Diurnal variations of serum testosterone levels in intact and gonadectomized male and female rhesus monkeys.

A radioimmunoassay for serum testosterone which does not require chromatographic separation was used to measure the diurnal variations in intact and orchidecomized males and intact and ovariectomized females. The intact male rhesus monkey shows a distinctive diurnal variation in serum levels of testosterone characterized by lower values during the day and a marked increase in the early evening (1900-2200 hr). The testosterone levels remain high throughout most of the lights-off period in the intact male. In contrast to the intact male, the markedly lowered serum levels of testosterone in the orchidectomized male were higher during the day and consistently showed a nadir during the early evening (2000-2200 hr). The evening nadir of testosterone levels was 51.0% lower than the 24-hr mean whereas the maximum serum level was 46.4% higher. A similar circadian pattern of testosterone was seen in both the intact and ovariectomized females. The testosterone values were higher during the day and consistently showed a nadir during the early evening. These results suggest that the adrenal secretion of testosterone varies in a diurnal pattern characterized by an early evening nadir. This adrenal pattern is overshadowed by a much larger gonadal rhythm in the intact male.     

性腺甾体激素对雌,雄大鼠下丘脑血管升压素mRNA水平的影响

实验用１０－１１周龄经阉割的雌、雄Ｓｐｒａｇｕｅ－Ｄａｗｌｅｙ大鼠进行。以３末端异羟基洋地黄毒甙标记的２６个碱基长的寡核苷酸作为检测探针,用核酸斑点杂交技术检测大鼠下丘脑血管升压素ｍＲＮＡ水平。在假手术对照组,雄性大鼠下丘脑ＡＶＰｍＲＮＡ水平经雌性大鼠高４５％（Ｐ〈０．０５）,血浆渗透压高于雌性大鼠（Ｐ〈０．０５）。摘除卵巢的大鼠下丘脑ＡＶＰｍＲＮＡ深恶痛绝经假手术组雌性大鼠高３０％（Ｐ〈０．０５     

Early kinetics of antibody response to inactivated influenza vaccine

The aim was to examine the rapidity of haemagglutination inhibiting (HI) antibody response induced by immunization with a current inactivated trivalent influenza vaccine. Five to six sequential serum samples collected in autumn 1992 from each of 68 vaccinees in three age groups were studied for HI antibodies to ten influenza virus strains representing vaccine and epidemic viruses. Geometric mean titres, response rates and protection rates are presented. Response rates of > 70% were overall, but not until two weeks after the vaccination. Significant two- and four-day post-vaccination antibody responses were detected only occasionally. In previously vaccinated persons, average antibody titres to some of the viruses decreased during the first days after the vaccination. In the subsequent samples, the titres remained lower than in persons who were not vaccinated against influenza in preceding years. Protection against influenza infection may be frequently developed not until two weeks after vaccination. This has relevance to prophylactic administration of amantadine and rimantadine when an influenza A outbreak is imminent and the vaccination is late.     

Gender dependent effects of testosterone and 17β-estradiol on bone growth and modelling in young mice

