RESUMO
We studied the modifications of the vasoactive intestinal peptide (VIP) receptor/effector system from the rat seminal vesicle after chronic ethanol ingestion. Ethanol treatment resulted in a decreased height of the secretory epithelium of seminal vesicle as well as in a weight loss of this gland. These morphological changes were accompanied by an increase of immunoreactive vasoactive intestinal peptide (VIP) levels and a decrease of the stimulatory effect of VIP adenylate cyclase activity in the seminal vesicle. The loss of sensitivity of the enzyme to VIP was conceivably related to a decrease in the affinity of VIP receptors rather than to a decrease in their number. The changes in the affinity of the VIP receptors were accompanied with a lower sensitivity of VIP binding to GTP, which suggest an uncoupling between the receptor and the transductor molecules. However, chronic exposure to ethanol did not modify either the levels of G-protein subunits (alpha(s) and alpha(i1/2)) or the GTPase activity from seminal vesicle membranes. Moreover, ethanol feeding did not affect adenylate cyclase activity stimulated by forskolin or by Gpp(NH)p. Thus, ethanol-induced changes in the sensitivity of adenylate cyclase to VIP appear to be attributed to an alteration in the VIP-receptor/G-protein interphase rather than in the G-protein/adenylate cyclase connection.
Assuntos
Depressores do Sistema Nervoso Central/farmacologia , Etanol/farmacologia , Receptores de Peptídeo Intestinal Vasoativo/metabolismo , Glândulas Seminais/metabolismo , Adenilil Ciclases/metabolismo , Animais , Western Blotting , Depressores do Sistema Nervoso Central/sangue , Reagentes de Ligações Cruzadas , AMP Cíclico/metabolismo , Etanol/sangue , GTP Fosfo-Hidrolases/metabolismo , Proteínas de Ligação ao GTP/metabolismo , Masculino , Membranas/efeitos dos fármacos , Membranas/metabolismo , Membranas/ultraestrutura , Radioimunoensaio , Ratos , Ratos Wistar , Glândulas Seminais/efeitos dos fármacos , Glândulas Seminais/ultraestrutura , Testosterona/sangue , Peptídeo Intestinal Vasoativo/metabolismoAssuntos
Trifosfato de Adenosina/farmacologia , Carbacol/farmacologia , AMP Cíclico/metabolismo , Fosfatos de Inositol/metabolismo , Neuropeptídeos/metabolismo , Neuropeptídeos/farmacologia , Próstata/citologia , Próstata/metabolismo , Receptores do Hormônio Hipofisário/metabolismo , Receptores de Peptídeo Intestinal Vasoativo/metabolismo , Peptídeo Intestinal Vasoativo/metabolismo , Peptídeo Intestinal Vasoativo/farmacologia , Animais , Bucladesina/farmacologia , Divisão Celular/efeitos dos fármacos , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Células Cultivadas , Células Epiteliais , Epitélio/efeitos dos fármacos , Masculino , Neurotransmissores/metabolismo , Neurotransmissores/farmacologia , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase , Próstata/efeitos dos fármacos , Ratos , Ratos Wistar , Receptores de Polipeptídeo Hipofisário Ativador de Adenilato CiclaseRESUMO
The present study in purified rat Leydig cells shows that arachidonic acid may act as an intratesticular factor regulating LH-mediated testicular steroidogenesis. Arachidonic acid decreased, in a dose-dependent manner, the LH-stimulated cAMP and testosterone levels, over 2 h incubation. Incubation of Leydig cells with arachidonic acid did not modify 125I-hCG binding to the cells as compared to control, showing that the action of arachidonic acid is not related to a decrease of hCG binding to the cells. Forskolin-stimulated cAMP and testosterone production were inhibited by 51.65 and 70.9%, respectively, in the presence of arachidonic acid (100 microM), although the ED50 for the diterpene was not changed. When isobutyl-methyl-xanthine was added to the incubation medium, the same percentage of inhibition was found indicating that arachidonic acid inhibition of cAMP production is not due to stimulation of Leydig cell phosphodiesterase activity. Pretreatment of the cells with pertussis toxin, to inactivate Gi, was also without effect on arachidonic acid inhibition of LH-stimulated cAMP production, but pertussis toxin abolished the inhibitory effects of arachidonic acid when adenylate cyclase was stimulated with forskolin. However, arachidonic acid addition resulted in inhibition of LH- and forskolin-stimulated testosterone production, even if the cells were pretreated with pertussis toxin. It can be concluded that: (1) The inhibitory effect of arachidonic acid is neither due to a decrease of hCG binding to Leydig cells nor to a stimulation of cell phosphodiesterase activity; (2) arachidonic acid modulates cAMP production at two different levels, either by activation of Gi protein and by inhibition of Gs protein or adenylate cyclase; (3) the effect of arachidonic acid on steroidogenesis is also beyond cAMP formation.