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      Influence of Diabetes on the Gonadotropin Response to the Negative Feedback Effect of Testosterone and Hypothalamic Neurotransmitter Turnover in Adult Male Rats

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          Abstract

          The influence of diabetes on the gonadotropin response to the negative feedback effect of testosterone (T) and hypothalamic neurotransmitter turnover rates in adult male rats was evaluated. Adult male Sprague-Dawley rats were made diabetic by an intraperitoneal injection of streptozotocin (STZ; 5 mg/100 g body weight) in citrate buffer. Vehicle-injected rats served as controls. On day 9, all rats were bilaterally castrated and treated subcutaneously on alternate days with either peanut oil or T propionate (TP) in peanut oil (100 µg/rat). Plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), and T concentrations were measured by specific radioimmunoassays from blood samples collected on day 1 (before castration) and 2, 4, 6, and 7 days after castration. On day 7 after castration (day 15 after vehicle or STZ treatment), 1 h before autopsy, the rats were injected intraperitoneally with saline or a tyrosine hydroxylase inhibitor, α-methyl-p-tyrosine (25 mg/100 g BW), for the measurements of norepinephrine (NE) and dopamine turnover in median eminence and medial basal hypothalamus (MBH). Circulating FSH, LH, PRL, and Tlevels were significantly lower (FSH and T: p < 0.001; LH and PRL: p < 0.05) in gonad-intact rats treated with STZ than in vehicle-injected animals. The castration-induced increase in plasma LH levels was attenuated in diabetic rats. The suppressive effect of T on LH secretion was significantly greater (p < 0.001) in STZ-treated rats relative to TP-treated nondiabetic controls. Castration in both diabetic and nondiabetic rats increased (p < 0.001) FSH secretion, but these increases were not different until day 6 after castration, when plasma FSH levels in control rats significantly increased (p < 0.01), than in diabetic animals. In STZ-treated rats, the suppressive effect of TP on plasma FSH levels was significantly increased. The NE turnover rates in median eminence and MBH were significantly lower (p < 0.001) in castrated diabetic rats than in castrated controls. The MBH NE turnover was reduced after TP treatment in both subgroups, but the relative decline was much greater (p < 0.01) in diabetic rats. These results clearly indicate that induction of diabetes by STZ treatment reduces gonadotropin and PRL secretion and increases the sensitivity of the hypothalamic-pituitary axis to the negative feedback effect of T on gonadotropin secretion. The effect of diabetes on gonadotropin secretion in the adult male rat is probably due to the suppression of noradrenergic neuronal activity of the hypothalamus.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1991
          1991
          04 April 2008
          : 54
          : 1
          : 30-35
          Affiliations
          Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Ill., USA
          Article
          125847 Neuroendocrinology 1991;54:30–35
          10.1159/000125847
          1681439
          dd148771-599f-4d49-bd85-a0bdf62c0fc4
          © 1991 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.

          History
          : 09 May 1990
          : 30 November 1990
          Page count
          Pages: 6
          Categories
          Original Paper

          Endocrinology & Diabetes,Neurology,Nutrition & Dietetics,Sexual medicine,Internal medicine,Pharmacology & Pharmaceutical medicine
          Diabetes,Negative feedback,Testosterone,Luteinizing hormone,Norepinephrine,Hypothalamus

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