This study examined the effects of estrogen (17β-estradiol) and testosterone on the growth of long bones in male and female mice, with and without gonadectomy. Weight and nose-to-tail length were determined at 3 weeks of age at time of gonadectomy, 7 days later at the onset of hormone therapy, and throughout the treatment period. Gonadectomized mice exhibited an initial weight gain during the pretreatment period but length was unaffected. Hormone treatment altered weight gain in surgical and intact animals in a gender- and hormone-dependent manner. Estradiol enhanced weight gain in intact mice, but inhibited weight gain in ovariectomized mice. Lower doses of estradiol increased weight gain in orchiectomized mice at early time points. Testosterone increased weight in intact females and males, but not in gonadectomized mice. Estradiol increased nose-to-tail length in intact females at early time points, but inhibited length in ovariectomized females at later times, and it decreased length in intact males. Testosterone increased length in normal females and normal males. Serum Ca was unaffected by ovariectomy, but orchiectomy resulted in decreased levels. Estradiol reduced serum Ca in gonadectomized animals; serum Ca was increased by estradiol treatment in intact females. Changes in tibial bone weight, ash weight and mineral composition, and relative sizes of epiphyseal and metaphyseal bone were gender-, gonadectomy- and hormone-specific. Bone weight was greater in ovariectomized mice. Ash weight per bone was comparable, but there was an increase in Ca and P content with ovariectomy. Estradiol increased bone weight, ash content, and bone Ca and P in ovariectomized and intact females. Orchiectomy alone did not alter bone weight, ash content, or Ca and P, but orchiectomized mice were sensitive to estradiol; all parameters were increased in the orchiectomized animals treated with estradiol. Analysis of the ash content and Ca and P per mg bone, rather than per bone, demonstrated estradiol and testosterone alter net bone formation, but not the amount of mineral per unit bone. Ovariectomy increased hypertrophic cartilage. While estradiol did not alter tibial area in ovariectomized mice, it caused an increase in intact females. The total amount of growth plate cartilage in ovariectomized animals was decreased by estradiol to levels typical of intact animals due to a greater decrease in the hypertrophic cartilage in the ovariectomized mice, as well as a greater increase in metaphyseal bone area. Testosterone had no effect on these parameters in the females. Orchiectomy decreased the amount of growth plate cartilage, but increased the hypertrophic zone. Estradiol increased growth plate cartilage in intact male mice, but decreased it in orchiectomized mice. This difference was also seen in the hypertrophic zone. Total growth plate cartilage and hypertrophic cartilage were increased by testosterone in intact males, whereas metaphyseal and epiphyseal bone area were decreased. The results show for the first time that there is a gender-specific response in both male and female mice to both estradiol and testosterone, whether or not the animals have been gonadectomized. For many parameters, orchiectomized mice behave like females in response to both sex steroids, indicating that the male gonad is needed for mouse bone to exhibit the male phenotypic response to estradiol and testosterone.     

Natural antibodies in healthy adults.

The serum of 100 adults living in Budapest was examined for isohaemagglutinin titre with haemaglutination, for staphylococcal-antitoxin titre with haemolysis inhibition and for bacterial antibody titre against 17 different groups of bacteria with passive haemagglutination. Antibody levels in males, except for certain bacterial antibodies, were somewhat lower than in females. The antibody titres, especially in men, decreased gradually from 20 to 50 years of age and were usually lower in Rh negative than in Rh positive persons.     

Estradiol influences on pattern of gonadotropin secretion in bovine males during the period of changed responses to estradiol feedback in age-matched females

When ovaries are removed prior to puberty, administration of exogenous 17 beta-estradiol (E2) decreases concentrations of luteinizing hormone (LH) below that of ovariectomized heifers receiving no E2. Subsequent to the time age-matched intact heifers reach puberty, exogenous E2 increases secretion of LH in ovariectomized heifers above that of ovariectomized heifers receiving no E2. The hypothesis that E2 would inhibit gonadotropin secretion in bovine males during the time E2 no longer inhibited gonadotropin secretion in age-matched bovine females was tested. Males (n = 12) and females (n = 12) were gonadectomized at 241 +/- 3 days of age, and half of each sex (6 males and 6 females) were administered a 27-cm E2 implant. An additional group of males (n = 6) and females (n = 6) remained intact and served as controls. Blood samples were collected (to quantify LH and follicle-stimulating hormone [FSH]) from all animals at 15-min intervals for 24 h at 1, 7, 13, 17, 21, 25, 29, 33, 37, and 43 wk after gonadectomy. Additional blood samples were collected twice weekly from control females to monitor progesterone and onset of corpus luteum function (451 days of age). E2 inhibited frequency of pulses of LH (p less than 0.01) and decreased mean concentration of LH and FSH (p less than 0.01) at Week 1 in gonadectomized males treated with E2 compared to gonadectomized males not administered E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian function in Holstein cows immunized against pregnant mare serum gonadotrophin

