Biomedical subjects
Publications and source records attributed to R Maraud.
A morphological and physiological study of an embryonic thyroid grafted in a chick embryo showed that it developed according to the endocrine status of the host. Its relative age appreciated at various stages of embryonic life is different from that of a gland developing normally during similar lengths of time.
The capability of an embryonic testis graft to induce a male gonadal sex differentiation in genetically female chick embryos was significantly enhanced by the administration of a antiestrogenic drug (tamoxifen). This observation reinforces the view that the experimentally-induced testis differentiation depends chiefly on a inhibition of estrogen influence.
The mesonephros of the chick embryo normally begins to regress during the second half of embryonic life. Experimental methods, such as adenohypophysis grafting, hypophysectomy or use of antithyroid drugs, which stimulate or depress the thyroid function of the embryo, modified accordingly the regressive processes occurring in the mesonephric Malpighian corpuscles, particularly at the level of the glomerular basement laminae. These results as well as the known sensitivity of the mesonephros to thyroxine and the concordance between the steps of embryonic thyroid development and the mesonephric modifications show that the thyroid normally plays a major determining role in this phenomenon.
A hypophyseal pars distalis from an 11-day-old chick embryonic donor was implanted in the extraembryonic coelom of a 3-day-old recipient in order to evaluate the reactions of the thyroid of the host embryo and thus the functional capabilities of the grafted pituitary related to the thyroid. The graft did not modify the general growth of the embryo, but strongly influenced thyroidal development. The volume, colloid content, and radioiodide uptake of the thyroid gland were significantly increased, from Day 10 of incubation, compared with controls, as was the development of cytological structures, studied with the electron microscope. However, all these characteristics progressively returned to normal values between Days 14 and 17, in spite of the presence of this additional hypophysis. The grafted hypophysis thus acted autonomously during a first period resulting in increased stimulation of the thyroid. However, from Day 14, the influence of the graft decreased progressively and disappeared after Day 16. This signified the loss of its autonomy, and the mechanism of this loss, particularly the possible role of the hypothalamus, is discussed.
Female chick embryos grafted with a piece of embryonic testis manifest in a high percentage of cases a regression of their Müllerian ducts (MD) under the influence of a anti-Müllerian hormone (AMH) secreted by the graft. Puromycine or cAMP administered to grafted females reduced significantly the percentage of those presenting a MD regression. In the present work puromycin or cAMP was administered to the male graft-donor embryos and not to the grafted females as was done previously. A testis graft from a puromycin-pretreated donor was significantly less active on the MD than that from a normal embryo. It could be then concluded that puromycin acted at the level of the testis by inhibiting the AMH production. On the other hand, the treatment of donors with cAMP did not modify their testes with regard to their action on the grafted female MD. This showed that cAMP directly protected the MD against the AMH.
The sex differentiation of the female chick embryo can be totally inverted toward the male sex by an early extraembryonic testis grafting. This sex reversal remains permanent, as shown by three adult fowls described in this paper. They possess two testes associated with normally differentiated male excretory ducts and their Müllerian ducts have regressed. The development of male sex characteristics such as external features, behavior and complete spermatogenesis is evidence that these cocks have endocrine and exocrine capabilities similar to those of normal cocks. Although these cocks were able to mate with female fowls, they were sterile. A mechanism is discussed by which grafted testes induce such modifications in females. Hypotheses considering the heterogametic sex (female in birds) as exerting a dominant influence on the phenotypic sexual differentiation can be discarded in light of our results because a homogametic testis provokes the definitive sex inversion of a female.
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The human Sipple syndrome associates a thyroid-C-cell tumor and a pheochromocytoma. A treatment with the antithyroid drug thiamazole allows obtaining experimentally a similar syndrome in rat. Present paper seeks to analyse changes which happened in the medullary zone of adrenal glands before and during the development of the tumors. During the treatment by thiamazole both adrenal cortex and medulla were atrophied. After the treatment was stopped, the weight of the gland increased, as compared with its previous state, and this was chiefly due to the hyperplasia of medullary cells, from which pheochromocytomas originate. The initial atrophy of adrenal gland depends on the thiamazole-induced hyperthyroidism, but the mechanism of the medullary hyperplasia subsequent to the treatment ending is unknown. It results probably from a secondary hyperthyroidism.
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When rats are treated by an antithyroid drug as the thiamazole, an hyperplasia of the parafollicular thyroideal cells can occur during the treatment, as shown in our previous works, or not, as in the present experiment. This difference depends on the dose of drug used, but it both cases parafollicular tumours never appear during this treatment. Whatever was the initial reaction of the parafollicular cells during the treatment, an important hyperplasia of these cells always expands after its stop and is frequently followed by the development of parafollicular tumours. Then, the initial hyperplasia sometimes obtained is not prerequisite for the formation of neoplasm. The mechanism of tumoral formation must be investigated in the disorders which follow the stop of the treatment.
Sipple syndrome, associating a C cells or parafollicular thyroid tumor and a pheochromocytoma of the medullary part of adrenal gland, can be experimentally induced with the use of an antithyroid drug, the thiamazole, in the rat. The treatment is applied here either between 3 and 11 months, or between 6 and 14 months of age. Tumors appear a long time after the treatment is stopped. Hypotheses are proposed to explain this phenomenon.
During life of normal rat, it appears an hyperplasia of thyroïdeal C cells, eventually till tumors, a progressive hypertrophy of parathyroïd glands and a fall of calcemia. Chronological study of these phenomena shows that C cells hyperplasia precedes parathyroïd hypertrophy. This last so appears as a reaction against hypocalcemia provoked by hyperplasia of parafollicular cells.
After administration of testosterone propionate to male chick embryos and chickens, their testis have an activity, on the retrogression of mullerian ducts, much more important than that observed in testis of normal subjects of the same age, activity measured by grafting testis fragments in undifferentiated female chick embryos. The results suggest that testosterone gives such an effect by inhibiting pituitary gonadotropins, peculiarly FSH.
When embryonic testes are grafted in the coelom of female chick embryos, one observes significantly related effects on the mullerian ducts which regress more or less and on the gonads, with inhibition of the left ovary and eventual transformation of the right rudiment into a testes. The hormone responsible for mullerian regression is also a testes inductor.
Hypothyroidism is induced in rats treated with thiamazole, an antithyroid drug. If this phase lasts long enough, the follicular cells develop adenomas. Within the same period, the number of parafollicular or C cells increases threefold on an average, but without producing corresponding adenomas, the formation of which is inhibited. When treatment is stopped, a second phase appears during which thyroid function reverts to normal. The previously observed inhibition disappears, and, after a period of latency, the hyperplastic C cells develop parafollicular adenomas. The type of tumors to be found in treated rats (either of them, or both simultaneously) is determined by respective durations of the two phases. The endocrine mechanisms of these phenomena are discussed.
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The population of wild boars living in the wood of Chize contains 25 % of animals having a clear coloured fur. Chromosomal study of these, don't reveal any anomaly of number or structure of their chromosomes. This modification seems be due to a genic mutation and not to an eventual hybridization with domestic pigs.
Theophyllin and puromycine, inhibitors of the enzyme phosphodiesterase and AMPc are all able to inhibit the retrogression of mullerian ducts in the female chick embryo, grafted with an embryonic testis. We can think that these results are explained by an inhibitory action of AMPc on the mechanisms responsible for the mullerian retrogression. So the chick embryo reacts similarly as do the mammalian embryo.