Seasonal variations of androgens, estrogens, and progesterone in the different lobules of the testis and in the plasma of Salamandra salamandra

Temperature Extreme Events Decrease Endocrine and Immune Reactive Scope in Bullfrogs (Lithobates catesbeianus)

Currently, effects of increased atmospheric temperature, in the context of ongoing climate change, have been investigated in multiple organisms and levels of biological organization. While there has been a focus on the impacts of increased mean temperature, an emergent and equally important point is the consequences of recurrent exposure to extreme temperature events, simulating heat waves. This study investigated the effects of serial exposure to high temperatures on immune and endocrine variables before and after exposure to an acute secondary stressor in bullfrogs (Lithobates catesbeianus). Adult males were divided into three groups and subjected to three thermal regimes: control (c; constant 22°C); experimental 1 (E1; kept at 22°C and exposed to 4 days of 30°C every 16 days); and experimental 2 (E2; kept at 22°C and exposed to 4 days of 30°C every 6 days). Blood samples were collected on the last day of key extreme heat events. Two weeks after the last extreme heat event, animals were subjected to restraint stress (1 h) and sampled again. Blood samples were used to determine neutrophil: lymphocyte ratio, plasma bacterial killing ability, as well as, corticosterone and plasma testosterone levels. Overall, we found exposure to extreme heat events did not affect immune and endocrine variables over time. Meanwhile, the previous exposure to extreme heat events modulated the responsiveness to restraint. The amplitude of increased corticosterone plasma levels and neutrophil: lymphocyte ratio in response to restraint decreased with the number of previous exposures to extreme heat events. These results suggest that exposure to extreme climatic events has hidden effects on bullfrog's stress response, expressed as diminished reactive scope to a novel stressor. This represents a highly deleterious facet of climate change since diminished responsiveness prevents proper coping with wildlife challenges.

Seminiferous Epithelium Cycle in Bombina orientalis

The purpose of the present study was to examine the seminiferous epithelium cycle of Bombina orientalis using a light microscope. The cycle was divided into a total of 10 stages, according to the morphological characteristics of the cells. The spermatogenetic cells included primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatid and sperm. At stage I, the primary spermatogonia was located closer to basal lamina of the seminiferous tubule without spermatocyst formations. Especially at the stage II, the secondary spermatogonia were located in the spermatocyst. The primary and secondary spermatocytes were found from stages III to VI. The secondary spermatocytes were smaller in size than the primary spermatocytes, but they had thicker nucleoplasm and smaller nuclei. The round-shaped, early sperm cells were formed in stage VII, and further divided at stage VIII to have more concentrated nucleoplasm before division to matured sperm cells. At stage X, the matured sperm cells emerged from the spermatocyst. Considering the above results, this study presented the special characteristics in the generation and type of sperm formation. The germ cell formation occurred in various stages, like the perspectives of Franca et al (1999), ultimately, providing taxonomically useful information.

Seminiferous Epithelium Cycle in Bombina orientalis

The purpose of the present study was to examine the seminiferous epithelium cycle of Bombina orientalis using a light microscope. The cycle was divided into a total of 10 stages, according to the morphological characteristics of the cells. The spermatogenetic cells included primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatid and sperm. At stage I, the primary spermatogonia was located closer to basal lamina of the seminiferous tubule without spermatocyst formations. Especially at the stage II, the secondary spermatogonia were located in the spermatocyst. The primary and secondary spermatocytes were found from stages III to VI. The secondary spermatocytes were smaller in size than the primary spermatocytes, but they had thicker nucleoplasm and smaller nuclei. The round-shaped, early sperm cells were formed in stage VII, and further divided at stage VIII to have more concentrated nucleoplasm before division to matured sperm cells. At stage X, the matured sperm cells emerged from the spermatocyst. Considering the above results, this study presented the special characteristics in the generation and type of sperm formation. The germ cell formation occurred in various stages, like the perspectives of Franca et al (1999), ultimately, providing taxonomically useful information.

