Development of hypophysis and differentiation of its secretory cells at the early postembryonic development of silver carp Hypophthalmichthys molitrix (cyprinidae)

Silver carp Hypophthalmichthys molitrix hatches from the envelope at phase 19 a day after fecundation (water temperature 26–28°C) with body length 5.2 mm. The formation of hypophysis begins 7–8 h after hatching of the embryo. The first chromophilic cells (acidophiles in adenohypophysis) appear at the age of 9 days; the first basophilic cells (thyrotropocytes) at the age of 17–20 days, when juveniles are at stage III. The gonadotropic function is formed in the ontogenesis of silver carp at the age of 40–45 days, i.e., almost a month after the appearance of elementary sexual cells in the gonads. The differentiation of gonadotropocytes in mesoadenohypophysis to two functionally active types of cells (central and peripheral) is also completed by this time.     

The histological picture of the hypothalamus (the nucleus preopticus) and hypophysis in male Anguilla anguilla L. treated with hormones

Studies were conducted on the effect of human chorionic gonadotropin (HCG), testosterone and desoxycorticosterone acetate (DOCA) on the histological picture of the nucleus preopticus (NPO), hypophysis and gonads of male European eels. It was ascertained that none of the injections used changed the content of the Gomori-positive material within the NPO cells. HCG and testosterone injections altered the histological picture of the hypophysis and injections of HCG influenced the gonads by accelerating their maturity. The injections of DOCA did not change the histological picture of the hypophysis and gonads in male eels.     

Features of the Formation of an Ovulatory Wave of Hypophysis Gonadotropins in High Fecundity Fish

Study on the state of bighead carp Aristichthys nobilis females' central and peripheral of hypothesis gonadotropocytes at light and electron microscopy levels after stimulation of ripening a chorionic gonadotropin revealed that the amount of secretory material diminishes in both types of cells. Intensive excretion of both secretory granules and content of cisterns of the granular endoplasmic reticulum take place. Formation by the hypophysis of an ovulatory wave of the gonadotropin in the females with different fecundity differs due to the change in proportions of processes of mero- and holocrine secretion.     

Experimental identification of a hypothalamic gonadotropic centre

Summary In a large group of adult female and male specimens of Rana temporaria all nervous pathways to the median eminence and hypophysis were extirpated without disturbing the normal blood supply of the median eminence and hypophysis. The total interruption of the nervous pathways persisted in all animals. In all animals gametogenesis and seasonal development of the gonads and of the secondary sexual characteristics were absent. In another large group of animals, the pars ventralis of the tuber cinereum of the hypothalamus was isolated from the brain. The pars ventralis retained its normal connections with the median eminence and hypophysis. The normal blood supply of the whole isolated region (pars ventralis tuberis + median eminence + hypophysis) was preserved. Four months after operation, in the majority of the animals, the isolation was still complete. In all animals, normal gametogenesis and seasonal development of the gonads and of the secondary sexual characteristics had occurred.In accordance with previous experiments, the present experiments showed that the pars ventralis tuberis contains an important gonadotropic centre. The activity of the gonadotropic centre of the pars ventralis tuberis is, at least, mainly exerted by its influence on the gonadotropic function of the pars distalis of the hypophysis. This is shown morphologically by a gradient of nuclear volume and by the mean nuclear volume of the P.A.S. positive cells of the pars distalis. The influence of the gonadotropic centre on the pars distalis is exerted by A.F.-negative nerve fibres to the median eminence. It is highly probable that all these nerve fibres end on the primary capillary network of the hypophysial portal system. The experiments strongly suggested that the axon endings of the gonadotropic centre would influence the gonadotropic activity of the pars distalis of the hypophysis by releasing of gonadotropic releasing factors into the blood capillaries of the median eminence.The gonadotropic centre of the pars ventralis tuberis is necessary for the normal gametogenesis and for the seasonal development of the gonads and of the secondary sexual characteristics. So far as concerned the gametogenesis and the seasonal development of the gonads, the function of the gonadotropic centre is largely autonomous.Exclusion of the function of a part of the pars ventralis tuberis produces quantitative, but no qualitative changes in gametogenesis.     

