Lis Olesen Larsen

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.

Effects of isoenergetic overfeeding of either carbohydrate or fat in young men.

Ten pairs of normal men were overfed by 5 MJ/d for 21 d with either a carbohydrate-rich or a fat-rich diet (C- and F-group). The two subjects in each pair were requested to follow each other throughout the day to ensure similar physical activity and were otherwise allowed to maintain normal daily life. The increase in body weight, fat free mass and fat mass showed great variation, the mean increases being 1.5 kg, 0.6 kg and 0.9 kg respectively. No significant differences between the C- and F-group were observed. Heat production during sleep did not change during overfeeding. The RQ during sleep was 0.86 and 0.78 in the C- and F-group respectively. The accumulated faecal loss of energy, DM, carbohydrate and protein was significantly higher in the C- compared with the F-group (30, 44, 69 and 51% higher respectively), whereas the fat loss was the same in the two groups. N balance was not different between the C- and F-group and was positive. Fractional contribution from hepatic de novo lipogenesis, as measured by mass isotopomer distribution analysis after administration of [1-(13)C]acetate, was 0.20 and 0.03 in the C-group and the F-group respectively. Absolute hepatic de novo lipogenesis in the C-group was on average 211 g per 21 d. Whole-body de novo lipogenesis, as obtained by the difference between fat mass increase and dietary fat available for storage, was positive in six of the ten subjects in the C-group (mean 332 (SEM 191)g per 21 d). The change in plasma leptin concentration was positively correlated with the change in fat mass. Thus, fat storage during overfeeding of isoenergetic amounts of diets rich in carbohydrate or in fat was not significantly different, and carbohydrates seemed to be converted to fat by both hepatic and extrahepatic lipogenesis.

Effects of hypophysectomy in the cyclostome, Lampetra fluviatilis (L.) Gray

A description is given of the sexual development in normal river lampreys [Lampetra fluviatilis (L) Gray], together with a report on its response to different temperatures. The effects of total or partial hypophysectomy on sexual development, reduction in length of the body, and occurrence of death after spawning are described. After extirpation of the pro- and mesoadenphypophysis secondary sexual characters develop only sporadically. No release of sperm into the body cavity is found in males, but spermatogenesis proceeds and spermatozoa are produced. In females ovulation is not accomplished, but growth of eggs continues, although at a reduced level compared with normal females. The results of partial hypophysectomy show that gonadotropin is produced in the measoadenohypophysis and probably also in the proadenohypophysis. In males appearance of secondary sexual characters and release of sperm into the body cavity seem to depend on the same gonadotropic hormone, but in females it is suggested that two different hormones are secreted, one inducing egg growth and secondary sexual characters, and the other being necessary for ovulation. The possibility that reduction in length before spawning and death after spawning are dependent upon hypophysial hormones different from gonadotropin is discussed.

Structure of the toad epidermis during the moulting cycle

SummaryChanges in the ultrastructure of the toad epidermis during the moulting cycle are described on the basis of 17 skin preparations fixed in consecutive phases of the cycle.Our previous light microscopical findings that morphological changes are mainly restricted to a short period prior to and after shedding are confirmed. Differentiation of zonulae occludentes in the new replacement layer after shedding is described and discussed in relation to the changes in ion permeability after the moult.Changes in appearance and distribution of filaments and of two different types of granules during the moulting cycle are described and discussed in relation to current views on amphibian keratinization; it is concluded that the initial phase of keratinization in the toad is very rapid and with a high degree of synchrony, whereas the laying-down of interfibrillar, central dense matrix in the new stratum corneum takes up to 24 hours and is less synchronous.The separation of the old stratum corneum from the replacement layer is gradual; it may be accomplished by rupture of “ pillars ” bearing the desmosomal complexes between stratum corneum and the replacement layer, or by breaking within the desmosomes themselves. Observed changes in granular content of the replacement layer are considered of no importance for this process, since the time sequence of discharge into the subcorneal space is not correlated with the initiation of separation. Other possible mechanisms of separation are discussed.

