Document Detail

Ovulation in PMS-treated rats with gonadotropin releasing hormone after pentobarbital and melatonin block.
MedLine Citation:
PMID:  768798     Owner:  NLM     Status:  MEDLINE    
The immature rat that has been induced to ovulate with pregnant mare serum (PMS) has proven to be a valuable model for the study of antiovulatory compounds. This paper describes an extension of this model in order to attempt to study the site of action of substances such as pentobarbital and a pineal compound, melatonin. A first experiment was designed to define a specific time for injecting pentobarbital in order to inhibit ovulation. In this study immature female rats were given injections with 25 IU PMS; pentobarbital was given at various times after PMS treatment. This study showed that sodium pentobarbital (35 mg/kg, i.p.) inhibits LH release and ovulation when rats have been anesthetized between 2 and 6 p.m. on day 2 after PMS treatment. In a second experiment ovulation was blocked with pentobarbital (35 mg/kg, i.p., beginning at 12 noon and at 2 p.m. on day 2 after PMS treatment) and completely restored to normal with the s.c. injection of 2 mug GnRH at 2 and 4 p.m. on day 2 after PMS treatment. In the third experiment, varying doses of GnRH were studied for their capacity to overcome the pentobarbital block. This study showed that 2 mug, 1 mug, 500 ng, and 250 ng of GnRH at 2 and 4 p.m. on day 2 after PMS treatment were equipotent in causing ovulation. In a fourth experiment ovulation was blocked with melatonin and this block was overcome with exogenous GnRH. In the last study exogenous GnRH was shown to restore ovulation after being blocked by both melatonin and pentobarbital. This evidence suggests that pentobarbital and melatonin inhibit ovulation by inhibiting the secretion of endogenous GnRH.
Experiment 1 was designed to determine the optimum time to ensure blockage of ovulation with pentobarbital in 25-day-old Sprague-Dawley rats. In further experiments gonadotropin-releasing hormone (GnRH) was used to overcome the ovulatory block by pentobarbital and melatonin. In Experiment 1 pregnant mare's serum (PMS) was injected sc in doses of 25 IU between 8 and 9 A.M. on Day 0. In later experiments, only 8 IU were used. Sodium pentobarbital was injected at 12 noon and 2 P.M. on Day 2, 35 mg/kg ip. Rats were sacrificed on Day 3 at 72 hours after PMS treatment. The sodium pentobarbital had inhibited luteinizing hormone (LH) release and ovulation. In Experiment 2 ovulation was blocked with pentobarbital given as before but completely restored to normal with the sc injection of 2 mcg of GnRH given at 2 or 4 P.M. on Day 2 after PMS treatment. In Experiment 3, varying doses of GnRH to as low as 250 ng were equally effective in causing ovulation. In Experiment 5, exogenous GnRH restored ovulation after it was blocked by both melatonin and pentobarbital. Results suggest that pentobarbital and melatonin inhibit ovulation by inhibiting the secretion of endogenous GnRH.
S Sorrentino
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Neuroendocrinology     Volume:  19     ISSN:  0028-3835     ISO Abbreviation:  Neuroendocrinology     Publication Date:  1975  
Date Detail:
Created Date:  1976-05-10     Completed Date:  1976-05-10     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0035665     Medline TA:  Neuroendocrinology     Country:  SWITZERLAND    
Other Details:
Languages:  eng     Pagination:  170-6     Citation Subset:  IM; J    
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MeSH Terms
Depression, Chemical
Gonadotropin-Releasing Hormone / pharmacology*
Gonadotropins, Equine / pharmacology*
Melatonin / administration & dosage,  pharmacology*
Pentobarbital / administration & dosage,  pharmacology*
Time Factors
Reg. No./Substance:
0/Gonadotropins, Equine; 33515-09-2/Gonadotropin-Releasing Hormone; 73-31-4/Melatonin; 76-74-4/Pentobarbital

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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