Six Holstein-Friesian cows were immunized against pregnant mare serum gonadotrophin (PMSG) using Freunds' adjuvant during the mid-luteal phase of the estrous cycle. Antibody response was maintained by five booster immunizations at 2- to 3-wk intervals. Four cows were treated with a single intramuscular injection of PMSG (2350 I U) 107 d after primary immunization. Cloprostenol (500 ug) was administered at 56 h and 72 h after the treatment with PMSG; the cows were inseminated three times at 12-h intervals starting 56 h after cloprostenol treatment. Five days after insemination, the animals were slaughtered and their reproductive organs were recovered to quantify the population of corpora lutea and unovulated follicles (>10 mm dia). Antibody titres and progesterone concentrations were determined from blood samples collected either on alternate days or twice a week. Initially, progesterone concentrations were measured in milk samples. All cows produced antibodies, and titres were elevated within 6 to 9 d following each booster immunization. After each boost, however, the antibody titres declined rapidly. Progesterone concentrations declined to below 1 ng/ml after two weeks of initial immunization and remained low throughout the study, except in one cow that ovulated on Day 75. All animals were observed to have large follicular cysts during this period. Treatment with PMSG induced a single ovulation in one cow. Ovulations were neither induced by PMSG nor observed in any of the other animals. In PMSG-treated animals, the mean number of large follicles (5.0) was greater than in those which were not treated (2.0). The results of this study suggest that low titres of antibodies against PMSG are sufficient to disturb ovarian activity, result in follicular cysts and block multiple ovulations in response to exogenous PMSG.     

Natural or hormone-induced sexual and social behaviors in the female brown lemming (Lemmus trimucronatus)

The behaviors of intact or ovariectomized, estradiol benzoate-treated or estradiol benzoate followed by progesterone-treated female brown lemmings were compared. Intact, diestrous females engaged in more social interactions with a male than did ovariectomized females (Experiment 1). In the first 5 min of a 1-hr mating exposure (Experiment 2, Test A) intact females in natural estrus engaged in more social and sexual behaviors than did ovariectomized females in estrogen-induced estrus. However, during the last 5 min of the 1-hr exposure (Test B) ovariectomized females receiving estrogen alone continued to show high levels of sexual activity with a male partner, while intact estrous females or females receiving estrogen followed by progesterone showed an apparent drop in sexual receptivity and an increase in aggressivity. Aggressive behaviors, as indexed by threat-leap behaviors on the part of the female may increase in the presence of progesterone. Declines in sexual activity, occurring within 1 hr of progesterone injection, were apparently dependent on the interaction of progesterone and copulatory events which may affect both the male and female.     

Potential contribution of prenatal estrogens to the sexual differentiation of mate preferences in mice

The neural mechanisms controlling sexual behavior are sexually differentiated by perinatal actions of gonadal hormones. We recently observed using female mice deficient in alpha-fetoprotein (AFP-KO) and which lack the protective actions of AFP against maternal estrogens, that exposure to prenatal estrogens completely defeminized their potential to show lordosis behavior in adulthood. Therefore, we determined here whether mate preferences were also affected in female AFP-KO mice. We observed a robust preference for an estrous female over an intact male in female AFP-KO mice, which were ovariectomized in adulthood and subsequently treated with estradiol and progesterone, whereas similarly treated WT females preferred the intact male over the estrous female. Gonadally intact WT males preferred the estrous female over the male, but only when visual cues were blocked by placing stimulus animals behind opaque partitions. Furthermore, when given the choice between an intact male and a castrated male, WT females preferred the intact male, whereas AFP-KO females showed no preference. Finally when given the choice between an estrous female and an ovariectomized female, WT males preferred the estrous female whereas AFP-KO females preferred the ovariectomized female or showed no preference depending on whether they could see the stimulus animals or not. Taken together, when AFP-KO females are tested under estrous conditions, they do not show any male-directed preferences, indicating a reduced sexual motivation to seek out the male in these females. However, they do not completely resemble males in their mate preferences suggesting that the male-typical pattern of mate preferences is not solely organized by prenatal estrogens.     

Prolactin as a factor in the uterine response to progesterone in rabbits

The direct effect of prolactin on uteroglobin production and on uterine endometrial oestrogen and progesterone receptor concentrations was tested by using ovariectomized rabbits (at least 12 weeks) treated with prolactin; prolactin + progesterone; prolactin + oestradiol + progesterone; oestradiol + progesterone; or progesterone alone. Prolactin treatment produced a significant (P less than 0.05) increase in the concentration of cytosolic oestrogen and progesterone receptors, restoring the concentrations to values found at oestrus. However, the concentration of nuclear receptors remained low. In the remaining treatment categories there was no significant (P greater than 0.05) increase in the concentration of oestrogen and progesterone receptors compared with those in ovariectomized controls. However, the sequential treatment of ovariectomized animals with prolactin + progesterone stimulated uteroglobin production to a concentration equal to that found in intact rabbits on the 5th day of pregnancy. This was not achieved by prolactin or progesterone alone or with oestradiol. These results suggest that prolactin acts as an essential factor in the rabbit uterine response to progesterone, perhaps by the modulation of progesterone receptor activity.     

