Male Secondary Sexual Characters Research Articles

Finishing Broiler Toms Using an Estradiol 17β Implant Together with a High Energy-Low Protein Final Feed

Wrolstad Small White toms were implanted with 10 mg of estradiol 17β monopalmitate (EMP) at 8 weeks of age. Common corn-soybean meal feeds were given through to 12 weeks, then one-half the birds from control and EMP groups received either an adequate (16% protein, 3166 kcal ME/kg) or high energy-low protein (HE-LP, 12%, 3373 kcal) feed to 14 weeks.No differences in weight gain and feed conversion occurred between EMP and control treatments at 12 weeks but at 14 weeks when the HE-LP diet had been fed the implanted birds performed better than controls. The HE-LP feed led to body weights and feed efficiencies below that of toms given adequate diet. In all cases, EMP elicited male secondary sex characteristics rather than feminization.Processing losses were increased with EMP and when the HE-LP feed had been given. Both treatments also improved finish assessment and were additive to the extent that a substantial increase in grade occurred. Effects on carcass composition, yield of commercial cuts, and cooking loss were small. Implantation, reduced meat yield percentage of breast and thigh. The increase in grade advantage from combining EMP with a feed that forced fat depostion more than compensated for the adverse effects.

Seasonal effects of photoperiod and temperature on spermatogenesis and male secondary sexual characters in the three-spined stickleback, Gasterosteus aculeatus L.

Effects of photoperiod (16 h light (L): 8 h dark (D) and 8 h L: 16 h D) and temperature (18 and 8 °C) on spermatogenesis and androgen-dependent kidney hypertrophy in the three-spined stickleback were studied in alternate months of the year. In winter 16 h L: 8 h D in combination with 18 °C stimulated secondary sexual characters, whereas in spring other regimes were also stimulatory. Spermatogenesis was more active and the kidney more suppressed in 8 h L: 16 h D at 18 °C than in other groups in winter. In the natural annual cycle spermatogenesis is quiescent from the beginning of winter until the end of the breeding season in summer. Decline of secondary sexual characters in July is accelerated by high temperature. High kidney epithelium is never found together with vigorous spermatogenesis, indicating androgen-inhibition as a major factor in the control of spermatogenetic activity.

RAPID ORIGIN OF SEXUAL ISOLATION AND CHARACTER DIVERGENCE IN A CLINE.

The recent revival of interest in modes of speciation without geographic isolation (reviewed by Bush, 1975; Endler, 1977; White, 1978) makes it appropriate to reinvestigate mechanisms for clinal speciation first outlined in genetic terms by Fisher (1930, Ch. 6). He noted that following adaptive divergence of geographical or ecological races, if hybrids are at a disadvantage, genetic variation in mating preferences (and/or habitat preferences) could lead to the evolution of a decreased frequency of hybridization. This mechanism for the evolution of sexual isolation was popularized by Dobzhansky (1940, 1951, 197 0 , Ch. 11) who believed it could occur only after secondary contact between races which had become partially reproductively isolated by postmating mechanisms (see also Sturtevant, 1938; Muller, 1940; Sibley, 1961; Mayr, 1963, p. 525-526, 548-559). Fisher (1915, 1930) also described a process of runaway sexual selection which can produce exponentially increasing rates of evolution in male secondary sexual characters and female mating preferences. As argued below, the latter mechanism is potentially much more powerful for initiating sexual isolation and character divergence along a cline than is selection against hybridization. Population genetic models have shown that when hybrids between geographic races are at a substantial disadvantage a narrow hybrid zone will evolve, followed perhaps by formation of reversed clines (i.e., reproductive character displacement) around the contact zone, and slow or limited diffusion of the genetic differences to remote regions by migration (Crosby, 1970; Endler, 1977; Caisse and Antonovics, 1978). However, if populations in the contact zone have comparatively low mean fitness, in part due to hybrid disadvantage, and if there is a net immigration from surrounding regions, gene flow may prevent the evolution of sexual isolation or may limit it to the contact zone (Littlejohn, 1969; Hall, 1973). Hybrid zones of apparent long standing are known in various animal taxa where neither widespread sexual isolation nor localized reproductive character displacement has occurred (Mayr, 1963, p. 548-550; Bigelow, 1965; White, 1978, Ch. 6). In contrast with the localized origin and slow or restricted spread of sexual isola-

Models of speciation by sexual selection on polygenic traits

The joint evolution of female mating preferences and secondary sexual characters of males is modeled for polygamous species in which males provide only genetic material to the next generation and females have many potential mates to choose among. Despite stabilizing natural selection on males, various types of mating preferences may create a runaway process in which the outcome of phenotypic evolution depends critically on the genetic variation parameters and initial conditions of a population. Even in the absence of genetic instability, rapid evolution can result from an interaction of natural and sexual selection with random genetic drift along lines of equilibria. The models elucidate genetic mechanisms that can initiate or contribute to rapid speciation by sexual isolation and divergence of secondary sexual characters.

