Endocrine control of antler growth in red deer stags

Observations of body weight, testis size, antler status, plasma testosterone and prolactin were made on 12 red deer stags during their first 2 years of life. Six of the stags were fed to appetite throughout the study (Group A) and 6 were fed a 70% restricted diet during each winter (Group B). In addition 6 of the stags , 3 from each group, were studied in more detail; LH and testosterone were measured either after a single injection of LH-RH or in samples taken at frequent intervals over a period of 8 or 24 h. During the study the stags became sexually mature, developed first their pedicles and then antlers and showed at least one complete cycle of casting and regrowth of the antlers . The stags in Group A developed their testes and pedicles about 2 months earlier than did those in Group B. Pedicle initiation was associated with increasing plasma testosterone levels in response to changes in LH secretion, and antler development occurred when testosterone levels were low or decreasing. Cleaning of the velvet was associated with high levels of plasma testosterone. Antler casting occurred when plasma testosterone concentrations were low or undetectable and prolactin levels were high or increasing. The relationship between LH and testosterone varied during the study; in spring when the testes and antlers were growing, relatively high levels of LH were associated with only small peaks of testosterone, yet in summer, when antler growth was complete and the antlers were clean of velvet, low LH concentrations were associated with large peaks of testosterone.     

Effect of antiandrogen cyproterone acetate on the development of the antler cycle in Southern pudu (Pudu puda)

The antler cycle of pudu is similar to other cervids, but unlike most boreal deer, male Southern pudu (Pudu puda) exhibits two seasonal peaks of LH and testosterone. In that respect, pudu is similar to roe deer. Whereas the antler cycle in some deer species, such as roe deer or white-tailed deer, is very sensitive to variation of testosterone, in other cervids, such as fallow deer or reindeer, a blockade of androgens with cyproterone acetate (CA) has little or no effect on the timing of the antler casting. In order to test the sensitivity of pudu antlers to variations of androgens, CA (administered 2x weekly at 50 mg/buck) was injected intramuscularly for 3 weeks in 5 adult male pudu, starting February 19 (late summer). Four other males of similar age served as controls. The experiment was performed at the University of Concepcion, Chile, latitude 36.6 degreeS. Blood samples were taken once a week between January 19 and April 3. In CA-treated bucks, the antlers were cast approximately 3 weeks after the initiation of CA treatment and a new antler growth began almost immediately. The antlers reached about 5 cm in length, before ceasing to grow at the end of April, when they became mineralized and were subsequently polished. CA had no effect on the already declining levels of LH. Plasma levels of testosterone in controls increased from February 15, whereas in CA-treated bucks remained depresses until March 21. It is concluded that similarly to white-tailed deer, the antler cycle of Southern pudu is very sensitive to manipulation of androgen levels.     

Regrowth of amputated velvet antlers with and without innervation

The influence of removing portions of the growing antler of yearling red deer stags on subsequent regeneration of the antler in the same season was studied. The influence of the innervation of the antler on such regeneration was the subject of a further study. When the top 0.5-1 cm was removed from antlers 9-17 cm long, growth was slightly reduced in that season. When the antler/pedicle length was reduced to 6-10 cm in antlers 16-38 cm long, branched antlers regrew in 11 out of 13 cases provided the amputation was carried out early in the growing season, i.e., before mid-December. Denervated antlers were shorter, lighter, and of different shape compared with controls, but they were of similar density. Denervation was confirmed histologically. Cleaning of velvet and casting of antlers following castration were unaffected by denervation. It would appear that although nerves affect the size and shape of the antler, they are not essential to the actual control of antler growth and regeneration.     

Territory Establishment and Antler Cycle in Male Roe Deer

Territory establishment and antler cycle in male roe deer, Capreolus capreolus, were studied in two areas in south-eastern Sweden during 1989–1993. Initial territorial behaviour was observed in early Mar., when overlap between male ranges decreased from 66 % to 0 % over a 3–6-wk period, as determined from telemetry data. The decrease was associated with an increased number of agonistic interactions. Most territories were established at the end of Mar. to early Apr., with a tendency for males re-establishing old territories to be first. In all years, territories were taken up 1–3 wk before males shed velvet from their antlers. The distance between geometric centres of neighbouring males in winter and after territory establishment increased from 164 to 364 m. Former territory holders moved the geometric centres of their winter range and subsequent territory a shorter distance than first-year territorials, 129 and 267 m respectively. Territory defence ceased after the rut in late Aug., and the spatial relations between neighbours reverted to the situation before the territorial season. Neither velvet shedding nor antler casting was correlated with male age (yearlings excluded), which contradicts earlier statements. Neither were there any associations between timing of antler casting and subsequent velvet shedding, nor vice versa. Hence, a male casting antlers early one year derives no advantage by early shedding the next season. Furthermore, to be in hard antlers is not a prerequisite for territory take-up, whereas antlers probably are necessary for maintaining the area throughout the season. Functional aspects on roe buck territoriality are also discussed.     

