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Biomedical subjects

L J Guillette

Publications and source records attributed to L J Guillette.

At least 73 records · Page 4Linked to original sources
PubMed1990

Absence of daily cycles in plasma sex steroids in male and female tuatara (Sphenodon punctatus), and the effects of acute capture stress on females.

The possible existence of daily cycles in plasma concentrations of sex steroids was examined in wild male and female tuatara (Sphenodon punctatus). Samples were collected from freshly captured animals at dusk, middle of the night, dawn, and middle of the day in January (summer) and July (winter). Males showed daily cycles in mean body temperature (Tb) in both seasons but no daily cycle in mean plasma testosterone concentration in either season. Vitellogenic female tuatara in January and females in mixed reproductive condition in July also showed significant daily variation in Tb. However, there were no daily cycles in mean plasma concentrations of estradiol, testosterone, or progesterone in either group of females. Vitellogenic female tuatara subjected to an acute capture stress (3-hr confinement) in January had mean plasma concentrations of estradiol and testosterone that did not differ from those of free-roaming females. However, progesterone and Tb were significantly higher in captives than in free-roaming females. The elevation in progesterone may result from physical confinement, the difference in Tb, or both. These data suggest that seasonal fluctuations in circulating concentrations of plasma sex steroids in tuatara can be determined using samples collected at different times of the 24-hr cycle. However, the effects of acute capture stress and/or changes in Tb on plasma progesterone concentrations need to be considered in future studies on this and possibly other female reptiles.

Animals↗
PubMed1990

Arginine vasotocin-induced prostaglandin synthesis in vitro by the reproductive tract of the viviparous lizard Sceloporus jarrovi.

Two experiments were performed to determine whether arginine vasotocin (AVT) stimulates synthesis of prostaglandins (PGs) in reptilian oviducts. Homogenized oviducal tissue from female Sceloporus jarrovi in early and late pregnancy were cultured with radiolabeled (14C) prostaglandin precursor, arachidonic acid (AA). In late pregnancy, oviducts exposed to AVT exhibited a greater conversion of AA to PGF2 alpha than did controls, whereas in early pregnancy there was no difference. The conversion of AA to other prostaglandins (PGA2, PGD2, PGE2, PGI2) was not influenced by AVT. The second experiment examined whether endogenous in vitro synthesis of PGF and PGE2 from intact, pregnant oviducts was stimulated by AVT (50 ng/ml; 100 ng/ml). Both doses of AVT induced a similar, significant rise in PGF concentrations within 30 min whereas no significant increase was noted in PGE2 concentrations until 90 min after treatment. Indomethacin pretreatment blocked synthesis of both PGF and PGE2 for 30 min following AVT treatment. These data indicate that AVT induces a highly specific rise in the synthesis of PGF from the oviduct of female S. jarrovi in late pregnancy. Furthermore, the prostaglandin-stimulating effect of AVT in reptiles appears homologous with the effect of oxytocin in mammals and AVT in birds. We hypothesize that this interaction is an evolutionarily conserved relationship found in all amniote vertebrates.

Animals↗
PubMed1990

Indomethacin influences arginine vasotocin-induced parturition and oviposition in lizards (Sceloporus jarrovi and Sceloporus undulatus ).

The effect of the prostaglandin blocker indomethacin on arginine vasotocin-induced birth was examined. Gravid female, oviparous (Sceloporus undulatus ) and viviparous (Sceloporus jarrovi ) lizards were pretreated with saline or indomethacin, a potent blocker of PG synthesis. Pretreatment was followed by an intraperitoneal injection of AVT. Pretreatment with indomethacin significantly delayed the onset of AVT-induced oviposition in S. undulatus , whereas it had no effect on latency to birth in S. jarrovi . Female S. jarrovi treated with indomethacin, however, gave birth to only part of the total litter, whereas control females gave birth to complete litters. In viviparous females, an interaction of embryonic age with pretreatment was evident; females having more developed embryos decreased birth latency significantly and increased the percentage of parturition when compared with females that had embryos at earlier stages of development. Our data suggest that although exogenous AVT can stimulate oviposition or parturition, these events occur more rapidly and completely when prostaglandin synthesis is not inhibited.

