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PubMed2000

Blood viscosity and hematological changes during prolonged submergence in normoxic water of northern and southern musk turtles (Sternotherus odoratus).

Musk turtles (Sternotherus odoratus) can survive at least 150 days of submergence in normoxic water at 3 degreesC, during which time there are large increases in packed cell volume (PCV). We investigated the effects of submergence in normoxic water at 3 degreesC on the blood viscosity of musk turtles from northern (Massachusetts) and southern (Alabama) locales. Blood was collected from air-breathing turtles and after 20, 50, 100, and 150 days of submergence in normoxic water at 3 degreesC. Hematological responses to submergence were similar in the two groups, therefore the results were combined. Packed cell volume increased steadily above that of controls after 20, 50, 100, and 150 days of submergence. Hemoglobin concentration also progressively increased above that of controls after 20, 50, and 100 days of submergence but declined to near control values after 150 days. Blood viscosity increased with increasing PCV; however, blood viscosity of musk turtles appears less affected by PCV than is blood viscosity of mammalian species. As such, musk turtles appear to be able to maintain adequate blood flow to tissues while increasing the oxygen carrying capacity of the blood during prolonged submergence. However, after 150 days submergence, oxygen delivery should decrease due to a reduced oxygen carrying capacity of the blood and an increased resistance to blood flow, which may limit the length of time these turtles can remain viable during hibernation.

Alabama↗
PubMed2000

The role of the integument as a barrier to penetration of ice into overwintering hatchlings of the painted turtle (Chrysemys picta).

Hatchlings of the North American painted turtle (Chrysemys picta) spend their first winter of life inside a shallow, subterranean hibernaculum (the natal nest) where they may be exposed for extended periods to ice and cold. Hatchlings seemingly survive exposure to such conditions by becoming supercooled (i.e., by remaining unfrozen at temperatures below the equilibrium freezing point for body fluids), so we investigated the role of their integument in preventing ice from penetrating into body compartments from surrounding soil. We first showed that hatchlings whose epidermis has been damaged are more likely to be penetrated by growing crystals of ice than are turtles whose cutaneous barrier is intact. We next studied integument from a forelimb by light microscopy and discovered that the basal part of the alpha-keratin layer of the epidermis contains a dense layer of lipid. Skin from the forelimb of other neonatal turtles lacks such a layer of lipid in the epidermis, and these other turtles also are highly susceptible to inoculative freezing. Moreover, epidermis from the neck of hatchling painted turtles lacks the lipid layer, and this region of the skin is readily penetrated by growing crystals of ice. We therefore conclude that the resistance to inoculation imposed by skin on the limbs of hatchling painted turtles results from the presence of lipids in the alpha-keratin layer of the epidermis. Neonates apparently are able to avoid freezing during winter by drawing much of the body inside the shell, leaving only the ice-resistant integument of the limbs exposed to ice in the environment. The combination of behavior and skin morphology enables overwintering hatchlings to exploit an adaptive strategy based on supercooling.

Adaptation, Physiological↗
PubMed2000

Hepatic changes in the freeze-tolerant turtle Chrysemys picta marginata in response to freezing and thawing.

Select hepatic changes in the freeze-tolerant hatchling turtle, Chrysemys picta marginata, were studied in response to freezing at -2.5 degrees C and thawing. Upon freezing, a small, selective increase in the liver weight with no increase in body weight was seen suggestive of an hepatic capacitance response. In all turtles studies, lobular differences in the hepatic content of glycogen were evident: the smaller lobe contained twice as much glycogen as the larger lobe. The response to freezing and thawing was comparable. Total hepatic glycogen levels of turtles were reduced approximately 60 per cent from control levels in the frozen state and recovered to >80 per cent of control levels in the thawed state. Compared to the control state, turtle blood glucose levels were: unchanged after 12 h in the cool state; reduced 28 per cent after 24 h and increased two-fold after 48 h in the frozen state; and increased 4.5-fold in the thawed state. Thus, changes in hepatic glycogen metabolism occur without large changes in blood glucose levels. In turtle liver plasma membranes, the hepatic alpha(1)-adrenergic receptor was barely detectable and did not change. The beta(2)-adrenergic receptor was expressed at high levels and, compared to control levels, was: unchanged after 12 h in the cool state; reduced 20 per cent after 24 h and 40 per cent after 48 h in the frozen state. On thawing, this receptor was 50 per cent of control levels. While catecholamines working through the beta(2)-adrenergic receptor may effect early hepatic glycogen breakdown in response to freezing, other factors must be involved to complete the process. The plasma membrane-bound enzyme gamma-glutamyltranspeptidase displayed a different pattern of changes indicative of selective modulation: it was increased 2.7-fold over control levels in the cool state; unchanged in the frozen state; and increased 1.8-fold in the thawed state. The activity of the kidney enzyme was decreased in the cool state and slightly increased in the frozen and thawed states emphasizing the tissue-specific nature of the changes in the activity of gamma-glutamyltranspeptidase in response to freezing and thawing. The similarities and differences of the hepatic changes in response to freezing and thawing in the freeze-tolerant hatchling turtle to those we have previously reported for the freeze-tolerant frog are discussed.

