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The Jones Institute for Reproductive Medicine, Department of Obstetrics and Gynecology, Eastern Virginia Medical School, Medical College of Hampton Roads 855 W. Brambleton Ave, Suite B, Norfolk, Virginia 23510
The dose-response effects of a single administration of Nal-Lys-GnRHant (antagonist) on serum LH and FSH concentrations were compared to the effects of Nal-Glu-GnRHant in monkeys. Twenty ovariectomized monkeys were divided into four sc treatment groups: a) 1.0 mg/kg Nal-Glu-GnRHant; or Nal-Lys-GnRHant at b) 0.3; c) 1.0; d) 3.0 mg/kg. Each monkey received vehicle (propylene glycol/water, 1:1) on day 0, followed by an antagonist preparation on day 11. Serum LH and FSH were measured by RIA; serum LH was also measured by in vitro bioassay. The short-term effects were similar among the four treatment groups. Typically, serum LH declined (p < 0.05) within 4 to 8 h, achieving maximal reduction by 24 h. Serum FSH levels declined more slowly, but were significantly reduced by 24 h (p < 0.05). Recovery during the study interval to pretreatment control values occurred in only two groups: a) Nal-Glu-GnRHant (1.0 mg/kg) by day 4 posttreatment and b) Nal-Lys-GnRHant (0.3 mg/kg) by day 2 post-treatment. Monkeys receiving 1.0 or 3.0 mg/kg Nal-Lys-GnRHant had a prolonged inhibition of serum LH and FSH levels. In all animals, serum FSH and LH returned to control levels within 2 months. The duration of gonadotropin inhibition was also prolonged when the Nal-Lys-GnRHant was administered iv. In contrast, Nal-Glu-GnRHant reduced serum LH and FSH for 3 days or less in all monkeys. The serum bioassayable LH levels paralleled those of immunoassayable LH.
The prolonged inhibition of gonadotropin secretion following Nal-Lys-GnRHant distinguishes its action from those of previous GnRH antagonists and make this compound of great interest for clinical investigations.
& Supported in part by the CONRAD program, funded by the USAID, Washington, D.C.
* Portions of this work were presented at the 70th Endocrine Society Meeting, New Orleans, Louisiana, 1988
# Postdoctoral Research Fellow of the Rockefeller Foundation
+ To whom correspondence should be addressed
Received July 29, 1988.
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