Role of oestradiol in the regulation of the seasonal antler cycle in female reindeer, Rangifer tarandus.

Reindeer (or caribou), Rangifer tarandus, is the only extant species of deer in which females as well as males normally develop antlers that are cast and regrown each year. This study investigated the role of ovarian oestradiol in the regulation of the seasonal antler cycle in female reindeer. Ovariectomized Norwegian reindeer living outdoors in northern Norway (69 degrees N) were treated with continuous-release subcutaneous Silastic implants containing oestradiol, which maintained the blood concentrations of oestradiol within the physiological range for the mating season from June to October-November. The treatment with oestradiol induced the synchronized maturation of the antlers and rapid cleaning of the velvet-like skin in August-September in the ovariectomized reindeer, a pattern very similar to that observed in ovary-intact controls living under the same conditions. The removal of the steroid implant in October-November caused the premature casting of the antlers in early winter in two of five animals, while the remainder cast at the normal time in spring; this response was seen whether the animals had received one or two oestradiol implants in autumn. The antlers developed by the ovariectomized, oestradiol-treated females were significantly heavier and carried more branches than the ovariectomized animals without oestradiol replacement, and were marginally heavier than the antlers of intact controls. These results support the view that oestradiol is the biologically active steroid secreted by the ovary in intact female reindeers that induces the normal development of the antlers. Oestradiol stimulates the growth and mineralization of the antler bone, the cleaning of the velvet, and suppresses the casting of the hard antlers. This endocrine control ensures that the hard antlers, which function as weapons, are retained throughout the autumn and winter when the females are normally pregnant and when competition between females over food in the snow is most intense; hence there is a reproductive advantage to explain the evolution of antlers in females.     

Influence of photoperiod on the seasonal pattern of secretion of luteinizing hormone and testosterone and on the antler cycle in roe deer (Capreolus capreolus).

Annual variations in concentrations of luteinizing hormone (LH) and testosterone in plasma were analysed in relation to the antler cycle in six adult male roe deer exposed to a natural photoperiod (latitude 46 degrees 10'N) and in four adult males maintained in a constant short-day photoperiod (8 h light: 16 h dark) for a year, from the winter solstice at which time both groups of animals had antlers in velvet. The animals were sampled, every 15 min for 2 or 4 h at intervals of one month for a year. Under both natural and experimental conditions, LH concentrations were high from January to March, but in the experimental conditions they decreased between April and May-June, whereas in the natural conditions they increased. Plasma LH concentration was lowest between July and November in animals under natural photoperiod, whereas under 8 h light:16 h dark photoperiod a second increase in plasma LH occurred between August and September. Between March and August, concentrations of plasma testosterone increased under natural photoperiod, whereas under experimental photoperiod there was a biphasic pattern of plasma testosterone with peaks between February and May and between September and November. Under natural photoperiod, antlers were cast in November, 369 +/- 6 days after the previous antlers were cast. Under experimental photoperiod, antlers were cast after 193 +/- 10 days, and a new set developed. The sexual cycle of the male appears to be initiated by an endogenous rhythm in winter and is then maintained by hormonal changes resulting from increasing photoperiod in spring.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of social cues on the reproductive endocrinology of male brown-headed cowbirds: field and laboratory studies

Captive male brown-headed cowbirds exposed to long days exhibit gonadal growth and have elevated plasma testosterone (T) levels. This photoperiodic response is enhanced if males are housed with female cowbirds: Photostimulated males with females increase plasma testosterone levels sooner than do individually housed photostimulated males. Peak plasma T levels are similar in both groups, although peak levels are maintained longer in males housed with females. The gonadal cycle is similarly affected; males in the presence of females have earlier gonadal recrudescence and maintain mature gonads longer than do photostimulated males without females. Plasma corticosterone levels increase in the unpaired males, suggesting that removal of social cues is stressful for these birds. Free-living paired males have significantly higher plasma testosterone levels than do unpaired/unknown males early in the season, when social relationships are being established; the levels are similar thereafter. There is no difference between the two groups in testicular maturation rates; nor do they differ in plasma corticosterone levels at any time of the season. These results suggest that social stimuli are important in modulating the secretion of testosterone in males early in the season when pairing occurs, and possibly late in the season as well, probably to prevent termination of breeding prior to that of females.     

