Serum gonadotropin and steroids associated with breeding activities in the green sea turtle,Chelonia mydas: II. Mating and nesting in natural populations

Circulating levels of gonadotropins (FSH and LH) and sex steroids (estrogen, testosterone, and progesterone) were examined in mating and nesting animals from three breeding aggregations of green sea turtles (Chelonia mydas). Copulating males were characterized by relatively low levels of both gonadotropins and high androgen levels, but the latter did not differ from values previously observed in prebreeding males. Females showed significant changes in all hormones studied, except estradiol. The patterns of changes in gonadotropins and steroids as well as their absolute values were similar among the three natural breeding aggregations and captive turtles studied previously. Serum or plasma LH showed slight but variable increases between mating and nesting animals, whereas FSH was consistently elevated at the time of nesting. Field studies demonstrate that this rise in FSH is a transient surge of no more than a few hours' duration: FSH does not rise until the middle of the nesting process, when oviposition begins, and FSH declines before or immediately after oviposition is completed. Thus, this peak in FSH apparently does not initiate nesting behavior. Testosterone did not differ between mating and nesting in females, but it dropped significantly in the first days following nesting (i.e., in the internesting interval when ovulation occurs). Progesterone values were also similar between mating and nesting samples, but this steroid along with LH frequently showed a pronounced elevation in the 1–2 days postnesting; their elevation was considered to represent the “ovulatory surge”. Since this progesterone and LH surge only occurs if a nesting turtle is allowed to oviposit, the presence of shelled oviducal eggs probably suppresses ovulation.     

Immunological studies with the gonadotropins and their subunits from the green sea turtle Chelonia mydas

Antisera generated in rabbits against highly purified follicle-stimulating hormone (FSH), luteinizing hormone (LH), and the β subunit of LH from the green sea turtle, Chelonia mydas, were used to obtain additional biochemical information on the chemical and biological relatedness between the two turtle gonadotropins. Evidence that the antisera were directed against the biologically active gonadotropins was obtained from neutralization studies. At concentrations of 1 ml of antiserum per 100 μg of hormone, FSH and LH could each be selectively neutralized with homologous antisera. These results provide additional evidence that both gonadotropins have intrinsic biological activities in assays related to testis growth and androgen production in lizards and in vitro androgen production by snake testes. Each antiserum ($\text{a}\text{s}$) showed some binding to the heterologous radioiodinated hormone, but binding was clearly maximal with homologous tracer, and some of this cross-reaction was shown to be due to heterogeneity in antibody populations. Highly specific radioimmunoassays (RIAs) were developed for both FSH and LH with these antisera. When FSH $\text{a}\text{s}$ was used in conjunction with ¹²⁵I-labeled FSH, Chelonia LH and thyroid-stimulating hormone (TSH) showing virtually no cross-reaction (e.g., contamination of LH with FSH was < 1%). Alternatively, RIA using either LHβ $\text{a}\text{s}$ or LH $\text{a}\text{s}$ combined with ¹²⁵I-labeled LHβ as tracer was highly specific for LH and especially the β subunit; there was no cross-reaction with either FSH, TSH, or the α subunit of LH. When LH $\text{a}\text{s}$ was used with ¹²⁵I-labeled α as tracer, the specificity of the RIA was reduced; in this case, LHβ alone showed no cross-reaction but LHα was highly potent. Thus, these systems provide a means for studying the importance of the two separate subunits in immunorelatedness among pituitary glycoprotein hormones and for measurement of circulating gonadotropin levels.     

