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Biomedical subjects

P Licht

Publications and source records attributed to P Licht.

At least 73 records · Page 4Linked to original sources
PubMed1992

Serum gonadotropins and gonadal steroids associated with ovulation and egg production in sea turtles.

Changes in serum concentrations of gonadotropins and gonadal steroids during the periovulatory period were monitored in green, Chelonia mydas, and loggerhead, Caretta caretta, sea turtles. Turtles were from natural populations that nest on a coral island on the Great Barrier Reef. After nesting, each turtle was transferred to a holding tank and held for a maximum of 8 days. A time series of blood samples was obtained from each of five sea turtles (three C. mydas and two C. caretta) starting immediately after nesting and then at approximately 12-hr intervals until the time of release. Prior to release back into the ocean, each turtle was examined by laparoscopy to verify that ovulation had occurred. Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone (PRO), and testosterone (T) in both species exhibited significant changes during this period. Surges of FSH, LH, and PRO were evident within approximately 20 to 50 hr after each turtle had nested. The significant change in FSH concentration during the periovulatory period is the first such report for a reptile. Coincident with maximal concentrations of FSH, LH, and PRO was a decline in T concentrations in both species. Estradiol-17 beta concentrations were near or below assay sensitivity in the C. mydas, whereas those in the C. caretta were detectable but exhibited no significant changes. The dynamic changes in FSH, LH, PRO, and T concentrations are consistent with the hypothesis that these hormones facilitate specific physiological events during ovulation and egg production.

Animals↗
PubMed1992

Effect of infundibular lesions on GnRH and LH release in the frog, Rana temporaria, during hibernation.

The effects of lesions and deafferentations on accelerated hibernatory ovulation and on the concentration of GnRH in blood collected from the hypothalamo-pituitary area along with the blood and pituitary levels of luteinizing hormone (LH) in hibernating female frogs, Rana temporaria, were studied. The lesions to the caudal portion of the nucleus infundibularis ventralis resulted in: (1) an elevation in GnRH concentration in blood collected from the hypothalamo-pituitary area (x +/- SEM = 51 +/- 9.5 and 100 +/- 15 pg/ml in control and lesioned females, respectively), (2) an increase in plasma LH (from 11 +/- 1.3 to 14.7 +/- 2.5 ng/ml in controls to 73.1 +/- 12.0 and 74.2 +/- 15.8 ng/ml in lesioned females at 3 and 7 days), and (3) accelerated ovulations whose onset advanced as the hibernation season progressed. Histological and immunohistochemical analyses of the brains showed that GnRH seems to be stored during hibernation in the median eminence and suggested that the complete disruption of projections to the median eminence is prerequisite for accelerated ovulation. The influence of the hypothalamic inhibitory action on the release of GnRH and the way in which GnRH is transferred to the pituitary gland are discussed.

Analysis of Variance↗
PubMed1992

Measurement of plasma thyroxine binding protein in relation to thyroidal condition in the turtle, Trachemys scripta, by radioimmunoassay.

Polyclonal (rabbit) antisera were generated against a high-affinity plasma thyroxine (T4) binding protein (TBP) purified from the turtle, Trachemys scripta, and used to develop a specific radioimmunoassay (RIA). The RIA demonstrated the presence of an immunochemically related protein in the plasma of several other species of Trachemys and in members of several other genera from the same family, Emydidae. Plasma from all nonemydids and some emydid genera either showed no competition or nonparallelism in RIA. The presence and level of radioimmunoassayable TBP in diverse species correlated with results of previous comparative measurements of T4 binding activity. However, an immunoreactive protein of the same molecular weight as TBP was identified in all turtles by Western blot analysis. More detailed studies in T. scripta demonstrated that variations in plasma T4 binding activity induced by experimental or environmental manipulations were related to differences in TBP concentrations. The concentration of TBP varied by orders of magnitude (from less than 1 to ca. 150 mg/liter) in euthyroid animals; levels showed ontogenetic changes (virtually absent in hatchlings) and were directly related to thyroidal status. Experimentally induced hypothyroidism (goitrogen treatment or surgical thyroidectomy) resulted in a marked suppression of TBP, and T4 treatment prevented its decline or reinstated it. Thus, in the turtle, this T4 transport protein may exist in higher concentrations and its levels are more variable and show a different relationship to thyroid activity than the analogous T4 binding globulin (TBG) in mammals.