Effect of estradiol on the spontaneous activity of individual neurons in the arcuate area of the hypothalamus at different stages of the estrus cycle in rats

Microiontophoretic application of estradiol into the arcuate region of the hypothalamus increased the activity of single neurons in the majority of experiments. This reaction was more pronounced at the stage of dietrus-1 and diestrus-2 than during proestrus. It is supposed that the changes in the prevailing reactions of the arcuate region neurons to the estradiol administration in the course of the estrual cycle were determined by the level of the endogenous estrogens and gonadotropins of the hypophysis in the peripheral blood.     

Hypophysis--thyroid gland--gonads in boys of the pubertate period in south areas of Archangelsk region

The hormonal level dynamics of hypophysis, thyroid gland and sex steroids was analyzed in respect to the puberty. Concentrations of gonadotropins and sex streroids were increased whereas concentrations of thyroid hormones was decreased. The amplitude of hypophysis and thyroid hormones were narrowed whereas the range of sex steroids was extended during the puberty. In early stages of puberty, the interhormonal correlations existed on some levels (hypophysis or peripheral gland), but in late stage the intersystem and polyhormonal relations were formed. Thyroid hormones play a leading role in sexual maturity regulation. The sexual maturity is prolonged, the variance of sexual stages being quite wide. The range of gonadotropin shifted to the left side in comparison with children in moderate latitudes.     

The gonadotropic centre of the tuber cinereum hypothalami and ovulation

Summary In adult female specimens of Rana temporaria, the pars ventralis of the tuber cinereum of the hypothalamus was isolated from the brain. The isolated pars ventralis retained its normal connections with the median eminence and hypophysis. The normal blood supply of the whole isolated region (pars ventralis tuberis + median eminence + hypophysis) was preserved.The results showed (1) that, in accordance with previous experiments, as far as concerned gametogenesis, seasonal development of the gonads and of the secondary sexual characteristics, the function of the gonadotropic centre of the pars ventralis tuberis is largely independent of nervous connections between the pars ventralis of the tuber cinereum and the brain; (2) that, in animals in which the pars ventralis tuberis was isolated from the brain at the beginning of the seasonal development of the ovaries, the L.H. secretion is disturbed during the ovulation period; (3) that consequently, in such animals, the stimulating activity of the isolated gonadotropic centre on the L.H. secretion of the hypophysis is too weak to cause ovulation; (4) that nervous connections between the isolated region and the preoptic region of the brain are indispensable for ovulation.     

The overlapping effects of thyrotropin and gonadotropins on chick embryo gonads in vitro

Pieces of 12- and 15-day-old chick embryo testes and ovaries were cultured in vitro in the presence of thyrotropin (TSH), gonadotropins (FSH + LH) and adrenocorticotropin (ACTH) for different periods. All the explants of treated gonads differentiated into typical testes or ovaries according to their genetic sex. The gonads of 12-and 15-day-old chick embryos showed a good response to both thyrotropic and gonadotropic stimulation. On the other hand, they did not respond to adrenocorticotropic stimulation. Fifteen-day-old chick embryo testes were grown in tissue culture in the presence of the said hormones. Gonadotropins and TSH enhanced the growth and migration of testicular cells as compared with the control or ACTH treated group. In addition, they maintained the germ cells on the upper surface of epithelial cells. These results have confirmed our previous results in vivo in that gonadotropins and thyrotropin hormones accelerated the development of 12- or 15-day-old chick embryo gonads.     

How we almost discovered LH receptors, but didn't

The metabolism of gonadotropins was unclear until the 1960s. The chief theory, utilization of gonadotropins by gonads, was unproven, but radioimmunoassay indicated that the levels of luteinizing hormone entering the ovary were higher than the levels in the ovarian veins. The availability of radiolabeled proteins opened the possibility of following the fate of gonadotropins in the end organ. Independently, two teams in Tel Aviv and Seattle researched the uptake of radiolabeled human chorionic gonadotropin by rodent ovary. Both concluded that the ovary bound gonadotropin; however, neither pursued the mechanism of the observation, gonadotropin receptors on ovarian cells. Had they done so, the course of discovery and study of cell surface receptors might have been altered.     