Testicular structure and germ cells morphology in salamanders

Testes of salamanders or urodeles are paired elongated organs that are attached to the dorsal wall of the body by a mesorchium. The testes are composed of one or several lobes. Each lobe is morphologically and functionally a similar testicular unit. The lobes of the testis are joined by cords covered by a single peritoneal epithelium and subjacent connective tissue. The cords contain spermatogonia. Spermatogonia associate with Sertoli cells to form spermatocysts or cysts. The spermatogenic cells in a cyst undergo their development through spermatogenesis synchronously. The distribution of cysts displays the cephalo-caudal gradient in respect to the stage of spermatogenesis. The formation of cysts at cephalic end of the testis causes their migration along the lobules to the caudal end. Consequently, the disposition in cephalo-caudal regions of spermatogenesis can be observed in longitudinal sections of the testis. The germ cells are spermatogonia, diploid cells with mitotic activity; primary and second spermatocytes characterized by meiotic divisions that develop haploid spermatids; during spermiogenesis the spermatids differentiate to spermatozoa. During spermiation the cysts open and spermatozoa leave the testicular lobules. After spermiation occurs the development of Leydig cells into glandular tissue. This glandular tissue regressed at the end of the reproductive cycle.

Ambiguities in the relationship between gonadal steroids and reproduction in axolotls (Ambystoma mexicanum)

Axolotls (Ambystoma mexicanum) are aquatic salamanders that are widely used in research. Axolotls have been bred in laboratories for nearly 150 years, yet little is known about the basic biology of reproduction in these animals. We investigated the effects of changing day length, time of year, and food availability on levels of circulating estradiol and androgens in adult female and male axolotls, respectively. In addition, we examined the effects of these variables on the mass of ovaries, oviducts, and eggs in females and on mass of testes in males relative to each individual's body weight, to calculate a form of gonadosomatic index (GSI). In both sexes, GSI was not correlated with levels of circulating steroids. In female axolotls, estradiol levels were influenced by food availability, changes in day length, and season, even when animals were held at a constant temperature and day length was decorrelated with calendar date. In addition, the mass of ovaries, oviducts, and eggs varied seasonally, peaking in the winter months and declining during the summer months, even though our animals were not breeding and shedding eggs. In males, levels of androgens appeared to vary independently of external conditions, but GSI varied dramatically with changes in day length. These results suggest that reproduction in axolotls may vary seasonally, as it does in many other ambystomid species, although both male and female axolotls are capable of reproducing several times each year. The physiological basis of this ability remains enigmatic, given the indications of seasonality contained in our data.

Testosterone-immunopositive primordial germ cells in the testis of the bullfrog, Rana catesbeiana

In amphibia, steroidogenesis remains quiescent in distinct seasonal periods, but the mechanism by which spermatogenesis is maintained under low steroidogenic conditions is not clear. In the present study, testosterone location in the testes of Rana catesbeiana was investigated immunohistochemically during breeding (summer) and nonbreeding (winter) periods. In winter, the scarce interstitial tissue exhibited occasional testosterone immunopositivity in the interstitial cells but the cytoplasm of primordial germ cells (PG cells) was clearly immunopositive. By contrast, in summer, PG cells contained little or no immunoreactivity whereas strong immunolabelling was present in the well-developed interstitial tissue. These results suggest that PG cells could retain testosterone during winter. This androgen reservoir could be involved in the control of early spermatogenesis in winter and/or to guarantee spermiogenesis and spermiation in the next spring/summer. The weak or negative immunoreaction in the summer PG cells might reflect consumption of androgen reservoir by the intense spermatogenic activity from spring to summer. Thus, besides acting as stem cells, PG cells of R. catesbeiana could exert an androgen regulatory role during seasonal spermatogenesis.

Testicular morphological changes during the seasonal reproductive cycle in the bullfrog Rana catesbeiana

Spermatogenesis and steroidogenesis undergo seasonal variations during the reproductive cycle in amphibians. Testicular morphological and morphometric seasonal variations as well as interstitial lipidic inclusions and intralobular glycoconjugates were evaluated during seasonal cycle of Rana catesbeiana. Testes of frogs collected during the annual seasons were weighed for calculation of GSI (Gonadosomatic index). Seminiferous lobule diameters (DSL) and volume densities of seminiferous lobules (VvSL), excretory ducts (VvED), and interstitial tissue (VvIT) were analyzed. Semithin sections were submitted to Periodic Acid-Schiff (PAS) and Alcian Blue (AB) methods for detection of glycoconjugates, while lipidic inclusions were detected by Sudan Black B. GSI showed no significant variations during the year. Since VvED and VvIT increased significantly during summer and were inversely proportional to VvSL, a compensatory effect between the testicular compartments may be related to the maintenance of GSI. During autumn/winter, larger lobular diameters were observed in comparison to spring/summer when spermiogenesis and spermiation were commonly observed. The increased VvIT and the numerous lipidic inclusions in the interstitial cells during summer suggest a relationship between spermiogenesis and steroidogenesis. Besides the structural stability variations occurring in the IT and SL, a possible paracrine interaction between ED and IT should be also involved in the IT development during summer. The presence of PAS and AB-positive globular structures were observed in the seminiferous lobules and excretory ducts. These structures containing acid glycoconjugates appear to be Sertoli cell apical portions, which are accumulated in the lumen of the seminiferous lobules mainly during spermiation.