Effects of androgenic gland ablation on male primary and secondary sexual characteristics in the Malaysian prawn, Macrobrachium rosenbergii (de Man) (Decapoda, Palaemonidae), with first evidence of induced feminization in a nonhermaphroditic decapod

Male Macrobachium rosenbergii (de Man), categorized into three developmental stages according to possession of male gonopore complexes, appendixes masculina, and mature chelipeds, were subjected to bilateral androgenic gland ablation (andrectomy). Andrectomized males initially lacking appendixes masculina and mature chelipeds do not develop them; those initially possessing appendixes masculina and mature chelipeds do not lose them. Growth rate of the appendixes masculina, however, is reduced. Andrectomized males are unable to redifferentiate amputated or accidentally lost appendixes masculina and mature chelipeds. Instead, the appendages regenerate as immature forms. Andrectomized M. rosenbergii possess atrophied testes and vasa deferentia. Histological sections of the testes revealed a reduction in number of spermatogenic lobules. Spermatogonia and primary spermatocytes were commonly found; secondary spermatocytes and spermatids were found only occasionally. Andrectomy appears to inhibit but not prevent meiosis. Feminization occurred in five andrectomized males. Complete feminization, including initiation of oogenesis and development of oviducts and female gonopores, occurred in males andrectomized in the youngest developmental stage. Males andrectomized in later developmental stages were either partially feminized or not feminized. Reimplantation of androgenic glands reverses the effects of andrectomy. Remasculinization, as evidenced by differentiation of appendixes masculina, was noted after the first postimplantation molt. The testes of remasculinized males were normal in gross anatomy and spermatogenic ability. The data indicate a uniform function for the androgenic glands with respect to male primary and secondary sexual characteristics among the Amphipoda, Isopoda, and Decapoda. Past theories on androgenic gland function are modified in light of the present information.

Effects of sexual maturation and sex steroid hormone treatment on the temperature preference of the guppy, Poecilia reticulata (Peters)

In a horizontal temperature gradient, male guppies prefer a significantly lower temperature (24.5 °C) than females (28.2 °C) or juveniles (28.1 °C). Treatment of juveniles and females with testosterone lowers their preferred temperature to that of males. The reduction in the preferred temperature of testosterone-treated juveniles can occur without the development of male secondary sexual characters. Estrogen treatment of juveniles is without effect, as is treatment of males with estrogen or testosterone. It is postulated that testosterone acts at the level of the hypothalamic thermoregulatory centre.

Sex inversion in domesticated strains of the swordtail,Xiphophorus helleriHeckel (Pisces, Osteichthyes)

Abstract In Xiphophorus helleri several alleged instances of sex inversion in females were described. Later researchers, doubting such findings, regarded the species as having separate sexes, of males, strong and weak, and females, strong and weak, in relation to the differing ratios of male and female sex determiners, and they considered the alleged sex inverted specimens to be cases of arrhenoidy of old females or weak males, in which the male secondary sex characters appear late so that in the male immature stage they could be mistaken for young females. The present investigation confirms these last two observations but it also shows that exceptional individuals are firstly in a female phase and produce broods, and secondly they enter a functional male phase. Virgin females mated with these hermaphrodites in male phase produce broods with a low percentage of males, in accordance with the hypothesis on the polyfactorial sex determination in Xiphophorus helleri. From our experiments it is suggested that ...

Male Secondary Sexual Characters of the Eurycea bislineata (Amphibia, Urodela, Plethodontidae) Complex in the Sourthern Appalachian Mountains

Polymorphism of male secondary sexual characters occurs among populations nominally assignable to Eurycea bislineata in the southern Appalachian Mountains. Two male morphs are recognized, one identified as E. b. wilderae and the other designated morph A. Male E. b. wilderae possess mental hedonic glands, seasonally enlarged premaxillary teeth, cirri and reduced temporal musculature. Male morph A lack mental hedonic glands, seasonally enlarged premaxillary teeth and cirri and possess strongly developed temporal musculature.

