Role of testosterone in the early stage of spermatocytogenesis in rats.

The role of testosterone in the early stage of spermatocytogenesis was investigated in newborn rats. The testes of rats, either 0 or 6 days of age, were implanted into those of hypophysectomized adult rats that had or had not been injected with testosterone propionate (TP) after hypophysectomy and also into those in intact adult rats. All the animals were autopsied 17 or 11 days later when the implanted testes reached 17 days of age. The implanted testes were examined for cellular components in the seminiferous tubules. In an additional experiment, newborn rats were injected with TP or cyproterone acetate, an antagonistic substance against androgen, daily for the first 17 days of life and examined for testes. Proliferation of supporting cells and development of seminiferous tubules were less remarkable in the testes of newborn rats which had been implanted into the testes of hypophysectomized rats than in those which had been implanted into the testes of intact adult rats. Proliferation of supporting cells was not stimulated by TP, but development of seminiferous tubules was slightly promoted. Progress in spermatocytogenesis from gonocytes to pachytene primary spermatocytes was observed in the testes of newborn rats which had been implanted into the testes of hypophysectiomized rats. It was not so marked after injection with TP. These results suggested that testosterone might have stimulated development of seminiferous tubules and maturation of spermatocytes in the early stage of spermatocytogenesis by its synergistic action with a gonadotropin, possible follicle-stimulating hormone.     

Molecular control of rabbit follicular testosterone production. Role of protein and RNA after stimulation with luteinizing hormone.

The time and dose dependence of the relationship between uptake of labelled precursors into protein and RNA and production of testosterone by rabbit follicles was examined. Although testosterone production was stimulated by luteinizing hormone at concentrations between 0.1 and 10 microgram/ml, the uptake of [3H]leucine into protein was significant only when the concentration of luteinizing hormone was greater than 2.5 microgram/ml. Increased production of testosterone was observed within 15 min of stimulation with luteinizing hormone whereas uptake of [3H]leucine was only significant at 90 min. Puromycin (40 microgram/ml) and cycloheximide (10 microgram/ml) in the presence of luteinizing hormone inhibited the synthesis of both testosterone and protein. However, lower concentrations of puromycin (0.1, 1 and 10 microgram/ml) and cycloheximide (1 microgram/ml) had no effect on luteinizing hormone-induced testosterone production but significantly inhibited protein synthesis by 58, 37, 31 and 71%, respectively. Actinomycin D (20, 80 and 160 microgram/ml) alone and in combination with 5 microgram luteinizing hormone/ml severely inhibited uptake of [3H]uridine into RNA without affecting testosterone production. However, with 1 microgram actinomycin/ml, testosterone production was significantly (P less than 0.01) greater than in the presence of luteinizing hormone alone. These results cast doubt on the obligatory role of RNA and protein synthesis in rabbit ovarian follicular steroidogenesis.     

Testosterone implanted in the preoptic area of male Japanese quail must be aromatized to activate copulation

Intracranial implantation of minute pellets of gonadal steroids was combined with aromatase inhibitor treatment to determine if aromatization within the preoptic area (POA) is necessary for androgens to activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, implantation of pellets of testosterone propionate (TP) or estradiol benzoate (EB) in the POA of castrated males restores male-typical copulatory behavior. In Experiment 1, adult male castrated quail were implanted intracranially with 200-micrograms pellets of equimolar mixtures of crystalline TP + cholesterol (CHOL), TP + 1,4,6-androstatriene-3,17-dione (ATD, an aromatase inhibitor), EB + ATD, or CHOL and behavior-tested with intact males and females. Copulation was stimulated by POA implants containing TP or EB (three of six CHOL + TP males and two of seven ATD + EB males copulated vs zero of four CHOL males), but copulation was not inhibited by combining ATD with TP (three of four ATD + TP males copulated). In Experiment 2, adult male castrated quail were injected systemically with ATD or oil for 6 days prior to and 14 days after intracranial implantation of 200-micrograms pellets containing the same amounts of TP or EB as in Experiment 1. The ATD injections completely blocked copulatory behavior in males with TP implants in the POA such that ATD/TP and Oil/TP mount frequencies differed significantly, but failed to block copulation in males with EB implants in the POA (proportions of males copulating were ATD/EB, 6/8; ATD/TP, 0/6; Oil/TP, 4/7). The cloacal foam gland, an androgen-sensitive secondary sex character, was unaffected by the dose of ATD used. We conclude that activation of copulatory behavior by TP implants in the POA is not due to nonspecific effects of high local testosterone concentrations but rather to aromatization. These results support the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to activation of male-typical copulatory behavior.     

