Biomedical subjects

L J Guillette

Publications and source records attributed to L J Guillette.

At least 55 records · Page 3Linked to original sources

PubMed1995

Insulin-like growth factor-I in the plasma of two reptiles: assay development and validations.

Radioimmunoassays (RIAs) of insulin-like growth factor-I (IGF-I) in nonmammals are complicated by two problems: decreased specificity due to heterologous assays and assay interference from IGF binding proteins. We have developed and validated an RIA for the detection of IGF-I in reptilian plasma that circumvents these problems. Biochemical validations show parallelism between standard curves, plasma dilutions, and internal standards. Further, biological validations indicate that (1) plasma IGF-I levels are significantly reduced in nonreproductive, female American alligators (Alligator mississippiensis) with high plasma estradiol-17 beta concentrations compared to individuals with low plasma estradiol-17 beta concentrations and (2) plasma IGF-I concentrations are elevated in juvenile Trachemys scripta elegans turtles fed higher quality diets (defined by protein and energy content). These results provide impetus for future studies of IGF-I in reptiles.

Alligators and Crocodiles↗

PubMed1995

Size-dependent, sex-dependent, and seasonal changes in insulin-like growth factor I in the loggerhead sea turtle (Caretta caretta).

This study examines size-dependent, sex-dependent, and seasonal fluctuations in plasma insulin-like growth factor-I (IGF-I) concentrations in loggerhead sea turtles (Caretta caretta). Loggerhead turtles (n = 158) were captured in shrimp trawler nets during a 12-month survey in Cape Canaveral Channel, Florida. Plasma samples were analyzed using a validated heterologous radioimmunoassay. Large turtles (> 75 cm straight-line carapace length) had significantly higher plasma IGF-I concentrations than small turtles (< or = 75 cm; P < 0.0001). Plasma IGF-I concentrations did not vary seasonally in small turtles, but large turtles had significantly higher plasma IGF-I concentrations during the spring and summer months (P < 0.005). Within the large turtles, adult males had significantly lower IGF-I concentrations than females and subadult males (P < 0.05). These results and a review of loggerhead turtle natural history suggest that the seasonal fluctuations in plasma IGF-I of adult turtles are due to elevated IGF-I levels in reproductively active female turtles. Further research is needed to examine correlations between reproductive activities and plasma IGF-I concentrations in reptiles.

Animals↗

PubMed1995

Reproductive impairment in the Florida panther: nature or nurture?

Many of the remaining members of the endangered Florida panther (Felis concolor coryi) population suffer from one or more of a variety of physiological, reproductive, endocrine, and immune system defects including congenital heart defects, abnormal sperm, low sperm density, cryptorchidism, thyroid dysfunction, and possible immunosuppression. Mercury contamination, determined to be the cause of death of a female panther in 1989, was presented as the likely cause of thyroid dysfunction. As genetic diversity in the species was less than expected, all of the other abnormalities have been attributed to inbreeding. However, exposure to a variety of chemical compounds, especially those that have been identified as environmental endocrine disrupters (including mercury, p,p'-DDE, and polychlorinated biphenyls), has elicited all of the listed abnormalities in other species. A number of these contaminants are present in South Florida. An exposure pathway has been identified, and evidence presented in this paper, including the fact that there appears to be no significant difference between serum estradiol levels in males and females, suggests that many male panthers may have been demasculinized and feminized as a result of either prenatal or postnatal exposure. Thus, regardless of the effects of inbreeding, current evidence seems to indicate that environmental contaminants may be a major factor contributing to reproductive impairment in the Florida panther population.

Animals↗

PubMed1995

Gonadal steroidogenesis in vitro from juvenile alligators obtained from contaminated or control lakes.

The ubiquitous distribution of many contaminants and the nonlethal, multigenerational effects of such contaminants on reproductive, endocrine, and immune systems have led to concerns that wildlife worldwide are affected. Although the causal agents and effects are known for some species, the underlying physiological mechanisms associated with contaminant-induced reproductive modifications are still poorly understood and require extensive research. We describe a study examining the steroidogenic activity of gonads removed from juvenile alligators (Alligator mississippiensis) obtained from contaminated or control lakes in central Florida. Synthesis of estradiol-17 beta (E2) was significantly different when ovaries from the contaminated and control lakes were compared in vitro. Additionally, testes from males obtained from the contaminated lake. Lake Apopka, synthesized significantly higher concentrations of E2 when compared to testes obtained from control males. In contrast, testosterone (T) synthesis from all testes examined in this study displayed a normal pattern and produced concentrations greater than that observed from ovaries obtained from either lake. Interestingly, the pattern of gonadal steroidogenesis differs from previously reported plasma concentrations of these hormones obtained from the same individuals. We suggest that the differences between the in vivo and in vitro patterns are due to modifications in the hepatic degradation of plasma sex steroid hormones.