Effect of gonadotropins,thyrotropin, and adrenocorticotropin on the development of 12-day chick embryonic gonads

Summary Gonadotropins (FSH+LH) and thyrotropin (TSH) stimulated the development of 12-day embryonic gonads, whereas adrenocorticotropin (ACTH) did not show any significant effect. It is concluded that the gonads of 12-day chick embryos have the capacity to respond to both gonadotropic and thyrotropic stimulation. This suggests that at the time when the hypothalamo-pituitary-thyroid axis begins to develop, the capacity of gonadal receptors to distinguish between gonadotropins and thyrotropin has not been established.     

Effect of photoperiod on the incorporation of 3H-thymidine into the gonads of Carassius auratus

Gldfish, Carassius auratus of varying sizes were conditioned in continuous light or darkness f or 10, 20 and 30 days and the incorporation of ³H-thymidine into the gonads was investigated to attempt to develop a bioassay for fish gonadotropins.
The 24-hour gonadal ³H-thymidine of 10-day conditioned fish was significantly less at the dose level of 0.5 μCi ³H-thymidine/fish compared to 1.0, 2.0 and 3.0 μCi/fish which gave gonadal activities not significantly different from each other. Thus, for all subsequent work the dose of 1.0 μCi/fish was used.
Photoperiod of continuous light or darkness had little effect on fish weighing less than 11 g but in fish 11-15 g conditioned for 20 days in darkness and fish greater than 16 g conditioned for 10 days in darkness, depression in gonadal ³H-thymidine incorporation occurred. In fish 11-15 g, prolonged conditioning for 30 days in darkness induced more gonadal activity than was observed at 20 days.
The effect of injection of Channa striatus pituitary extract at doses of 1 mg/10 g body weight and 5 mg/10 g body weight induced a significant increase in ³H-thymidine incorporation in the gonads over saline injected controls. The results suggest the potential of using photoperiod as a means of inducing regression of gonads of suitable fish in a bioassay of gonadotropins.     

Embryonic sex hormones in birds

Hormone activity of embryonic gonads in birds was demonstrated by grafting and culture experiments. Anti-Müllerian hormone responsible for the regression of the Müllerian ducts in the male is most probably a glycoprotein. Whether the testis also secretes testosterone has long been disputed, but most arguments are against this possibility. From early stages of development, the ovary secretes estrome and estradiol. However, it could not be demonstrated unambiguously whether estrogen is identical with the sex inducing substance in the female. The hypophysis seems to control ovarian estrogen secretion at 10-13 days of incubation in the chick embryo.     

Intragonadal signalling mechanisms in the control of steroid hormone production

In the gonads, there are two recognized signal transduction mechanisms which operate in the processing of hormonal stimuli. The gonadotropins, follicle stimulating hormone and luteinizing hormone, act primarily through the generation of cyclic AMP. Several other hormonal regulators in the ovary and the testis, such as gonadotropin releasing hormone and prostaglandin F₂ stimulate inositol lipid metabolism following receptor binding. This triggers a cascading mechanism which ultimately results in the generation of increased cytosolic free calcium levels, enhanced protein kinase C activity, and liberation of arachidonic acid. There is also evidence that luteinizing hormone shares in the activation of this pathway. In this review, the significance of these signal transduction pathways is discussed in relation to the effects of various hormones on steroid biosynthesis in the gonads.     