Journal Article↗
PubMed1990

Endocrinology of oviposition in the tuatara (Sphenodon punctatus): I. Plasma steroids and prostaglandins during natural nesting.

Plasma concentrations of estradiol, progesterone, prostaglandin (PG) E2 and PGF were measured during three stages of the natural nesting cycle of the tuatara (Sphenodon punctatus), a rare New Zealand reptile. Specifically, we tested whether nesting activity in this species is correlated with significant modifications in plasma concentrations of these hormones. Tuatara dig a nest over a period of several nights, oviposit a complete clutch on a single night, and then guard that nest for several nights. We observed no significant changes in mean plasma concentrations of estradiol or progesterone among the different stages of nesting. In contrast, PGE2 was elevated during nest digging and oviposition but declined significantly during nest guarding. Plasma PGF was elevated during nest digging, rose significantly during oviposition, and declined to basal levels during nest guarding. These data indicate that oviposition in reptiles is associated with elevated plasma concentrations of PGs, suggesting that these hormones function in causing oviducal contractions and/or luteolysis. Moreover, these data suggest that the role of PGs in oviducal function may have been conserved throughout evolution of the amniote vertebrates.

Animals↗
PubMed1988

Histology and functional morphology of the female reproductive tract of the tortoise Gopherus polyphemus.

The oviducts of 25 tortoises (Gopherus polyphemus) were examined by using histology and scanning electron microscopy to determine oviductal functional morphology. Oviductal formation of albumen and eggshell was of particular interest. The oviduct is composed of 5 morphologically distinct regions; infundibulum, uterine tube, isthmus, uterus, and vagina. The epithelium consists of ciliated cells and microvillous secretory cells throughout the oviduct, whereas bleb secretory cells are unique to the infundibulum. The epithelium and endometrial glands of the uterine tube histologically resemble those of the avian magnum which produce egg albumen and may be functionally homologous. The isthmus is a short, nonglandular region of the oviduct and appears to contribute little to either albumen or eggshell formation. The uterus retains the eggs until oviposition and may form both the fibrous and calcareous eggshell. The endometrial glands are histologically similar to the endometrial glands of the isthmus of birds, which are known to secrete the fibers of the eggshell. These glands hypertrophy during vitellogenesis but become depleted during gravidity. The uterine epithelium may supply "plumping water" to the egg albumen as well as transport calcium ions for eggshell formation. The vagina is extremely muscular and serves as a sphincter to retain the eggs until oviposition. Sperm are found within the oviductal lumen and endometrial glands from the posterior tube to the anterior uterus throughout the reproductive cycle. This indicates sperm storage within the female tract, although the viability and reproductive significance of these sperm are unknown.

Animals↗
PubMed1987

Luteal morphology, atresia, and plasma progesterone concentrations during the reproductive cycle of two oviparous lizards, Crotaphytus collaris and Eumeces obsoletus.

From ovulation to oviposition, the corpora lutea of the oviparous lizards Crotaphytus collaris and Eumeces obsoletus exhibit three stages of luteal development: 1) luteogenesis, 2) luteal maturity, and 3) luteal regression. Each stage exhibits distinct characteristics, involving changes in: 1) luteal volume, 2) nuclear diameter of cells within the luteal cell mass, and 3) thecal development. Plasma progesterone concentration is greatest during luteogenesis and is positively correlated with ovarian atresia, although atresia occurred throughout the period of gravidity. These data suggest that in these two species, the corpora lutea secrete high amounts of progesterone immediately following ovulation and exhibit morphologically distinct stages of growth and regression.