Animals↗
PubMed2002

Experimental manipulation of steroid concentrations in circulation and in egg yolks of turtles.

Steroid hormones in egg yolks are increasingly recognized as an important component of maternal and offspring fitness in oviparous vertebrates. Yet, except for in birds, the mechanism by which females allocate these resources is poorly understood. We manipulated systemic levels of hormones in reproductively mature female red-eared slider turtles (Trachemys scripta elegans) with silastic implants to test the hypothesis that hormones are allocated to developing follicles as a quantitative function of circulating levels in the females. Turtles exhibited similar amounts (<1 ng/ml) of circulating steroids (dihydrotestosterone, estradiol-17 beta, or testosterone) in early September immediately prior to experimental manipulation. After treatment with silastic implants, circulating levels of steroids increased markedly. By the following April after hibernation, circulating levels of dihydrotestosterone had returned to preimplantation levels, but circulating levels of estradiol-17 beta and testosterone in estradiol-17 beta- and testosterone-treated turtles, respectively, remained substantially elevated through April. Focusing on testosterone, we detected nearly six-fold higher concentrations in yolk from mature follicles from testosterone-treated turtles than in yolk from mature follicles from control turtles. Our results provide support for the hypothesis that concentrations of steroids in egg yolks of turtles reflect circulating concentrations of steroids during follicular development rather than the hypothesis that females selectively allocate specific amounts of steroid hormones to each egg separately. Our findings also highlight an unambiguous physiological mechanism by which nongenetic maternal effects in oviparous species can directly influence the nutritional milieu experienced by developing embryos.

Animals↗
PubMed1993

Binding affinities of thyroxine-binding proteins in turtle plasma.

Binding affinities (Ka) for thyroxine (T4) by blood plasma and purified plasma proteins from two turtles, the slider (Trachemys scripta) and snapper (Chelydra serpentina), were compared with those of a human using equilibrium dialysis. The purified T4 binding protein (TBP) from T. scripta had a high affinity that was lower by about fivefold than that of human TBG (3.2 x 10(9) vs 1.7 x 10(10) M-1). The affinity of T4 binding by TBP was similar to that determined for whole plasma from this species. T. scripta plasma stripped of TBP by affinity chromatography showed a greatly reduced Ka (2.8 x 10(5) M-1) similar to that of albumin purified from the same species (3.6 x 10(5) M-1), as well as a marked increase in free T4 (9.7%) as compared to whole turtle plasma (0.13%). The T4 binding of snapping turtle plasma (Ka = 5 x 10(5) and free T4 = 2.7%) was similar to that of the TBP-stripped plasma and albumin. Binding affinities for the two turtle and human albumins were similar. Because of low concentrations of albumin in the turtle blood (estimated at ca. 10 mg/ml based on binding), TBP probably accounts for a greater proportion of T4 binding in the slider turtle than does TBG in the human; e.g., when plasma T4 and TBP are elevated in T. scripta, > 98% of bound T4 would be associated with TBP. When both TBP and T4 are depressed (e.g., as in hatchlings), free T4 may actually be higher than in conditions when total T4 is elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Corticosterone secretion in response to capture and handling in free-living red-eared slider turtles.

