P.G.W.J. Van Oordt

Function and cytology of the normal and autotransplanted pars distalis of the hypophysis in the toad Bufo bufo (L)

The functional activity of the pars distalis following heterotopic and homoiotopic autotransplantation has been studied in adult toads of both sexes in the spring, about a month after breeding, and in the autumn on toads with mature gonads. Gonadotropic Function. In males, the homoiotopic grafting of the pars distalis maintained about normal spermatogenesis and interstitial cell activity, but ectopic transplants caused a strong reduction of interstitial cell activity, though spermatogenesis was only slightly reduced. In the spring experiment, there was no significant difference in the ovaries of the two graft-bearing groups, which were intermediate between the normal and the hypophysectomized controls. In autumn females, however, the ovaries of 5 of 8 toads with homoiotopic grafts atrophied, as in the hypophysectomized controls. The 3 remaining toads had ovaries of nearly normal size filled with mature eggs, but there were strong indications that in these 3 toads also the mature eggs that were present at the time of operation degenerated immediately after the operation, and was followed by a phase of extensive growth and maturation of small oocytes during the 2 months of the experiment. All females with ectopic grafts had atrophic ovaries at the end of the experiment. Adrenocorticotropic Function. This function was normal in the toads with homoiotopic grafts. No corticotropic function could be demonstrated in the ectopic grafts although the cytological study of males in the spring experiment showed that, in general, the adrenocortical cells in the toads bearing ectopic grafts appeared more active than those in the hypophysectomized controls. Thyrotropic Function. Thyroidal uptake of 131I in the autumn experiment was used to evaluate thyrotropic function. Uptake was normal in toads with homoiotopic grafts, but reduced in the toads with ectopic grafts. In the males with ectopic grafts, the 131I accumulation in the thyroids was not significantly higher than in the thyroids of the hypophysectomized controls. Fat Bodies. In the autumn experiment, feeding was insufficient to maintain body weight, and the fat bodies were greatly reduced in both normal controls and in the toads with homoiotopic grafts. Hypophysectomized controls, however, possessed large fat bodies despite an even greater loss of body weight. In the toads with ectopic grafts, net mobilization of fat from the fat bodies was intermediate between the normal and hypophysectomized controls. In the spring experiment, feeding was efficient. All groups increased in weight, and all showed fat deposition. Cytology of Pars Distalis. Four of the five tinctorial cell types, described for the pars distalis of Bufo bufo, were observed: carminophils, orangeophils, globular basophils, and violet cells. In most of the controls the carminophils and orangeophils were storing secretory granules; the globular basophils and the violet cells showed signs of secretory activity. All four cell types remained largely unchanged in the area of the homoiotopic grafts, bordering the median eminence and pars intermedia. In the rest of such grafts and in the heterotopic transplants cysts were formed, and degeneration and dedifferentiation of cells took place; carminophils and orangeophils had slightly degranulated, globular basophils had become strongly regressed in number and granulation, and violet cells had almost completely disappeared. Generally, there existed a close correlation between the state of the target organs and the morphological signs of secretory activity of the pars distalis cells. It is suggested that not only the globular basophils, but also the violet cells have a gonadotropic function, and are responsible for the development and maintenance of the interstitial Leydig cells in the testis.

Estrone and estradiol participation during exogenous vitellogenesis in the female rainbow trout, Salmo gairdneri

Abstract Ovarian steroids were treated for their ability to induce vitellogenin synthesis in the liver of the rainbow trout, Salmo gairdneri . These steroids were chosen because they had been reported to induce vitellogenin in the plasma of teleosts, i.e., estrone, estradiol, and testosterone, or because they were synthesized during vitellogenesis, as was the case with the above steroids and androstenedione and 17α-hydroxyprogesterone. Immature trout were ovariectomized and injected daily for 7 days. The administered doses of steroid were 100, 250, and 500 ng/g body wt. Only estradiol and estrone induced vitellogenin in the plasma; estrone had about 5% of the potency of estradiol. A dose-effect curve was determined for estradiol in the range from 25 to 1000 ng/g body wt. A maximal amount of 7 mg vitellogenin/ml plasma was found following the administration of a dose of 250 ng/g estradiol. Vitellogenin was not present in the plasma of animals treated with saline, nor could it be detected in the liver, not even after the administration of estradiol. Estradiol administration increased the total plasma protein concentration from 35 to maximally 51 mg/ml and decreased the total piver protein concentration from 163 to minimally 118 mg/g. The relative weight of the liver increased from 12.9% to maximally 22.4%. Vitellogenin was not detected in the liver of any of the experimental animals, indicating a low storage and rapid secretion of vitellogenin. The other steroids influenced some of the variables, but never was the total pattern of effect comparable to that of estradiol. Estradiol is found to be the ovarian steroid that physiologically regulates the synthesis of vitellogenin in the liver of the rainbow trout; estrone is less active. Experiments undertaken to determine the effects of the combined presence of estrone and estradiol revealed that estrone was capable of boosting the vitellogenic effect of estradiol when compared to the induced vitellogenin levels following treatment with a combination of testosterone and estradiol. The vitellogenin concentrations induced by a certain dose of one of the combinations of estrone and estradiol approximated the concentrations induced by the same dose of estradiol alone. This effect was independent of the ratio in which estrone and estradiol were administered. These findings could not be explained by conversions of estrone into estradiol or by the vitellogenic activity of estrone alone. The estrone, estradiol, and vitellogenin concentrations in the plasma of the experimental animals were in the same range as determined previously in untreated mature vitellogenic females. Vitellogenin and estradiol levels were found to correlate in experimental animals treated with estradiol ( r = 0.627; N = 20). This was not the case in animals treated with combinations of estrone and estradiol. In these animals, however, the sum of estrone and estradiol levels in the plasma correlated with vitellogenin levels ( r = 0.724; N = 42). Vitellogenin was not detected in the liver of any of the experimental animals, which indicates a low storage and rapid secretion of vitellogenin. The importance of viewing the sum of estrone and estradiol plasma levels in connection to physiological studies of the regulation of exogenous vitellogenesis in the rainbow trout is discussed.