The role of genotype, social stress, and season of the year in regulation of hormonal function of murine testis in vitro

Micropopulations consisting of six male mice of different genotypes were studied (each of lines A/He, CBA/Lac, C57BL/6J, DD, YT, and PT was represented by one male). Interlinear differences in the level of social dominance and the effects of genotype, social hierarchy, and season on in vitro testosterone production by testes were examined under different incubation conditions. The testosterone production was estimated under control conditions and under stimulation with human chorionic gonadotropin (CG). Significant genetic differences in the initial and CG-stimulated testosterone production by testes incubated in vitro were found. By the control production, the genotypes fell into two groups: lines C57BL/6J, A/He, and CBA/Lac had low production of the hormone; lines YT, PT, and DD, high production. By responsiveness of gonads to CG, the genotypes fell into three groups: line CBA/Lac had low testosterone production by testes; lines C57BL/6J, A/He, YT, and DD, line PT, intermediate production; and line PT, high production. The obtained data indicate stability of genetic polymorphism for the responsiveness of testes to gonadotropins, because neither season nor the formation of social hierarchy could significantly change the interlinear differences. In line PT characterized by high hormonal activity of gonads in the control and under stimulation with gonadotropins, males became dominant in a significantly greater number of cases studied during the formation of hierarchy in micropopulations. The dynamics of both control production of a male sex hormone and responsiveness of testes to CG was established in vitro during the formation of social hierarchy; the effects of season on this dynamics were revealed. Specific characteristics of secretory activity of testes were detected in the control and under stimulation with gonadotropins, depending on incubation conditions. Seasonal and genotypic characteristics of the responsiveness of testes to CG were revealed under different incubation conditions. Genotypic characteristics indicate interlinear differences in the degree of inertia of testosterone biosynthesis on exposure to gonadotropins.     

Role of Genotype, Social Stress, and Season in the Regulation of Hormonal Function of Testes Incubated in Vitro in Mice

Micropopulations consisting of six male mice of different genotypes were studied (each of lines A/He, CBA/Lac, C57BL/6J, DD, YT, and PT was represented by one male). Interlinear differences in the level of social dominance and the effects of genotype, social hierarchy, and season on in vitro testosterone production by testes were examined under different incubation conditions. The testosterone production was estimated under control conditions and under stimulation with human chorionic gonadotropin (CG). Significant genetic differences in the initial and CG-stimulated testosterone production by testes incubated in vitro were found. By the control production, the genotypes fell into two groups: lines C57BL/6J, A/He, and CBA/Lac had low production of the hormone; lines YT, PT, and DD, high production. By responsiveness of gonads to CG, the genotypes fell into three groups: line CBA/Lac had low testosterone production by testes; lines C57BL/6J, A/He, YT, and DD, line PT, intermediate production; and line PT, high production. The obtained data indicate stability of genetic polymorphism for the responsiveness of testes to gonadotropins, because neither season nor the formation of social hierarchy could significantly change the interlinear differences. In line PT characterized by high hormonal activity of gonads in the control and under stimulation with gonadotropins, males became dominant in a significantly greater number of cases studied during the formation of hierarchy in micropopulations. The dynamics of both control production of a male sex hormone and responsiveness of testes to CG was established in vitro during the formation of social hierarchy; the effects of season on this dynamics were revealed. Specific characteristics of secretory activity of testes were detected in the control and under stimulation with gonadotropins, depending on incubation conditions. Seasonal and genotypic characteristics of the responsiveness of testes to CG were revealed under different incubation conditions. Genotypic characteristics indicate interlinear differences in the degree of inertia of testosterone biosynthesis on exposure to gonadotropins.     

Hormonal status in different phenotypic forms of Black Sea trout <Emphasis Type="Italic">Salmo trutta labrax</Emphasis>

In three phenotypic forms (parrs, trout form, and kumzha form) of fish-farm Black Sea trout (age 1+) and wild Black Sea trout (age 1+ and 2+), Salmo trutta labrax, inhabiting the basin of the Mzymta River, the content of monoamines (dopamine, noradrenalin, and serotonin) and of their metabolites (3,4-dihydroxyindolacetic acid, 3-methoxy-4-hydroxyphenyl glycol, and 5-hydroxyindolacetic acid) was investigated in brain regions (forebrain, optic tectum, brainstem, hypothalamus, and hypophysis) and the level of cortisol, thyroxin, triiodothyronine, growth hormone, and adrenocorticotropic hormone was investigated in blood. Data on length and weight of fish body and maturation stage of gonads are indicated. The hormonal level differs in the fish of different phenotypic forms. It is the highest in specimens of the kumzha form which completed parr-smolt transformation. Among wild fish, numerous mature females at age 1+ were found which indicated the presence of a dwarf form of the Black Sea trout in the Caucasus in the Mzymta River.     

