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      Pituitary Luteinizing Hormone Microheterogeneity in the Afternoon of Proestrus in Rats: Some New Insights

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          Abstract

          Objective: The aim of the present report was to determine the possible modifications in rat pituitary LH isoforms induced by the spontaneous increase in GnRH at the time of the preovulatory gonadotropin surge. Design: The changes in the quantitative pattern and relative proportions of pituitary LH isoforms in rats on the afternoon of proestrus [INT-P(PM)] were evaluated by comparison with other stages of the estrous cycle (diestrus-1, diestrus-2 and estrus) and ovariectomized (7 and 30 days earlier) animals killed in the morning and in the afternoon of the corresponding day. Methods: The chromatofocusing technique (pH gradient 11.00–7.00) was used to analyze the different molecular species of intrapituitary LH. Results: Pituitary LH from diestrus-1 animals, considered as a baseline pattern in the cycling rat, eluted as 11 isoforms distributed in pH 9.62–8.82, with greater percentages in pH 9.50–9.01. Except for INT-P(PM) pituitaries, there were no major differences in the pattern of LH heterogeneity in the pituitaries of rats from various stages of the cycle. In contrast, significant changes in the charge distribution and relative abundance of LH isoforms were found in the pituitaries from INT-P(PM) rats. INT-P(PM) pituitaries resolved in 16 LH isoforms with a significant shift to less alkaline pIs (pH 9.62–8.11), the more abundant being focused within pH 9.00–8.51. Conversely, a shift to more basic isoforms resulted after ovariectomy, leading to the accumulation of less mature isoforms in the gonadotrope. Conclusions: Presumably, the use of animals on INT-P(PM), at the time of the preovulatory LH surge, made it possible to discriminate such changes in LH isoform distribution. That GnRH, released in association with the rising phase of the LH surge, induces these changes in pituitary LH polymorphism appears to be the most likely possibility. In a previous study we demonstrated that GnRH stimulated galactose incorporation into LH in vitro. In the case of pituitaries from INT-P(PM) rats, the shift toward less alkaline isoforms could potentially result from sialylation of increased terminal galactose.

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          Author and article information

          Journal
          HRE
          Horm Res Paediatr
          10.1159/issn.1663-2818
          Hormone Research in Paediatrics
          S. Karger AG
          1663-2818
          1663-2826
          2002
          2002
          08 August 2002
          : 58
          : 1
          : 8-15
          Affiliations
          Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina
          Article
          63210 Horm Res 2002;58:8–15
          10.1159/000063210
          12169775
          © 2002 S. Karger AG, Basel

          Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

          Page count
          Figures: 3, Tables: 1, References: 37, Pages: 8
          Categories
          Original Paper

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