Delay in the age of balano-preputial skinfold cleavage and alterations in serum profiles of testosterone, 5 alpha-androstane-3 alpha,17 beta-diol, and gonadotropins in adult rats treated during puberty with luteinizing hormone releasing hormone

Previous work has shown that chronic treatment of intact, immature male rats with luteinizing hormone releasing hormone (LHRH) decreases sex accessory gland weights and results in retardation of the normal developmental increase in the ratio of serum testosterone (T)/5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-Diol) via an apparent enhancement of testicular 5 alpha-reductase or 3 alpha-hydroxysteroid oxidoreductase activities. In the present work, androgen dependent balano-preputial skinfold cleavage was significantly delayed by approximately one week in intact, immature male rats which were treated daily for two weeks with either 1.0 micrograms, 2.5 micrograms or 5.0 micrograms of LHRH during a discrete phase of pubertal development (28-41 days of age). In intact, adult (62 day old) animals which received LHRH treatments during pubertal development, serum T concentrations and sex accessory gland weights were reduced compared to control animal values. Serum 3 alpha-Diol content in the adult rats was either unaltered or increased significantly depending on the LHRH dosage employed during sexual development. Serum luteinizing hormone concentrations were not different between control and LHRH-pretreated adult rats whereas the highest dosage of LHRH employed (5.0 micrograms) during puberty resulted in a significant elevation of adult serum follicle stimulating hormone levels. It is suggested that chronic LHRH treatment of the male rat during puberty results in a perturbation in testicular androgen biosynthetic activities and an impairment of pituitary-testicular hormone feedback mechanisms which persist at least through early adulthood.     

Dihydrotestosterone promotes fighting behavior of female mice

Female mice injected once with dihydrotestosterone (DHT) or testosterone propionate (TP) on the day of birth fought sooner following the commencement of chronic exposure to testosterone in adult life than did animals administered only the oil vehicle at birth. Also, adult nonperinatally androgenized females fought in response to chronic exposure to DHT or TP. It appears that DHT shares with TP the ability both to sensitize the perinatal CNS to testosterone and to activate fighting behavior in the adult.     

Effect of testosterone on n-methyl-d, l-aspartate-induced growth hormone secretion in male swine

Previous research from our laboratory demonstrated that n-methyl-d, l-aspartate (NMA), a potent agonist of glutamate, increased growth hormone (GH) secretion in barrows and boars. To determine if testosterone modulates NMA-induced GH secretion, Poland China x Yorkshire swine were challenged with NMA in a model that compared GH responses in boars with those of barrows or barrows treated with testosterone propionate (TP). Boars and barrows weighing 112.6+/-1.4 kg (mean +/- SE) were fitted with indwelling jugular vein catheters. Barrows (n = 16) were given i.m. injections of TP (25 mg in corn oil) twice daily from d 0 to d 6. Boars (n = 16) and control barrows (n = 15) received twice daily injections of corn oil. On d 6, blood was sampled every 15 min for 4 h. Two h after sampling began, all animals received an i.v. injection of NMA at a dose of 2.5 mg/kg body weight. Mean testosterone concentrations (ng/ml serum) were similar (P > .1) for boars (8.1+/-0.8) and barrows receiving TP (7.3+/-0.3), but were greater in both cases (P < .05) than for barrows receiving corn oil (.2+/-.01). Prior to NMA injections, mean GH concentrations were similar (P > .1) among groups and averaged 2.7+/-.2 ng/ml serum across treatments. Serum concentrations of GH after NMA increased (P < .05) similarly among groups and averaged 6.3+/-0.3 ng/ml across treatments during the 2-h period after injection. These results were not supportive of a role for testosterone as a modulator of NMA-induced GH secretion in male swine.     

