Sexual differentiation of the steroid feedback mechanism regulating follicle-stimulating hormone secretion in the Syrian hamster

The ability of gonadal steroid hormones to influence tonic follicle-stimulating hormone (FSH) secretion was investigated in Syrian hamsters. In Experiment 1, males were castrated as adults, and administered testosterone in 20-, 30-, 40-, and 50-mm silastic capsules (s.c.) at 67, 74, 81, and 88 days, respectively. Circulating FSH was reduced by testosterone in a dose-dependent manner. A similar FSH response to testosterone in adulthood was evident in neonatally androgenized hamsters given testosterone proprionate (TP) on Days 0 and 1 of life. By contrast, the absence of gonadal androgens during the neonatal period (females ovariectomized at 60 days of age and males orchidectomized at birth) resulted in only a partial suppression of circulating FSH by even the highest dose of testosterone during adulthood. Treatment with estradiol benzoate at birth failed to produce a masculine response to androgen in adulthood. In Experiment 2, using a similar protocol, the nonaromatizable androgen, dihydrotestosterone, produced a dose-dependent suppression in serum FSH in males castrated in adulthood (30-, 60-, 90-mm capsules). However, dihydrotestosterone failed to alter the hypersecretion of FSH produced by orchidectomy at birth in males or in females ovariectomized at 60 days of age and treated neonatally with either vehicle or TP. In Experiment 3, treatment with estradiol (10-, 20-, 30-mm capsules) decreased serum FSH in gonadectomized hamsters in a dose-dependent manner; males and females treated neonatally with TP were more responsive to estradiol as adults compared to neonatally orchidectomized males or females treated with vehicle at birth.(ABSTRACT TRUNCATED AT 250 WORDS)     

Androgens stimulate sex change in protogynous grouper,Epinephelus coioides: spawning performance in sex-changed males

We examined the efficacy of androgens (1.0 mg/kg body mass), testosterone (T), 11-ketotestosterone (11-KT), 17alpha-methyltestosterone (MT), testosterone propionate (TP) or androgen mixture (T, MT and TP in an equal ratio), for induction of sex change in protogynous orange-spotted grouper, Epinephelus coioides. The spawning performance in sex-changed males was also investigated. MT and androgen mixture at a dose of 1.0 mg/kg BW induced a sex transition and completion of spermatogenesis up to the functional male phase. The androgen mixture was most effective. Significantly, higher plasma T levels were found in MT and androgen mixture groups compared to control and other androgen implantation (T, TP or 11-KT) groups. We found that plasma levels of estradiol-17beta (E2) or 11-KT were not different among treated groups. Sex-changed males could successfully fertilize mature eggs. Fertilization and hatching rates were of 23.5-70.4% and 8.4-44.6%, respectively. The data demonstrated that induction of sex change by exogenous androgens in groups could apply to the aquaculture field for seed production.     

Evidence for high levels of androgen in peripheral plasma during postnatal development in a marsupial: the gray short-tailed opossum (Monodelphis domestica).

Plasma samples were assayed for androgen in gray short-tailed opossums (Monodelphis domestica) on the day of birth and at selected ages through adulthood. Levels of androgen in mixed-sex plasma pools of animals 4 and 8 days of age were higher than in either sex at all other ages examined. At postnatal Days 16, 30, and 60 (weaning), levels of androgen were equivalent in males and females and as high as in adult males. In both sexes, androgen levels were lower at postnatal Day 84 (juveniles) than at younger ages; after puberty, levels were significantly higher in males than in females. These findings are discussed with respect to similarities and differences between marsupials and eutherians in hormonal environment during the perinatal period and with respect to the possible role of androgens in sexual differentiation of the gray opossum brain.     

Maternal gestational androgens are associated with decreased juvenile play in white-faced marmosets (Callithrix geoffroyi)