Development of the pulmonary surfactant system in the green sea turtle, Chelonia mydas

This study describes the developmental changes in pulmonary surfactant (PS) lipids throughout incubation in the sea turtle, Chelonia mydas. Total phospholipid (PL), disaturated phospholipid (DSP) and cholesterol (Chol) harvested from lung washings increased with advancing incubation, where secretion was maximal at pipping, coincident with the onset of pulmonary ventilation. The DSP/PL ratio increased, whereas the Chol/PL and the Chol/DSP ratio declined throughout development. The phospholipids, therefore, are independently regulated from Chol and their development matches that of mammals. To explore whether hypoxia could elicit an effect on the development of the PS system, embryos were exposed to a chronic dose of 17% O2 for the final approximately 40% of incubation. Hypoxia did not affect incubation time, absolute, nor relative abundance of the surfactant lipids, demonstrating that the development of the system is robust and that embryonic development continues unabated under mild hypoxia. Hypoxia-incubated hatchlings had lighter wet lung weights than those from normoxia, inferring that mild hypoxia facilitates lung clearance in this species.     

Annual and diurnal cycles in plasma testosterone and thyroxine in the male green sea turtle Chelonia mydas

Male plasma testosterone (T) and thyroxine (T4) were monitored over several annual cycles in a captive breeding colony of green sea turtles, Chelonia mydas. Daily and annual water temperatures varied by only approximately 1 and 3 degrees, respectively. A pronounced season cycle in plasma T was evident in the population as a whole and in individual animals: plasma T was at a nadir (approximately 3 ng/ml) in September-November and then increased progressively to a peak (27-39 ng/ml) in April; levels began declining immediately thereafter, coincident with the onset of copulatory behavior. By contrast, plasma T4 remained uniform (approximately 9 ng/ml) throughout the year and, thus, could not readily account for the decline in androgen levels. Plasma hormones were relatively stable over a 24-hr period at three times a year, and there was a correlation for individual plasma T levels sampled in April and May. Thus, limited sampling should allow identification of seasonal rhythms and individual variability in plasma T levels. Testis mass and spermatogenic activity were significantly greater in January than in September; i.e., spermatogenesis and androgen secretion were not "uncoupled." Copulatory activity began in April but did not peak until May-June, after plasma T had significantly declined. However, there was a significant (but weak) correlation between individual peak levels of plasma T (i.e., in April) and the quantitative level of mating activity (time spent mounting and number of mates) measured for the entire subsequent season. Thus, green turtles do not exhibit the "postnuptial" type of testis cycle typical of many temperate-zone turtles, and the levels of plasma androgen may be important for initiating and maintaining sex behavior, although they are not tightly linked during the mating season.     

Isolation and properties of sea turtle (Chelonia mydas) pituitary prolactin

Sea turtle prolactin (PRL) was isolated in a highly purified state from sea turtle pituitary side fractions obtained from other studies and some of its biological, chemical, and immunological properties were determined. Sea turtle PRL is a protein of 22-24 kDa [sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis]. Its sole amino terminal amino acid residue is leucine. The amino acid composition of sea turtle PRL is similar to ovine PRL and is characterized by a high content of aspartic acid (20 residues), glutamic acid (34 residues), serine (19 residues), and leucine (24 residues). It possess three disulfide bonds and 2 tryptophan residues which is also characteristic of many species of PRL. As with PRLs of other species, it displayed multiple stained bands in disc gel electrophoresis, at pH 8.3. Biologically, sea turtle PRL was active in pigeon crop-sac assay but the dose-response characteristics were nonparallel when compared to ovine PRL. An antiserum against sea turtle PRL was raised in rabbit and a homologous radioimmunoassay was developed with a sensitivity of 2.8 ng for sea turtle PRL. Sea turtle gonadotropins did not cross-react, but sea turtle growth hormone showed a 5% cross-reactivity. Pituitary extracts from other species of turtles displayed parallel inhibition curves to the sea turtle PRL. Extracts and prolactin preparations from several birds, snakes, alligator, and marsupials cross-reacted, but in a nonparallel fashion. Bullfrog pituitary extract and Tilapia PRL showed no cross-reaction at high doses. Several purified mammalian PRLs (pig, sheep, human, horse, dog) showed minimal or no ability to cross-react in the RIA.     