Long-term stimulatory effects of a continuous infusion of LHRH agonist on testicular function in male red deer (Cervus elaphus)

Red deer stags were infused continuously with the LHRH agonist buserelin at 180-270 micrograms/day (1.2-1.8 micrograms/kg/day) for 72 days starting in late winter with the aim of suppressing reproductive function and inducing premature casting of the antlers. Contrary to expectation, the treatment resulted in a long-term stimulation of testicular activity lasting at least 2 months; the increases in plasma concentrations of testosterone were associated with an increase in aggressive behaviour and the development of rutting odour in the urine. The stags cast their antlers at the normal time in spring after the end of the treatments. The results indicate that the pituitary gonadotroph cells in the stag can continue to secrete LH in response to chronic exposure to an LHRH agonist and do not become rapidly desensitized. The effect of the agonist is therefore to cause significant stimulation of testicular activity which is a conspicuous response in the non-breeding season when the stags are already in a hypogonadal state.     

The relationship between sexual and aggressive behaviour, and pituitary and testicular activity during the seasonal sexual cycle of rams, and the influence of photoperiod

Six adult Soay rams were housed under artificial lighting conditions with alternating 16-week periods of long (16 h light: 8 h darkness) and short days (8L:16D) During long days the rams were reproductively quiescent: the abrupt change from long to short days induced a specific succession of responses in the reproductive system. Plasma LH and FSH levels began to increase after 2-4 weeks, followed almost immediately by a rise in plasma testosterone levels accompanied by growth of the testes. Testicular activity continued to increase during short days and the greatly elevated androgen levels apparent after 5-10 weeks caused changes in the peripheral target organs, including growth of the epididymides, development of the sexual flush on the exposed ventral skin and heightened genital sensitivity. High testosterone levels were also associated with an increase in aggressive (scored by a mechanical device) and sexual (incidence of Flehmen) behavior which was at peak about 1 month after the start of the peak androgen levels. The change to long days was associated with a decrease in plasma gonadotrophin levels within 2 weeks followed by a progressive decline in all reproductive parameters measured. Implantation of a low dose of testosterone (200 mg) during the period of reproductive quiescence induced the development of the sexual flush and an increase in genital tactile sensitivity, although behaviour was not significantly affected. The annual changes in reproductive physiology and behaviour of 12 Soay rams living under natural lighting conditions were recorded for comparison with the experimental situation. The nadir of the sexual cycle was in the spring and early summer, and the sequence of events culminating in the mating season in the autumn was similar to that induced experimentally.     

Experimental studies on the annual cycles of thyroid and adrenocortical functions in relation to the reproductive cycle of drakes.