Androgen receptor (AR), estrogen receptor-alpha (ER-alpha) and estrogen receptor-beta (ER-beta) expression in the testis of the newt, Triturus marmoratus marmoratus during the annual cycle

Expression of androgen receptor (AR), estrogen receptor alpha (ER-alpha) and estrogen receptor beta (ER-beta) in the testis of the marbled newt (Triturus marmoratus marmoratus) was investigated, with special attention to changes during the annual testicular cycle, using light microscopy immunohistochemistry and Western blot analysis. Primordial germ cells, primary and secondary spermatogonia and spermatocytes showed a positive reaction to the 3 receptor antibodies during the annual reproductive cycle. Follicular cells were positive to AR, ER-alpha and ER-beta during the spermiogenesis and quiescence periods in the glandular tissue. Interstitial cells showed reactivity to AR, ER-alpha and ER-beta in the spermiogenesis and the quiescence periods, and presented no labelling to these receptors in the proliferative period. These findings suggest that, as in mammals, there is an androgen-estrogen regulation of the function and development of the newt testis.

Seasonal variations in sex steroids and male sexual characteristics in Scyliorhinus canicula

Concentrations of testosterone, progesterone, Delta4-androstenedione, dihydrotestosterone, 11-ketotestosterone, estrone, estradiol-17beta, 5alpha-androstane, 3alpha, 17beta-diol, and 17alpha-hydroxy, 20beta-dihydroprogesterone were determined by radioimmunoassays in the blood plasma and testicular homogenates of Scyliorhinus canicula. Samples were collected almost every month for 27 months. The weights and sizes of reproductive organs and sperm reserves were also measured over the same period. Quantitatively, testosterone was the principal steroid present. Testicular and epididymal weights, sperm reserves, and clasper size varied throughout the year, but not always in a synchronous fashion. Most of the testicular steroids had an annual peak, generally in February, except for progesterone. The plasma concentrations of progesterone, Delta4-androstenedione, and androgens presented various degrees of fluctuation over the year, but were not synchronized: maxima occurred during autumn-winter for androgens and progesterone, during spring for Delta4-androstenedione. Thus, various aspects of S. canicula reproductive function appear to be influenced by season, the sea temperature being, most probably, a major determinant in this respect.

A nonsteroidal follicular factor is involved in maturation process of Xenopus laevis oocytes

Xenopus laevis postvitellogenic ovarian follicles release into conditioned medium nonsteroidal factor(s) that potentiate progesterone-induced oocyte maturation. The molecular weight of this factor is between 1000 and 10,000 Da. The potentiating activity is suppressed when follicles are incubated with cyanoketone to inhibit steroidogenesis, suggesting that the secretion of the potentiating factor can be modulated in vitro. These results indicate that the steroid-independent pathway in vitro, previously reported in oocytes exposed to insulin or IGF-1 to induce meiotic resumption, may be of physiological importance.

Sex steroid profile and plasma vitellogenin during the annual reproductive cycle of the crested newt (Triturus carnifex Laur.)