Alligators and Crocodiles↗

PubMed1995

Defining the role of pollutants in the disruption of reproduction in wildlife.

Although chemical exposure has been associated with reduced reproduction in certain North American fish, reptiles, and mammals, definitive cause-and-effect data are lacking in many instances. Because the increasing use and global transport of industrial chemicals pose significant risk to successful reproduction, methods should be developed that can define the geographic extent and magnitude of injury and risk to wildlife. Because industrial chemicals are articles of commerce, information about injury to wildlife has been contentious and too often ineffective in changing societal behavior. The following strategies are advocated for inferring causal relationships. First, a balanced and comprehensive assessment of the data is necessary to determine the geographic extent of exposure and reproductive effects associated with environmental pollution. Initial efforts to document reproductive injury should focus on specific ecosystems in which detrimental effects have been observed, but lack sufficient causal data. Model systems (including experimental mesocosms or field ecosystems) should be identified or designed that can adequately test multigenerational reproductive effects. Mechanistic data from supportive laboratory studies on reproductive toxicity, quantitative structure-activity relationships, and bioaccumulation can be used to predict effects of related pollutants and to determine risk. Such information is essential to prevent future injury to wildlife and to prioritize the numerous remediation decisions facing our society.

Animals↗

PubMed1995

Organization versus activation: the role of endocrine-disrupting contaminants (EDCs) during embryonic development in wildlife.

Many environmental contaminants disrupt the vertebrate endocrine system. Although they may be no more sensitive to endocrine-disrupting contaminants (EDCs) than other vertebrates, reptiles are good sentinels of exposure to EDCs due to the lability in their sex determination. This is exemplified by a study of alligators at Lake Apopka, Florida, showing that EDCs have altered the balance of reproductive hormones resulting in reproductive dysfunction. Such alterations may be activationally or organizationally induced. Much research emphasizes the former, but a complete understanding of the influence of EDCs in nature can be generated only after consideration of both activational and organizational alterations. The organizational model suggests that a small quantity of an EDC, administered during a specific period of embryonic development, can permanently modify the organization of the reproductive, immune, and nervous systems. Additionally, this model helps explain evolutionary adaptations to naturally occurring estrogenic compounds, such as phytoestrogens.

Animals↗

PubMed1994

Number and state of rat ovarian mast cells after exogenous administration of luteinizing hormone.

Diestrous rats were treated with an injection of luteinizing hormone (LH), and their ovaries were examined for mast cell number and stage of degranulation at 2 and 4 hr post-injection. LH tripled the number of medullary mast cells at 2 hr. The source or origin of the additional mast cells is unknown. Comparison of the present results with other studies of rat ovarian mast cell dynamics suggests the occurrence of a reduction in mast cell number in early to mid-proestrus followed by an LH-induced increase in late proestrus.

Animals↗

PubMed1994

Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida.

The reproductive development of alligators from a contaminated and a control lake in central Florida was examined. Lake Apopka is adjacent to an EPA Superfund site, listed due to an extensive spill of dicofol and DDT or its metabolites. These compounds can act as estrogens. Contaminants in the lake also have been derived from extensive agricultural activities around the lake that continue today and a sewage treatment facility associated with the city of Winter Garden, Florida. We examined the hypothesis that an estrogenic contaminant has caused the current failure in recruitment of alligators on Lake Apopka. Supporting data include the following: At 6 months of age, female alligators from Lake Apopka had plasma estradiol-17 beta concentrations almost two times greater than normal females from the control lake, Lake Woodruff. The Apopka females exhibited abnormal ovarian morphology with large numbers of polyovular follicles and polynuclear oocytes. Male juvenile alligators had significantly depressed plasma testosterone concentrations comparable to levels observed in normal Lake Woodruff females but more than three times lower than normal Lake Woodruff males. Additionally, males from Lake Apopka had poorly organized testes and abnormally small phalli. The differences between lakes and sexes in plasma hormone concentrations of juvenile alligators remain even after stimulation with luteinizing hormone. Our data suggest that the gonads of juveniles from Lake Apopka have been permanently modified in ovo, so that normal steroidogenesis is not possible, and thus normal sexual maturation is unlikely.