The complete amino acid sequence of prolactin from the sea turtle (Chelonia mydas)

The complete amino acid sequence of prolactin (PRL) from a reptile, the sea turtle (Chelonia mydas), was determined for the first time. Sequence analysis was performed on fragments obtained from cleavage of intact and performic acid-oxidized hormone with lysyl endopeptidase, Staphylococcus aureus protease, and o-iodosobenzoic acid employing manual Edman degradation. The sea turtle PRL consists of 198 amino acid residues with three disulfide linkages formed between residues 4-11, 58-173, and 190-198 and possesses heterogeneity indicated by four replacements at positions 55, 145, 148, and 171. Sequence comparison with other vertebrate PRLs revealed that the degree of sequence identity conforms well to expectations based on phylogeny except for the rodent PRLs; sea turtle PRL has 86% identity with chicken PRL; 81% with horse, pig, and fin whale PRLs; 75-71% with cattle, sheep, and human PRLs; 60-56% with mouse and rat PRLs; and 35-31% with carp, salmon, and tilapia PRLs.     

Reevaluation of the relative activities of the pituitary glycoprotein hormones (follicle-stimulating hormone, luteinizing hormone, and thyrotrophin) from the green sea turtle, Chelonia mydas

The discovery that the follicle-stimulating hormone (FSH) previously prepared from the green sea turtle, Chelonia mydas, contained a major neurohypophysial contaminant prompted a repurification and characterization of the glycoprotein hormones in this turtle. Results reaffirmed the physicochemical distinctiveness of the three hormones. Minimal cross-contamination between hormones (less than 2%) was achieved by ion-exchange chromatography, subunit dissociation (of contaminating luteinizing hormone (LH], gel filtration, and immuno-affinity chromatography. New preparations of FSH and thyrotrophin (TSH) derived from adult pituitaries proved to be more potent than those described previously (the degree depending on the nature of the assay); FSH showed the expected increase in activity based on estimated contamination of previous preparations. LH was similar to original preparations except for enhanced activity in FSH radioreceptor assays. Binding assays (in heterologous and homologous systems) again demonstrated the general absence of an FSH-specific receptor in the reptilian (chelonian and squamate) testes. In an in vivo bioassay in the lizard Anolis, the turtle FSH was orders of magnitude more potent than LH in stimulating both testis growth and androgen secretion, but in vitro LH was considerably more potent than FSH in stimulating androgen secretion in squamate and chelonian testes. Thus, the possibility exists that androgen secretion in some chelonian systems may exhibit a high degree of LH specificity like that of mammals and birds.     

The complete amino acid sequence of growth hormone from the sea turtle (Chelonia mydas)

The complete amino acid sequence of growth hormone (GH) from a reptilian species (the sea turtle, Chelonia mydas) has been determined for the first time. The hormone was reduced, carboxymethylated, and subsequently cleaved in turn with cyanogen bromide and Staphylococcus aureus protease. The intact protein was also cleaved with lysyl endopeptidase and o-iodosobenzoic acid. The resulting fragments were exclusively separated by reversed-phase high-performance liquid chromatography and subjected to sequence analysis by automated gas-phase sequencer employing the Edman method. The sea turtle GH consist of 190 amino acid residues with two disulfide linkages formed between residues 52-160 and 180-188, and possesses a microheterogeneity, indicated by the presence or absence of an additional alanine residue at the N-terminus. Sequence identities of sea turtle GH to other species of GH are 89% with chicken GH, 79% with rat GH, 68% with blue shark GH, 58% with eel GH, 59% with human GH, and 40% with a teleostean GH such as chum salmon. On the basis of amino acid sequence comparisons, a molecular phylogenetic tree is proposed.     