The annual reproductive cycle of the crested newt, Triturus carnifex, has been studied in the field. Temperatures, rainfall, humidity, and photoperiod were recorded throughout the year. Adult male and female newts were sampled monthly; snout vent lengths, crest heights of males, and body ovarian, oviducal, testicular, and abdominal gland weights were recorded. Plasma samples were assayed for androgen, estradiol-17 beta, and progesterone by radioimmunoassay and for vitellogenin by enzyme-linked immunosorbent assay. Air, deep water, water surface, and soil temperatures were low from October to March, but increased in April and May without consistent summer variations. Ovarian and oviducal weights increased in October to reach maximum values between January and March (reproductive period). Crest height and abdominal gland weight in males mirrored the ovarian and oviducal pattern, while testicular weights were maximal in October and November. In females, plasma androgens were high during the reproductive period, and plasma estradiol peaked sharply in March, while plasma progesterone changed little. In the males plasma androgen and estradiol concentrations were similar to those of females, while plasma progesterone was significantly correlated with the cycle in testicular weight. In both sexes androgens showed a significantly negative correlation with air and water surface temperature. Plasma vitellogenin peaked in March but it did not correlate with either ovarian weight or plasma estradiol concentrations. These data support and confirm those previously reported for newts under laboratory conditions. The negative correlation between androgens and temperature suggests that this hormone may trigger the reproductive process. Moreover the correlations between plasma progesterone and testicular weight may indicate that this hormone is involved in male newts reproduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Sexual steroids in Salamandra salamandra (L.) during ontogeny

In order to investigate the ontogeny of steroid secretions during the juvenile phase, sexual steroids were extracted and assayed after chromatographic separation in the gonads and plasma of male and female salamanders Salamandra salamandra L. at three characteristic postlarval stages. All specimens were collected in the wild. The immature stage is characterized, in the female, by high dihydrotestosterone (DHT) and 5 alpha-androstandiol levels, low progesterone concentration, and an absence of testosterone in the ovary. Just before sexual maturity a regular increase in plasma levels of estradiol and testosterone was observed. In the male, progesterone and DHT are at a relatively high level in the testis of the immature stage but concentrations decrease in subadults. In young adults, concentrations of progesterone are greater than they are in the immature animals. Sexual maturity is characterized by a large increase in testicular and plasma testosterone as well as a relative decrease in DHT, 5 alpha-diols, and estrone. The progesterone liberated into the plasma was negligible. Diols seem to play an important part in the ontogeny of sexual function.

Neuroendocrine, behavioral, and morphological changes associated with the termination of the reproductive period in a natural population of male rough-skinned newts (Taricha granulosa)

Male rough-skinned newts (Taricha granulosa) were collected from the same natural population every second week from early April to mid-June. They were either field-tested for their sexual responsiveness or used to measure the plasma concentrations of androgens and corticosterone, the brain concentrations of immunoreactive (ir) gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT), and morphological parameters. During the experimental period, the percentage of sexually responsive males gradually declined from 100 to 4%, concurrent with a decrease of plasma concentrations of androgens, but not corticosterone. Concentrations of irGnRH in two brain regions (medial septum; ventral telencephalon containing the nervus terminalis) did not change significantly during this time. In the infundibulum, irGnRH concentrations increased from the end of May to mid-June, which coincided with an increase in plasma androgen concentrations, a marked increase in testis weights, and a decrease of the proportion of males with spermatozoa in their vas deferens. During this period, no changes in irAVT concentrations in four brain regions (infundibulum; pars distalis of the pituitary; interpeduncular nucleus; cerebrospinal fluid) were detected, but significant changes were observed for irAVT in the dorsal preoptic area that were not correlated with the seasonal changes in behavior. Also, during this period, there were decreases in mean body weight and tail height, and in the proportion of males with smooth skin and dark nuptial pads. These results are discussed in view of our current knowledge of the endocrine mechanisms that regulate sexual behaviors and secondary sex characteristics in male amphibians.

Trout steroidogenic testicular cells in primary culture. II. Steroidogenic activity of interstitial cells, Sertoli cells, and spermatozoa

Somatic cells (interstitial cells and Sertoli cells) were prepared either as single cells or in clusters, from spermatogenic and mature trout testes, according to Loir (1988), and cultured for 10-14 days. Sertoli cells are 3 beta-HSD negative when prepared from testes resuming spermatogenesis and from mature testes, but they are 3 beta-HSD positive in spermatogenic testes. Progesterone, 17 alpha-hydroxyprogesterone (17 alpha-OH-P), and free androgens are secreted by interstitial cells, 11-ketotestosterone (11KT) being the predominating steroid produced immediately after seeding. These cells also produce high levels of glucuronated androgens. At least in mature spermiating testes they do not secrete estradiol. After isolation, interstitial cells would lose most of their ability to secrete 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha 20 beta-OH-P) but they would recover it later. Testicular spermatozoa, which convert 17 alpha-OH-P independently of s-GtH, constitute a second source of this progestagen. In addition, our results suggest that Sertoli cells could be able to secrete 17 alpha-OH-P and also progesterone. A possible participation of the intralobular production of the former progestagen to the local regulation of germ cell maturation is evoked.