Characterization of a cytoplasmic androgen receptor in the male secondary sexual character of green frog (Rana esculenta)

In the thumb pad of male Rana esculenta an androgen receptor has been demonstrated. The cytoplasmic receptor has a proteinaceous nature with a KD for testosterone of 3.12 ± 3.4 S.D. × 10−10 M and a number of sites of 333 ± 133 S.D. fmol/mg of proteins. A Stokes radius of 40 A and a sedimentation coefficient of 3.40 ± 0.5 S.D. were determined. Using these parameters a molecular weight of ~ 57,000 and a f/f = 1.58 were calculated. Optimum binding was found at 0–10°C at pH 7.5. The [H3]-testosterone-receptor complex is focused on a pH 5–7 gradient at pH 5.4. A t12 of 105min and a dissociation rate of 0.00413 min−1 for testosterone were determined. Using the nuclear exchange assay, carried out at 0–4°C. a KD of 2.85 × 10−9 M and a number of sites of 9 pmol/mg DNA were estimated for nuclear receptor.

Testicular Steroid Metabolism In Vitro in an XX‐Male

XX‐males are known to display dysgenetic gonads with failing sperm production. Since defective male gametogenesis has in certain instances been proposed to be related to an aberrant intratesticular steroid biosynthesis (Steinberger et al. 1974), we have analysed the metabolism of [3H] progesterone in vitro in an XX‐male.The 33‐year‐old patient was sterile and demonstrated high levels of gonadotrophic hormones in the peripheral circulation, though he displayed ordinary male secondary sex characteristics. Testicular biopsy specimens were incubated with [3H] progesterone. This radiolabelled precursor was found to be avidly metabolized along the so‐called “Δ4‐pathway” towards biologically active C19‐androgens in this XX‐male, as in testicular tissue derived from adult control subjects.Furthermore, the relative metabolism of [3H] progesterone per mg of testicular tissue incubated, was observed to be significantly higher in the dysgenetic gonadal tissue derived from the present XX‐male as compared to the metabolism in the control subjects.The amount of [3H] 17α‐hydroxyprogesterone synthesized in the XX‐male was very high, and also the ratio of [3H] 20α‐dihydroprogesterone:[3H]‐17α‐hydroxyprogesterone was found to be remarkably small, i. e. a pattern repeatedly observed in other hypergonadotrophic individuals (Kjessler & Berg 1976b).The present investigation thus demonstrated that intratesticular steroidogenesis along the Δ4‐pathway in vitro may be excellent in dysgenetic gonadal tissue with an XX‐chromosomal constitution.

Effect of the mouse mutants testicular feminization and sex reversal on hormone-mediated induction and repression of enzymes.

The mouse mutants testicular feminization and sex reversal have been used to investigate hormone-mediated induction and repression of enzymes. Tfm/Y animals were already known to be androgen insensitive, rendering the androgen-inducible enzymes ADH and beta-glucuronidase noninducible because of an inherited deficiency of a cytosol androgen-receptor complex. The animals display female secondary sexual characteristics. Sxr/+,XX animals display male primary and secondary sexual characteristics with small testes. We demonstrate (1) that the Tfm mutation is pleiotropic, preventing repression of an androgen-repressible enzyme (ornithine aminotransferase) as well as induction of androgen-inducible enzymes, (2) that an estrogen-inducible enzyme (histidine decarboxylase) is not affected by the Tfm mutation, and (3) that Sxr/+,XX animals produce enough androgen for malelike activities of androgen-sensitive enzymes. It was also discovered that histidine decarboxylase repressed by androgen in normal animals, rather than being unaffected by it in Tfm/Y animals, is in fact induced. This unexpected phenomenon is discussed and an explanation is suggested for it.