Exposure to ovarian steroids elicits a female pattern of plasma cortisol levels in castrated male macaques.

Our recent observations (1) that there is a difference in circadian patterns of plasma cortisol levels between male and female macaques and (2) that after gonadectomy these differences in the patterns and in the levels of cortisol were reduced prompted us to investigate how 17 beta-estradiol (E2) and progesterone affect cortisol secretion in orchidectomized male rhesus macaques. Five male macaques, castrated as adults, were implanted subcutaneously with segments of silastic tubing filled with E2 and with progesterone in a manner such that the levels and the sequence of these hormones mimicked those that occur during the menstrual cycle of intact female macaques. Since previous studies had shown that the difference in cortisol patterns was due to higher levels in females during the day, these studies were conducted from 0800 to 2000 hours. Blood samples were collected in an adjacent room at 15-minute intervals. Separate trials were conducted 2 weeks after E2 was implanted and levels were 110 +/- 14 pg/ml and again 2 weeks later after progesterone was implanted and E2 levels were 59 +/- 15 pg/ml; progesterone levels averaged 4.0 +/- 0.65 ng/ml. Mean plasma concentrations of cortisol (microgram/100 ml) for the 12-hour period were three-fold higher in orchidectomized males treated with E2 (17.2) and with E2 + progesterone (18.0) than in intact males (4.9). Levels in males treated with ovarian steroids were double that (8.5 micrograms/100 ml) observed for intact females.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood risk factor metabolites associated with heart disease and myocardial fatty acids in copper-deficient male and female rats

Intact and castrated males and intact and ovariectomized female rats were fed a copper-deficient diet in order to establish whether the protection provided in females against cardiovascular pathology and mortality is due to endogenous sex hormones, and different levels of blood lipids and/or myocardial fatty acids. Seventy-three male and female rats were assigned to a copper-deficient diet (0.6 micrograms of copper/g diet) containing 62% fructose for 8 weeks. Twelve of the male rats underwent castration and 12 of the females were ovariectomized. All animals exhibited high levels of plasma cholesterol, triglycerides, and uric acid, which were neither affected by the sex of the rat nor by the surgical treatment. The composition of fatty acids of the myocardium was similar in males and females. Except for those animals that were sacrificed by us, all other male rats died of heart pathology. In contrast, none of the female rats exhibited heart pathology and none died of the deficiency. It is suggested that heart pathology and mortality in copper deficiency are sex related and not due to high levels of plasma cholesterol, triglycerides, and uric acid or to differences in myocardial fatty acid composition.     

Differential hormonal control of aggression and sexual behavior in female Syrian hamsters

These experiments were designed to test the effects of chronic estradiol treatment on aggression and sexual behavior in female hamsters. Isolated female hamsters were ovariectomized and tested for their behavioral responses to a group-housed, ovariectomized female hamster (aggression test) and a group-housed, intact male hamster (sexual behavior test). Following these baseline tests, the experimental females were implanted sc with Silastic capsules containing different concentrations of estradiol (100, 25, 10, or 0%) diluted with cholesterol and retested 3, 7, 10, and 14 days after implantation. High levels of aggression were observed on the baseline test, with no changes in aggression toward an intruder female observed for any implant group on subsequent tests. Despite these high levels of aggression toward another female, most of the estradiol-treated females (80% at 14 days) were sexually responsive in the presence of a male. There was no effect of Silastic estradiol concentration on sexual behavior, even though a range of serum estradiol levels (39–105 pg/ml) resulted. Lordosis latencies decreased and lordosis durations increased over the extent of estradiol treatment. Seventeen days after Silastic implantation, all females were injected with progesterone and retested. Estradiol-treated females showed an extreme reduction in aggression toward a stimulus female, as well as a further stimulation of sexual behavior after progesterone treatment. High levels of aggression in cholesterol-treated females (0% estradiol) were maintained even after progesterone injection, and these females never displayed any sexual responsivity. These results suggest that sexual behavior in the female hamster is sensitive to estradiol alone, whereas the inhibition of aggression requires the combination of estradiol plus progesterone.     