Trout steroidogenic testicular cells in primary culture. I. Changes in free and conjugated androgen and progestagen secretions: effects of gonadotropin, serum, and lipoproteins

Isolated trout steroidogenic testicular cells were cultured for 10-15 days, either mixed with other round cells or after enrichment in interstitial cells. Free and conjugated progestagen and androgen secretions were assayed using specific radioimmunoassays (RIA). Free progesterone, 17 alpha-hydroxyprogesterone (17 alpha-OH-P), 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha,20 beta-OH-P), androstenedione, testosterone (T), and 11-ketotestosterone (11KT) were produced by testicular cells prepared from testes in spermatogenesis and mature testes. Discrete amounts of dehydroepiandrosterone (DHA) and of estradiol were secreted by mixed testicular cells prepared from mature testes, but no estradiol was detected in interstitial cell media. Conjugated androgens were produced by interstitial cells. While the production of progestagens by cells from spermatogenetic and mature testes either remained constant or increased throughout culture duration, those of free and conjugated androgens progressively decreased to low values whatever the components added to the medium. When salmon gonadotropin (s-GtH) was present permanently, androgen (free and conjugated) and progestagen secretions were stimulated for 3 to 4 days. When GtH was present discontinuously (1 day in every 3 days), the sensitivity of the cells was maintained for at least 7 days. While the GtH-stimulated/basal ratio was high for androgens, it was rather low for 17 alpha 20 beta-OH-P as compared to the values obtained with testis fragments. Trout serum (5%) stimulated the secretion of free and conjugated T and 11KT when testes were mature, but not when they were in spermatogenesis, while it stimulated 17 alpha 20 beta-OH-P secretion at the two stages. Total trout lipoproteins (125-500 micrograms/ml) stimulated 17 alpha 20 beta-OH-P secretion by cells from spermatogenetic testes, but not 11KT secretion.

Annual cycle of pituitary and plasma gonadotropins and plasma sex steroids in a wild population of the toad, Bufo japonicus

Pituitary and plasma gonadotropins and plasma sex steroids of free-living toads, Bufo japonicus, were measured monthly from March 1981 to February 1982 and examined in relation to gonadal cycles. Toads were captured at Mizuno, Saitama Prefecture. Individual blood samples were collected by cardiac puncture within 3 min of capture in the field. In males, testicular weight was maximal in August. Plasma follicle-stimulating hormone (FSH) levels changed in association with testicular weight. Plasma androgen levels showed a small peak in November and a large peak in March just prior to breeding. Plasma luteinizing hormone (LH) levels changed in parallel with plasma androgen levels. In females, neither plasma FSH nor LH alone were correlated significantly with ovarian weight. However, ovarian and oviductal weights both correlated significantly with plasma steroid levels. Plasma estradiol levels showed a sharp peak in March, followed by a rapid decrease to the minimum in April. A gradual increase of estradiol occurred from July to November in parallel with an increase in ovarian weight. Changes in plasma progesterone and androgen levels in females resembled those for estradiol. However, the changes in progesterone were not so marked as in estradiol. Plasma androgen levels in females were especially high between January and March. In both sexes, the pituitary gonadotropin contents changed in parallel with plasma levels of both FSH and LH. The pituitary almost always contained more LH than FSH, while the reverse was true in the plasma in both sexes. In addition, plasma FSH levels increased markedly in early summer when plasma LH remained unchanged (males) or increased only slightly (females). These results indicate that the toad may serve as excellent material for the study of differential control of FSH and LH secretion.

Seasonal cycles in testicular activity in the frog, Rana perezi

Studies of seasonal testicular cycle based on spermatogenetic activity and direct measurement of plasma testosterone were made in male frog Rana perezi obtained from its natural biotope in the Iberian Peninsula. Testosterone plasma level was determined by radioimmunoassay and exhibited notable differences according to season: plasma testosterone was lowest (less than 0.5 ng/ml) in summer and then increased progressively to reach a peak in spring (3-4 ng/ml), coincident with mating. After spermiation, when an increase in temperature and photoperiod in the natural habitat occurs, levels decline. Fat bodies also show a pronounced seasonal cycle with total regression following breeding and maximal development in winter. However, testicular weight was independent of seasons, and no significant change was observed throughout the year. Histological evidence indicates that although cell nests of different types are present every month of the year, the most important spermatogenetic activity is initiated in summer. The possible relationship between spermatogenetic activity and testosterone production and the importance of environmental factors as synchronizers of seasonal reproduction are discussed.