The corticosterone response to capture and handling was measured in free-living red-eared slider turtles, Trachemys scripta elegans. To determine the ability of this species to exhibit this endocrine response, slider turtles were bled at the time of removal from hoop nets and again at 30 and 60 min following capture to create plasma profiles of acute corticosterone secretion from individuals. Plasma corticosterone concentration increased significantly with handling time. The greatest rise in corticosterone was within the first 30 min following capture and handling, with this rate of increase declining over the next 30 min of restraint. There was no correlation between corticosterone levels at the time of capture and the length of time it took to get the sample if the sample was taken within the first 10 min after capture. However, when these samples were included with those taken from other turtles sampled 11 to 25 min after capture, hormone levels were significantly correlated with handling time. This suggests that the critical time to obtain an initial sample that best represents the predisturbance level in slider turtles is within 10 min. There was no correlation between the turtles' energetic condition and initial corticosterone concentrations. Plasma corticosterone values at all sampling times were comparable to those observed in other reptile species. The results from this study may be used to investigate the effects of unpredictable resources on reproductive success and survival in freshwater turtles.

Animals↗
PubMed1998

Endogenous yolk steroid hormones in turtles with different sex-determining mechanisms.

Maternal transfer of nutrients, including steroid hormones, to embryos during gestation in viviparous amniotes is well known, but the concordant process in oviparous amniotes is poorly understood. Recent evidence suggests that steroid hormones are present in freshly laid eggs of archosaurs and that their concentrations may influence offspring phenotypes. This process might be especially important in reptiles with temperature-dependent sex determination (TSD), because embryonic sex determination as well as other traits is thought to be influenced by temperature-dependent steroid metabolism. To evaluate the potential importance of endogenous steroid hormones to developing reptilian embryos, we (1) measured testosterone and estradiol-17beta levels in fresh eggs from natural populations of three species of turtles with TSD and two with genotypic sex determination (GSD), (2) evaluated testosterone concentrations within and among clutches of two turtle species with TSD, and (3) correlated clutch testosterone concentrations with incubation length, body mass, and sex ratio of offspring of two turtle species with TSD from eggs incubated at pivotal sex-determining temperatures. Turtles with TSD had higher levels of yolk testosterone (up to approximately 300 ng/g) than turtles with GSD (up to approximately 15 ng/g), suggesting a potential functional dichotomy between these two classes of sex-determining mechanisms; concentrations of yolk estradiol-17beta were low and fairly uniform among all five species (approximately 1 ng/g). Yolk testosterone varied substantially among, and relatively little within, clutches, indicating considerable potential as a mechanism behind clutch effects on offspring phenotypes. Steroid concentrations were unrelated to order of oviposition, unlike in birds, but yolk testosterone levels were correlated with incubation length and possibly with offspring sex ratio. Embryos of Chelydra serpentina serpentina from clutches with higher yolk testosterone hatched soonest at 21.8 degreesC; the opposite was true for Trachemys scripta elegans embryos incubated at 28.2 degreesC. At 27.6 degreesC, C. s. serpentina clutches with higher yolk testosterone produced more male-biased offspring sex ratios. Taken together, these results are strikingly consistent with published data on other oviparous amniotes and with the known physiology of follicular development and embryonic sexual differentiation in these disparate taxa. The findings of these experiments suggest that yolk testosterone in turtle eggs may be biologically significant.

Animals↗
PubMed1999

Plasma steroid interactions during high-density green turtle nesting and associated disturbance.