During seminiferous tubule maturation testosterone and synergistic action of FSH with estradiol support germ cell survival while estradiol alone has pro-apoptotic effect

During establishment of spermatogenesis at the prepubertal age, an early germ cells apoptotic wave occurs likely aimed to remove abnormal germ cells and to maintain a proper cell number ratio between maturating germ cells and Sertoli cells. Here we assessed Sertoli and germ cell apoptosis in relation to morphological parameters of Sertoli cell maturation in neonatal rats under the influence of testosterone, estradiol and FSH given alone or in combinations. From postnatal day (PND) 5th to 15th male rats were daily injected with: 1) 2.5 mg of testosterone propionate (TP), or 2) 12.5 microg of 17beta-estradiol benzoate (EB), or 3) TP+EB, or 4) 7.5 IU of human purified FSH (hFSH), or 5) hFSH+EB or solvents (control-C). Autopsy was performed on PND 16th. Sertoli cell nuclei area and incidence of seminiferous tubule lumen formation (LF) were taken as markers of Sertoli cell maturation. Sertoli and germ cell apoptosis was assessed using TUNEL method. In comparison with C, the area of Sertoli cell nuclei was significantly reduced after EB (25.7+/-2.0 vs. 30.9+/-1.6 microm2 for C, p<0.001) and increased after hFSH+EB (33.1+/-2.3 microm2, p<0.05). Incidence of LF was completely arrested by steroid hormone treatments given separately, significantly inhibited after TP+EB (median: 0.0%, vs. 2.0% for C p<0.05) and significantly enhanced after hFSH+EB (median: 51.0%, p<0.001). hFSH alone did not influence LF. Incidence of TUNEL positive Sertoli cells significantly increased after EB (median: 2.9% vs. 0.5% for C, p<0.05) or TP+EB (median: 2.2%, p<0.01) and was not affected by other treatments. Incidence of TUNEL positive germ cells increased significantly after EB alone (median: 4.4% vs. 2.5%, for C, p<0.01 ) and was significantly decreased by hFSH+EB (median: 0.5%, p<0.01). CONCLUSIONS: 1) Administration of testosterone or estradiol to immature rats inhibits Sertoli cell maturation. 2) Estradiol stimulates Sertoli and germ cell apoptosis while testosterone has no effect. 3) Testosterone eliminates estradiol--induced germ cell apoptosis when both hormones act in concert. 4) FSH in concert with estradiol, but neither one of the hormone alone, accelerate Sertoli cell differentiation and effectively inhibit germ cell apoptosis. 5) During seminiferous tubule maturation testosterone and the synergistic action of FSH with estradiol support germ cell survival while estradiol alone has an inhibitory, pro-apoptotic effect.     

Differential sensitivity of mounting and lordosis control systems to early androgen treatment in male and female hamsters.

The effects of early testosterone propionate (TP) treatment on the adult sexual behavior of hamsters were investigated in two experiments. In Expt. I, male and female pups were injected with oil vehicle or 1, 5, 10, 50, 100, or 250 μg of TP 24 hr after birth. In Expt. II, males and females received either oil or 10 μg of TP on the day of birth (Day 1), Day 3, Day 5, Day 7, or Day 9. At 70 days of age all animals were gonadectomized and 10 days later tested for lordosis behavior after estrogen and progesterone priming. One week after the test for female behavior all females began receiving 500 μg of TP each day and were tested for mounting and intromission behavior three times at 10 day intervals. Lordosis behavior was inhibited by as little as 5 μg of TP given 24 hr after birth. In males this dose produced the maximal effect, but in females increasing dosages resulted in a proportional decrease in lordosis duration. One μg of TP neonatally facilitated later mounting and intromission behavior in females and 250 μg of TP was no more effective than 1 μg. Lordosis duration was inhibited in females by 10 μg of TP on either Day 1 or 3, however, mounts and intromissions were facilitated by TP treatment on Day 1, 3, 5 or 7. These experiments demonstrate that the mechanisms mediating masculine behavior are more sensitive to neonatal TP treatment than are the mechanisms mediating lordosis behavior.     