Seasonal variation in plasma catecholamines and adipose tissue lipolysis in adult female green sea turtles (Chelonia mydas)

We investigated three aspects of potential interrenal regulation of reproduction in female green sea turtles, Chelonia mydas. First, seasonal trends in plasma catecholamines were examined from female C. mydas at different stages of their reproductive cycles. Second, variation in catecholamine levels during a nesting season were analysed in relation to restraint time, and ecological variables such as nesting habitat, body size, and reproductive investment. Third, catecholamine and corticosterone (CORT) induced lipolysis was investigated with adipose tissue collected from gravid green turtles, using in vitro incubations. Plasma epinephrine (EPI) was lowest in non-vitellogenic (1.55 +/- 0.26 ng/ml) and post-breeding (1.57 +/- 0.22 ng/ml) females, and highest in courting females (2.87 +/- 0.28). Concentrations of norepinephrine (NE) and EPI were relatively constant throughout a nesting season, and not significantly related to restraint time, reproductive investment or nesting habitat. In vitro concentrations of CORT (>3 ng/ml) and NE (2 ng/ml) induced significant release of glycerol after 6h of incubation. Epinephrine tended to induce an antilipolytic affect at low concentrations (0.25 ng/ml) and a net lipolytic response at higher concentrations (>1 ng/ml). Our data suggest that EPI may play a role in regulating body condition during vitellogenesis, and maintaining energy stores during prolonged aphagia during courtship and nesting in female green sea turtles. Furthermore, we provide preliminary evidence that suggests that catecholamine production may be either down regulated or de-sensitised in gravid female C. mydas.     

Changes in plasma levels of adrenaline, noradrenaline, glucose, lactate and CO2 in the green turtle, Chelonia mydas, during peak period of nesting

Plasma concentrations of stress hormones [adrenaline (ADR), noradrenaline (NR)], lactate, glucose and CO2 were monitored during peak nesting period (May-October) at different phases of nesting in the green turtle, Chelonia mydas. These include, emergence from sea, excavating body and nest chambers, oviposition, covering and camouflaging the nest and then returning to sea. Turtles that completed all phases of nesting including oviposition before returning to sea were considered "successful" turtles, while those that completed all phases but failed to lay their eggs were "unsuccessful". Blood samples were taken from the cervical sinus within 5min of capture to avoid stress due to handling. The turtles were usually sampled for blood between 20:00 and 1:00h of nesting time to ensure uniformity in the sampling. Plasma ADR and NR values were highly significant (P<0.001) in successful turtles over emergence, excavating and unsuccessful turtles. Plasma glucose levels remained stable throughout the nesting phases while lactate levels were significantly higher in successful turtles over the other phases (P<0.05) which signifies anaerobic metabolism during nesting. Plasma CO2 values were negatively correlated with ADR and NR (r=-0.258, P=0.03; r=-0.304, P=0.010), respectively. Hematocrit was significantly higher in successful phase (P<0.05) compared to other phases, and this may signify a higher degree of stress in successful turtles. Body temperature were significantly lower (P<0.005) in the excavating phase compared to the other three phases. Overall, body temperatures were lower than sand temperatures around the nest, which may indicate a behavioral thermoregulation used by the turtles during nesting. This information will be of value to the ongoing conservation program at Ras Al-Hadd Reserve in the Sultanate of Oman.     

Plasma hormone levels in the green turtles Chelonia mydas during peak period of nesting at Ras Al-Hadd-Oman

Circulating estradiol (E(2)), progesterone (Pro), testosterone, and corticosterone (B) levels were monitored in the green turtles Chelonia mydas during different nesting phases. Successful nesting includes emergence from sea, chamber and nest excavation, oviposition, burying the nest, and returning to sea. Unsuccessful nesting includes chamber and nest excavations but without oviposition. Blood samples were taken from the cervical sinus and collected within 5-min of capture to minimize stress. The samples were collected between 2000 and 0100 h during the peak season (May-October). High-performance liquid chromatography using a u.v. detection system coupled with tandem quadrupole mass spectrometry was used to measure B. Plasma B levels were significantly higher in successful and unsuccessful phases over emergence and excavation phases. However, B levels in successful versus unsuccessful or emergence versus excavation phases were not significantly different. Plasma steroid levels were measured by the Coat-A-Count RIA technique. Pro levels were significantly higher (P<0.005) in successful over unsuccessful turtles and also successful turtles over turtles in the other phases (P<0.01). The Pro levels immediately after nesting were found to be higher than that reported previously. Plasma testosterone values were higher in successful turtles but not significantly different from the turtles in other phases. Estrogen levels were undetected in all phases. Overall, the hormone values during different phases of nesting may play a major role in formulating the nesting behavior and physiology of the nesting activities in the green turtle.     

