Reproduction   citetrack
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS  
Journal of Reproduction and Fertility (1991) (1991) 92 407-414
DOI: 10.1530/jrf.0.0920407
Copyright © 1991 Society for Reproduction and Fertility
This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Currie, W. D.
Right arrow Articles by Rawlings, N. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Currie, W. D.
Right arrow Articles by Rawlings, N. C.

Morphine, naloxone and the gonadotrophin surge in ewes

W. D. Currie, I. B. J. K. Joseph and N. C. Rawlings

Summary. Possible endogenous opioid peptide regulation of the preovulatory gonadotrophin surge was examined in ewes during the breeding season. Intact ewes (n = 54) were synchronized by treatment for 12 days with intravaginal sponges releasing medroxyprogesterone acetate. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion prior to and during the gonadotrophin surge were not affected by naloxone (0·33 mg/kg body wt per h) administered from the time of medroxyprogesterone acetate withdrawal until 30 h after the onset of oestrus (n = 6). Morphine was administered in 4 patterns: (i) 0·25 mg morphine/kg body wt per h from medroxyprogesterone acetate withdrawal until 30 h after the onset of oestrus (n = 6), (ii) 0·25 mg morphine/kg body wt per h from 24 to 48 h after medroxyprogesterone acetate withdrawal (n = 6), (iii) 0·50 mg morphine/kg body wt per h from 24 to 36 h after medroxyprogesterone acetate withdrawal (n = 6) and (iv) 0·50 mg morphine/kg body wt per h from 18 to 30 h after medroxyprogesterone acetate withdrawal (n = 6). Oestrus and the gonadotrophin surge were delayed, but not blocked, in all cases of morphine administration (P < 0·05). Inconsistent effects of morphine on circulating oestradiol and gonadotrophin concentrations prior to the gonadotrophin surge suggest that the delays are not due to reduced gonadotrophic support of ovarian oestradiol output. Morphine may reduce responsiveness of central behavioural and gonadotrophin surge-generating centres to the oestradiol signal.

The absence of effects of naloxone on gonadotrophin secretion suggest that suppression of LH secretion by opioid peptide activity is reduced after the end of the luteal phase. However, the failure of morphine to block the gonadotrophin surge suggests that reduced opioid peptide activity, at morphine sensitive receptors, is not critical to the surge in ewes.

Keywords: gonadotrophins; morphine; naloxone; oestrus; ewe




This article has been cited by other articles:


Home page
 EndocrinologyHome page
R. L. Goodman, L. M. Coolen, G. M. Anderson, S. L. Hardy, M. Valent, J. M. Connors, M. E. Fitzgerald, and M. N. Lehman
Evidence That Dynorphin Plays a Major Role in Mediating Progesterone Negative Feedback on Gonadotropin-Releasing Hormone Neurons in Sheep
Endocrinology, June 1, 2004; 145(6): 2959 - 2967.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
T. A. Richter, D. S. Spackman, J. E. Robinson, S. Dye, T. G. Harris, D. C. Skinner, and N. P. Evans
Role of Endogenous Opioid Peptides in Mediating Progesterone-Induced Disruption of the Activation and Transmission Stages of the GnRH Surge Induction Process
Endocrinology, December 1, 2001; 142(12): 5212 - 5219.
[Abstract] [Full Text] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS  
Copyright © 1991 by the Society for Reproduction and Fertility.