Whole-mount autoradiography study of DNA synthetic activity during postnatal development and androgen-induced regeneration in the mouse prostate

Ventral and dorsolateral prostatic lobes (VP and DLP), obtained from mice at different ages and at different intervals after castration or treatment of castrated males with testosterone propionate (TP), were microdissected into two-dimensional arrays and incubated in vitro with 14C-thymidine. Labeled whole-mount specimens were fixed and dried onto glass slides, dipped into photographic emulsion, and processed autoradiographically. The morphological pattern of DNA synthetic activity was similar in the VP and DLP. During early postnatal periods (10-15 days after birth), DNA synthetic activity was highest at the distal ductal tips (near the capsule) and considerably lower in proximal ducts (near the urethra). At 30 days of age, DNA synthesis was almost totally confined to the distal ducts, with exceedingly low labeling in the proximal ductal areas. In the prostate of the intact or castrated adult, DNA synthesis was nearly absent throughout the gland, but silver grains were still observed on the ductal tips. During androgen-induced prostatic regeneration, DNA synthesis was detectable only in distal ducts 24 h after TP was administered. Labeling intensity reached a maximum on the third day of TP treatment in both distal and proximal ductal areas, thereafter, it subsided to focal labeling confined mostly to distal ducts. These results demonstrate that levels of DNA synthetic activity vary considerably within the prostate on a regional basis. Explanation of this heterogeneity in DNA synthetic activity within the prostate gland is fundamental to understanding the mechanism of androgenic regulation of prostatic growth and development.     

Effects of in vivo administration of testosterone propionate on in vitro production of follicle-stimulating hormone and luteinizing hormone by pituitaries of pony mares

The in vitro incorporation of [3H]leucine into immunoprecipitable follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was assessed for pituitaries from pony mares treated with testosterone propionate (TP) or oil (controls). Mares were treated every other day with TP (n = 4) at 350 micrograms/kg of body weight or with an equivalent volume of oil (n = 4). One day following the sixth injection of TP, each mare received an intravenous injection of gonadotropin releasing hormone (GnRH) at 1.0 micrograms/kg body weight and was bled frequently for 4 h. Treatment of mares with TP reduced FSH (P less than 0.05) and LH (P less than 0.01) concentrations in daily blood samples and increased (P less than 0.01) the amount of FSH secreted in response to GnRH compared with control mares. Incorporation of [3H]leucine into immunoprecipitable FSH was also greater (P less than 0.01) in pituitaries from TP-treated mares compared with control mares on both a per mg tissue and per anterior pituitary basis. The amount of LH secreted after GnRH, the amount left in the pituitary and the incorporation of [3H]leucine into LH were not affected by treatment. These results confirm earlier conclusions drawn from indirect evidence that androgens increase the production of FSH in the mare.     

Thyroidal modulation of androgenic expression in mice submandibular gland

We investigated the influence of testes and thyroid gland on the maintenance of biochemical parameters and of [3H]R1881 binding sites of adult mice submandibular gland (SMG). Castration (Cx) performed at beginning of puberty prevented sex-dependent SMG development without interfering with maximal androgen binding capacity. Thyroidectomy (Tx) had strong effects on SMG, mainly by lowering the number of androgen binding sites. All alterations could be fully reverted after treatment with testosterone (5 mg/animal, single dose) or with thyroxine (T4, 250 micrograms/animal per day during 5 days). The effects of Cx on SMG could be reverted by therapy with testosterone, T4, or with both hormones (testosterone + T4) in a non-synergistic fashion. It is shown the importance of thyroidal activity on the physiological maintenance of androgen receptors in the murine SMG; the role played by thyroid gland seems to be essential for the full expression of the androgen-dependent SMG activity in adult mice.     