The dopminergic inhibition of the gonadotropin-releasing hormone-induced gonadotropin release: An in vitro study with fragments and cell suspensions from pituitaries of the African catfish, Clarias gariepinus (Burchell)

Pituitary fragments and pituitary cell suspensions of the African catfish in a perifusion system released gonadotropic hormone (GTH) spontaneously. After a few hours of perifusion a baseline of GTH release was established. The dopamine (DA) agonist apomorphine (APO) caused a decreased in the release from pituitary fragments but not from pituitary cell suspensions. APO abolished the luteinizing hormone-releasing hormone analog (LH-RHa)-induced GTH release from both pituitary fragments and cell suspensions. It was concluded that DA inhibits the GTH release induced by gonadotropin-releasing hormone.

Steroid glucuronides of the seminal vesicle as olfactory stimuli in African catfish, Clarias gariepinus

Abstract Electrical responses were obtained from the olfactory epithelium (electro-olfactogram, EOG) and from the olfactory tract of female African catfish. The EOG response of females to holding water of males depends on the presence and the size of the males seminal vesicle. Male catfish thus appeared to release odorants originating from the seminal vesicle. The fluid from this exocrine gland is a highly stimulatory odorant because it contains steroid glucuronides. Higher levels of steroid glucuronides in the seminal vesicle fluid of feral spawning males makes the fluid more potent as an olfactory stimulus, whereas removal of the glucuronides diminished the response. Ovulation did not affect the sensitivity to these complex mixtures of glucuronides in the seminal vesicle fluid. The olfactory epithelium of females also responded to solutions of individual synthetic steroid glucuronides. Of the glucuronides tested, 5β-pregnane-3α,17α-diol-20-one-3α-glucuronide was the most potent odorant. It had a detection threshold of approximately 10 −11 M . Thresholds for the other glucuronides ranged between 10 −9 and 10 −6 M . The present data demonstrate the importance of seminal vesicle steroid glucuronides as olfactory cues.

The gonadotropin-producing and other cell types in the distal lobe of the pituitary of the common frog, Rana temporaria.

Pituitaries of male Rana temporaria were fixed in Bouin-sublimate, sagittally sectioned at 4 μ, and stained with different trichrome methods, with PAS-orange G, Gabes AF or Herlants Alcian blue-PAS-orange G. Four chromophilic cell types have been described in the distal lobe of the pituitary, i.e. α-cells or acidophils, β-cells or amphiphils type I, γ-cells or amphiphils type II, and δ-cells or cyanophils. The same cell types were observed in sagittal sections of the pars distalis of Bufo bufo and Xenopus laevis. β-Cells were absent from the pituitaries of juvenile Rana temporaria. One and three years after castration hyperactivity was observed in the β-cells. Secretory activity of these cells was reduced after the administration of testosterone, and was stimulated in frogs which were kept at high temperatures during the hibernation period. Moreover, in two out of four frogs the γ-cells had increased in number three years after gonadectomy, and a correlation was found between the atrophy of the secondary sex characters and the regression of the γ-cells in frogs which were kept at high temperatures. It is inferred that the β-cells produce a gonadotropic hormone, probably FSH, and that the γ-cells may secrete ICSH.

The regulation of gonadotropin release by neurohormones and gonadal steroids in the African catfish, Clarias gariepinus

The secretion of gonadotropic hormone (GTH) from the pituitary of teleosts is considered to be regulated by neuropeptides and neuroamines of cerebral origin and steroid hormones from the gonads. This paper reviews our studies concerning the control of GTH release in the African catfish, Clarias gariepinus. It was demonstrated that luteinizing hormone releasing hormone (LHRH) stimulates GTH release and that the gonadotropin release-inhibiting activity of dopamine is restricted to the LHRH-induced GTH release. With regard to the inhibitory action of steroid hormones on GTH release, a hypothesis was postulated which links together the inhibitory actions of dopamines and gonadal steroids. According to this hypothesis, only aromatizable androgens should feed back on the release of GTH and the effects of catecholestrogens and dopamine on GTH release should be comparable.

