The pyrethroid pesticide esfenvalerate suppresses the afternoon rise of luteinizing hormone and delays puberty in female rats.
BACKGROUND
One of the most widely used classes of insecticides is the synthetic pyrethroids. Although pyrethroids are less acutely toxic to humans than to insects, in vitro studies have suggested that pyrethroids may be estrogenic.


OBJECTIVE
We assessed pubertal effects by orally administering 0.5, 1.0, and 5.0 mg/kg/day of the type II pyrethroid esfenvalerate (ESF) to female rats beginning on postnatal day (PND) 22 until vaginal opening. ESF administration suppresses serum estradiol and delays pubertal onset.


METHODS
To assess possible hypothalamic and/or pituitary effects, animals received 0.5 or 1.0 mg/kg ESF or corn oil on PNDs 22-29. On PND30, we drew three blood samples (200 microL) from each rat at 15-min intervals beginning at 1000 hours, and again at 1500 hours. To test hypothalamic responsiveness, after the third afternoon sample, all animals received an intravenous injection of N-methyl-d,l-aspartic acid (NMA; 40 mg/kg), and then we drew two more samples. We performed a second experiment as above except that animals received luteinizing hormone-releasing hormone (LHRH; 25 ng/rat) to test pituitary responsiveness.


RESULTS
Basal levels of luteinizing hormone (LH) in the afternoon hours were higher in control animals than in animals treated with 1.0 mg/kg ESF (p < 0.05). Furthermore, NMA- and LHRH-stimulated LH release was similar in control and ESF-treated animals, indicating that both hypothalamic and pituitary responsiveness, respectively, were unaffected.


CONCLUSIONS
Although the hypothalamus is able to respond to exogenous stimuli, absence of a normal afternoon rise in LH would indicate a hypothalamic deficit in ESF-treated animals.
Pine
Michelle D
MD
Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77843-4458, USA. mpine@cvm.tamu.edu
Hiney
Jill K
JK
Lee
Boyeon
B
Dees
W Les
WL
D000818:Animals; D005260:Female; D007306:Insecticides / Q000494:pharmacology / Q000633:toxicity*; D007986:Luteinizing Hormone / Q000097:blood*; D009570:Nitriles / Q000494:pharmacology / Q000633:toxicity*; D011722:Pyrethrins / Q000494:pharmacology / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D012741:Sexual Maturation / Q000187:drug effects*
D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; D007986:Luteinizing Hormone; C017690:fenvalerate
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