Evaluation and characterization of congenital hypothyroidism in rdw dwarf rats

The rdw rat is a new strain of dwarf mutant that has decreased blood thyroxine (T4) and growth hormone (GH) concentrations and testicular enlargement during development and aging. To confirm whether this strain can be used as a new hypothyroid model, the experiments reported here were carried out, using adult rdw rats, rdw rats treated with thyroxine, and clinically normal (N) Wistar-Imamichi rats. Clinical parameters of deficient thyroid function in rdw rats were chosen for evaluation and characterization. Body weight, hemoglobin (Hb) concentration, hematocrit (Hct), glucose (GLU), and systolic blood pressure were significantly lower, and serum values for aspartate transaminase (AST), total cholesterol (TC), total protein (TP), and blood urea nitrogen (BUN) were higher in rdw than in N rats. Serum concentrations of total T4 and free triiodothyronine (FT3) were significantly lower, and serum thyroid-stimulation hormone (TSH) concentration was markedly higher in rdw than in N rats. Serum GH concentration was significantly lower in rdw than in N rats. Results of histologic examination indicated that the thyroid gland of rdw rats was markedly atrophied, compared with that of N rats. Results of clinical examination of organs and hematologic and biochemical values in rdw rats corresponded to those of the hypothyroid state in humans. Most organ weights (heart, kidney, spleen, and adrenal gland), hematologic and biochemical values (Hb, Hct TC, TP, BUN), blood pressure, and serum hormone (TSH and GH) values underwent substantial restoration (partial or complete) toward normal in response to replacement therapy. In conclusion, the rdw rat is a useful model of congenital hypothyroidism.     

Effect of electrostimulation of the hypothalamus on protein biosynthesis in organs of adult and aged rats

The effect of hypothalamus electrical stimulation on total protein biosynthesis was studied in skeletal muscle, heart, liver, adrenal cortex and thyroid gland of adult rats. In adult animals hypothalamus stimulation provokes a pronounced increase in 3H-leucine incorporation into total protein of all tissues, as well as into liver chromatin proteins. No significant changes were observed in protein biosynthesis when hypothalamus of old rats was stimulated. This can serve as evidence of age-related decrease in the ability of the hypothalamus to stimulate protein synthesis in peripheral tissues.     

Testosterone increases singing and aggression but not male-typical sexual partner preference in early estrogen treated female zebra finches

Female zebra finches given estradiol benzoate (EB) as nestlings and testosterone propionate (TP) as adults show masculinized sexual partner preference, preferring females instead of males. This suggests an organizational effect of EB on sexual partner preference in a socially monogamous species that pairs for life. It is not known whether there is an activational hormone effect on sexual partner preference in this species, or whether adult testosterone treatment is necessary for masculinized preference to be expressed. In this experiment females were injected with EB daily for the first 2 weeks posthatching. As adults they were given TP filled or empty implants. Subjects were then given two-choice preference tests with male vs female stimuli, in which singing as well as proximity to the stimuli was recorded, followed by tests in a group aviary for social behavior and pairing preference. Females with TP implants sang more than females with empty implants and were more aggressive toward other females. They did not, however, differ from females with empty implants in any measure of sexual partner preference. Neither group showed a marked preference for males; instead both groups were equally interested in males and females. Thus adult testosterone treatment is not necessary for early estrogen treated females to show a shift in sexual partner preference in the male-typical direction.     