Alligators and Crocodiles↗

PubMed1993

Localization of insulin-like growth factor-I-like immunoreactivity in the reproductive tract of the vitellogenic female American alligator, Alligator mississippiensis.

Insulin-like growth factor I (IGF-I) is a 70 amino acid, mitogenic polypeptide, which, in mammals, acts through an endocrine, paracrine, and/or autocrine pathway to regulate growth and development. The primary goal of this study was to determine whether or not IGF-I-like immunoreactivity is present in the oviduct of the vitellogenic American alligator, Alligator mississippiensis, and if immunoreactivity patterns vary among the three functional oviducal regions: the albumen-secreting tube region, the anterior, fiber-secreting uterus, and the posterior, calcium-secreting uterus. Immunolocalization of IGF-I-like immunoreactivity was accomplished using a polyclonal antihuman rabbit antiserum with an immunoperoxidase staining system. IGF-I-like immunoreactivity was detected in all three oviducal regions of the vitellogenic alligator. The presence of IGF-I-like immunoreactivity in the oviduct suggests this hormone could function in the growth and proliferation of the alligator oviduct. Furthermore, the presence of IGF-I-like immunoreactivity in the tubal glands, which secrete components of the egg white, suggests that growth factors such as IGF-I may be synthesized by these glands and incorporated into the albumen during egg formation.

Alligators and Crocodiles↗

PubMed1992

Effects of arachidonic acid, prostaglandin F2 alpha, prostaglandin E2, and arginine vasotocin on induction of birth in vivo and in vitro in a viviparous lizard (Sceloporus jarrovi).

The ability of arachidonic acid (AA) and prostaglandins of the two series to induce parturition in vivo and oviducal contraction in vitro was studied in the viviparous lizard Sceloporus jarrovi. Injection of PGF2 alpha, PGE2, or AA during late pregnancy stimulated parturition within 2 hr in a threshold-dependent fashion. In contrast, during mid pregnancy, females did not respond. Surgically removed and cultured oviducts from females in late pregnancy gave "birth" in response to AA, PGF2 alpha, and PGE2. Oviducts from S. jarrovi in mid pregnancy responded to PGF2 alpha but not to AA. Addition of arginine vasotocin, a potent stimulator of PG synthesis, either alone or with AA to oviduct cultures stimulated rapid and complete birth in vitro from oviducts obtained from late, but not mid pregnant, females. Stage of pregnancy mediates the response of the lizard oviduct to prostaglandin stimulation.

Analysis of Variance↗

PubMed1992

Alligators provide evidence for the evolution of an archosaurian mode of oviparity.

The female reproductive tract of birds is different from that of other oviparous amniotes in that the eggshell membranes and calcareous layer are formed in separate regions of the uterus; the isthmus and shell gland, respectively. Phylogenetically, birds are included among the archosaurs, along with crocodilians and dinosaurs. Many dinosaurs were oviparous, producing hard-shelled eggs, yet the reproductive system of dinosaurs has proven difficult to investigate, due to poor preservation of soft anatomy. In this study, we examined functional morphology and eggshell formation in a reptilian archosaur, the American alligator, and demonstrated that the crocodilian reproductive tract has separate uterine regions for formation of the eggshell membranes and calcareous layer. These uterine regions are ultrastructurally comparable to the isthmus and shell gland of birds, and may be homologous. This similarity of reproductive functional morphology between crocodilians and birds may implicate the evolution of an archosaurian mode of oviparity that may shed light on dinosaur reproduction.

Alligators and Crocodiles↗

PubMed1991

Exogenous progesterone or indomethacin delays parturition in the viviparous lizard Sceloporus jarrovi.

Female Sceloporous jarrovi in late pregnancy given an ip injection of progesterone (50 ng/g body wt) or indomethacin (4 micrograms/g body wt) exhibited no change in the length of pregnancy when compared to saline-treated controls. In contrast, pregnant females given subcutaneous implants (constant release pellets) containing progesterone or indomethacin exhibited significantly delayed parturition when compared with females given control implants. Indomethacin treatment also disrupted the normal birth process when it occurred, as all females receiving this compound exhibited parturition of only a portion (24-32%) of the total clutch. A similar phenomenon occurred in one experiment following implantation of progesterone pellets. Histological examination of the corpora lutea and oviduct indicated no obvious difference in structure among any of the treatment groups.