Raine Island in the Northern Great Barrier Reef constitutes an extremely high-density green turtle (Chelonia mydas) rookery. On this island, competitive interactions for nesting space and subsequent disturbance of individual nesting are widespread. High-density nesting often delays successful oviposition by one or more nights. There is little information on how hormones in female reptiles interact during competitive reproductive events in such high-density nesting populations. In this three-part study we investigated the interactions between density (within and between rookery/ies), nesting success and failure, and plasma steroid profiles in green turtles. First, we compared levels of plasma corticosterone (B) and combined testosterone + 5alpha-dihydrotestosterone (T + DHT) in turtles during five stages of oviposition in both a high-nesting-density sector (1 turtle/m2) and a low-nesting-density sector (0.1 turtle/m2). Second, we investigated the relationship between increasing delays (0, 1, 2, 3, and 6 days) in successful oviposition and the plasma steroids B and T + DHT. Third, we assessed a comparative measure of steroid hormone levels of females at low-density sites on Raine Island (high-density rookery) and Number Seven Sandbank (low-density rookery). Despite a significant trend suggesting high-density nesting turtles elaborated more plasma B than turtles in low-density sectors, the magnitude of this increase was small. We suggest that this increase may be an artifact of increased metabolic demand and hence catabolism of energy substrates associated with high-density nesting. Plasma T + DHT remained stable in response to density-dependent effects associated with nesting. Furthermore, prolonging successful oviposition because of multiple nightly disturbance failed to elicit any change in either plasma B or T + DHT. These data suggest that green turtles may be exhibiting adrenal desensitization to prevent both physical and behavioral disturbances interfering with reproduction. We suspect that down-regulating the acute adrenocortical response may represent an adaptive trade-off mechanism for optimizing current reproductive success at the potential expense of survivorship.

Animals↗
PubMed2001

Stress responses and sexing of wild Kemp's ridley sea turtles (Lepidochelys kempii) in the northeastern Gulf of Mexico.

Plasma corticosterone, glucose, and testosterone concentrations were measured in wild, immature specimens of the highly endangered Kemp's ridley sea turtle (Lepidochelys kempii) to determine effects of acute handling stress. Thirty-nine free-ranging turtles were captured by entanglement net near the Cedar Keys, Florida. Blood samples were collected immediately after retrieval from the net, and at 30 min (n = 15) and at 60 min (n = 29) thereafter. Mean plasma corticosterone and glucose concentrations increased significantly with time. No significant difference was observed over time for mean testosterone concentrations. Approximately half of the turtles demonstrated an increase in plasma testosterone after 60 min of captivity while the others demonstrated a decrease. Initial testosterone concentrations were used to determine the sex of individual turtles. Fifty-nine percent of turtles were classified as female, 33% as male, and 8% as indeterminant. The results of this study demonstrate a responsive hypothalamic-pituitary-adrenal axis and hyperglycemia in immature Kemp's ridley turtles during acute handling stress.

Animals↗
PubMed1996

Temporal and geographic variation of organochlorine residues in eggs of the common snapping turtle (Chelydra serpentina serpentina) (1981-1991) and comparisons to trends in the herring gull (Larus argentatus) in the Great Lakes basin in Ontario, Canada.

Common snapping turtle (Chelydra serpentina serpentina) eggs from five sites within the Great Lakes basin, and from a reference site in north-central Ontario were collected during 1981-1991 and analyzed for four organochlorine pesticides, polychlorinated biphenyls (PCBs) including six non-ortho PCBs, polychlorinated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). The pattern of geographic variation was consistent over time in eggs with Cootes Paradise/ Hamilton Harbour and Lynde Creek eggs on Lake Ontario containing the highest concentrations and most PCDD and PCDF congeners among all sites. Eggs from Cranberry Marsh on Lake Ontario contained organochlorine concentrations similar to those from Big Creek Marsh and Rondeau Provincial Park on Lake Erie except PCDDs and PCDFs which occurred at higher concentrations and more congeners were detectable in Cranberry Marsh eggs. Concentrations of most contaminants in turtle eggs from Algonquin Park, the reference site, have significantly decreased in the past decade. Dieldrin concentrations, however, increased in Algonquin Park eggs from 1981 to 1989. Significant decreases in concentrations of hexachlorobenzene, mirex and PCBs occurred between turtle eggs collected in 1981/84 and 1989 at Big Creek Marsh and Rondeau Provincial Park, whereas there was no significant change in concentrations of p,p'-DDE and dieldrin. In Lake Ontario eggs, concentrations of PCBs, p,p'-DDE and dieldrin increased significantly between 1984 and 1991. Differences were also found in patterns of temporal variation in contamination between herring gulls (Larus argentatus) and snapping turtles which were attributed to differences in diet. Elevated and continued contamination in turtle eggs from Lake. Ontario is probably due to a combination of local sources of chemicals and consumption of large migratory fish that spawn in wetlands inhabited by these turtles.