Aging↗
PubMed1992

Accelerated reproductive development in juvenile male ground squirrels fed a high-fat diet.

Male golden-mantled ground squirrels held at 23 degrees C were fed high-fat (HF) or standard (chow) diets. In December, ambient temperature was reduced to 6 degrees C, food was removed, and frequency and duration of torpor bouts were monitored continuously by radiotelemetry. Reproductive condition and body composition were assessed upon terminal arousal in the spring. Juvenile males fed the HF diet weighed more than chow-fed controls before and throughout the hibernation season and had significantly greater lipid masses at terminal arousal. Testes masses and plasma testosterone concentrations were substantially higher in HF than in chow-fed juveniles. The accelerated reproductive development of fatter squirrels was not contingent upon increases in the total number of days spent in torpor, number of torpor bouts, or the average duration of each arousal from torpor. Access to the HF diet had no effect on body mass, adiposity, or reproductive status of adult male ground squirrels in spring. Threshold levels of white adipose tissue and associated differences in availability of metabolic fuels may be permissive for testicular growth during the hibernation season. Juveniles exceed this threshold only when fed the HF diet.

Aging↗
PubMed1992

Evidence for a modulation of human chorionic gonadotropin (hCG) subunit messenger ribonucleic acid levels and hCG secretion by gamma-aminobutyric acid in human first trimester placenta in vitro.

The cytotrophoblasts are the site of production of liberins and statins in human placenta, whereas the syncytiotrophoblasts synthesize tropic hormones. These placental cell layers seem to interact like the hypothalamus and pituitary. In the central nervous system, gamma-aminobutyric acid (GABA)-ergic neurons represent one important control mechanism that seems to influence the lutropin biosynthesis indirectly (via gonadoliberin) and directly. It was the objective of the present study to find out whether GABA also may influence the biosynthesis and secretion of hCG by human first trimester placenta. Already one single pulse of GABA (1 h; 0.01-100 microM) stimulated hCG secretion significantly (P less than 0.0001). GABA also induced a marked increase in the mRNA levels of both subunits, with an optimum at 10 microM. The effect on hCG secretion was mimicked by the GABA-A receptor agonist muscimol (P less than 0.002), but under the experimental conditions used (multiple pulses; 1 microM), only the beta mRNA was increased. The GABA-A receptor antagonist bicuculline (two pulses; 10 microM) suppressed basal hCG secretion (P less than 0.001) and abolished the episodic secretion pattern observed in the control cultures. Applying a combination of equimolar amounts of GABA and bicuculline, hCG secretion and the episodic secretion pattern were similar as in control cultures. The data seem to suggest a regulation of hCG biosynthesis in human first trimester placenta in which GABA is involved, probably acting via GABA-A-like receptor sites.

Bicuculline↗
PubMed1992

Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 1. Infancy to sexual maturity.

This report is concerned with hormone concentrations accompanying sexual maturation in a highly 'masculinized' female mammal, the spotted hyaena, Crocuta crocuta. Plasma concentrations of testosterone, androstenedione and oestrogen were determined by radioimmunoassay in a longitudinal study of 12 female and eight male hyaenas 2.5-62.5 months old. Concentrations of testosterone were significantly higher in males than in females after 26.5 months of age, but earlier measurements did not differ between sexes. Mean testosterone concentrations in adult female hyaenas (0.4-0.5 ng ml-1) were similar to those in several other female mammals that do not display a 'masculine' profile, but mean concentrations of androstenedione (2.5-5.5 ng ml-1) in female hyaenas were significantly higher than in males (1.0-2.0 ng ml-1), at most ages. Oestrogen could not be detected (less than 0.03 ng ml-1) in females until about 14 months of age and then increased (to approximately 0.13 ng ml-1) between 18 and 30 months; oestrogen remained undetectable in males. This rise in oestrogen in females corresponded to nipple enlargement and to changes in the size and elasticity of the urogenital meatus, permitting copulation and parturition through the clitoris. Gonadectomy (two males and four females) at 4-7 months resulted in nondetectable concentrations of testosterone and oestrogen and a marked attenuation in androstenedione (to approximately 0.39 ng ml-1), indicating that the gonads are the major source of these three steroids. Gonadectomy also eliminated sex differences in weight, nipple development and elasticity of the urogenital meatus.