The annual variations in the basal plasma contents of testosterone, thyroxine and corticosterone have been measured in Peking drakes living outdoors, in Southern France. 10 The plasma testosterone titer underwent a more than 20-fold increase during the vernal reproductive period (March-April). In early June the circulating testosterone fell to near autumnal values, and the testosterone MCR was augmented. These were the first manifestations of the cessation of the vernal reproductive period. 20 The plasma thyroxine levels were minimal in autumn, moderately augmented (40%) in winter (January-March), but exhibited a 3-fold increase in early June. The resulting steep (13-fold) increase of the plasma thyroxine/testosterone ratio preceded the onset of the post-nuptial moult. 30 Modifications of testosterone secretion and clearance rate similar to those occurring in June were initiated in spring by i.m. injections of thyroxine at a dosage (1 mg/d) that induced June-July thyroxine plasma levels. On the other hand, an experimentally induced steep decrease of testosterone (castration) induced enhanced plasma thyroxine concentrations similar to the June values, while an induced (10 mg/d testosterone i.m.) hypertestosteronemia corresponding to the reproductive period depressed the plasma thyroxine levels. Strong reciprocal negative interactions between testis and thyroid might therefore afford a partial explanation of the peculiar thyroxine/testosterone imbalance that occurred in June immediately prior to the moult. 40 Cold-exposed "short-day" (December) ducks exhibited a marked increase in plasma thyroxine levels, while exposure of December ducks to "long days" (18L-6D) at 25 degrees C depressed the thyroxine titers. The inhibitory effect of "long days" on the blood level of thyroxine was further evident in castrated ducks. Exposure of "short day" ducks (December) to a combined treatment by "long days" (18L-6D) and cold (4 degrees C) produced an endocrine picture similar to the January-March pattern, i.e. highly increased testosterone plasma levels, but unaffected testosterone MCR, together with a moderate increase in plasma thyroxine concentration. 50 Corticosterone plasma concentrations increased during the reproductive season, as a result of a seasonally augmented binding-capacity of the CBG. Exogenous testosterone (10 mg/d) which induced spring-like circulating levels of male hormones, caused a similar increase in CBG-bound and total corticosterone levels. 60 In June the MCR of both corticosterone and aldosterone were elevated (as was the testosterone MCR). Similarly enhanced MCR of both corticosteroids were brought on in spring by an exogenous thyroxine treatment, leading to a June-like state of hyperthyroxinemia.     

Seasonal variations in semen characteristics, semen cryopreservation, estrus synchronization, and successful artificial insemination in the spotted deer (Axis axis)

Ten adult male spotted deer were monitored over a 2-year interval to determine seasonal variations in testicular size, semen characteristics and serum testosterone concentrations, and to determine if there was an association between season and type of antler. Mean (+/-S.E.M.) testicular volume (118.8+/-4.6 cm(3)), serum testosterone concentration (1.2+/-0.1 ng/mL), semen volume (4.1+/-0.6 mL), sperm concentration (338.3+/-24.9 x 10(6) mL(-1)), percentage of morphologically normal sperm (79.1+/-2.8%), and percentage of motile sperm (66.5+/-1.5%) were higher (P<0.05) in hard antler deer (peaked from March to May) than in deer with velvet antlers or in deer in which the antler has been shed. Thus, March-May was considered the physiologic breeding season for these deer; at this time, all stags had hard antlers. Furthermore, a Tris-citrate-based semen extender containing 4% glycerol and 20% egg-yolk was adequate for cryopreservation of semen. Estrus was induced with an implant containing norgestomet, timed transcervical AI was done with fresh semen, and 3 of 10 females were pregnant at 60 days, with fawns born 120 (premature), 240 and 243 days after AI. These results were considered a model for the use of assisted reproductive techniques to conserve other critically endangered deer species of India.     

The role of sex hormones in the growth of antler bone tissue. I: Endocrine and metabolic effects of antiandrogen therapy.

Cyproterone acetate (CA), an antiandrogenic compound, was used in order to investigate the role of testosterone in bone growth processes. The formation of Haversian systems in the growing antlers of white-tailed deer (Odocoileus virginianus) were substantially affected by only 3.5 mg of CA kg/wk. The mineralization processes of the bone matrix were almost completely blocked and the antlers persisted in growing throughout the whole year. Plasma levels of thyroxine, alkaline phosphatase and GH were higher while cortisol and testosterone levels were lower than in controls. No differences were registered in plasma levels of Ca, P or urea nitrogen. Despite hypertrophy of interstitial tissue, spermatogenesis was almost completely blocked. The sexual behaviour and the body appearance of experimental animals was typical for castrates.     

Induction of early rutting in male red deer (Cervus elaphus) by melatonin and its dependence on LHRH

Eight red deer stags, 2 control, 3 control-immunized (i.e. a low titre of LHRH antibodies after active immunization 2 years earlier) and 3 superior cervical ganglionectomized, were given a s.c. implant of melatonin in May at the nadir of the sexual cycle; 5 other stags remained untreated. All the melatonin-treated animals shed the velvet-like skin from the antlers in June or July at least 1 month before the untreated controls, and had an early increase in blood plasma testosterone concentrations. The treated stags were also precocious in the development of rutting behaviour, although this inductive effect was blocked dramatically in the control-immunized stags after a booster immunization against LHRH; these animals failed to show any further reproductive development and cast their antlers. It is concluded that continuous exposure to melatonin in early summer will induce premature seasonal testicular development, an effect dependent on the secretion of LHRH, and similar to that produced by exposure to short daylengths.     

