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1.
Domest Anim Endocrinol ; 32(3): 201-15, 2007 Apr.
Article in English | MEDLINE | ID: mdl-16677794

ABSTRACT

Female mutant restricted ovulator (RO) chickens of the White Leghorn strain carry a naturally occurring single nucleotide mutation in the very low density lipoprotein receptor (VLDLR) gene. Due to this mutation, RO hens fail to express a functional VLDLR protein on the oocyte membrane, which results in an impaired uptake of circulating yolk precursor macromolecules. Mutant RO hens subsequently develop hyperlipidemia and generally fail to lay eggs due to follicular atresia. Since RO hens also reportedly have three-fold higher basal plasma estrogen concentrations, combined with four-fold lower levels of circulating progesterone as compared to wild-type (WT) hens, we hypothesized that RO hens would have an increased abundance of pituitary progesterone receptor (PR) mRNA and PR isoforms A and B as well as alterations in circulating gonadotrophin levels. Quantitative PCR assays revealed significantly greater (P

Subject(s)
Chickens/metabolism , Follicle Stimulating Hormone/blood , Luteinizing Hormone/blood , Pituitary Gland/metabolism , Receptors, LDL/genetics , Receptors, Progesterone/metabolism , Amino Acid Substitution , Animals , Chickens/blood , Chickens/genetics , Estrogens/blood , Female , Hypothalamo-Hypophyseal System/metabolism , Ovary/anatomy & histology , Point Mutation , Progesterone/blood , Protein Isoforms/genetics , Protein Isoforms/metabolism , RNA, Messenger , Receptors, Progesterone/genetics , Reproduction
2.
Environ Toxicol Chem ; 25(1): 233-40, 2006 Jan.
Article in English | MEDLINE | ID: mdl-16494247

ABSTRACT

The herbicide atrazine has gained recent attention for its reported effects on reproduction in amphibians. The present study examined the putative effects of atrazine during sexual maturation in the photostimulated female Japanese quail. Furthermore, the effects of atrazine on birds administered exogenous gonadotropin (pregnant mare serum gonadotropin [PMSG]) were investigated. Atrazine was administered up to 1,000 ppm in the diet to female quail undergoing photoperiodically induced sexual maturation. At high dietary concentrations, atrazine exhibits signs of overt toxicity with reductions in growth, feed intake, and liver weights, but these effects were dependent on the timing of treatment administration. Atrazine did not influence the weights of reproductive tissues (ovary and oviduct) or circulating concentrations of luteinizing hormone (LH). However, high concentrations of atrazine depressed circulating concentrations of estradiol. Treatment with atrazine for four weeks during sexual maturation inhibited growth but did not affect any other parameter assessed (feed intake, liver, ovary, or oviduct weights or the circulating concentrations of LH and estradiol). In birds receiving daily injections of PMSG, atrazine reduced growth, feed intake, and liver weights. However, PMSG-induced gonadal and oviduct growth was not affected by atrazine. The present results suggest that dietary atrazine exhibits limited reproductive toxicity in female quail during sexual maturation and only at concentrations above ecological relevance.


Subject(s)
Atrazine/toxicity , Coturnix/physiology , Herbicides/toxicity , Animals , Estradiol/blood , Female , Liver/drug effects , Liver/growth & development , Luteinizing Hormone/blood , Organ Size , Ovary/drug effects , Ovary/growth & development , Oviducts/drug effects , Oviducts/growth & development , Sexual Maturation/drug effects
3.
Gen Comp Endocrinol ; 146(2): 91-9, 2006 Apr.
Article in English | MEDLINE | ID: mdl-16427052

ABSTRACT

In birds, changes in hypothalamic gonadotropin-releasing hormone-I (GnRH-I) content and release are correlated with reproductive stages. This study examined the distribution and expression level of GnRH-I mRNA in anatomically discrete hypothalamic nuclei throughout the turkey reproductive cycle and following photostimulation. GnRH-I mRNA expression was determined using in situ hybridization in non-photostimulated (NPS), egg-laying (LAY), incubating (INC) and photorefractory (REF) hens. Overall, GnRH-I mRNA expression was greatest in the nucleus commissurae pallii (nCPa) and around the organum vasculosum lamina terminalis (OVLT), with less expression observed in the nucleus septalis lateralis (SL), cortico-habenula cortico-septum area, and within the nucleus preopticus medialis. GnRH-I mRNA expression was significantly increased in nCPa, OVLT, and SL after NPS hens (6L:18D) were exposed to a 30 or 90 min pulse of light beginning 14 h after first light (dawn). GnRH-I mRNA abundance within nCPa, OVLT and SL was greater in LAY than in NPS and INC hens, while mRNA expression was least in REF hens. These results indicate that GnRH-I mRNA expression in birds is sensitive to light stimulation during the photosensitive period and can be used to more precisely characterize their different reproductive stages.