Trout Sertoli and Leydig cells: isolation, separation, and culture

Trout testes at various stages of maturation were dissociated by perfusion at 12 degrees C with collagenase plus pronase and then with collagenase alone, followed by slight shaking overnight in 1% bovine albumin. This step provided a suspension of isolated somatic and germ cells, clusters of interstitial cells, and either intact spermatogenetic cysts (meiotic testes) or clusters of Sertoli cells (other testes). Most of the spermatozoa were removed from the testis cell suspension by centrifugation in Percoll (density 1.065 g/ml). Sertoli and Leydig cells were prepared by a two-step separation method: 1) the testis cell suspension was separated by sedimentation at unit gravity into "isolated cell" and "cell cluster" populations; 2) these populations were fractionated by isopyknic centrifugation in Percoll gradients. In terms of somatic cell composition, a nearly pure Sertoli cell (clusters) population was obtained between 1.017 and 1.033 g/ml and a Leydig cell (clusters) enriched population of between 1.033 and 1.048 g/ml (testes resuming spermatogenesis) or 1.048 and 1.062 g/ml (other testes). These various cell populations were cultured in modified Leibovitz L15 medium for 10-15 days. When seeded, the Sertoli cells had a normal ultrastructure that remained unchanged for at least 10 days, and the steroidogenic activity of Leydig cells could be stimulated by salmon gonadotropin. Leydig cells remained 3 beta-HSD positive and produced progesterone and 17 alpha, 20 beta-OH progesterone for at least 11 days. This study points out that viable and differentiated trout somatic testicular cells can be prepared and cultured for several days.

Gonadotropin action on androgen synthesis in short-term incubation of explants and dispersed cells of the testis of Xenopus laevis

Testis cells of the toad Xenopus laevis were dissociated with collagenase and the cell suspension was enriched for steroidogenic cells by Percoll gradients. Results suggested that cells should be preincubated during a 6-h period before stimulation with gonadotropin. Our results indicate that a 2-h incubation period with gonadotropin was necessary to obtain a significant response. Furthermore, the cells can be maintained in a functional state longer than mammalian testis cells. Different gonadotropins were used to stimulate androgen production, and their effects were compared in both dissociated cells and testicular explants. Cells were more sensitive to luteinizing hormone (LH) and follicle stimulating hormone (FSH) than the explants (ED50LH = 0.041 +/- 0.003 micrograms for cells and 0.097 +/- 0.002 micrograms for explants: ED50FSH = 0.41 +/- 0.03 micrograms for cells and 0.63 +/- 0.03 micrograms for explants). Moreover, human chorionic gonadotropin (hCG) which only stimulates testicular explants at high doses, failed to stimulate the androgen production of dissociated cells; this indicates a low sensitivity of amphibian testis to hCG and a possible damaging effect of collagenase on the receptors of isolated cells.

Plasma and testicular estradiol and plasma androgen profile in the male frog Rana esculenta during the annual cycle

Seasonal plasma and testicular estradiol levels were measured in the male frogs, Rana esculenta, by radioimmunoassay. In plasma samples a simultaneous measurement of androgens was carried out in order to investigate a possible relationship between androgens and estradiol-17 beta. Concomitantly with the estradiol-17 beta peak in plasma and testes during the April-May period, plasma androgens sharply decreased.

Androgen and estrogen levels in the plasma of Pleurodeles waltl, Michah., during the annual cycle. I. Male cycle

Sex steroid levels in the plasma of the male Pleurodeles waltl were determined by radioimmunoassay of blood samples taken monthly from each newt during an 18-month period. Androgen levels varied according to season with annual peaks in October-November and in March. The position of these two peaks was the same in the 2 years studied. Testosterone was the principal androgen measured, while the levels of dihydrotestosterone and 4-androstenedione were lower but fluctuated in parallel with that of testosterone. The 17 beta-estradiol levels were very low or undetectable. Androgen levels during the year were synchronous between the several newts studied. The cyclical variations in the steroid levels agreed with the morphological modifications of sexual characteristics during the annual cycle.