Browsing by Author "ROA, JP"

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    CELLULAR MECHANISMS OF ESTROGEN-INDUCED AND DOPAMINE-INDUCED CONTROL OF GLANDULAR KALLIKREIN IN THE ANTERIOR-PITUITARY OF THE RAT
    (1993) ROA, JP; POWERS, CA; SILVA, R; VIO, CP
    Glandular kallikrein (GK, a trypsin-like serine protease) exhibits estrogen induction and dopamine repression in rat pituitary lactotrophs. Steroid induction may reflect primary actions to increase selectively the synthesis of specific proteins, or may be part of broad cellular responses secondary to steroid-induced phenotype transitions. This study examined the cellular mechanisms underlying estrogen and dopaminergic control of lactotroph GK using a quantified immunocytochemical approach. Pituitaries from ovariectomized rats exhibited little GK staining. Estradiol treatment for 10 days produced dose-dependent increases in pituitary mass, the percentage of lactotrophs (indicating lactotroph proliferation) and the percentage of GK-positive cells. Also, GK staining intensity was dependent upon estradiol dose, increasing 4-fold between 5 mu g and 50 mu g/48 h. Dopamine receptor blockade with haloperidol (2.5 mg/kg/24 h) elicited weak GK immunostaining in 46% of the lactotrophs in the absence of estradiol, and markedly potentiated GK staining intensity elicited with low but not high doses of estradiol. The results suggest that GK induction is a primary estrogen effect, and is not secondary to a phenotype transition: the induction is enhanced by estrogen-induced lactotroph proliferation. Dopaminergic systems strongly inhibit GK induction by low estradiol levels. This dopaminergic modulation may shift the induction of lactotroph GK to physiological events associated with high estradiol levels or low dopaminergic tone.
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    LOCALIZATION OF IMMUNOREACTIVE GLANDULAR KALLIKREIN IN LACTOTROPHS OF THE RAT ANTERIOR-PITUITARY
    (1990) VIO, CP; ROA, JP; SILVA, R; POWERS, CA
    Glandular kallikrein (a trypsin-like serine protease) is an estrogen-induced and dopamine-repressed protein in the rat anterior pituitary which predominantly exists as a latent zymogen (prokallikrein). Its regulation, presence in estrogen-induced pituitary tumors in F344 rats, and expression in GH3 cells has suggested a localization in lactotrophs (prolactin-producing cells). This study examined the cellular origin of glandular kallikrein using immunocytochemical techniques. Anterior pituitaries from estrogen-treated rats were fixed and embedded in paraffin (for preparation of semi thick sections; 5 .mu.m) or methacrylate (for preparation of thin sections; 1 .mu.m). Glandular kallikrein immunostaining was readily detected in the perinuclear (Golgi) region of parenchymal cells of the anterior pituitary in both thin and semi thick sections. Two-color double immunoperoxidase staining of thin and semi thick sections indicated that glandular kallikrein was localized in cells containing prolactin (PRL) but not other pituitary hormones. Immunoperoxidase staining of consecutive serial thin sections with alterating antisera confirmed a localization of glandular kallikrein in lactotrophs. The results establish that glandular kallikrein is colocalized with PRL in lactotrophs of the rat anterior pituitary. This is consistent with the hypothesis that the function of anterior pituitary glandular kallikrein is linked to PRL in some fashion-possibly as a PRL-processing protease.