The induction of male sexual behavior in red deer (Cervus elaphus) by the administration of testosterone to hinds and estradiol-17β to stags

One-gram implants of testosterone were placed subcutaneously in two adult intact and one castrated red deer hinds, and 100-mg implants of estradiol-17β were given to three castrated and two intact red deer stags. Their sexual behavior was then observed in the wild and in captivity for up to 3 years. Testosterone initially produced prolonged and intense estrous behavior in the hinds; this gradually gave way to behavior normally shown only by rutting stags, such as flehmen, herding threats, and roaring. Testosterone-implanted hinds rose in the dominance hierarchy as measured by competition for food. Pregnancy, or the administration of progestagens, suppressed most of this testosterone-induced behavior. Testosterone also induced development of male secondary sexual characteristics such as formation of small antler pedicles (but not antlers), hypertrophy of the clitoris and neck musculature, and development of a neck mane and male rutting odor. Estradiol-17β mimicked the behavioral effects of testosterone when given to castrated stags, stimulating all components of rutting behavior. In intact stags, the only effects were to abolish antler casting and stimulate roaring; normal rutting behavior continued unchanged. In contrast to the effects of testosterone, estradiol-17β did not influence the social status of either intact or castrated stags. The distinctions between the behavioral effects of androgens and estrogens are ill defined and are determined more by the prior sexual differentiation of the brain and the duration of steroid treatment, than by the nature of the steroid.

Seasonal Variations in Plasma Testosterone Level in Male Eastern Wild Turkeys

Testosterone level was determined, by radioimmunoassay, on 137 plasma samples obtained from male eastern wild turkeys (Meleagris gallopavo) over a 15-month period, in Alabama. Ninety-three samples were obtained from 3 pen-reared birds by making collections every 2 weeks for 62 consecutive weeks; 14 samples were from trapped birds; and 30 were from gobblers killed during the regular spring hunting season. Plasma testosterone levels for pen-reared birds at 6 weeks of age (July 1974) were 3263 ng/100 ml; whereas those at 34 weeks of age (January 1975) and just prior to breeding season were 87-108 ng/100 ml. Mean plasma testosterone level in January-February for the mostly adult trapped birds was 202.2 ? 61.9 ng/100 ml compared to 146.0 ? 62.3 ng/100 ml for the subadult pen-reared birds. Values for the mostly adult gobblers killed during the March-April hunting season was 344.9 -+110.8 ng/100 ml compared to 254.4 _ 140.5 ng/100 ml for the subadult pen-reared turkeys. Changes in behavior and body conformation in relation to changes in plasma testosterone level are discussed for the three pen-reared turkeys. J. WILDL. MANAGE. 41(2):784-188 Knowledge of the seasonal variations in sex hormone level in male eastern wild turkeys is important for a more precise delineation of the bird's breeding season, and also for a better understanding of its behavioral and anatomical changes. This information can be useful to game managers as an additional tool for evaluating reproductive status in wild populations. Information regarding the seasonal variations in plasma testosterone levels in either wild or domestic turkeys is lacking. Furthermore, no specific value for plasma testosterone level has been reported for males of either wild or domestic turkeys. In a brief abstract, Zimmerman and Wentworth (1974) reported that they had measured the serum testosterone level in large white domestic turkeys in response to changes in photoperiod; however, they gave no specific data. Arcos (1975) reported the isolation of testosterone from the ovarian blood of the laying turkey but did not quantify the level. Plasma testosterone level for the male domestic fowl has been reported as 84-783 ng/100 ml (Furr and Thomas 1970) and for the mallard (Anas platyrhynchos) as 65-270 ng/100 ml by Jallageas and Attal (1968, cited by Bell and Freeman 1971). Changes in the circulating level of the androgens, and more specifically testostero e, are responsible for changes in male secondary sex characteristics in most vertebrates. These may include cyclic or acyclic changes in body color, body conformation, vocalization, breeding condition and sexual b havior (Turner and Bagnara 1971). Male eastern wild turkeys exhibit both behavioral and anatomical changes during their breeding season. Birds become belligerent toward other males, and courtship display toward females becomes active. Seasonal changes in body conformation include increased brilliance of facial color in caruncles and throat wattle, and the development of a large fatty breast sponge. All of these changes presumably are related to changes in the circulating levels of androgens, particularly testosterone. We wish to thank W. H. Hamrick, Wildlife Biologist, Alabama Department of Conservation, and J. R. Gwaltney, research 184 J. Wildl. Manage. 41(2):1977 This content downloaded from 157.55.39.243 on Thu, 06 Oct 2016 04:56:19 UTC All use subject to http://about.jstor.org/terms SEASONAL VARIATIONS IN WILD TURKEY TESTOSTERONE ? Lisano and Kennamer 185 assistant, Auburn University, for their assistance in obtaining blood samples. We are also grateful for the technical assistance of H. E. Whatley, graduate assistant, Auburn University, in the determination of plasma testosterone levels. MATERIALS AND METHODS