Seasonal changes in plasma leptin concentration related to antler cycle in Iberian red deer stags

The aim of this study is to describe the leptin cycle in male Iberian red deer (Cervus elaphus hispanicus) and relate it to antler and testosterone cycles. An additional aim is to assess the relationship between the plasma leptin concentration during antlers’ growth and their final size. Therefore, blood from 21 Iberian red deer males was sampled monthly to analyse leptin and testosterone. At the same time the deer were weighed and their body condition was assessed. The length of antlers was measured every 2 weeks and, after casting, their final length and perimeters were taken. Leptin showed a seasonal cycle, with a peak in June that decreased as testosterone increased. Low values were observed in autumn, winter and early spring. The relationship observed between leptin and body mass or body condition score was different in spring, when plasma testosterone concentration is low, than in autumn, when testosterone increases. Leptin peak amplitude was positively related to final antler size. In conclusion, the relationship between leptin and body mass and body condition score changes through the year, possibly due to the influence of androgens and photoperiod. There was a positive relationship between plasma concentration of leptin during antler growth and final antler length.     

Effects of environmental conditions, human activity, reproduction, antler cycle and grouping on fecal glucocorticoids of free-ranging Pampas deer stags (Ozotoceros bezoarticus bezoarticus)

In this study, a commercial enzyme immunoassay (EIA) was validated in detecting glucocorticoids in Pampas deer feces, in order to investigate the influence of several factors on the adrenocortical function. Fecal samples, behavioral data and information concerning male grouping and antlers status were collected at a monthly basis during a 1 year period from free-ranging stags living at Emas National Park, Brazil (18 degrees S/52 degrees W). The results revealed that concentrations of fecal glucocorticoids in winter were significantly higher than those corresponding to spring and summer. In addition, dry season data presented higher levels than during the wet season. Significant difference was found between fecal levels of breeding stags in summer and nonbreeding stags, whereas no difference was observed between breeding stags in winter and nonbreeding stags. On the other hand, males from areas with frequent human disturbance exhibited higher glucocorticoid concentrations and flight distances than individuals from areas of lower human activity. Males with antlers in velvet had elevated levels compared with animals in hard antler or antler casting. Also, we found that glucocorticoid levels were higher in groups with three or more males than in groups with only one male. The flight distances showed positive correlation with fecal glucocorticoid. These data indicate that fecal glucocorticoid provides a useful approach in the evaluation of physiological effects of environment, inter-individuals relationship and human-induced stressors on free-ranging Pampas deer stags.     

Testosterone and estradiol concentrations in serum, velvet skin, and growing antler bone of male white-tailed deer

The growth and mineralization of antlers correlate with the seasonal variation of serum androgens. Whereas seasonal levels of testosterone (T) in plasma are well established, steroid concentrations have not yet been determined in the tissues of growing antlers. Therefore, RIA was used to determine T and 17beta estradiol (E2) in serum, and three areas (tip, middle, and base) of the antler bone and the antler skin, called velvet. Blood and antler tissues of white-tailed deer (Odocoileus virginianus) were collected from May to August. The difference between levels of T and E2 among the sites was calculated using the square root transformation followed by a mixed model analysis with individual deer and an interaction of individual and year (individual(*)year) as a random factor. Concentrations of T in serum (799+/-82 pg/ml) were higher than T values in the velvet (589+/-58 pg/ml, P<0.01) and in the antler bone (538+/-58 pg/ml, P<0.001). Estradiol concentrations differed among antler tissues and serum (P<0.001) and between years (P<0.01). Estradiol concentrations in serum (25+/-25 pg/ml) were consistently lower than those in antler bone (208+/-11 pg/ml, P<0.001) and velvet (150+/-12 pg/ml, P<0.001). The E2:T ratio in serum was 1:10-60. The same ratio for the antler bone was only 1:2-3 and for the velvet 1:3.5. It is concluded that higher T and lower E2 concentrations found in plasma, as compared to antler bone or antler velvet, may indicate a partial metabolism of systemic androgens into estrogens xin the tissues of growing antlers.     

