PMID- 16515688
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20060505
LR  - 20240322
IS  - 1740-3391 (Electronic)
IS  - 1740-3391 (Linking)
VI  - 4
DP  - 2006 Mar 3
TI  - Toxic effects of methoxychlor on the episodic prolactin secretory pattern: 
      possible mediated effects of nitric oxide production.
PG  - 3
AB  - BACKGROUND: This work addresses the issue of whether methoxychlor (MTX) exposure 
      may modify the ultradian secretion of prolactin through changes in the synthesis 
      of nitric oxide (NO) induced by Nomega-nitro-L-arginine methyl ester (L-NAME) in 
      the hypothalamic-pituitary axis. Associated changes in dopamine (DA) content in 
      the anterior (AH), mediobasal (MBH) and posterior hypothalamus (PH) and median 
      eminence (ME) were evaluated. METHODS: Two groups of animals (MTX and MTX+L-NAME 
      treated) received subcutaneous (sc) injections of MTX at a dose of 25 mg/kg/day 
      for one month. The other two groups of animals (control and L-NAME treated) 
      received sc vehicle injections (0.5 mL/day of sesame oil), during the same period 
      of time to be used as controls. Forty hours before the day of the experiment, 
      animals were anaesthetized with intrapritoneal injections of 2.5% tribromoethanol 
      in saline and atrial cannulas were implanted through the external jugular vein. 
      Plasma was continuously extracted in Hamilton syringes coupled to a peristaltic 
      bomb in tubes containing phosphate-gelatine buffer (to increase viscosity). The 
      plasma was obtained by decantation and kept every 7 minutes for the measurement 
      of plasma prolactin levels through a specific radioimmnunoassay and DA 
      concentration by high-pressure liquid chromatography (HPLC). RESULTS: Prolactin 
      release in animals from all experimental groups analyzed was episodic. Mean 
      plasma prolactin levels during the bleeding period, and the absolute pulse 
      amplitude were increased after MTX or Nomega-nitro-L-arginine methyl ester 
      (L-NAME) administration. However MTX and L-NAME did not modify any other 
      parameter studied with the exception of relative pulse amplitude in MTX treated 
      rats. L-NAME administration to rats treated with the pesticide reduced mean 
      plasma prolactin levels and the absolute amplitude of prolactin peaks. Peak 
      duration, frequency and relative amplitude of prolactin peaks were not changed in 
      the group of rats treated with MTX plus L-NAME as compared to either control or 
      MTX treated rats. Whereas MTX decreased DA content in the ME and increased it in 
      the AH, its content did not change in the MBH or PH, as compared to the values 
      found in controls. Also, L-NAME administration decreased DA content in the ME as 
      compared to controls. However, L- NAME administration to MTX exposed rats, 
      markedly increased DA content in the ME as compared to either MTX treated or 
      control rats. L-NAME administration increased DA content in the AH as compared to 
      the values found in non-treated rats. However L-NAME administration to MTX 
      exposed rats did not modify DA content as compared to either MTX treated or 
      control rats. L-NAME administration did not modify DA content at the MBH nor in 
      saline treated nor in MTX treated rats. However, the values of DA in the MBH in 
      MTX plus L-NAME treated animals were statistically decreased as compared to 
      L-NAME treated rats. In the PH, L-NAME administration increased DA content as 
      compared to the values found in non-treated animals. L-NAME administration to MTX 
      exposed rats also increased DA content as compared to either MTX treated or 
      control rats. CONCLUSION: The results suggest the existence of an interaction 
      between MTX and L-NAME in the modulation of the ultradian prolactin secretion at 
      the pituitary levels. The possibility of an indirect effect mediated by changes 
      in DA content at the ME requires further examination.
FAU - Lafuente, Anunciacion
AU  - Lafuente A
AD  - Laboratorio de Toxicologia, Facultad de Ciencias, Universidad de Vigo, Campus de 
      Orense, Las Lagunas, 32004 Orense, Spain. lafuente@uvigo.es
FAU - Cabaleiro, Teresa
AU  - Cabaleiro T
FAU - Cano, Pilar
AU  - Cano P
FAU - Esquifino, Ana I
AU  - Esquifino AI
LA  - eng
PT  - Journal Article
DEP - 20060303
PL  - England
TA  - J Circadian Rhythms
JT  - Journal of circadian rhythms
JID - 101200389
PMC - PMC1450319
EDAT- 2006/03/07 09:00
MHDA- 2006/03/07 09:01
PMCR- 2006/03/03
CRDT- 2006/03/07 09:00
PHST- 2005/11/22 00:00 [received]
PHST- 2006/03/03 00:00 [accepted]
PHST- 2006/03/07 09:00 [pubmed]
PHST- 2006/03/07 09:01 [medline]
PHST- 2006/03/07 09:00 [entrez]
PHST- 2006/03/03 00:00 [pmc-release]
AID - 1740-3391-4-3 [pii]
AID - 10.1186/1740-3391-4-3 [doi]
PST - epublish
SO  - J Circadian Rhythms. 2006 Mar 3;4:3. doi: 10.1186/1740-3391-4-3.