Studies on the immunochemical relatedness among tetrapod gonadotropins and their subunits with antisera to sea turtle hormones

Immunological relatedness among gonadotropins from the four classes of tetrapods was studied with three antisera ($\text{a}\text{s}$) raised in rabbits against follicle-stimulating hormone (FSH), luteinizing hormone (LH), and LHβ subunit from the green sea turtle, Chelonia mydas. Only pituitaries or FSH from turtles showed appreciable cross-reaction in the homologous RIA for Chelonia FSH, and preparations from the heterologous suborder Pleurodira showed weaker and less complete cross-reactivity than from species of Cryptodira. However, the Chelonia FSH $\text{a}\text{s}$ was capable of neutralizing the biological activity of crocodilian FSH and showed specific binding to ¹²⁵I-labeled FSH from birds and mammals (but not amphibians). Considerable immunorelatedness was evident among the LH preparations of different species and this appeared to result primarily from common antigenic determinants on the α subunits of LH. First, all chelonian, crocodilian, and avian LH preparations showed high activity in RIA based on anti-Chelonia LH serum and ¹²⁵I-labeled Chelonia LHα as tracer; in fact, several of these heterologous species of LH were more potent than the Chelonia LH. LH from eutherian mammals (human, ovine, bovine) showed essentially no cross-reactivity, but preparations of ovine LHα and kangaroo LH showed measurable activity in LHα RIA. Second, the antiserum for LH, which contained antibodies to the LHα subunit, neutralized the biological activity of LH from other species of turtles, crocodilians, and a mammal (sheep). Third, ¹²⁵I-labeled preparations of avian (turkey) and mammalian (ovine and rat) LH showed specific binding to this antiserum. In contrast, parallel tests with an antiserum raised against Chelonia LHβ showed high cross-reactions only with LHs from other species of turtles; i.e., little or no cross-reaction with any nonchelonian species was indicated in RIA, neutralization tests, or binding studies with ¹²⁵I-labeled hormones. Gonadotropins from amphibians and snakes showed no cross-reaction in any tests with any of the three antisera used. This conspicuous lack of immunological cross-reactivity of snake gonadotropins, especially with antibodies to LHα, provides further evidence for a pronounced structural divergence between the hormones of squamates and the other reptilian orders.     

Seasonal changes in serum gonadal steroids associated with migration, mating, and nesting in the loggerhead sea turtle (Caretta caretta)

Adult male loggerhead sea turtles, Caretta caretta, exhibited a "prenuptial" spermatogenic cycle that was coincident with increased concentrations of serum testosterone (T). Serum T was high during the months when migration and mating have been recorded for males. In contrast to females, males appear to be annual breeders. Nine reproductively active female C. caretta (as verified through laparoscopy) were tagged with sonic transmitters and were repeatedly bled prior to migration. Four months prior to the nesting season, the ovaries of reproductively active females had hundreds of vitellogenic follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles). Approximately 4-6 weeks prior to migration from feeding grounds to mating and nesting areas, serum estradiol-17 beta (E2) concentrations increased significantly and remained high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During a 1- to 2-week period prior to migration, serum E2 decreased significantly, while serum T concentrations increased (at least) until the time of migration. Serum T, E2, and progesterone (PRO) were elevated during nesting if a turtle was going to nest again during that nesting season. During the last nesting of a season, turtles had low serum concentrations of T, E2, and Pro. The prenuptial pattern of gonadal recrudescence and gonadal steroid production in both male and female C. caretta contrasts with those of many temperate freshwater turtles, and this type of reproductive pattern may have been facilitated by adaptation to a tropical marine environment.     