Effects of sex hormones on fulminant hepatitis in LEC rats: a model of Wilson's disease.

LEC rats, which have hereditary hepatitis and have recently been proposed as an animal model for Wilson's disease, were examined to determine the effects of sex hormones on fulminant hepatitis. After the rats had undergone ovariectomies or orchidectomies (castration) and were compared with intact rats, the age at the onset of fulminant hepatitis was not substantially altered but the survival rates decreased from 50% to 12.5% for females and 75% to 14.3% for males, indicating that sex hormones did not influence the occurrence of fulminant hepatitis but influenced mortality due to fulminant hepatitis. When testosterone was administered to the ovariectomized or orchidectomized rats, the survival rate increased to over 90% in both sexes. In contrast, estradiol did not affect the survival rate of either sex but affected the onset of fulminant hepatitis. That is, with the administration of estradiol, the age at which serum GPT activity reached its maximum was delayed 4 weeks in ovariectomized rats and 6 weeks in orchidectomized rats as compared with intact rats. A similar but somewhat weaker tendency appeared in rats given progesterone. The results of our study indicate that sex hormones have no effect on the rate of occurrence of hepatitis but affect the progression of hepatitis. In particular, testosterone increased the survival rate of rats with fulminant hepatitis, and exogenous estradiol delayed the onset of hepatitis for several weeks.     

Increased fat deposition in injured skeletal muscle is regulated by sex-specific hormones

Sex differences in skeletal muscle regeneration are controversial; comparisons of regenerative events between sexes have not been rigorously defined in severe injury models. We comprehensively quantified inflammation and muscle regeneration between sexes and manipulated sex-specific hormones to determine effects on regeneration. Cardiotoxin injury was induced in intact, castrated and ovariectomized female and male mice; ovariectomized mice were replaced with low- or high-dose 17-β estradiol (E(2)) or progesterone (P4). Extent of injury was comparable between intact mice, but females were more efficient in removal of necrotic debris, despite similar tissue levels of inflammatory cells and chemokines. Myofiber size during regeneration was equivalent between intact mice and after castration or ovariectomy (OVX) but was decreased (P < 0.001) in ovariectomized mice with high-dose E(2) replacement. Intermuscular adipocytes were absent in uninjured muscle, whereas adipocyte area was increased among regenerated myofibers in all groups. Interestingly, intermuscular fat was greater (P = 0.03) in intact females at day 14 compared with intact males. Furthermore, castration increased (P = 0.01) and OVX decreased adipocyte accumulation. After OVX, E(2), but not P4, replacement decreased (P ≤ 0.03) fat accumulation. In conclusion, sex-dependent differences in regeneration consisted of more efficient removal of necrosis and increased fat deposition in females with similar injury, inflammation, and regenerated myofiber size; high-dose E(2) decreased myofiber size and fat deposition. Adipocyte accumulation in regenerating muscle was influenced by sex-specific hormones. Recovery following muscle injury was different between males and females, and sex-specific hormones contributed to these differences, suggesting that sex-specific treatments could be beneficial after injury.     

Gender differences in steroid modulation of angiotensin II-induced protein kinase C activity in anterior pituitary of the rat

To investigate whether the various steroid hormones can modulate the basal and angiotensin II-induced protein kinase C (PKC) activity in the anterior pituitary of the rat, female and male intact and ovariectomized female Wistar rats were treated in vivo with estradiol (E2), progesterone (P), dehydroepiandrostendione sulfate (DHEA-S), and pregnenolone sulfate (PREG-S). Estradiol caused the increase of basal PKC activity in intact and ovariectomized females, but did not change the enzyme activity in males. In ovariectomized animals the increase of PKC activity was lower than in intact females. Progesterone decreased PKC activity only in intact animals. DHEA-S strongly enhanced activity of PKC in ovariectomized females. Pregnenolone sulfate did not significantly change PKC function of all studied groups. Incubation with AngII enhanced the PKC activity in intact (without steroid treatment) animals of both genders. In females, AngII and estradiol together rise the PKC-stimulated phosphorylation in greater degree than used separately. Treatment with other investigated steroids reduced the effect of AngII. In intact males every examined hormone turned back the stimulatory effect of AngII on PKC activity. These data suggest that gender differences in PKC activity are likely related to hormonal milieu of experimental animals and may depend in part on the basic plasma level of estrogens.     