Testosterone in tropical birds: effects of environmental and social factors

Previous investigations suggest that male tropical birds have lower plasma testosterone concentrations than northern latitude species. To test whether this generalization is valid, we analyzed all currently available plasma testosterone data of tropical birds. We focused on peak breeding testosterone levels using phylogenetic and conventional statistics. Explanatory variables considered were social mating system, type of territoriality, breeding season length, and altitude. On average, tropical birds had lower mean peak testosterone levels than northern temperate birds. However, in several tropical species, testosterone levels were well within the range of northern latitude birds. Without controlling for phylogeny, breeding season length, type of territoriality, and altitude explained a significant proportion of the variance in testosterone levels. The shorter the breeding season, the higher the testosterone levels. Tropical birds that defend a breeding season territory had higher testosterone levels than birds that were year-round territorial or colonial, and testosterone levels were positively correlated with altitude. When controlling for phylogeny, only breeding season length predicted testosterone levels. In conclusion, we propose to refine previous notions of low plasma testosterone levels in tropical birds: short breeding seasons and perhaps environmental conditions at high altitudes precipitate conditions under which high testosterone levels are beneficial in the tropics.     

Variation in fecal testosterone levels, inter-male aggression, dominance rank and age during mating and post-mating periods in wild adult male ring-tailed lemurs (Lemur catta)

In primate species exhibiting seasonal reproduction, patterns of testosterone excretion in adult males are variable: in some species, peaks correlate with female receptivity periods and heightened male-male aggression over access to estrous females, in others, neither heightened aggression nor marked elevations in testosterone have been noted. In this study, we examined mean fecal testosterone ( f T) levels and intermale aggression in wild adult male ring-tailed lemurs residing in three groups at Beza Mahafaly Reserve, Madagascar. Results obtained from mating and post-mating season 2003 were compared to test Wingfield et al. [1990. Am Nat 136:829-846] "challenge hypothesis", which predicts a strong positive relationship between male testosterone levels and male-male competition for access to receptive females during breeding season. f T levels and rates of intermale aggression were significantly higher during mating season compared to the post-mating period. Mean f T levels and aggression rates were also higher in the first half of the mating season compared with the second half. Number of males in a group affected rates of intermale agonism, but not mean f T levels. The highest-ranking males in two of the groups exhibited higher mean f T levels than did lower-ranking males, and young males exhibited lower f T levels compared to prime-aged and old males. In the post-mating period, mean male f T levels did not differ between groups, nor were there rank or age effects. Thus, although male testosterone levels rose in relation to mating and heightened male-male aggression, f T levels fell to baseline breeding levels shortly after the early mating period, and to baseline non-breeding levels immediately after mating season had ended, offsetting the high cost of maintaining both high testosterone and high levels of male-male aggression in the early breeding period.     

Effect of sex and prior exposure to a cafeteria diet on the distribution of sex hormones between plasma and blood cells

It is generally assumed that steroid hormones are carried in the blood free and/or bound to plasma proteins. We investigated whether blood cells were also able to bind/carry sex-related hormones: estrone, estradiol, DHEA and testosterone. Wistar male and female rats were fed a cafeteria diet for 30 days, which induced overweight. The rats were fed the standard rat diet for 15 additional days to minimize the immediate effects of excess ingested energy. Controls were always kept on standard diet. After the rats were killed, their blood was used for 1) measuring plasma hormone levels, 2) determining the binding of labeled hormones to washed red blood cells (RBC), 3) incubating whole blood with labeled hormones and determining the distribution of label between plasma and packed cells, discounting the trapped plasma volume, 4) determining free plasma hormone using labeled hormones, both through membrane ultrafiltration and dextran-charcoal removal. The results were computed individually for each rat. Cells retained up to 32% estrone, and down to 10% of testosterone, with marked differences due to sex and diet (the latter only for estrogens, not for DHEA and testosterone). Sex and diet also affected the concentrations of all hormones, with no significant diet effects for estradiol and DHEA, but with considerable interaction between both factors. Binding to RBC was non-specific for all hormones. Estrogen distribution in plasma compartments was affected by sex and diet. In conclusion: a) there is a large non-specific RBC-carried compartment for estrone, estradiol, DHEA and testosterone deeply affected by sex; b) Prior exposure to a cafeteria (hyperlipidic) diet induced hormone distribution changes, affected by sex, which hint at sex-related structural differences in RBC membranes; c) We postulate that the RBC compartment may contribute to maintain free (i.e., fully active) sex hormone levels in a way similar to plasma proteins non-specific binding.