Utilization of U-14C amino acids or U-14C protein by adult Glossina morsitans during in utero development of larva

Administration of U¹⁴C protein hydrolysate in the diet of adult female Glossina morsitans at different times throughout the second reproductive cycle was followed by analysis of the distribution of radioactivity between the adult flies, their excreta, and the fully grown third instar larvae produced by these flies. A constant proportion of the total administered label was recoverable independently of the time lapse between administration and assay. Peak incorporation of labelled material occurred in the larva between the seventh and eighth day of a 9 or 10 day interlarval period, indicating that the larva feeds avidly on recently synthesized maternal uterine gland secretion at this time. Haemocoelic injection of U¹⁴C protein hydrolysate into similar adult females, between feeds, resulted in continued incorporation of labelled material by the larva to within 12 hr of parturition. Results are consistent with the hypothesis that uterine gland secretion and larval feeding continue throughout the intrauterine life of the larva.A constant and low proportion of detectable label remained in the adult fly while increased incorporation by the larva was paralleled by a reduction of detectable label in the adult excreta. This indicates direct competition between the uterine gland cells and those of the Malpighian tubules for free amino acids in the haemolymph.Administration of U¹⁴C protein in the adult diet did not result in incorporation of label by the developing larva, and the bulk was excreted as protein by the adult fly. Apparently the midgut trypsin of G. morsitans is incapable of splitting this labelled protein.Analysis of urine and haemolymph samples from flies in early pregnancy, recently fed on a diet containing U¹⁴C protein hydrolysate or U¹⁴C protein, shows that free labelled amino acids in the diet enter the adult haemolymph almost immediately after feeding, and are excreted along with dietary water during initial diuresis. The labelled protein used in these experiments was not taken up by the haemolymph and consequently did not appear in the urine.Implications are that the adult female G. morsitans possesses little storage capacity for substances in the diet which are destined to provide nutrients for the developing larva. Assuming a 48 hr digestion time, the digestive products of a blood meal ingested on day 5 or 6 of a 9 day interlarval period will provide the bulk of nutrients for larval growth. It is therefore significant that blood meals ingested at this time are larger than those ingested earlier or later in the cycle.     

Steroid-induced early protein synthesis in rat uterus and prostate.

An early 'induced protein', after exposure of the rat uterus to estradiol, is detected among the soluble proteins with a double-labelling technique and electrophoretic fractionation. Efforts have been directed to establish the subcellular distribution of the induced protein, since such a protein, observable 1 h after hormone administration, may play an important role in the subsequent amplified responses, especially in terms of RNA synthesis. Moreover such an early discrete induced protein was sought in a comparable system responding to another hormone, namely prostate and seminal vesicles under androgens. The induced protein was not found in uterine nuclei of 21-day-old rats after 1 h of estradiol action in vivo and 1 h of tissue incubation with labelled leucine. This negative result summarizes a search among different nuclear protein fractions using various procedures; nor was induced protein observed in mitochondrial and microsomal pellets. Contrary to these negative findings, slight changes of histone labelling were observed under the experimental conditions used to demonstrate induced protein. In addition histone acetylation was increased after 1 h of estradiol action in vivo and 15 min tissue labelling in vitro with radioactive acetate. Furthermore, an increase in total protein synthesis between 0 and 2 h after estradiol action was observed, the relative increase of incorporation of radioactive leucine into protein of estradiol-treated vs non-stimulated uteri being corrected for variations of the acid-soluble radioactive leucine pool. Attempts to obtain an early and discrete induced protein with androgens in prostate and seminal vesicles of immature or castrated rats after different times of exposure to testosterone, androstanolone and estradiol have been unsuccessful. The contribution of both negative and positive findings in steroid-induced early protein synthesis is discussed in the context of the current knowledge of hormone action.     