Exposure to androgens during prenatal development shapes both physiological and behavioral developmental trajectories. Notably, in rhesus macaques, prenatal androgen exposure has been shown to increase rough-and-tumble play, a prominent behavioral feature in males during the juvenile period in primates. While macaques are an Old World, polygamous species with marked sexually dimorphic behavior, New World callitrichine primates (marmosets and tamarins) live in cooperative breeding groups and are considered to be socially monogamous and exhibit minimal sexual dimorphism in social play, which suggests that androgen may affect this species in different ways compared to macaques. In addition, we previously described considerable variation in maternal androgen production during gestation in marmosets. Here we tested the association between this variation and variation in offspring rough-and-tumble play patterns in both males and females. We measured testosterone and androstenedione levels in urine samples collected from pregnant marmoset mothers and then observed their offspring's play behavior as juveniles (5-10 months of age). In contrast to findings in rhesus macaques, hierarchical regression analyses showed that higher gestational testosterone levels, primarily in the second semester, were associated with decreased rough-and-tumble play in juveniles, and this relationship appears to be driven more so by males than females. We found no reliable associations between gestational androstenedione and juvenile play behavior. Our findings provide evidence to suggest that normative variation in levels of maternal androgen during gestation may influence developmental behavioral trajectories in marmosets in a way that contradicts previous findings in Old World primates.     

Plasma androgens in children and adolescents. Part I: control subjects

In this cross-sectional study, plasma levels of dehydroepiandrosterone sulfate (DHEA-S), dehydroepiandrosterone (DHEA), delta 4-androstenedione (delta 4) and testosterone (T) were measured by RIA in 232 normal subjects of both sexes, aged 2 weeks to 20 years. The results were analyzed in relation to chronological age, body surface and pubertal stage. High levels of plasma androgens were found in newborn infants of both sexes. After 3 months of age, androgen levels were uniformly low and rose with increasing chronological age and body surface. The first significant increase in mean androgen levels was found for DHEA-S. It occurred after 6 years of age in girls and after 8 years in boys. DHEA and T rose in both sexes after 8 years of age. delta 4 increased steadily with chronological age and body surface in both sexes. When androgen levels were related to body surface, a first significant increase was observed above 1.00 m2 for the four androgens, in both boys and girls. Above 1.20 m2 and 12 years of age, girls had higher mean levels of DHEA-S, DHEA and delta 4, but lower mean T levels than boys of the same body surface and chronological age. Before puberty, a positive correlation was found in both sexes between the plasma androgen levels on the one hand, and both chronological age and body surface on the other. Plasma androgen levels markedly increased at stage P2 in both sexes, and further increased with pubertal development. During puberty, girls had higher plasma delta 4, but lower plasma T levels than boys of the same pubertal stage. Plasma DHEA-S and DHEA levels were similar in both sexes. In contrast to the plasma androgens, plasma cortisol levels did not show any change in relation either to chronological age or to body surface or pubertal development. Body surface appears to be as good a discriminating factor as chronological age, at least in young children. It also appears from this study that DHEA-S is a good guide for the clinical evaluation of adrenal maturation and may be very useful in evaluating patients with growth or pubertal disturbances.     

Déficit androgénique lié à l’âge. Que faut-il attendre de l’androgénothérapie?

With the exception of disease or drug-induced changes in Leydig cell function, aging is accompanied by specific changes of androgen status in healthy men. The level of testosterone production decreases in contrast with the rise in plasma protein testosterone binding capacity. Free testosterone, considered to be the biologically active fraction, decreases, leading to tissue androgen deficiency. The resulting clinical picture mimics hypogonadism, including physical and psychological asthenia, decreased libido and sexual behaviour, increased fat mass and decreased lean mass, gynaecomastia, osteoporosis and pro-atherogenic metabolic changes. The cut-off value for plasma testosterone below which androgen deficiency can be considered to be responsible for clinical signs is a key point which determines the therapeutic approach. In the absence of clearly validated data in healthy aging males, this cut-off value has been consensually defined as the mean plasma testosterone levels of men between 30 and 50 years of age minus two standard deviations, corresponding to the zone of hypogonadism in adult males. The association of clinical signs compatible with hypogonadism and reduced total (or preferably bioavailable) plasma testosterone level justifies initiation of hormone replacement therapy after excluding any contraindications (especially prostatic). The aim of this treatment is to reverse the consequences of age-related hypogonadism. Some benefits of this treatment have been clearly demonstrated, such as a decrease of fat mass, and an increase of lean mass and muscle strength. Similarly, bone mineral density increases, particularly in men with the lowest pretreatment plasma testosterone levels. It must be stressed that these changes are observed in truly hypogonadal aging men, but not in aging men with normal plasma testosterone levels. Testosterone replacement therapy can promote the development of gynaecomastia, while dihydrotestosterone tends to reduce gynaecomastia. Finally, androgen replacement therapy appears to improve a hypogonadism-related decrease in libido or sexual behaviour, provided other associated non-endocrine factors have been previously treated. Androgen replacement therapy improves well-being, and physical and psychological asthenia in hypogonadal men. However, this treatment has not been demonstrated to be effective in healthy aging men. Although androgen replacement therapy does not have a negative impact on lipid parameters, its possible cardiovascular protective effects have not yet been demonstrated. In conclusion, androgen replacement therapy, respecting the contraindications, is beneficial in patients of all ages with clearly demonstrated hypogonadism, but has no efficacy on symptoms in other cases.     