Animals↗
PubMed2002

Cloning and expression of the turtle (Trachemys scripta) immunoglobulin joining (J)-chain cDNA.

The J-chain protein is a M(r) 15000 polypeptide associated with polymeric IgA and IgM. The complete cDNA sequences of human, mouse, cow, brushtail possum, chicken and frog J chains have been previously reported, but nothing is known about the cDNA and amino acid sequences of reptilian J chain. Here, we determined a turtle J-chain cDNA sequence by RT-PCR and RACE, and examined J-chain mRNA and protein expression by Northern blotting and immunohistochemistry. This turtle J-chain cDNA was 1934 bp and had an open reading frame of 477 nucleotides, encoding 159 amino acids. The mature J-chain protein is composed of 137 amino acids, M(r) approximately 15000. The deduced amino acid sequence of the turtle J chain was highly homologous to that of human (60%), mouse (61%), cow (60%), rabbit (60%), chicken (69%), brushtail possum (65%), Rana catesbeiana (47%) and Xenopus laevis (58%). Eight cysteine residues were located at the same positions as in these other species, with the exception of X. laevis. PROSITE database analysis indicated the presence of two N-glycosylation sites in turtle, one of which was novel. Northern blot analysis revealed that turtle J-chain mRNA was expressed in lung, stomach, spleen and intestine. In addition, immunohistochemistry showed J-chain-positive plasma cells in the intestine and spleen. These results suggest the presence of a mucosal immune system mainly composed of J-chain-containing Ig in the turtle.

Amino Acid Sequence↗
PubMed2003

Comparative analyses of serum vitellogenin levels in male and female Reeves' pond turtles (Chinemys reevesii) by an immunological assay.

A quantitative immunological method was developed for measuring serum vitellogenin levels of Reeves' pond turtles (Chinemys reevesii) to investigate the effects of endocrine disruptors on the freshwater ecosystem. Vitellogenin was induced by injecting estradiol-17beta into C. reevesii turtles (adult females, juvenile females, and males) and was purified from the turtle serum by EDTA-MgCl2 precipitation followed by gel filtration. Using a polyclonal antibody raised against C. reevesii vitellogenin, an enzyme-linked immunosorbant assay was established. The detectable range, recovery of vitellogenin, and coefficient of variation in this assay were 0.0040-1.0 microg.ml(-1), 85.3-109% and 3.4-11.5%, respectively. This assay was also applicable for measurement of the concentrations of vitellogenins from other species, Japanese pond turtles (Mauremys japonica) and red-eared turtles (Trachemys scripta). The serum vitellogenin concentration of 131 C. reevesii turtles captured at a Japanese local river was measured by the assay. In females, vitellogenin ranged from 0.10 microg.ml(-1) to 15,000 microg.ml(-1) with two peaks, 0.10-1.0 microg.ml(-1) (juveniles) and 1,000-10,000 microg.ml(-1) (adults). However, in males, it ranged from 0.10 microg.ml(-1) to 0.60 microg.ml(-1), showing one peak, 0.10-0.20 microg.ml(-1). Therefore, if relatively high concentrations of vitellogenin are detected in males or juvenile females, it is suggested that they would have been exposed to xenobiotic estrogens.

Animals↗
PubMed2006

The influence of body size on the diving behaviour and physiology of the bimodally respiring turtle, Elseya albagula.

In aquatic vertebrates that acquire oxygen aerially dive duration scales positively with body mass, i.e. larger animals can dive for longer periods, however in bimodally respiring animals the relationship between dive duration and body mass is unclear. In this study we investigated the relationships between body size, aquatic respiration, and dive duration in the bimodally respiring turtle, Elseya albagula. Under normoxic conditions, dive duration was found to be independent of body mass. The dive durations of smaller turtles were equivalent to that of larger individuals despite their relatively smaller oxygen stores and higher mass specific metabolic rates. Smaller turtles were able to increase their dive duration through the use of aquatic respiration. Smaller turtles had a relatively higher cloacal bursae surface area than larger turtles, which allowed them to extract a relatively larger amount of oxygen from the water. By removing the ability to respire aquatically (hypoxic conditions), the dive duration of the smaller turtles significantly decreased restoring the normal positive relationship between body size and dive duration that is seen in other air-breathing vertebrates.