Hormonal control of osmoregulation in the Chelonia I. The effects of prolactin and interrenal steroids in freshwater Chelonians

A study has been carried out of the effects of prolactin, aldosterone, and corticosterone on osmoregulation in three species of freshwater terrapin. The results suggest that the main action of prolactin may be to increase the GFR with subsequent changes in ion excretion. Aldosterone has been shown to stimulate potassium excretion and reduce the urinary Na/K ratio in normal animals and also to reduce the sodium excretion in salt-loaded terrapins. The results with spironolactone suggest it may mimic aldosterone rather than antagonise its action when administered in high doses. Corticosterone had a similar effect to aldosterone causing an increase in potassium excretion and a decrease in the Na/K ratio.     

Effect of paramethasone acetate on ovarian steroids and gonadotropins. I. Normal menstrual cycle.

In an attempt to elucidate the effect of paramethasone acetate on the hormonal profile of the normal menstrual cycle, 5 clinically healthy women, aged 24-36 yr, with ovulatory cycles were studied during a control menstrual cycle and during treatment with paramethasone acetate (6 mg/day). The length of the untreated cycle was 29.2 +/- 2.3 days as compared to 29.0 +/- 3.1 days during the paramethasone-treated cycle. Peak plasma E-2 level was 188.2 +/- 42.1 pg/ml in the control cycle and 74.4 +/- 15.3 pg/ml during paramethasone treatment (P is less than 0.05). Peak plasma 17 OH-P was 4.0 +/- 0.4 ng/ml in the control cycle and 1.6 +/- 0.2 ng/ml during the paramethasone treated cycle (P is less than 0.005). No significant differences in plasma progesterone were observed during the luteal phase of both cycles. Minimal and scattered differences were observed in plasma FSH. However, plasma LH levels were lower in the paramethasone acetate than in the control cycle almost throughout the entire period of study. Furthermore, midcycle LH peak in the control cycle was 958 +/- 104 ng/ml as compared to 283 +/- 24 ng/ml during the paramethasone treatment (P is less than 0.005). Despite these differences, ovulation occurred during paramethasone treatment based upon the observed rise in BBT, the plasma progesterone levels above 6 ng/ml and the secretory changes in the endometrium. These results suggest that: 1) Paramethasone may block E-2 synthesis at the ovarian level and , 2) Ovulation may still occur even in the presence of E-2 and LH plasma concentrations lower than those occurring in the normal menstrual cycle.     

Serum gonadotropins and follicular development in the Syrian hamster.

Hamster serum gonadotropins were measured by RIA at 4 h intervals during the estrous cycle. On the afternoon of proestrus both LH and FSH exhibited a surge, but unlike the situation in the rat and mouse FSH returned to "baseline" with LH by early evening of proestrus. Shortly following this return FSH concentrations increased and reached a second peak by noon on estrus which was equal in magnitude and longer in duration than that occurring on proestrus. FSH fell to its lowest levels on diestrus 2 (D2) and early proestrus. Serum gonadotropins were measured by RIA 6 h following unilateral ovariectomy on D2. A slight elevation of LH resulted while FSH increased to a level equal in magnitude to that found during the proestrous surge. In intact females administration of a total of 45 mug FSH in 5 injections on D2 resulted in ovulation of twice the normal number of eggs. The t1/2 of this rat FSH in the male hamster was found to be 122 minutes. The low levels of FSH during the cycle between D2 and proestrus, the large increase in serum FSH following unilateral ovariectomy, and the "doubled" ovulation in intact hamsters following the administration of FSH on D2, suggest that the serum FSH concentration on D2 is critical in determining the number of follicles which will be available for the subsequent ovulation.     