Endocrine and developmental correlates of unilateral cryptorchidism in a wild baboon

A wild, group-living 8.5-year-old adult baboon was found to have only a single palpable testicle, the only case of cryptorchidism found among more than 200 males that we have examined. This young adult had an unusually small body size for his age, one that was comparable to that of immature males two years younger, and during maturation his body mass was increasingly small for his age. As a young adult, he also had very low testosterone concentrations, which, in combination with his small size, history of impaired growth, and the absence of any obvious scars around the scrotum, suggest that this is a case of spontaneous unilateral cryptorchidism of unknown cause rather than one of monorchidism arising from injury. Despite striking differences in his growth, adult body size, and testosterone levels, the male's cryptorchidism seemed to have relatively little effect on his social and sexual maturation in his natal group. Nonetheless, it may be related to his inability to gain entry into another group after dispersal.     

Endocrine correlates of intra-specific variation in the mating system of the St. Peter's fish (Sarotherodon galilaeus)

The Challenge Hypothesis postulates that androgen levels are a function of the social environment in which the individual is living. Thus, it is predicted that in polygynous males that engage in social interactions, androgen levels should be higher than in monogamous animals that engage in parental care. In this study, we tested this hypothesis at the intra-specific level using a teleost species, Sarotherodon galilaeus, which exhibits a wide variation in its mating system. Experimental groups of individually marked fish were formed in large ponds with different operational sex-ratios (OSR) to study the effects of partner availability on blood plasma levels of sex steroids [11-ketotestosterone (11-KT), testosterone (T), and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P)] and gonadosomatic index (GSI). Polygyny mostly occurred in the female biased OSR groups. 17,20beta-P and gonadosomatic index did not differ among OSR groups. However, 11-KT was high in male biased OSR and positively correlated with aggressive challenges, thereby supporting the central postulate of the Challenge Hypothesis. The results of T were the inverse of those of 11-KT, probably because 11-KT is metabolized from T. 11-KT levels of polygynous males did not differ neither from those of monogamous males, nor from those of males that participated in parental care. These results do not support the expected relationships between polygyny, parental care, and androgen levels. The differences from expectations for 11-KT may be related to the fact that in S. galilaeus, the mating and the parenting phase are not clearly separated and thus, males may still fight and court while they are brooding.     

Sociodemographic Correlates of Fecal Androgen Levels in Wild Male White-Handed Gibbons (Hylobates lar)

Despite the central role of testosterone in influencing many aspects of the male life cycle, information on the influence of social and behavioral factors associated with androgen output is available for only a few primate species, mainly those living in multimale–multifemale societies. We collected 322 fecal samples and measured fecal testosterone metabolite levels in 19 adult male white-handed gibbons (Hylobates lar) from 13 groups living in the Khao Yai National Park, Thailand, to examine the extent to which androgen output is related to sociodemographic variables (social organization, social status, presence of infants, age) in a socially flexible species, i.e., pair-living/multimale groups. We predicted that androgen levels would be higher in males 1) that live in potentially more unstable single-male/single-female units; 2) that are primary (dominant) vs. secondary; 3) that live in groups with dependent infants; and 4) that are of prime vs. senior age. We found marked differences in androgen levels among males and a significant effect of time of the year. Males living in pairs exhibited significantly higher androgen concentrations vs. males living in multimale groups, and males residing in groups with infants showed a significant increase in androgen levels throughout the sampling year. However, we found no relationship with male age or social status. The increased androgen output found in both pair-living males and those residing with infants might be a physiological mechanism that facilitates male aggression to cope with potential threats posed by social challenges and the demand for infant/group defense, respectively. More generally, our data indicate that in socially flexible species male androgen output is less strongly linked to key life-history variables than in species that live permanently in multimale–multifemale groups.     