Animals↗
PubMed2003

RT-PCR detection of the expression of the polymerase gene of a novel reptilian herpesvirus in tumor tissues of green turtles with fibropapilloma.

An alpha-herpesvirus has recently been associated with green turtle fibropapilloma (FP). To further understand the etiological role of this newfound green turtle herpesvirus (GTHV) in the pathogenesis of FP, expression of GTHV polymerase ( pol) gene was determined in tumors and normal-appearing nontumor tissues and organs from five green turtles suffering multiple fibropapillomas, using reverse transcription-polymerase chain reaction (RT-PCR). Amplification of RNA prepared from tumor tissues evidenced the substantial expression of GTHV DNA pol gene in all specimens tested (15/15). However, GTHV pol gene expression in normal-appearing tissues and organs of affected animals was limited (4/45), and GTHV mRNA was detected only in periorbital tissue (1/2), gall bladder (2/5) and lung (1/5) by nested RT-PCR. By contrast, RT-PCR evaluation of RNA isolated from non-tumored turtles revealed undetectable expression of this herpesvirus gene. cDNA sequence analysis revealed that GTHV gene sequences were identical in different tumors. Our data represent the first evidence of the replication of this putative turtle herpesvirus in affected green turtles and fibropapilloma tissues are always active sites of GTHV mRNA synthesis. These findings extend and substantiate the pathogenic association of GTHV with FP.

Animals↗
PubMed1993

Unchanged [3H]MK-801 binding and increased [3H]flunitrazepam binding in turtle forebrain during anoxia.

In order to determine if functional changes in N-methyl-D-aspartate receptors and GABAA receptors play a role in the remarkable anoxia tolerance of freshwater turtle brain, we used autoradiographic techniques to assay [3H]MK-801 and [3H]flunitrazepam binding in turtle forebrain after turtles had been subjected to anoxia for 2 or 6 h. The effects of glutamate, glycine, competitive N-methyl-D-aspartate antagonists, glycine antagonists, polyamines, magnesium, and zinc on [3H]MK-801 binding were the same in anoxic and control turtle forebrains. These results indicate that NMDA receptor regulation plays no role in the adaptive responses to anoxia in turtle brain. In contrast, [3H]flunitrazepam binding was significantly increased in the anoxic dorsal cortex and striatum. The most parsimonious explanation for elevated benzodiazepine receptor binding is that the rise in extracellular GABA levels known to accompany anoxia enhances benzodiazepine receptor affinity. It is possible, however, that GABAA receptor upregulation during anoxia increases the effectiveness of the inhibitory action of released GABA and contributes to the anoxia tolerance of turtles.

Animals↗
PubMed1988

Gonadotropin-releasing hormone from brains of reptiles: turtles (Pseudemys scripta) and snakes (Thamnophis sirtalis parietalis).

Gonadotropin-releasing hormone (GnRH)-like peptides were present in whole brain extracts of turtle (Pseudemys scripta) and snake (Thamnophis sirtalis parietalis) with higher content and concentration in the turtle brain. The peptides were identified by cross-reactivity profiles with four GnRH antisera and by retention times on reverse-phase high-pressure liquid chromatography (HPLC) compared with synthetic GnRH standards. Turtle brain extracts contained two HPLC peaks that cross-reacted with GnRH antisera; these peaks eluted from the HPLC in the same positions as chicken I and II GnRH. Snake brain extracts contained only one major HPLC peak (and two minor peaks in some brains) that cross-reacted with anti-GnRH sera; the major peak eluted with the same retention time as chicken I GnRH. Mammalian, salmon, and lamprey GnRH-like peptides were not detected. In extracts from both turtle and snake brains, the cross-reactivity profile of the HPLC peaks compared with those of synthetic chicken I and II GnRH showed a similar order of sensitivity with four antisera. It is likely that chicken I and II GnRH-like peptides were present in ancestral reptiles prior to the evolution of the three living reptilian subclasses of Anapsida (turtle), Lepidosauria (snake and lizard), and Archosauria (alligator). This assertion is based on the present demonstration and work by others showing that chicken I and II GnRH-like peptides are in turtle and alligator, chicken I is in snake, and chicken II is in lizard.

