Endogenous opioids and the control of seasonal LH secretion in Soay rams

Author:

Ebling F. J. P.,Lincoln G. A.

Abstract

ABSTRACT Soay rams were treated with naloxone and/or morphine at different stages of their annual reproductive cycle to study the role of endogenous opioid peptides in the control of pulsatile LH secretion. The responses in intact rams were compared with those shown by pinealectomized (PNX) or superior cervical ganglionectomized (SCGX) rams which had a different annual testicular cycle. Naloxone (4–6 mg/kg i.v.) given to intact rams at four times of the year induced significant increases in LH pulse frequency in the breeding season in September and December, but minimal responses in the non-breeding season in June. Similar treatments given to PNX or SCGX rams induced good responses in March, June and September and the poorest response in December; the different seasonal pattern between the intact and PNX/SCGX rams was correlated with differences in the timing of their testicular cycles. Morphine (1 mg/kg i.v.) induced a significant decrease in LH pulse frequency when given to intact rams in October, but no significant effects were observed when morphine was given to sexually inactive rams in early July. Naloxone (1 mg/kg i.v.) given concurrently with morphine in October reversed the suppressive effect and resulted in an actual increase in LH pulse frequency above pretreatment levels. Morphine-treated rams showed normal LH responses to injections of LH-releasing hormone (LHRH) indicating that the site of opiate inhibition was on hypothalamic LHRH secretion rather than on pituitary LH release. Chronic treatment of intact and PNX rams with naloxone 1 mg/kg every 4 h for 7 days) in April and October produced the expected acute increase in LH pulse frequency in the intact rams in October, and at both times of year in the PNX rams, however there was no sustained increase in LH secretion in response to chronic naloxone in any of the treatment groups. The response to the second naloxone injection was much reduced and was absent after 3 days; responsiveness to naloxone was restored within 2 days of stopping the chronic treatment. The overall results indicate that an endogenous opioid mechanism is involved in the tonic inhibition of LH secretion and that this mechanism is most active in the breeding season when both naloxone and morphine have marked effects on pulsatile release of LH. Regulation of endogenous opioids in the hypothalamus may be part of the mechanism by which environmental factors modulate steroid negative-feedback control of LHRH and thus LH secretion in seasonally breeding mammals. J. Endocr. (1985) 107, 341–353

Publisher

Bioscientifica

Subject

Endocrinology,Endocrinology, Diabetes and Metabolism

Cited by 76 articles. 订阅此论文施引文献 订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献

同舟云学术

1.学者识别学者识别

2.学术分析学术分析

3.人才评估人才评估

"同舟云学术"是以全球学者为主线,采集、加工和组织学术论文而形成的新型学术文献查询和分析系统,可以对全球学者进行文献检索和人才价值评估。用户可以通过关注某些学科领域的顶尖人物而持续追踪该领域的学科进展和研究前沿。经过近期的数据扩容,当前同舟云学术共收录了国内外主流学术期刊6万余种,收集的期刊论文及会议论文总量共计约1.5亿篇,并以每天添加12000余篇中外论文的速度递增。我们也可以为用户提供个性化、定制化的学者数据。欢迎来电咨询!咨询电话:010-8811{复制后删除}0370

www.globalauthorid.com

TOP

Copyright © 2019-2024 北京同舟云网络信息技术有限公司
京公网安备11010802033243号  京ICP备18003416号-3