Animals↗
PubMed1987

Changes in oviducal vascularity during the reproductive cycle of three oviparous lizards (Eumeces obsoletus, Sceloporus undulatus and Crotaphytus collaris).

Histologically derived estimates and ink suspension vascular casts were used to examine oviducal vascular changes. Vascularity peaked during gravidity and was correlated with maximal plasma progesterone concentrations. The vascular increase in the oviducal tissue was attributed exclusively to increased capillary densities. The greatest change occurred in the anterior uterus where incubation and egg shell secretion occur. Similar patterns of change in vascularity occurred in the infundibulum, although not as extreme as that seen in the anterior uterus, whereas no significant alterations were noted in the posterior uterus. These modifications mimic the pattern of vascular change occurring in viviparous lizards during simple placentation. We suggest that major changes in uterine vascularity may not be required for the evolution of simple chorioallantoic placentae in lizards.

Animals↗
PubMed1985

Effect of deluteinization on plasma progesterone concentration and gestation in the lizard, Anolis carolinensis.

Plasma progesterone concentration in deluteinized female lizards, as determined by radioimmunoassay, did not decrease significantly, as compared to non-surgical controls until 48 hr after surgery. Sham surgery induced a significant increase in plasma progesterone concentration 24 hr after surgery. Progesterone concentration then declined to an intermediate level not significantly different from non-surgical control or deluteinized females. Plasma progesterone concentration in non-surgical control specimens exhibited no significant changes during the 96 hr in which animals were examined. Oviposition did not occur in the control or sham groups whereas three of eight of the deluteinized females did oviposit by 48 hr.

Animals↗
PubMed1985

Response of amphibian (Ambystoma tigrinum) oviduct to arginine vasotocin and acetylcholine in vitro: influence of steroid hormone pretreatment in vivo.

Oviducts of the salamander Ambystoma tigrinum contract in vitro in response to stimulation by arginine vasotocin (AVT) and acetylcholine (ACh). Steroid hormone pretreatment significantly affects the responsiveness of the oviductal tissue to AVT and ACh. Oviducts initially pretreated with estradiol, testosterone and saline or a combination of estradiol and testosterone exhibit no response to AVT and only saline or estradiol/testosterone treated oviducts respond to ACh. Secondary pretreatment with progesterone stimulated a significant increase in responsiveness to AVT and ACH in all groups.

Acetylcholine↗
PubMed1984

Luteolysis induced by prostaglandin F2 alpha in the lizard, Anolis carolinensis.

The effect of exogenous prostaglandin F2 alpha (PGF) on luteal function and morphology was examined in the lizard, Anolis carolinensis. Reproductively active females were injected with 1.0 micrograms PGF, 0.1 micrograms PGF, or 0.05 ml saline. Animals were killed 2, 6, or 24 hr after injection. Prostaglandin treatment induced luteolysis as evidenced by significant decreases in plasma progesterone concentration in animals sacrificed 6 and 24 hr after treatment. Both doses of PGF were effective. However, 0.1 micrograms PGF induced luteolysis in less than 50% of the treatment group. Luteal degradation became apparent at the cellular level 24 hr after PGF treatment whereas no significant changes were observed in corpora lutea of the 2- or 6-hr postinjection specimens. These data suggest that PGF is a luteolytic agent in reptiles.

Animals↗
PubMed1983

The relationship among ovarian condition, steroid hormones, and estrous behavior in Anolis carolinensis.