Prevalence of dyslipidemia and mean blood lipid values in Taiwan: results from the Nutrition and Health Survey in Taiwan (NAHSIT, 1993-1996)

This paper reports the blood lipid status of people aged 4 years and older in Taiwan. The data is based on the Nutrition and Health Survey in Taiwan (NAHSIT: 1993-1996), which adopted a multi-stage, stratified clustering sampling scheme. Altogether, 5097 subjects (2451 males and 2646 females) had data on triglyceride and 5643 subjects (2736 males and 2907 females) had data on cholesterol. We found that (a) cholesterol levels of males were lower than females in mid-to old age group (> or = 45 years old); (b) triglyceride values of females were lower than males in young adulthood (19-44 years), but higher than males after the age of 45 years, and (c) adult females had higher HDL-C value and lower ratio of total cholesterol to HDL-C than males. The prevalence of hypercholesterolemia was 10.2% in adult males and 12.6% in mid-to-old aged men, and that in females was 11.2% and 24.4%, respectively. The prevalence of hypertriglyceridemia was 13.4% and 6.1% in adult males and females (> or = 19 years as a whole), respectively. It was 12.3% in mid-to-old aged men (> or = 45 years), and 11.9% in women. The mean cholesterol values were similar to values of several previous surveys in different areas of Taiwan. But it was higher than those in some areas of Mainland China, and lower than those of western countries. People in metropolitan cities had a higher level of blood cholesterol than other areas. The average triglyceride values of males and females were higher than those of previous studies in Taiwan and of people in Mainland China. Mountainous stratum with predominantly aboriginal residents had higher level of triglycerides and body mass index (BMI) than other strata. The associations between dietary intakes of men and women and blood lipids were examined controlling for age and BMI. Result showed that Keys score, which was derived from saturated fat, polyunsaturated fat and dietary cholesterol of a 24-hour recall, was positively related to blood cholesterol and LDL-C in men, but not in women. Average alcohol intakes per day were related to HDL-C positively, but LDL-C negatively in men and women. The regional differences in blood lipid profiles in Taiwan are consistent with the dietary and life-style variations island-wide.     

Gonadal hormones during puberty organize environment-related social interaction in the male rat

This study examined the role of gonadal androgens during puberty on the development of environment-related social interaction (SI) in male rats. SI in an unfamiliar environment versus SI in a familiar environment was evaluated in young adult rats as a function of sex and gonadal status. Intact male rats at 60 days of age exhibited a differential response to the two environments, whereas SI in intact female rats at 60 days was equivalent in the two environments. Furthermore, male rats castrated as juveniles and tested for SI at 60 days displayed a pattern of environment-related SI similar to SI in intact adult female rats. This effect of juvenile castration on SI in male rats was prevented by chronic exposure to testosterone propionate (TP) over Days 30 through 60. SI in male rats castrated in adulthood, on the other hand, was not altered either 2 or 4 weeks postcastration. The results from this study indicate that pubertal secretions of gonadal androgen(s) are necessary for the development of environment-related SI in male rats. In contrast, secretions of gonadal androgens in adulthood do not appear to be critical for the continued expression of environment-related SI, as suggested by the observation that environment-related SI in male rats remains unchanged by castration in adulthood.     

Effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion in rats

The effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion and their relationships to gonadotropins were studied in rats. Mature Wistar male rats weighing approximately 300 g were made either uni- or bilaterally cryptorchid. Testicular inhibin and testosterone content and plasma levels of LH and FSH were examined 2 weeks later. A similar remarkable decrease in testicular inhibin content was found in uni- and bilaterally cryptorchid testes. On the other hand, the testicular testosterone content was significantly decreased only in unilaterally cryptorchid testis with an inverse increase in the contralateral testis. Plasma testosterone levels were normal and plasma LH and FSH increased significantly in both of the cryptorchid groups. These results showed that cryptorchidism impairs both Sertoli and Leydig cell functions. While testosterone production was compensated by increased LH for 2 weeks, neither inhibin secretion nor storage changed in cryptorchid or contralateral testes during the same period.     

Effects of testosterone and estrogen on hepatic levels of cytochromes P450 2C7 and P450 2C11 in the rat.