Aspects of sexual biology of the anomuran crab emerita asiatica

Male Emerita asiatica Milne Edwards are smaller than females. The secondary sexual characters of males and females are described in detail. Applying the method of Wenner (1972), sex ratio is calculated. The overlap in size range between males and females is too wide to suggest sex reversal. An analysis of secondary sexual characters in post-larval juveniles during megalopa settlement corroborates the view that males and females develop separately from the megalopa. The males acquire their sexual maturity soon after metamorphosis from the megalopa stage, whereas the females attain their sexual maturity only after considerable body growth. the males continue to grow to attain a maximum carapace length of 11 mm; they do not show any tendency towards changing their sex. This is evidenced by the fact that the weight increase of the gonadal apparatus is directly related to the increase in the male carapace length (CL) and body weight. On the other hand, retention of larval characters such as short eye stalk, toothless chelae of the fifth leg (in males up to 5 mm CL), together with the very small size suggest that the males are neotenic. Only males up to 5 mm CL were found to take part in mating. During mating, as many as 5 tiny males deposit their spermatophores in the pleopodal region of one female. This type of mating assures effective transfer of spermatophores in the turbulent environment inhabited. Spermatophores are pedunculate and embedded in a gelatinous matrix to form a long ribbon. There are two types of spermatophores in the ribbon, and they differ in detail from those of other anomuran species. The spermatozoa are rod-like, with a club-shaped acrosomal head. Five spines originate from the junction between head and body. The mode of sperm release from the spermatophores is described; oviducal secretion may be responsible for opening the spermatophore.

Sex-reversal and androgenic gland in the fish parasite Irona far (cymothoidae: isopoda: crustacea)

The sequence of changes in the primary and secondary sexual characters of the parasitic isopod Irona far during sex-reversal indicate that it is synchronised with the degeneration of the androgenic gland. The gonad is typically hermaphroditic. During the male stage the testicular utricles are large and active but the ovarian region remains undifferentiated. During the intermediate stage production of sperms is stopped and the ovarian region produces ova but without vitellogenesis in them. In the female stage the testicular utricles regress, ovary enlarges and there is increase in egg production and vitellogenesis. The male secondary sexual characters become highly developed during the male stage, regress in the intermediate stage, and finally disappear in the late female stage. Only during the female stage does the female secondary sexual character, viz, the oostegites appear. The androgenic gland shows signs of maximum secretion during the prepuberal and puberal male stages and least activity during the intermediate and early female stages, leading ultimately to total degeneration in the late female stage.

Effects of Testosterone and oestradiol on gonadectomized and intact male and female river lampreys ( Lampetra fluviatilis (L.) Gray)

Pellets of testosterone (25 mg) or oestradiol-17β (25 mg) were implanted into adult gonadectomized or intact male or female river lampreys before the period of sexual maturation. Testosterone induced male secondary sex characters in gonadectomized males and intact females, and oestradiol-17β induced female sex characters in gonadectomized females and intact males. The homologous sex hormones administered to intact males and females did not accelerate the appearance of secondary sex characters except for growth of the urogenital papilla in the male. The heterologous sex hormones caused a range of effects from inhibition of certain normal changes to stimulation of characters characteristic of the other sex. There was no marked inhibition of spermiation and ovulation, and no convincing signs of a negative feedback between sex hormones and gonadotropin secretion. Oestradiol released from the implanted pellets was found to act on untreated males kept in the same tank, so oestradiol can be transferred via the water from one lamprey to another. The intestinal hypertrophy observed after gonadectomy was not counteracted by sex hormones. Oestradiol in several lampreys increased the survival beyond the time of natural death after spawning of untreated lampreys. During the period of prolonged survival the rate of reduction in length of the body was slowed down.

Einfluss von androgenen auf die geschlechtsdifferenzierung verschiedener cichliden (teleostei)

The influence of testosterone propionate on gonad differentiation in Tilapia mossambica, Tilapia heudeloti, and Cichlasoma biocellatum was tested. Juvenile sexually undifferentiated animals were kept in water with 0.5 mg of testosterone propionate per liter. It became evident that the hormone treatment caused a strong feminization of the gonads in all these species, whereas spermatogenesis was depressed. Methyl testosterone (0.5 mg/1) also caused feminization but was accompanied by severe inhibition of ovarian development. In juvenile Tilapia heudeloti male secondary sex characters were induced following treatment with testosterone propionate; however, the gonads were feminized. In juvenile Hemihaplochromis multicolor male secondary sex characters were evoked precociously by treatment with 11-ketotestosterone, but this hormone did not change gonad differentiation.