Gonadotrophic stimulation of androgen secretion by the early fetal pig ovary in organ culture

An influence of gonadotropins on steroid secretion by the early fetal ovary of the domestic pig was shown by organ culture and radioimmunoassay. Gonads from fetuses at Days 32-37 of gestation were cultivated singly for 9-12 days in biologically supplemented medium. One member of each pair of gonads was exposed to human chorionic gonadotropin (hCG) or ovine luteinizing hormone (LH), and the other served as a control. A marked stimulating effect on androgen secretion was noted with both gonadotropins. The major androgen found was androstenedione, with secretion rates of greater than 200 ng/gonad per 24 h for some explants exposed to hCG. Little or no androstenedione production occurred unless gonadotropin had been added to the culture medium. Lesser amounts of testosterone (usually less than 5% of the total of androstenedione and testosterone) were present. The data demonstrate a remarkable latent capacity for androgen biosynthesis by the early fetal pig ovary.     

Behavior of the hypothalamo-hypophyseal axis in a patient with asymmetric mixed gonadal dysgenesis (chromosome pattern 45,XO/46,XY) before and after gonad excision after with arginine, GRH and TRH stimulation

In a 12 years old patient with asymmetric mixed gonadal dysgenesis (karyotype 45, XO/46,XY) a stimulation test with arginine, gonadotropin-releasing hormone (GRH) and thyreotropin-releasing hormone (TRH) was performed before and after exstirpation of the gonads as well as after application of sex steroids. FSH, LH, PRL, HGH, TSH, testosterone and oestradiol were determined by radioimmunoassay. The results show an intact hypothalamo-pituitary axis which reacts with a normal negative feedback with respect to the secretion of gonadotropins after application of sex steroids.     

Mechanism of action of tetracycline on the functional state of the adrenal cortex]

The mechanism of stimulation of the adrenal cortex function by tetracycline was studied on albino rats. It was shown that tetracycline administered orally in a dose of 200 mg/kg regularly induced an increase in the corticosterone levels in the peripheral blood of the animals by the 15th day of the antibiotic use. It was shown on the animals with an experimentally suppressed function of the hypophysis by prolonged administration of hydrocortisone acetate that tetracycline primarily stimulated the hypophysis function resulting in production and excretion of increased amounts of the adrenocorticotropic hormone into the blood. The hormone increased the production of corticosterone in the adrenal glands which resulted in its higher levels in the peripheral blood.     

Steroidogenic factor 1 (SF1) is essential for pituitary gonadotrope function

Knockout mice lacking the orphan nuclear receptor steroidogenic factor 1 (SF1) exhibit a complex endocrine phenotype that includes adrenal and gonadal agenesis, impaired expression of pituitary gonadotropins, and absence of the ventromedial hypothalamic nucleus (VMH). These multiple defects complicate efforts to delineate primary versus secondary effects of SF1 deficiency in different tissues, such that its direct role in gonadotropes remains uncertain. To define this role, we have expressed Cre recombinase driven by the promoter region of the common alpha subunit of glycoprotein hormones (alpha GSU), thereby inactivating a loxP-modified SF1 locus in the anterior pituitary gland. Although pituitary-specific SF1 knockout mice were fully viable, they were sterile and failed to develop normal secondary sexual characteristics. Their adrenal glands and VMH appeared normal histologically, but their testes and ovaries were severely hypoplastic. alpha GSU-Cre, loxP mice had normal levels of most pituitary hormones, but had markedly decreased expression of LH and FSH. Treatment with exogenous gonadotropins stimulated gonadal steroidogenesis, inducing germ cell maturation in males and follicular and uterine maturation in females--establishing that the gonads can respond to gonadotropins. The pituitary-specific SF1 knockout mice are a novel genetic model of hypogonadotropic hypogonadism that establishes essential role(s) of SF1 in pituitary gonadotropes.