The effects of exogenous hormone treatment on the expression of cytochromes P450 2C7 and P450 2C11 were studied in neonatally gonadectomized and sham-operated male and female rats. Hepatic levels of cytochrome P450 2C7 were found to be two- to threefold higher in intact adult female versus male rats. Neonatal gonadectomy resulted in a reversal of the relative cytochrome P450 2C7 levels in male and female animals at maturity. Expression of this isozyme was restored in ovariectomized females by estradiol treatment. Furthermore, neonatal and/or pubertal administration of estradiol to intact male rats induced cytochrome P450 2C7 to adult female levels. On the other hand, administration of testosterone at all times examined had no effect in intact female rats, but decreased cytochrome P450 2C7 to normal levels in neonatally castrated males treated during adulthood. Neonatal testosterone treatment also increased hepatic cytochrome P450 2C7 content in both ovariectomized females and intact males. These results indicate that estrogen is required for full expression of cytochrome P450 2C7 while the effect of testosterone is ambiguous. In comparison, neonatal gonadectomy of male rats abolished the adult expression of cytochrome P450 2C11. Normal levels were restored only by treatment with testosterone during adulthood. Neonatal testosterone treatment did not induce cytochrome P450 2C11 levels in gonadectomized rats of either sex. In contrast, neonatal estrogen treatment suppressed cytochrome P450 2C11 expression in intact adult male rats to the same extent as neonatal castration. These results indicate that androgen exposure during the adult, and not the neonatal, phase is essential for full expression of cytochrome P450 2C11.     

Steroid hormones and paternal care in the plainfin midshipman fish (Porichthys notatus)

The present study investigated the relationship between plasma steroid hormone levels and the expression ofpaternal behavior in the plainfin midshipman fish (Porichthys notatus), where males may simultaneously care for multiple clutches in different stages of development. Blood samples were collected from free-living parental males during that part of the breeding season when males may be found in various stages of parental care. Plasma 11-ketotestosterone levels were significantly higher in males with empty nests and nests containing only eggs than in males with nests containing embryos. All males with nests containing embryos had undetectable testosterone levels, whereas testosterone levels were detectable in many males with empty nests or nests containing only eggs. Estradiol levels were detectable in only a few males from nests with no eggs or nests containing only eggs. Cortisol levels were not correlated with stage of paternal care or with handling time. These results follow the frequently reported vertebrate pattern of declining androgen levels over the course of the breeding season or during the period of parental care. However, many male midshipman guarding nests containing only eggs had androgen levels similar to those of males whose nests contained no offspring. Thus the pattern of androgen levels exhibited by reproductively active parental male midshipman may reflect a compromise between investment in paternal care versus courtship and/or territoriality.     

Androgens and male mating behavior in rough-skinned newts, Taricha granulosa

Cyproterone acetate was administered either orally or intraperitoneally to intact, adult male newts, Taricha granulosa. The number of males that exhibited the courtship behavior of clasping when tested with nuptial females was not altered by the antiandrogen treatments. In males which were unresponsive to nuptial females, the occurrence of clasping was not evoked by injections for 4 days of testosterone, dihydrotestosterone, or 11-ketotestosterone. Further, the incidence of clasping was not significantly elevated by injections of prolactin and/or testosterone for 30 days. The effect of sexual activity on testosterone and dihydrotestosterone levels in male newts was determined by radioimmunoassay of plasma collected from males which were: (1) isolated from females; (2) allowed to clasp a female for 2 min; or (3) allowed to clasp a female for 1 hr. The testosterone and dihydrotestosterone levels were unchanged during this period of clasping. In February and again in June, plasma androgen concentrations were measured in males which differed in their propensity to initiate courtship when paired with females. Androgen levels were similar for males that clasped a female and males that never attempted to clasp a female. Plasma androgen levels in the male newt are apparently not correlated with sexual responsiveness.     

Gonadal function in young adults after surgical treatment of cryptorchidism.

In a follow-up study of 48 young men who had been surgically treated for cryptorchidism before puberty testicular function was assessed by examining the genitalia, testicular volume, secondary sex characteristics, semen, plasma luteinising hormone (LH) and follicle-stimulating hormone (FSH) concentrations after luteinising hormone-releasing hormone stimulation, and plasma testosterone concentrations. Clinical androgen effects were normal. The mean testicular volume of both testes was in the low normal range in those who had had unilateral cryptorchidism and below normal in those who had had bilateral cryptorchidism. Of 37 patients whose sperm counts were recorded (14 bilateral) six showed azoospermia (all bilateral), five had severe oligospermia (four bilateral), and 10 had moderate oligospermia (one bilateral). In nearly all those who had had bilateral cryptorchidism and most of those who had had unilateral cryptorchidism plasma gonadotrophin levels were increased. Four cases of possible partial LH deficiency were identified. Plasma testosterone concentrations were normal in all except two patients.     