Animals↗
PubMed1990

Relation of plasma thyroxine binding to thyroidal activity and determination of thyroxine binding proteins in a turtle, Pseudemys scripta.

The ability of plasma to bind thyroxine (T4) was examined in the turtle, Pseudemys scripta, in relation to variations in thyroidal state associated with age, sex, environment, and surgical and chemical manipulations. Relative plasma binding activity was assessed by use of binding to [125I]T4 on minicolumns of Sephadex G-25 (fine). Hypothyroidism induced by surgical thyroidectomy (Tx) or goitrogen (Methimazole) treatment resulted in a marked depression of plasma binding (50- to 100-fold) in juveniles, and T4 treatment restored binding after 4-6 weeks in long-term Tx animals and increased levels in intact animals. Among intact turtles or those made slightly hypothyroid by partial thyroidectomy, binding was consistently correlated with plasma T4. For example, juvenile turtles kept under continuous light and constant temperature (28 degrees) for 4.5 months showed a pronounced depression of plasma T4 (2.6 +/- 1.1 ng/ml) and binding capacity compared to animals raised under variable conditions (T4 = 69.6 +/- 22 ng/ml) for the last 2 months. Plasma T3 was less than 1 ng/ml in all cases. Binding levels in adult turtles were similar to juveniles, but females had significantly higher binding levels than males which paralleled differences in their plasma T4 (137 +/- 17.4 vs 83.9 +/- 13.8 ng/ml). These variations in binding were independent of total plasma protein and albumin. Plasma T4 binding measured on Sephadex G-25 was reversible and reduced by addition of exogenous T4. The affinity for T3 was 10- to 100-fold less than for T4. When plasma preincubated with [125I]T4 was electrophoresed on polyacrylamide slab gels (7% nonreducing) only a small percentage of radiolabel was associated with albumin and the majority with a slower migrating protein(s). Addition of unlabeled T4 displaced binding from the slower migrating region to the albumin and dye front (unbound). In contrast, plasma from Tx turtles showed only minimal binding and radiolabel was associated primarily with the albumin fraction. Elution of proteins from gels confirmed that only the slower migrating components bound T4 when tested on Sephadex G-25, and Tx animals lacked this binding component. The protein(s) responsible for most of the T4 binding appears to exist in low concentration. Limited comparative studies with human blood showed a similar binding activity on Sephadex G-25, but electrophoretic mobilities of binding proteins were distinct from those in the turtle. Evidence suggests that this binding protein is not prealbumin.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1991

Progesterone downregulates progesterone receptor, but not estrogen receptor, in the estrogen-primed oviduct of a turtle (Trachemys scripta).

Progesterone downregulates nuclear progesterone receptor (Rp) and estrogen receptor (Re) in the estrogen-primed mammalian uterus and chick oviduct. We sought to determine if this downregulation mechanism is operative in the turtle oviduct. Female turtles were primed for 4 days with 17-beta-estradiol, after which progesterone (5 mg) was administered by injection every 24 h. Re and Rp levels in progesterone-treated and control turtle oviducts were measured by [3H]steroid-binding assays (pyridoxal 5' phosphate method) at 12, 24, 48 and 72 hr after initial progesterone treatment. Serum progesterone levels of progesterone-treated turtles increased only slightly from 0 hr (0.3 ng/ml) to 12 hr (0.6 ng/ml) after progesterone administration, increased considerably by 24 hr (5.3 ng/ml), and remained elevated (6-8 ng/ml) through 72 hr. Cytosol and nuclear Rp levels of estrogen-primed turtle oviducts showed distinct seasonal variation, with Rp levels higher in spring and summer months than in winter months. There was no seasonal variation in Re levels. Both cytosol and nuclear Rp responded to progesterone treatment. Cytosol Rp levels of progesterone-treated oviducts were significantly reduced below control levels by 12 hr after progesterone administration and remained low through 72 hr. Nuclear Rp levels of progesterone-treated oviducts showed no change at 12 hr, increased at 24 hr and then dropped at 48 and 72 hr. However, progesterone did not downregulate Re in the turtle oviduct.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