Aging↗
PubMed1992

Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 2. Maternal and fetal steroids.

Concentrations of androgens (androstenedione, testosterone, 5 alpha-dihydrotestosterone), oestrogen and progesterone were measured in relation to pregnancy in the spotted hyaena (Crocuta crocuta). The gestation period was estimated to be about 110 days. There was a marked progressive rise in all the steroids starting in the first third of gestation. Chromatographic separation of plasma showed that much of the oestrogen is not oestradiol (only 12% of total measured) and that a significant fraction of the 'testosterone' may be dihydrotestosterone. In the final third of pregnancy, concentrations of androgen (especially testosterone plus dihydrotestosterone) in the female circulation reached the maximal values of adult males; the percentage of dihydrotestosterone relative to total testosterone plus dihydrotestosterone was higher in females (44 +/- 3.9%, n = 20) than in males (29.5 +/- 3.5%, n = 17). Plasma androstenedione was also significantly higher in females, but the increment was less than for oestrogen, testosterone and progesterone, and the temporal pattern was less clear. Samples from the maternal uterine and ovarian circulation showed that androstenedione is largely of ovarian origin and metabolized by the placenta, while testosterone, progesterone and oestrogen are primarily of placental or uterine origin. Fetal samples were taken from two mixed-sex sets of twins and one male singleton. Gradients across the placenta measured in the fetal circulation confirmed that the placenta metabolizes androstenedione and is a source of testosterone for the female fetus; there were no consistent differences in androgens between male and female fetuses. It is suggested that the conspicuous masculinization of the female spotted hyaena, especially evident in the external genitalia at birth, is a result, at least in part, of high placental production of testosterone or dihydrotestosterone derived from the metabolism of high maternal androstenedione.

Androgens↗
PubMed1991

Fatal sibling aggression, precocial development, and androgens in neonatal spotted hyenas.

Fatal neonatal sibling aggression is common in predatory birds but has not been previously reported in wild mammals. Spotted hyena females are strongly masculinized, both anatomically and behaviorally, apparently by high levels of androgens during ontogeny. Neonates display elevated androgen levels, precocial motor development, and fully erupted front teeth. Litters are usually twins, and siblings fight violently at birth, apparently leading to the death of one sibling in same-sex litters, whereas in mixed-sex litters both siblings usually survive.

Aggression↗
PubMed1991

Comparative survey of blood thyroxine binding proteins in turtles.

The nature of plasma thyroxine (T4) binding activity was surveyed in turtles; binding to [125I]T4 was measured on polyacrylamide gel electrophoresis--PAGE--and on minicolumns of Sephadex G-25. An electrophoretically distinct T4 binding protein was identified in all 8 species of Pseudemys studied and in 3 other genera (Chrysemys, Deirochelys, and Emyoidea) of the same family, Emydidae. Levels of this binding activity were highly variable among individuals, but they consistently showed a similar low relative mobility (Rf) compared to albumin, and a relatively low capacity was indicated by displacement with unlabeled T4. Two emydids (Terrapene, Clemmys) showed a similar slow migrating binding peak, but binding activity was low and not as easily displaced by unlabeled T4. T4 binding to albumins was minimal in most of these emydid species, even when binding to the higher affinity, low capacity component was low or displaced by unlabeled T4 (2.5 micrograms/ml). In contrast, there was no clear evidence for a similar high affinity, low capacity binding protein in any of the other 19 species representing 13 genera of 8 families from two suborders. In these species, binding activity on Sephadex G-25 was typically low and binding on PAGE was associated largely with albumin; binding levels for albumins were highly variable. In several nonemydids (from distant lineages), binding activity on Sephadex was elevated and PAGE showed a second binding protein distinct from albumin, but it had high capacity (not readily saturable). Thus, an evolutionary divergence in T4 transport proteins is suggested within Chelonia.

Animals↗
PubMed1991

Time-dependent changes in gonadotropin synthesis following gonadectomy in the frog, Rana pipiens.