Gonadal intraparenchymatous functional reserve in andropause

Blood plasma testosterone (T), estradiol (E2) levels and gonadal reserve in 43 patients aged between 50 and 66 years with andropause symptoms have been determined. The patients were divided into 3 subgroups depending on the severity of the symptoms. No significant difference was noted in T level of these patients compared to the range in younger males as well as a control group of corresponding age but with no andropausal symptoms. E2 level was significantly elevated in the observed group compared to the two control groups. No difference was noted in T and E2 levels between the 3 subgroups of the andropausal patients. Gonadal reserve in the observed group was significantly lower compared to the control groups of the younger males. No significant difference was noted in the gonadal reserve between 3 subgroups of the andropausal patients.     

Effect of neonatal injections of estradiol, testosterone and cryproterone acetate on plasma and testicular testosterone and on the genital system in adult male mice]

On day old male mice received a single injection of oestradiol benzoate, testosterone propionate or cyproterone acetate in order to study their action on testicular development, particularly testosterone secretion. Oestrogenization of newborn males leads, when the animals mature, to a high proportion or cryptorchidism, to atrophy of testes and seminal vesicles, and inhibition of spermatogenesis. Testosterone levels were reduced in the plasma. Testosterone propionate produced moderate reduction of testicular weight but spermatogenesis was not impaired. Plasma testosterone level was reduced. Cyproterone acetate increased significantly testicular testosterone level.     

Reproduction in the male sub-Antarctic fur seal Arctocephalus tropicalis

The reproductive tracts of male sub-Antarctic fur seals Arctocephalus tropicalis ( n = 123), taken at Gough Island (40° 20'S, 9° 54'W) between November 1977 and October 1978, were examined. The presence of spermatozoa in the epididymal tubules showed that all males ≥4 years old had reached puberty, and the marked slower increase in mean testis weight and baculum length suggested that sexual (social) maturity was approached by 8-year-olds. Full adulthood was attained at 10–11 years of age based on the peak in mean testis and prostate weights, and mean baculum length. Secondary sexual characteristics were only fully developed in males ≥9 years old. A significant decline in mean testosterone concentration, and in testis, epididymis and prostate weights showed that adult males were reproductively quiescent during winter from May to July when seminiferous and epididymal tubules had lowest mean diameters with no spermatozoa present. Both the mean plasma testosterone concentration and mean testis weight peaked twice during the austral summer. The first peak coincided with the breeding season, and the second peak with the moulting period when adult males were impotent. Photoperiodic cueing might explain this seasonal trend.     

Disturbed testicular descent in the rat after prenatal exposure to the antiandrogen flutamide.

Exposure of rats in utero to the anti-androgen flutamide resulted in feminization of the external genitalia that was noticeable at birth. This exposure also resulted in a high degree of cryptorchidism during adulthood. In most affected animals, testes were lying in 'ovary position' close to the caudal pole of the ipsilateral kidney. Cryptorchidism occurred despite normal prenatal development of the gubernacular cones and the transformation of these structures, postnatally, into muscular cremaster sacs. Inter- and intralitter variation in the response to prenatal exposure to flutamide was observed as well as intra-individual variation. Cryptorchidism frequently occurred unilaterally with right side cryptorchidism predominating. Cryptorchidism occurred in association with marked suppression of the growth of the ipsilateral epididymis and deferent duct. The possibility is considered that the poor development or absence of these structures contributes to cryptorchidism. Intra-individual variation supports the concept of the local nature of the influence of testis hormones in stabilization and further differentiation of the ipsilateral Wolffian duct derivatives. Cryptorchidism was enhanced when rats were treated postnatally with testosterone or oestradiol. The effect of testosterone was unexpected in view of the generally held hypothesis that androgens enhance testis descent. The effect of oestradiol was as expected: other animal models have been described in which induction of cryptorchidism by oestradiol occurs. Additional treatment with oestradiol caused further suppression of growth of the epididymis and deferent duct. The response to prenatal exposure to flutamide was not altered by further injections of flutamide postnatally. Such injections were without effect in males not exposed to flutamide prenatally except for minor, but statistically significant, testicular enlargement during adulthood. A model is thus presented that describes cryptorchidism as an endogenous developmental disorder.