Animals↗

PubMed1991

Inositol phosphate formation in uterine tissue from two species of reptiles is stimulated by arginine vasotocin and influenced by stage of reproduction.

Phosphoinositide hydrolysis, resulting in inositol trisphosphate (IP3) and diacylglycerol (DG) formation, has been implicated in oxytocin-stimulated pulsatile secretion of prostaglandin F2 alpha (PGF2 alpha) from uterine endometrium of sheep and other mammals. In reptiles, arginine vasotocin (AVT) stimulates uterine secretion of PGF2 alpha. These studies investigated the ability of AVT to stimulate incorporation of [3H]inositol into inositol mono-, bis-, and trisphosphates in two reptilian species. In Experiment 1, AVT stimulated (P less than 0.01) IP formation in uterine from late-gravid (150 to 291%) and postpartum (104 to 363%) Yarrow's spiny lizards (Sceloporus jarrovi). Inositol phosphate formation, in response to AVT, was greater (P less than 0.01 for IP3 and P less than 0.05 for total IP) for gravid (stage 40 embryos) and postpartum (1-2 days) lizards near the time of parturition than for lizards at other stages (stage 38-39 embryos or 7 days postpartum). Inositol phosphate formation was greater (P less than 0.05) in uterine tissue from gravid than from postpartum lizards. In Experiment 2, basal IP formation and the response to AVT were the greatest (P less than 0.01) in endometrium from late-gravid American alligators (Alligator mississippiensis). AVT stimulated (P less than 0.02) IP synthesis in uterine endometrium from vitellogenic (136 to 394%), early-gravid (7 to 270%), late-gravid (315 to 1002%), postpartum (86 to 313%), and nonreproductive (292 to 322%) alligators. Results indicate that (1) AVT stimulates IP formation in the uterus of reptiles; (2) uterine IP formation increases in late-gravid reptiles; and (3) increased responsiveness to AVT may occur at parturition or oviposition.

Animals↗

PubMed1991

Plasma estradiol-17 beta, progesterone, prostaglandin F, and prostaglandin E2 concentrations during natural oviposition in the loggerhead turtle (Caretta caretta).

Changes in plasma concentrations of steroids and prostaglandins (PGs) during natural nesting and oviposition in the loggerhead turtle were studied. Blood samples were obtained during nine distinct behavioral stages of oviposition. Emerging females had no detectable prostaglandin F (PGF) or prostaglandin E2 (PGE2) whereas plasma estradiol-17 beta averaged 255 pg/ml and mean plasma progesterone was 395 pg/ml. Plasma steroid concentrations did not vary significantly during nesting. In contrast, plasma PGF and PGE2 exhibited significant elevations during nest digging about 15 min after emergence. A further significant increase in plasma PGs was observed 10 min later during early oviposition. Plasma PGE2 peaked during mid oviposition whereas maximal plasma PGF levels occurred during nest covering although mean values were not significantly different than those observed during oviposition. Both PGs showed an abrupt decline (within 10 min) during body pit covering to concentrations similar to those observed during nest construction. Our data suggest that PGs have an active role during oviposition and nesting in the loggerhead turtle and are consistent with hypotheses that PGF2 alpha stimulates uterine contractions promoting egg expulsion while PGE2 may be more important in promoting cervical relaxation.

Animals↗

PubMed1991

The lack of influence of exogenous testosterone on male parental behavior in a neotropical frog (Eleutherodactylus): a field experiment.

Males of the Puerto Rican frog Eleutherodactylus coqui exhibit prolonged parental care (nest attendance and defense) of direct-developing eggs in nonaquatic nest sites. Earlier work showed that plasma androgen levels are significantly lower in males caring for eggs than in noncaring, calling males. In this study, we investigated the effects of elevated plasma androgens on parental care behavior by implanting either testosterone (T) or placebo (P) pellets in parental males brooding eggs in the field. Plasma androgen levels, assessed 4 days after pellet implantation, were six times higher in T males than in P males. Despite this increase, T males exhibited no changes in nest fidelity or brooding behavior. The results indicate that lower androgen levels, at least those corresponding to a decline in T during parental care, are not necessary to maintain parental behavior in this tropical frog.

