A. Guardabassi

The hypophysis of Xenopus laevis Daudin larvae after removal of the anterior hypothalamus

Abstract The region of the brain anterior to the tectum opticum, including the nucleus magnocellularis praeopticus , and other possible sites of anterior hypothalamic centers, has been removed from larvae of Xenopus laevis , the hypophysis being left intact. The larvae, the rate of development of which was somewhat delayed, have been reared for variable periods of time. In the absence of the hypothalamic neurosecretory nuclei the pituitary neural lobe underwent a complete regression and was therefore wholly lacking. In the pituitary distal lobe both acidophilic and thyrotropic cells appeared to be cytologically well-differentiated. After thiouracil administration a clear-cut goitrogenic response was shown by the thyrotropic cells; some acidophilic cells (presumably somatotropic ones) showed normal features, while abnormally large acidophilic granules occurred in certain other specifically located ones (presumably ACTH-secreting cells), indicating some possible cell disturbances. The possibility that the thyrotropic function of the pituitary is, at least in part, independent of the hypothalamus seems further supported by the results obtained in the present experiments. The lack of the neural lobe was accompanied by hypertrophy of the intermediate lobe. Hyperactivity was indicated by the hypertrophy and marked pyroninophilia of both the cytoplasm and nucleoli of its cells. In correlation with this, a higher pigmentation than normal was shown by the operated larvae, in which tightly packed and diffusely pigmented melanophores were seen to occur. The present findings are compared with other available data, and their significance is briefly discussed.

La cytologie hypophysaire chez Xenopus laevis Daud

RésuméLes auteurs ont étudié, à laide de différentes techniques cytologiques et histo-chimiques, la cytologie du lobe distal de lhypophyse chez 66 exemplairse ♂♂ et ♀♀ de Xenopus laevis, lesquels ont été traités au 4-methyl-2-thiouracil et au Percorten (acétate de désoxycorticostérone).Le tableau cytologique observé dans lhypophyse des exemplaires adultes et normaux, est fondamentalement en harmonie avec ce quavaient décrit les autres auteurs qui sétaient déjà occupés de la même espèce.Dans le cadre des cellules acidophiles, que le auteurs précédents avaient considérées toutes identiques, il a cependant été possible de distinguer — surtout à la suite du traitement expérimental — un comportement variable. Forts des résultats obtenus précédemment sur cette espèce et sur dautres, les auteurs estiment donc que les cellules acidophiles qui sont situées principalement à la partie antérieure du lobe, pourraient être les cellules responsables de la secretion de lACTH; quant aux cellules plus petites, plus allongées et moins nettement acidophiles qui se trouvent surtout à la partie ventrale et postérieure du lobe, elles constitueraient plutôt les cellules qui sécrètent lhormone somatotrope.Les auteurs décrivent en outre les transformations speciales (hypertrophie cellulaire, aspect particulièrement évident du nucléole, perte de la colorabilité typique, présence de granulations acidophiles aldéhyde-fuchsine positives) que subissent les cellules thyrotropes de lhypophyse de certains exemplaires élevés dans les aquariums du laboratoire, transformations qui vont de pair avec une hypertrophie et une altération fort marquées de la structure de la thyroïde.Ce résultat relatif à lhyperactivité thyrotrope, laquelle serait la cause à son tour de lhypertrophie et du tableau histologique dhyperfonction que présente la thyroïde, est discuté et interprété, à titre dhypothèse, en tant que la conséquence dune diminution de lhormone thyroïdien en circulation, ceci à la suite de conditions délevage peu propices.

The utilization of the calcareous deposits of the endolymphatic sacs of Bufo bufo bufo in the mineralization of the skeleton. Investigations by means of Ca45.

SummaryIn Bufo bufo bufo larvae treated with Ca45 prior to the onset of the mineralization of the skeletal pieces, fixed after 7 days treatment (early hind-limb bud stage), the greatest amount of Ca45 is detectable in the lumens of the endolymphatic sacs. A small amount of Ca45 is concentrated in the membranous labyrinth. By the end of metamorphosis the lumina of the endolymphatic sacs are only partially occupied by Ca45CO3 crystals. On the other hand Ca45 localization is evidenced in the epithelium lining the sacs and in the developing bones. The present observations seem to afford a demonstration that the Ca salts of the endolymphatic sacs take part in the ossification process.

On the early appearance of arginase activity in the liver of Bufo bufo larvae after prolactin treatment

Abstract In the liver of prolactin-treated Bufo bufo larvae, thyroid-dependent arginase activity is seen to arise at earlier stages than in controls. This finding lends further support to our assumption that prolactin induces activation rather than thyroid inhibition, as previously suggested by the cytological pattern of hyperactivity and enhanced thyroidal radioiodine uptake in prolactin-treated larvae at advanced metamorphic stages.

Effects of prolactin on arginase activity in the liver of Bufo bufo larvae under different experimental conditions

Abstract Exogenous thyroxine promotes the early appearance of arginase activity in the liver of normal and hypophysectomized Bufo bufo larvae. This effect does not seem to be exerted by endogenous prolactin (or a prolactinlike growth factor) which is secreted in higher amounts in radiothyroidectomized larvae as compared to normal larvae. Likewise, no arginase activity was recorded in the liver of thyroidectomized larvae after daily injection of 0.3 IU of mammalian prolactin. Since under the same conditions mammalian prolactin was seen to promote an early appearance of arginase in the liver of normal larvae, it is postulated that prolactin action is mediated by thyroidal stimulation.