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: II. Responses to acute stress in the laboratory.

Circulating concentrations of plasma corticosterone and gonadal steroids were measured in intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season.     

Blood concentrations of gonadotrophins, prolactin and gonadal steroids in males and in non-pregnant and pregnant female African elephants (Loxodonta africana)

No seasonal variation in any of the hormones measured was apparent in males or females. Testosterone levels in males increased around puberty (10-11 years) and remained significantly higher in adult than prepubertal males. This was not accompanied by any significant change in levels of LH, FSH or prolactin. In non-pregnant females there was no apparent difference in levels of LH, FSH or prolactin with age. There was a significant increase in progesterone around puberty (12 years) but there was considerable overlap in values between prepubertal and adult females. During pregnancy, progesterone levels were significantly higher than in non-pregnant females with maximum levels occurring at mid-pregnancy (9-12 months). However, there was considerable overlap in values between non-pregnancy and pregnancy. Concentrations of LH and FSH decreased significantly during mid-pregnancy while prolactin levels increased dramatically during pregnancy; after 7 months of gestation until term levels were always at least 8 ng/ml greater than in any non-pregnant female. It is suggested that this consistent increase in plasma/serum levels of prolactin can be used to diagnose pregnancy in the elephant.     

Intracellular progesterone receptors are differentially regulated by sex steroid hormones in the hypothalamus and the cerebral cortex of the rabbit

The aim of this study was to examine the role of sex steroid hormones in the regulation of intracellular progesterone receptors (PR) in the rabbit central nervous system. We determined PR concentration in cytosol preparations from the hypothalamus, the frontal, tempo-parietal and occipital cortex, by using the specific binding of the synthetic progestin [³H]ORG 2058. PR concentration was higher in the hypothalamus of intact adult females than in that of adult males and prepubertal females, whereas no significant differences were observed in the cerebral cortex of these animals. PR concentration was similar in the three cortical regions analyzed, indicating a homogeneous distribution of PR in the cerebral cortex. The administration of estradiol to ovariectomized animals increased PR concentration in the hypothalamus but not in the cortex. The administration of progesterone to ovariectomized rabbits did not modify PR concentration in any region, however when progesterone was administered after estradiol, it induced a significant diminution in hypothalamic PR concentration without effects in the cortex. These findings suggest that in the rabbit, PR are estrogen regulated in the hypothalamus but not in the cerebral cortex. In the latter, PR are not regulated by progesterone, whereas in the former the estrogen-induced PR are down-regulated by progesterone. Interestingly, hypothalamic PR constitutively expressed in ovariectomized animals are progesterone-insensitive.     

Immunocytochemical detection of estrogen and progesterone receptors in the rabbit submandibular gland.

Rabbit submandibular glands produce secretions involved in olfactory communication. The histology of these glands and their secretory activity are: sexually dimorphic; vary across the female reproductive cycle; and are modified by gonadectomy. This suggests that gonadal steroids regulate the structure and function of such glands. To further support this idea we assessed by immunocytochemistry the presence of estrogen and progesterone receptors in male and female rabbit submandibular glands. Immunoreactivity was detected only in the nucleus of acini cells. The number of estrogen receptor-immunoreactive cells/field varied among estrus (26 +/- 6; mean +/- S.E.), ovariectomized (19 +/- 2), and ovariectomized-estrogen-treated animals (13 +/- 3). Intact males showed a significantly smaller number of estrogen receptor-immunoreactive cells/field (12 +/- 1) than estrous females. Interestingly, progesterone receptor-immunoreactive cells were more abundant in estrous (32 +/- 7) than in ovariectomized animals (7 +/- 1). Estradiol benzoate (5 micrograms daily for 5 days) increased the number of progesterone receptor-immunoreactive cells/field in ovariectomized females (17 +/- 1). Intact males showed fewer progesterone receptor-immunoreactive cells/field (16 +/- 2) than estrous females. Results show that the rabbit submandibular gland is a target for estrogen and progesterone and support the idea that these hormones participate in regulating the physiology of this gland.