The lizard Anolis carolinensis ovulates a single egg alternately from each ovary every 14 days. The ovulated egg enters the ipsilateral oviduct, acquires a shell, and is oviposited 18 or 19 days later. Thus, there is only a single egg in one of the oviducts (one-egg condition) during most of the estrous cycle, but there is a 4-5 day period when a mature, shelled egg is in one oviduct while a recently ovulated egg is in the contralateral oviduct (two-egg condition). Analysis of ovarian follicular diameters indicates that the largest follicle in a single ovary exhibits a growth spurt about halfway through its 28-day vitellogenic growth phase. The corpus luteum, once formed from the ovulated follicle, exhibits a linear decrease in weight, becoming fully regressed just before oviposition of the egg in the ipsilateral oviduct. Plasma concentrations of estradiol-17 beta and progesterone are high in two-egg animals. After oviposition, plasma concentrations of progesterone are still high in one-egg animals whereas those of estradiol-17 beta are much lower. These ovarian and hormonal changes during the estrous cycle are discussed in relation to the probable sources of estradiol-17 beta and progesterone, the control of the alternating pattern of ovulation and oviposition, and the role of steroid hormones in female sexual receptivity in this species.

Animals↗
PubMed1980

Rat ovarian mast cells: distribution and cyclic changes.

Numerous tissue mast cells are present in the ovarian medulla and hilus and in the oviduct of rats. In the medulla, most of these mast cells are in the connective tissue of the stroma near blood and lymphatic vessels. During proestrus, many of the medullary mast cells totally degranulate and thus are not visible histochemically; they then regranulate during estrus. In contrast, the number of stainable mast cells in the ovarian hilus and oviduct does not change during the estrous cycle. Histofluorometric methods demonstrate that mast cells in the ovarian medulla and hilus, as well as the oviduct, contain histamine. In addition, the lining of small blood vessels in the ovarian medulla contains histamine. Thus, mast cell and blood vessel histamine secretion may play a role in ovarian function.

Animals↗
PubMedDate not supplied

A re-examination of variation associated with environmentally stressed organisms.

Variation is an essential feature of biological systems. Populations adapt to dynamic environments, in part, because of this variation. In this review, we re-examine phenotypic variation, especially in organisms living in polluted environments. A recent goal of ecotoxicology is to understand the sublethal effects of exposure to pollutants, e.g. responses to endocrine-disrupting contaminants. While variation is an inherent quality of organisms, variance is a statistical measure of the variation of a trait. Increased variance has been associated with organisms living at the perimeter of a population's range, introduced into novel environments, or exposed to pollution. Some researchers have proposed increased phenotypic variance in exposed populations as an evolutionary mechanism, and others have suggested its use as a biomarker. While we agree that variance often increases in the exposed population, we also recognize that the opposite phenomenon occurs. That is, variance can decrease from exposure to pollution. Altered variance in the exposed population-leading to heteroscedasticity-could result in erroneous conclusions (Type II errors). We suggest that exposure to endocrine-disrupting contaminants could influence the health of populations in ways that are not always represented by measures of central tendency, and that variance and distribution should also be examined in environmentally stressed wildlife.

Animals↗
PubMedDate not supplied

Environmental contaminants and reproductive abnormalities in wildlife: implications for public health?

At the onset of the industrial age, environmental contaminants began to pose a major threat to the health of wildlife. That threat appears to continue today. In the last three decades, the focus of our concern on the health consequences of environmental pollution has been on lethal, carcinogenic, and/or extreme teratogenic manifestations. Evidence from a number of sources suggests that another mechanism, endocrine-disruption, also must be examined. There is excellent laboratory and field evidence that man-made chemicals (xenochemicals) released into the environment act as hormones or antihormones. They act as endocrine-disrupting contaminants (EDCs). The release of EDCs occurred in the past and continues today. The development of the reproductive system is vulnerable to perturbation by EDCs. Wildlife studies demonstrate that both sexes are affected and experience modifications of gonadal and reproductive tract development or functioning and abnormal synthesis or metabolism of hormones. A number of abnormalities seen in the reproductive system of various wildlife species correlate with similar abnormalities described as rising in human populations. We suggest that wildlife are excellent sentinels of ecosystem health. Data from these wildlife studies present models and methodologies for examining human health.

Abnormalities, Drug-Induced↗