Subject(s)
Gonadotropin-Releasing Hormone/biosynthesis , Ovulation , Photoperiod , Turkeys/physiology , Animals , Female , Gonadotropin-Releasing Hormone/analysis , Gonadotropin-Releasing Hormone/genetics , Hypothalamus/physiology , RNA, Messenger/biosynthesis
4.
Domest Anim Endocrinol ; 31(2): 141-53, 2006 Aug.
Article in English | MEDLINE | ID: mdl-16300920

ABSTRACT

It is well established that GnRH can stimulate the release of LH and FSH in mammals. Two GnRHs have been found in the chicken hypothalamus, cGnRH-I and -II. There is controversy as to whether either peptide can stimulate release of FSH in birds. The present studies compared the ability of cGnRH-I and -II to stimulate the release of FSH and LH in chickens. Lamprey (l) GnRH-III may be a specific-releasing factor for FSH, as it selectively stimulates FSH release in rodents and cattle, and has been detected in the hypothalamus of rodents, sparrows and chickens. Therefore, the ability of lGnRH-III to stimulate LH and FSH release was also examined. In our first experiment, the effects of cGnRH-I and -II were studied using 17-week prepubertal females. Intravenous injection of cGnRH-II at 1 and 10 microg/kg BW significantly increased LH secretion more than did cGnRH-I. Neither peptide significantly increased plasma FSH levels. In our second study, we administered cGnRH-I, -II or lGnRH-III to mature males maintained on a short photoperiod. cGnRH-II was again more potent than cGnRH-I in stimulating LH release, while lGnRH-III produced a modest LH rise. No GnRH peptide provided specific or potent stimulus to FSH secretion, although the high dose of cGnRH-II modestly enhanced FSH levels in the adult male (P < 0.05). Our results are not consistent with the view that lGnRH-III is a specific FSH-releasing hormone across multiple classes of vertebrates. We conclude that the mechanism by which independent release of FSH occurs in chickens remains unresolved.


Subject(s)
Chickens/physiology , Follicle Stimulating Hormone/blood , Gonadotropin-Releasing Hormone/pharmacology , Luteinizing Hormone/blood , Animals , Chickens/blood , Female , Follicle Stimulating Hormone/metabolism , Gonadotropin-Releasing Hormone/analogs & derivatives , Luteinizing Hormone/metabolism , Male , Oligopeptides/pharmacology , Pyrrolidonecarboxylic Acid/analogs & derivatives , Pyrrolidonecarboxylic Acid/pharmacology , Secretory Rate/drug effects
5.
Toxicol Sci ; 86(1): 152-60, 2005 Jul.
Article in English | MEDLINE | ID: mdl-15829615

ABSTRACT

The herbicide atrazine is a putative endocrine disruptor. The present studies investigated the effects of atrazine in male Japanese quail during sexual maturation. Atrazine was administered for two weeks in the diet or systemically to birds under long photoperiods. Atrazine had no effect on mortality but depressed both feed intake and growth (average daily gain [ADG] in g/day) at dietary concentrations of 1000 ppm. Atrazine in the diet at 10 ppm, but at no other concentrations, increased testes weight and gonadal-somatic-index and decreased the seminiferous tubule diameter-to-testis weight ratio. However, there were no effects on absolute tubule diameter, relative stage of testicular development, or the presence of a lumen. Atrazine in the diet at 1000 ppm increased circulating concentrations of testosterone but this effect was not observed consistently in all studies. Dietary atrazine at 10 ppm increased circulating concentrations of estradiol. Moreover, in one study, atrazine at 1000 ppm in the diet decreased circulating concentrations of luteinizing hormone. Atrazine administered systemically exerted no effect on indices of growth or reproduction. Atrazine did not mimic the effects of either estradiol or tamoxifen in male quail; thus, atrazine did not exhibit overt estrogenic or anti-estrogenic activity. Conversely, atrazine augmented the effects of testosterone and estradiol on testis regression, presumably by increasing the negative-feedback effects of these sex-steroids on follicle stimulating hormone secretion. It is concluded that atrazine up to 1000 ppm in the diet may exert some effects on reproductive development in sexually maturing male birds, but these are inconsistent and modest.


Subject(s)
Atrazine/toxicity , Hypothalamo-Hypophyseal System/drug effects , Sexual Maturation/drug effects , Testis/drug effects , Animals , Coturnix , Feeding Behavior , Luteinizing Hormone/blood , Male , Organ Size/drug effects
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