Animals↗

PubMed1991

Effects of prostaglandin F2 alpha prostaglandin E2 and arachidonic acid on the induction of oviposition in vivo and in vitro in oviparous lizards.

Gravid females of four different species of oviparous lizard were treated in vivo with varying doses of prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 or arachidonic acid (AA). In contrast to previous studies examining birds and viviparous lizards, no dosage induced oviposition in any of the treated females. All females, however, did exhibit behaviors associated with oviposition. Intact oviducts removed from gravid females and placed in organ culture did oviposit when treated with 30 or 100 ng PGF2 alpha/ml of culture media. Arachidonic acid at similar concentrations also was effective in stimulating birth. These data suggest that prostaglandins can stimulate oviposition in oviparous lizards but further suggest that their action may be inhibited by oviducal innervation until just prior to natural birth.

Animals↗

PubMed1991

Effect of beta-adrenergic stimulation on uterine contraction in response to arginine vasotocin and prostaglandin F2 alpha in the gecko Hoplodactylus maculatus.

The effects of beta-adrenergic stimulation on uterine contractions occurring in response to arginine vasotocin (AVT) and prostaglandin F2 alpha (PGF2 alpha) were compared during late pregnancy in the viviparous gecko Hoplodactylus maculatus. High doses of AVT (150 or 1,500 ng/g body weight) induced birth in vivo, but PGF2 alpha at doses of up to 2,000 ng/g did not induce birth. The effect of AVT (150 ng/g) on birth rate in vivo was not enhanced by pretreatment 20 min beforehand with the beta-adrenoreceptor antagonist dichloroisoproterenol (2 micrograms/g), whereas the effect of PGF2 alpha (200 ng/g) was markedly enhanced: geckos treated with dichloroisoproterenol and then with PGF2 alpha showed rapid birth-related behavior and gave birth. Isolated uteri showed a tonic contraction in response to AVT (100 ng/ml) and to PGF2 alpha (1,000 ng/ml). Pre-exposure of isolated uteri to the beta-adrenoreceptor agonist isoproterenol (1 microgram/ml) caused relaxation; this pre-exposure did not block the tonic contraction occurring in response to AVT, whereas it completely blocked the tonic contraction induced by PGF2 alpha. We conclude that in H. maculatus, beta-adrenergic stimulation inhibits uterine contractions induced by PGF2 alpha but not those induced by AVT. These data are the first to show that beta-adrenergic stimulation inhibits uterotonic responses to PGF2 alpha in a reptile, and they suggest that the cellular mechanisms by which AVT and PGF2 alpha induce contraction may differ in this species. They also provide further evidence for similarities between mammals and reptiles in the effects of beta-adrenergic stimulation on uterine relaxation.

Animals↗

PubMed1991

Prostaglandins, oviducal function, and parturient behavior in nonmammalian vertebrates.

Extensive data show that in mammals and birds, prostaglandins (PGs) are associated with ovulation, luteal function, oviposition, and parturition, and that also in mammals they are associated with birth-related behavior and sexual receptivity. In mammals and birds, the ability of PGs to stimulate oviducal contractions varies regionally along the oviduct (i.e., there is a functional cervix or uterovaginal region that acts to retain eggs or embryos in utero during shelling or embryonic development). Furthermore, at least in mammals, there is neural control over oviducal contractions. In reptiles, PGs stimulate oviducal contractions, and these contractions may be overridden by neural control. No data are available on whether PGs stimulate oviducal contractions in amphibians or whether there is a functional cervix in amphibians or reptiles. We suggest that in ancestral amphibians with oviparity and external fertilization, eggs moved rapidly through the oviduct after ovulation and that ovarian and oviducal PGF served as an endocrine hormone coordinating oviducal contractions and central nervous system-controlled oviposition behavior. Furthermore, we hypothesize that there was little or no neural control over oviducal contractions and no functional cervix. These conditions may still exist in present-day oviparous amphibians. In contrast, we suggest that modern-day oviparous reptiles have evolved a functional cervix and neural control over PG-induced uterine contractions, allowing egg passage to be blocked and thus the development of egg retention. These characteristics may be viewed as exaptations for the evolution of viviparity.

Animals↗