Anterior pituitary glands from frogs gonadectomized (gonadx) for various periods (0-90 days) were labeled in vitro with 35S-methionine. Shortly (7-10 days) after gonadx, plasma levels and the in vitro basal pituitary secretion of LH and FSH are elevated compared to values in sham-operated frogs. However, LH and FSH become dissociated in long-term (over 40 days) gonadx frogs; FSH remains elevated while LH returns to sham levels. Gth (gonadotropin: LH and FSH) synthesis shows a similar pattern. Gth synthesis becomes elevated after gonadx, but returns to sham levels after 80 days. In short-term (15 days) gonadx females, LH and FSH each comprise approximately the same percentage of counts immunoprecipitated. In contrast, in long-term (90 days) gonadx females, nearly 100% of Gth synthesis can be accounted for solely by FSH; LH synthesis is barely or not detectable. Although the elevated in vitro secretion rate of LH and FSH following gonadx diminishes within 24 h in culture, Gth synthesis remains elevated. This study demonstrates that although the pattern of Gth secretion and synthesis generally parallel each other following gonadx, these two cellular processes can be dissociated from one another. Furthermore, it appears that in frogs, not only the secretion, but also the synthesis, of LH and FSH may be under independent regulation.

Animals↗
PubMed1991

The secretion of human chorionic gonadotropin as well as the alpha- and beta messenger ribonucleic acid levels are stimulated by exogenous gonadoliberin pulses applied to first trimester placenta in a superfusion culture system.

It is well documented that the hypothalamic decapeptide gonadoliberin (GnRH) controls the biosynthesis and secretion of pituitary gonadotropins; however, it is still unclear whether GnRH synthesized by the placenta plays the same role with respect to hCG. In the current study we have investigated the acute response of placenta tissue to a single GnRH pulse as well as the influence of GnRH pulses on the secretion of hCG and hCG mRNA concentrations elicited several hours after application of the peptide hormone. For this purpose we have used a superfusion culture model of first trimester placenta tissue (8-12 weeks of gestation). In the first hour after explantation of the tissue, hCG secretion was decreased, and increasing amounts of free subunits were released. Afterward, the original hCG secretion rates were recovered and maintained for several days, attended by decreased levels of free subunits in the culture medium. The superfusion model was superior to static incubations, since it showed approximately a 4-fold higher amount of hCG to be secreted within 24 h (day 3 of cultures). A single GnRH pulse (1 mumol/L; 30 min) caused a significantly increased transient release of hCG (P less than 0.0001). Two GnRH pulses (concentration range, 0.01-10 mumol/L; 30 min) applied 24 h after (first pulse) and in the interval between 36-48 h after (second pulse) the start of the superfusion culture elicited a long-lasting 2-fold increase in the hCG secretion rate, which rose approximately 6 h after the second GnRH pulse. This was correlated with increased mRNA concentrations measured by means of Northern blots of total RNA. At 0.02 mumol/L GnRH, 4-fold higher beta mRNA levels were observed. The alpha mRNA levels were 2.5-fold elevated. GnRH pulses of 0.01 and 10 mumol/L, respectively, were ineffective. A further effect of GnRH pulses was augmentation of the episodic character of hCG secretion. Our results suggest that GnRH causes different specific acute and late effects on the amount and pattern of hCG secretion as well as on hCG biosynthesis at the levels of both hCG subunit mRNAs.

Chorionic Gonadotropin↗
PubMed1990

Suprachiasmatic nuclei influence hibernation rhythms of golden-mantled ground squirrels.

Hibernation and body mass rhythms were studied in 13 golden-mantled ground squirrels maintained in an LD 12:12 photoperiod at 5 degrees C. Complete or partial ablation of the suprachiasmatic nuclei (SCN) disrupted normal hibernation rhythms. Over the course of 2 years, several animals progressed through 4 hibernation cycles, one squirrel manifested two abnormally long hibernation seasons, and another failed to hibernate. Squirrels with intact SCN exhibited normal circannual hibernation rhythms at intervals of 11.5 +/- 0.3 months. Hibernation coincided with the weight loss phase of the body mass cycle in control squirrels, but these two rhythms were dissociated in animals with lesions of the SCN. The annual plasma testosterone rhythm was normal or slightly phase-delayed in squirrels with SCN lesions maintained at 23 degrees C. The SCN may be part of a neural circuit that mediates circannual organization of hibernation rhythms.

Animals↗
PubMed1990

Stereological study of gonadotropes in the frog, Rana pipiens, after GnRH stimulation in vitro.

