(-6) M (10.72 +/- 3 ng/ml vs control 5.1 +/- 0.8 ng/ml, n = 3). The quantity of Prl release induced by TRH was markedly decreased in the presence of NDGA. However, the fraction of Prl release elicited by TRH, calculated as a percentage of the amount of Prl released prior to TRH application, was similar under control conditions, and in the presence of NDGA. In contrast, inhibition of the protein kinases A and G by H8 (10(-5) M) failed to alter basal Prl release but inhibited the effect of TRH by 58 +/- 6% (n = 3). These data suggest that in absence of inhibitory inputs the high sustained release of Prl observed in cultures of lactotrophs derived from lactating female rats depends on the availability of lipoxygenase metabolites, and that the blockade of lipoxygenase reduces the absolute amount of Prl released by TRH without suppressing the ability of TRH to stimulate Prl release.Life Sciences 02/1990; 47(20):1829-36. · 2.53 Impact Factor