BIOCHEMICAL AND MORPHOLOGICAL EFFECTS OF TESTOSTERONE TREATMENT ON DEVELOPING SYMPATHETIC NEURONS

Abstract— Neonatal rats were treated with testosterone propionate (TP) or isoproterenol (ISO) to determine whether (1) increases in salivary gland mass are associated with alteration of developing sympathetic neurons and (2) whether effects on neuron growth are secondary to altered target mass itself or to increases in salivary growth factors. TP treatment is known to result in salivary tubule hypertrophy and elevated nerve growth factor (NGF) content whereas IS0 treatment results in acinar hypertrophy and no known alteration in NGF. TP treatment increased submaxillary gland weight as well as tyrosine hydroxylase (T-OH) activity, adrenergic neuron numbers and total protein in the innervating superior cervical ganglion (SCG). Unilateral sialectomy prevented the increase in T-OH activity in the SCG, suggesting that the salivary glands were necessary for this effect. T-OH activity and total protein were elevated in the distant sixth lumbar sympathetic ganglion after TP treatment, suggesting that sympathetic development as a whole was affected and that humoral factors may be involved. Salivary gland weight was also elevated following ISO administration, but T-OH activity in the SCG was not affected. These observations suggest that TP treatment increases T-OH activity and sympathetic neuron numbers by alteration of specific salivary humoral growth factor(s).     

Testosterone and estradiol up-regulate androgen and estrogen receptors in immature and adult rat thyroid glands in vivo

Thyroid gland is one of the non-classical target organs for sex steroids. Presence of androgen and estrogen receptors in the neoplastic and non-neoplastic thyroid glands of mammalian species is well documented. The aim of the present study is to elucidate the changes in serum and thyroidal sex steroids, and their receptors in the thyroid gland of rats from immature to adult age under gonadectomized (GDX) and sex steroids replaced conditions. Normal Wistar male and female rats from immature to adult age (day 21, 30, 45, 60 and 160 post-partum (pp)) were used in the present study. One group (I) of rats was GDX at an early age (day 10 pp) and the other group (II) at the adult age (day 120 pp). Group I rats were sacrificed at different experimental periods such as 21, 30, 45 and 60 days pp, and group II rats were sacrificed at day 160 pp. Another group of GDX rats from group I and II were replaced with physiological doses of testosterone or estradiol. Serum and thyroidal concentrations of sex steroids were estimated by RIA method and the concentrations of receptors by radioreceptor assay. Gonadectomy significantly decreased serum and thyroidal testosterone and estradiol and concentrations of androgen receptor (AR) and estrogen receptor (ER) in the thyroid. Replacement of sex steroids to GDX rats restored the normal level of sex steroids, AR and ER. Therefore, it is suggested from the present study that (i). sex steroids up-regulate their own receptors in the thyroid, (ii). sex steroids may influence thyroid growth and the proliferation of thyrocytes by modulating their receptor concentrations in the thyroid.     

Selective and/or overlapping effect of pituitary hormones (thyrotropin, gonadotropin) on serum thyroxin and testosterone level in newly hatched cockerels

Follicle-stimulating hormone and thyrotropin administered perinatally to cockerels have an overlapping effect on the testis and on the thyroid gland. Both hormones when given in one single dose considerably increased the serum level of both thyroxin and testosterone. In the case of chronic treatment performed in the perinatal period, the thyroxin level will similarly increase, though to a smaller extent, while the testosterone level decreases. The experiments studying the direct effect on hormone secretion proved the overlapping effect of the hormones in the perinatal period.     

Quantitative modulation of thyroid iodide peroxidase by thyroid stimulating hormone

The activity of rat thyroid iodide peroxidase fell to 8% of the normal value 48 hours after hypophysectomy. Rats given injections of thyroid stimulating hormone manifested an enzyme activity indistinguishable from that of the sham-operated animals. Cycloheximide prevented the thyroid stimulating hormone-induced restoration of the enzyme activity. The incorporation of ¹⁴C-leucine into the thyroid gland decreased gradually and reached two thirds of the sham-operated group by 48 hours after hypophysectomy. Thyroid stimulating hormone administration prevented this decrease, as observed for iodide peroxidase activity. Thyroidal RNA contents decreased also in hypophysectomized rats, thyroid stimulating hormone treatment prevented the reduction of RNA contents and no significant change was observed in thyroidal DNA contents. These data are consistent with the idea that protein biosynthesis is involved in thyroid stimulating hormone regulation of thyroidal iodide peroxidase and that the life span of the peroxidase is less than 48 hours.