Further study on the changes in the concentration of prolactin-binding sites in different organs of Xenopus laevis male and female, kept under dry conditions and then returned to water (their natural habitat)

The binding of 125I-labeled ovine prolactin (125I-oPRL) to membranes from the kidney and liver of Xenopus laevis male and female specimens (Experiment I) and from the kidney, epidermis, and liver of female specimens (Experiment II) (1) kept in an aquatic environment, (2) exposed for 2 weeks to dehydrating conditions, and (3) then placed back into their aquaria after exposure to dehydrating conditions (Experiment II) was studied. No significant sex differences in PRL binding to kidney, epidermis, and liver were found. A highly significant drop in PRL specific binding to the membranes from the kidney and epidermis is brought about in the specimens from both sexes exposed to dehydrating conditions. The results obtained by MgCl2 treatment in vitro of the membranes under study for an estimation of total PRL receptor concentrations seem to point to an actual decrease in PRL specific binding sites. The values of PRL specific binding to the membranes from the liver are not affected by dehydration of the animals (Experiment I and II) or their subsequent rehydration (Experiment II). In rehydrated females (Experiment II), PRL binding values were closely related to those recorded in females permanently maintained in water (controls).

Prolactin binding sites in Xenopus laevis tissues: Comparison between normal and dehydrated animals

The binding of 125I-labeled ovine prolactin (125I-oPRL) to membranes from the kidney, epidermis, liver, and testis of Xenopus laevis adult specimens either kept in an aquatic environment or exposed for 2 weeks to dehydrating conditions was studied. Prolactin binding specificity was assayed through competition with several unlabeled hormones (oPRL, hGH, rGH, rLH, and porcine insulin). In the animal exposed to dehydrating conditions a statistically highly significant reduction in prolactin binding to the membranes from the kidney and epidermis was recorded. No significant variations were revealed by the membranes from the liver and testis. The reduction detected in the binding of 125I-oPRL is not related to the dissociation constant, but to the number of PRL binding sites. Since PRL ranks among the few peptide hormones whose rise in the bloodstream promotes an increase in the number of their own receptors, the reduction of its binding sites in Xenopus specimens exposed to dehydration might lend some support to our earlier hypothesis that transfer to a dehydrating environment may bring about, in this totally aquatic species, some decrease in the blood PRL levels.

Biochemical responses elicited in normal or prolactin-treated Xenopus laevis (Daudin) specimens by environmental changes

Abstract 1. 1. Biochemical responses to environmental changes were recorded in normal or prolactin-treated Xenopus laevis specimens. 2. 2. Maintenance on moist moss elicits the urea cycle activation, while prolactin does not; hepatic ammonia concentration decreases in both cases. 3. 3. In the animals reared on moist moss the activity of intestine alkaline phosphomonoesterase is enhanced, but drops significantly after prolactin treatment; this enzyme is not significantly reduced in fresh-water prolactintreated animals. 4. 4. Both rearing on moist moss and prolactin treatment elicit sodium gain in the muscle; permanence on moist moss leads to potassium loss which is abolished by prolactin.

Le glycogène et la glucose-6-phosphatase présents dans le foie d'exemplaires adultes de Xenopus laevis Daudin soumis à un traitement par le 4-méthy-2-thiouracile: Recherches biochimiques et histochimiques

Resume Faisant appel a des methodes biochimiques et histochimiques, les auteurs ont observe que le traitement, pendant 70 a 78 jours, par le 4-methyl-2-thiouracile provoquait, chez les exemplaires adultes de Xenopus laevis , une reduction dactivite de la glucose-6-phosphatase du foie. Cette reduction dactivite allait de pair avec la presence dun amas plus important de glycogene hepatique que chez les temoins. Les differences entre animaux normaux et animaux traites—quil sagisse de lactivite de la glucose-6-phosphatase ou de la quantite de glycogene hepatique—sont significatives, au point de vue statistique, an niveau : P = 0,02 (lorsquon calcule et t de Student). Les donnees cytologiques revelent, dans les cellules β des ilots de Langerhans de Xenopus laevis , un certain degre de degranulation que les auteurs interpretent comme un indice de mise en circulation dinsuline. Les auteurs discutent succinctement les rapports qui sont susceptibles dexister entre les resultats ci-dessus.

Mono- and triphosphate nucleotides, adenylatecyclase and phosphodiesterase activities in the intestine of normal or prolactin-treated Bufo bufo Larvae

Abstract The present investigation was undertaken in an attempt to assess to what extent, if any, changes in cyclic AMP levels (known to be affected by thyroidal hormones) in tissues are correlated with the delay in the intestinal regression elicited by exogenous prolactin in anuran larvae at advanced metamorphic stages, despite thyroid stimulation promoted by this hormone. The substrates of adenylatecyclase and phosphodiesterase reactions and the activities of both enzymes were assayed in the intestine of ovine prolactin-treated or untreated Bufo bufo larvae . The results obtained demonstrate the existence of significant differences in both the substrate levels and the rates of enzymatic activities. Appreciably lower cyclic AMP levels were recorded in prolactin-treated larvae, along with a considerable drop in adenylatecyclase and some rise in phosphodiesterase activities (the latter appearing to be involved to a lesser extent in the regulation of the levels of the cyclic nucleotide). The findings reported here are examined in the light of present-day knowledge of hormonal regulation of metamorphosis and on the basis of some data concerning the possible mechanism of action of cyclic AMP at the cellular level.