Previous physiological results have indicated the existence of two releasable pools of gonadotropins in amphibian pituitaries: an acute releasable pool that appears independent of protein synthesis, and a storage pool involved in chronic release that depends on protein synthesis. To elucidate the ultrastructural localization of these pools and the morphological changes induced in gonadotrope cells after treatment with gonadotropin-releasing hormone, we carried out a morphometric study of immuno-identified gonadotrope cells using an in vitro superfusion system. Treatment with gonadotropin-releasing hormone induced a degranulation of small (110-255 nm) and medium (236-360 nm) secretory granules as well as hypertrophy of the endoplasmic reticulum and Golgi complex. Simultaneous incubation with gonadotropin-releasing hormone and cycloheximide inhibited the release of secretory granules although the endoplasmic reticulum and Golgi complex were hypertrophied. These morphological results strongly suggest: (1) that gonadotropin-releasing hormone induces degranulation and hypertrophy of the biosynthetic machinery in gonadotrope cells; and (2) that the activation of the endoplasmic reticulum and Golgi complex by stimulation with gonadotropin-releasing hormone is independent of protein synthesis, while the release of secretory granules is protein synthesis-dependent. In addition, the second or "storage" pool of gonadotropin is associated mainly with the small and medium secretory granules.

Animals↗
PubMed1990

Steroidal modulation of pituitary gonadotropin-releasing hormone responsiveness in young turtles, Pseudemys scripta.

Steroid-modulated pituitary secretion and glandular content of gonadotropin (Gth: LH and FSH) was studied in young slider turtles. Injection (ip) of both 17 beta-estradiol (E2) and testosterone (T) reduced pituitary content of both Gths and caused significant inhibition of basal LH secretion and gonadotropin-releasing hormone (GnRH)-stimulated LH and FSH secretion measured in vitro. However, gonadectomy did not affect pituitary Gth secretion or response in these juveniles, and anti-estrogen and anti-androgen compounds had some steroid agonistic action on the pituitary gland. Exposure to E2, T, and 5 alpha-dihydrotestosterone (DHT) in vitro for 4, 24, or 48 hr either had no effect or completely inhibited pituitary GnRH responsiveness. Progesterone (P) alone had no effect on pituitary GnRH response and in combination did not alter the typical inhibitory effect of E2. There were several indications of differential effects of steroids on secretion of the two Gths, especially in response to GnRH and tetraethyl chloride (receptor independent) stimulation. The results suggest that steroids may act directly at the pituitary level to alter Gth secretion and that steroidal modulation of pituitary secretion might play a role in differential regulation of LH and FSH in turtles.

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↗
PubMed1990

The role of hormone binding in the cold suppression of hormone stimulation of the pituitary, thyroid, and testis of the turtle.

The ability of hormones to bind to their functional receptors on turtle (Pseudemys scripta) endocrine target tissues in the cold was tested by treating tissues with secretagogues at low temperatures (5-15 degrees) and then following subsequent target stimulation in the absence of secretagogue at a warm temperature (28 degrees). Administration of thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone, and growth hormone-releasing hormone to pituitaries at low temperatures (20 degrees or below) suppressed responses in growth hormone (GH) and thyrotropin (TSH) secretion and there was little or no response in pituitaries subsequent to warming. In contrast, gonadotropin-releasing hormone treatment of pituitaries, TSH treatment of thyroid glands, and gonadotropin (FSH and LH) treatment of testes in the cold (down to 5 degrees) was followed by a large response in the target glands (secretion of LH, thyroxine, and testosterone (T), respectively) following warming. Additional studies with FSH and LH showed that these hormones can bind to testes rapidly (within 5 min) at low temperatures where no acute response is observed, although the dose sensitivity and the extent of this priming in the cold are less than at warm temperatures. Thus, postreceptor events may be more important than binding per se for temperature effects on hormone responses of tissues, but even this component of cell function varies among tissues. The effects of a receptor-independent secretagogue (tetraethylammonium chloride), which causes cell depolarization by blocking K+ efflux, were also blocked at low temperatures in thyrotropes and somatotropes but not in gonadotropes. Rapid depressions in TSH and GH secretions following cooling of TRH-stimulated pituitaries and of T secretion in LH-stimulated testes provide further evidence for cold sensitivity of postreceptor processes in these tissues.

Animals↗