Restoration of libido in castrated red deer stag (Cervus elaphus) with oestradiol-17beta.

THE role of oestrogens in male reproduction remains an enigma. It is known that the stallion1,2 and the boar3 excrete enormous amounts of oestrogen in their urine, and that this is of testicular origin4,5; more modest amounts of oestrogen are secreted by the testis of the bull6, rat7, and man8–10. Interest in male oestrogen was recently reawakened by the discovery that the hypothalami of rats, rabbits, monkeys and men are capable of aromatising testosterone to oestradiol-17β (ref. 11). This indicated that oestradiol-17β might be the central mediator of androgenic effects, an idea that is beginning to receive support from a number of different experiments. For example, it has been established that newborn female rats can be sterilised equally effectively by small doses of either androgen or oestrogen12. In addition, the antioestrogen MER-25 will effectively inhibit this neonatal sterilisation even when it has been induced by testosterone19. It also seems significant that androgens which cannot be metabolised to oestrogen, such as dihydrotestosterone (DHT), have no apparent effect on the brain13–16, although they are potent stimulators of male secondary sexual characteristics. Whilst DHT alone cannot restore libido to a castrated male rat, the addition of a few microgrammes of oestradiol will restore libido completely17,18 and, recently, it has been shown that pharmacological doses of oestradiol benzoate are sufficient to restore all components of male reproductive behaviour to castrate male rats20.

Stereoscan electron microscope observations on Jaera nordmanni nordica Lemercier (Crustacea: Isopoda)

The mouthparts, male secondary sex characters and male copulatory structures of Jaera nordmanni nordica Lemercier (Crustacea: Isopoda) have been viewed with the Stereoscan Electron Microscope, and compared with the corresponding structures for the closely related Jaera albifrons Leach group of species. The mouthparts are identical thus suggesting a similar diet and feeding mechanism, and that competition for food occurs between J. n. nordica and Jaera ischiosetosa Forsman, the most euryhaline member of the/, albifrons group, in localities where they overlap. The role of the secondary sex characters in maintaining genetic isolation in the three forms of J. nordmanni is discussed with reference to the information available on the J. albifrons group. The male praeoperculum and appendix masculinum of J. n. nordica are described and a possible route for the transfer of spermatophores from the male to the female is postulated.

Pituitary-gonadal relations in male children and adolescents.

Extract: Data are provided on levels of circulating follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone in healthy male children and adolescents, and these levels are correlated with the stage of sexual maturation, bone maturation, whole body 40K content, and the 24-hr excretion of creatinine, estrogens, 17-hydroxy-corticosteroids, total 17-ketosteroids, and fractionated ll-deoxy-17-ketosteroids (see Tables I and II). Before age 6 there was no significant change with age in testis size or hormone concentrations. From age 6–10 years there was a gradual rise in testis size (Fig. 1), serum FSH (Fig. 4) and serum LH (Fig. 3), but no change in plasma testosterone (Fig. 2), which remained below 40 ng/100 ml. From age 11–17 years there was a doubling of mean testis length, continued rise in serum FSH, and a steeper rise in LH; these changes were accompanied by a 20-fold increase in plasma testosterone concentration, the appearance of male secondary sexual characteristics (Figure 5), more rapid bone maturation and whole body 40K accretion, and enhanced excretion of estrogens and ll-deoxy-17-ketosteroids. Mean levels of FSH in the adult range (> 10 μUg/100 ml) were achieved by age 8, and levels reached a plateau by age 15 (Fig. 6). Adult LH levels (> 2.5 μUg/100 ml) were reached by age 13 and a plateau was observed after 17 years. Plasma testosterone also ceased to rise after age 17. The data suggest that the testis may undergo progressive gonadotropin-mediated maturation in late childhood. Testosterone secretion by the Leydig cells at puberty may result from a further rise in LH levels. Speculation: Pituitary secretion of gonadotropins, particularly FSH, in male children is a gradual phenomenon, antedeating by several years the release of testosterone by the testis. This gradual rise may represent a progressive reduction in hypothalamic sensitivity to feedback by testicular steroids other than testosterone. In late childhood, rising FSH and LH levels may induce increased activity of the enzymes responsible for both synthesis and catabolism of tesoterone. At puberty, an LH-mediated reduction in reductase activity might then result in testosterone accumulation and secretion.