Changes in plasma levels of gonadotropins and sex steroids in the toad, Bufo japonicus, in association with behavior during the breeding season

Plasma levels of gonadotropins and sex steroids in Bufo japonicus were surveyed at different behavioral stages during the breeding period in March. All hormone levels were lower in torpid toads, which were found underground 1 week before the start of the breeding migration, than in active toads in the breeding season, although the levels were higher than those in the other months. LH and FSH levels in toads migrating toward a breeding pond were still low or only slightly elevated. Gonadotropin levels increased markedly when toads arrived at the pond and were highest for individuals actually in the pond. These LH and FSH surges occurred in both sexes, although peak levels were higher in females. Gonadotropin levels decreased in individuals of both sexes when they left the pond after breeding ("landed" individuals). LH and FSH levels in solitary males were significantly lower than those in amplexing males. In females, there was no significant difference in the level of any hormone between amplexing and solitary individuals. Circulating testosterone increased to the highest level in migrating males; this elevated level was maintained after arrival in the pond. DHT in males showed a pattern similar to that of testosterone. Both androgens decreased to the lowest level in landed males. In females, estradiol was dominant during migration, while progesterone became dominant shortly after arriving near or in the pond. This progesterone surge coincided with the LH surge. Androgen may stimulate amplexus behavior in male toads, and then amplexus seems to induce the LH surge that is necessary for spermiation. In females, however, amplexus seems to have no direct correlation with the gonadotropin surge, and the LH surge may induce the progesterone surge which causes ovulation.     

Somatic and immune responses to bovine growth hormone, bovine prolactin, and diethylstilbestrol in the green sea turtle.

Bovine growth hormone, bovine prolactin, and diethylstilbestrol were administered to 1-, 2-, 4-year-old green sea turtles (Chelonia mydas) to determine relative somatotropic activities. The growth hormone was the most potent in terms of stimulation of body weight and carapace length, while the prolactin demonstrated less pronounced somatotropic effects. Older turtles realized greater somatotropic responses even though younger turtles received proportionally higher doses of hormone. Diethylstilbestrol strongly retards growth at all ages in the immature green sea turtle and in this and other respects mimics the actions of estrogens. Two- and four-year-old turtles demonstrated a significant reduction in somatotropic responses to the mammalian hormones as the length of the treatment was increased. Sera from prolactin-injected turtles selectively bound ¹²⁵I-labeled ovine or bovine prolactin while controls did not. These results suggest that sea turtles have a highly sensitive immune system which will develop antibodies to a heterologous protein hormone in a relatively short time.     

Adrenal activity in the female lizard Lacerta vivipara jacquin associated with breeding activities

Variations of adrenal activity were studied in captive viviparous females Lacerta vivipara, in relation to breeding activities. The study was restricted to the period of active life which includes both the phase of annual reproduction and a phase of sexual inactivity. Significant seasonal changes in plasma corticosterone levels were measured with a peak during the second half of gestation followed by an abrupt fall at parturition. No significant variations in plasma aldosterone levels were observed. A limited extraovarian production of progesterone was detected which might be of adrenal origin. The half-life of injected tritiated corticosterone was not longer in pregnant than in nonreproductive females, suggesting that the peak of circulating corticosterone in pregnant females corresponds to an increase in the production rate of the hormone. The functional importance of the pituitary-adrenal axis was demonstrated in vivo: plasma corticosteroid levels dropped to the detection limit after adenohypophysectomy. Seasonal variations of adrenal sensitivity to synthetic ACTH 1-39 were examined in vitro, using a perifusion system. No significant variations were observed throughout the period of active life. These results suggest that the peak of plasma corticosterone during gestation can be ascribed to activation of the pituitary-adrenal axis. Experimental modifications of circulating corticosterone level during late gestation altered the timing of parturition, thus indicating that the fall of corticosterone just before term may be involved in the process of parturition in the female L. vivipara.