The brain-pituitary-gonadal axis in the rainbow trout, Salmo gairdneri: gonadal hormones and the maturation of gonadotropic cells.

SummaryIntact and castrated juvenile male rainbow trout (Salmo gairdneri) were treated with testosterone and gonadotropic hormone (GTH) to determine the maturational effects of these hormones on the GTH-cells. Electron-microscopic studies of the GTH-cells revealed that GTH and testosterone in intact animals, and testosterone in castrated fish, caused GTH-cell maturation: These cells now displayed the same appearance as GTH-cells in adult trout, including the presence of globules, a well-developed Golgi apparatus and rough endoplasmic reticulum, all of which were absent in GTH-cells of control animals. Animals with stimulated GTH-cells also had an increased GTH content of the pituitary; release of GTH could not be demonstrated. Animals treated with GTH exhibited an accelerated development of the testes, resulting in complete gametogenesis and elevated plasma testosterone levels. These results indicate that exogenous steroids as well as endogenous gonadal steroids can stimulate the full development of GTH-cells and accelerate GTH synthesis. The significance of this stimulating effect of the gonadal hormones with respect to the development of the brain-pituitary-gonadal axis and the onset of puberty is discussed.

The chemical nature of sex attracting pheromones from the seminal vesicle of the African catfish, Clarias gariepinus

Abstract In attraction tests, ovulated female African catfish, Clarias gariepinus , were attracted by the administration of 2.0 ml/l seminal vesicle fluid to the aquarium water. Lower doses (0.1 and 0.5 ml/l) were ineffective, and a high concentration (8.0 ml/l) seemed to have a repulsive effect. After fractionation of the fluid, an isolated steroid conjugate fraction appeared to contain the attractant. No other stimuli beyond this fraction were required to attract groups of female catfish after ovulation. Other constituents of the fluid such as polysaccharides, proteins, phospholipids and steroids failed to attract the females. GCMS analysis of the steroid conjugate fraction revealed the presence of eight different steroid glucuronides. After removal of these steroid glucuronides, the steroid conjugate fraction lost its attractive effect. A mixture of seven available synthetic steroid glucuronides was composed according to the quantitative results of the GCMS analysis. This mixture appeared to have a powerful dose-dependent attractive effect on ovulated females. It is concluded that a combination of various steroid glucuronides, present in seminal vesicle fluid, functions as a sex attractant, bringing male and female African catfish together shortly before spawning.

Immunofluorescence studies on gonadotropin releasing hormone (GRH) in the fore-brain and the neurohypophysis of the green frog, Rana esculenta L.

SummaryUsing antibodies against mammalian LH-RH, the double antibody immunofluorescence technique has been applied to serial cross sections of the brains of adult Rana esculenta. Immunoreactive material was found in perikarya of an unpaired nucleus in front of the preoptic recess. The axons of these perikarya also contain fluorescing material. They form a single bundle which passes under the preoptic recess, than splits into two tracts, one on either side of the optic chiasm. The two tracts reunite just before entering the median eminence. The axons end near the capillaries in the outer zone of the median eminence. The possibility of two separate centres for the stimulation of gonadotropic activity in the brains of anurans is discussed.

Gonadal steroidogenesis and the possible role of steroid glucuronides as sex pheromones in two species of teleosts

In general, female zebrafish,Brachydanio rerio, ovulate only in the presence of males. The stimulant must be pheromonal as even male holding water is capable of inducing ovulation. After ovulation the mating phase begins. During this phase the male follows the female and oviposition as well as fertilization takes place. Both the ovulation and the mating are controlled by pheromones synthesized by the gonads. Ovulation can be induced by testicular homogenates. After the lipid material has been extracted from the testicular homogenates, the remaining aqueous phase can still induce ovulation. However, when the aqueous phase is treated with the enzymeβ-glucuronidase, it loses the ability to induce ovulation. This is an indication that glucuronides, probably steroid glucuronides, are the compounds responsible.During the mating phase, ovulated female zebrafish become attractive to males. It was found that, after ovulation, ovarian extracts contain the compounds responsible for attracting males. The attractant consists of a mixture of steroid glucuronides.After incubation of the gonads with3H-precursors seven steroid glucuronides have been identified in the testis and five in the ovary.Under fish culture conditions the African catfish,Clarias gariepinus, can produce postivitellogenic oocytes throughout the year. However, in capitivity neither males nor females spawn. In female catfish maturation and ovulation can be induced by treatment with gonadotropins. It might be possible that, analogous to the zebrafish, some reproductive processes in the catfish have to be induced by pheromones. It has been demonstrated that pheromonal compounds released by the seminal vesicles are involved in the attraction of female conspecifics. The steroid glucuronide synthesizing capability of the testes and the seminal vesicles of the male catfish are examined, as well as that of the ovary before and after ovulation of the female catfish. Both testes and seminal vesicles appear to be capable of steroid biosynthesis but only the latter synthesizes steroid glucuronides. Six of these conjugates have been isolated and identified. In the female catfish the ovaries are capable of synthesizing seven steroid glucuronides, but only after ovulation.