Nature of the nervous control of pars intermedia function in amphibians: Rate of functional recovery after denervation

Abstract The rate and extent of recovery of the control of pars intermedia function have been followed in Xenopus laevis and Bufo bufo after denervation of the neurointer-mediate lobe of the hypophysis, and in metamorphosed Ambystoma mexicanum after extirpation and transplantation of the whole hypophysis onto the infundibulum. All three species behaved in a similar way. Control of intermedin release could not be demonstrated for at least some weeks after the operation, but in most cases a weak control was re-established after one to several months and up to 1 year. In one Xenopus , control had not reappeared even after a period of almost 2 year. After the reappearance of an incomplete control, further progress was slow and normal conditions were often never reached. The results are discussed, and it is concluded that the pattern of events during the re-establishment of control of pars intermedia function after sectioning of its nerve supply is consistent with the theory that this control is mediated by ordinary nerves and not by neurosecretory nerves.

Further observations on molting and its hormonal control in Bufo bufo (L.)

Abstract The normal molting in the toad Bufo bufo falls into two main phases. During the first, the stratum corneum separates from the underlying cells and is converted into a slough; the second main phase includes adoption of the molting position, secretion of mucus, and shedding and eating of the slough. Extirpation of the pars distalis of the hypophysis inhibits shedding, whereas the formation of new sloughs continues at an increased rate. A slough was most often found to form within 2 or 3 days after the operation. The premature formation of a slough after hypophysectomy could be further accelerated by injection of ACTH or corticosteroids about 18 hours, or a little more, after the operation. After such injections, a complete molt could be produced within about 6–9 hours. A molt has never been produced by injection of ACTH or corticosteroid in normal toads or in toads exposed to the hormonal deficiency following extirpation of the pars distalis for less than about 17 hours. The shedding behavior presumably results from the autonomous activity of a shedding center, since the behavior can proceed in an apparently normal way in the absence of the slough. However, shedding behavior could not be induced by injection of ACTH in the hypophysectomized toad in the absence of a slough. It is therefore suggested that the presence, or the formation, of the slough is necessary for the priming of the shedding center, and thus for the coordination of the formation of the slough and its subsequent shedding during normal molting. ACTH or corticosteroids are the only hormones known to induce molting in the toad Bufo bufo . Corticosterone was somewhat more effective than aldosterone in inducing molting in the hypophysectomized toads, whereas cortisol was relatively ineffective. It has not been possible to re-establish normal molting by single daily injections of ACTH or extracts of pars distalis, perhaps because of the highly varying levels of circulating adrenocortical hormones that result. The pattern of secretion of ACTH may therefore be of importance in securing normal molting. However, the rhythmic formation of the slough and its subsequent shedding is probably not timed by a corresponding rhythmic increase in adrenocortical activity, because premature molting never followed injections of ACTH in normal toads. It cannot be excluded that the molting rhythm is timed by a rhythmic decrease in adrenocortical activity. Nevertheless, it is considered more likely that the molting rhythm is inherent in the skin and proceeds independently of variations in the adrenocortical activity above a certain level.

Molting and its hormonal control in toads

Abstract A description is given of molting in normal toads, Bufo bufo (L.), and in toads with pars distalis of the hypophysis extirpated. Normal toads molted every seventh to eleventh day, at 20°–23°C, with no significant seasonal variation. Change of environment often suppressed molting for a few days. Extirpation of the pars distalis increased the frequency of formation and separation of new cornified layers, but suppressed shedding. In toads with extirpated pars distalis, repeated injections of extracts of pars distalis or of DCA caused more or less normal molts, at a frequency of about twice the normal. Usually the time interval between separation and shedding of the cornified layer was abnormally long. Thyroxine did not cause shedding, but shortened the time of survival of the operated toads. Repeated injections of extracts of pars distalis or of DCA into normal toads increased the frequency of molting, and often increased the time interval between separation and shedding of the cornified layer. Thyroxine likewise increased the frequency, but never caused abnormal loosening of the stratum corneum. Some reference is made to the functions of the endocrine system, in molting in vertebrates, from amphibians to mammals.

Effects of hypophysectomy before and during sexual maturation in the cyclostome, Lampetra fluviatilis (L.) gray

Abstract Extirpation of the pro- and mesoadenohypophysis was performed before and during sexual maturation in order to evaluate the influence of the hypophysis on mobilization of body tissue during starvation and on sexual development, both with respect to initiation and maintenance of the processes involved. Mobilization of tissue from the intestine and the body wall was examined in normal lampreys, and a correlation between reduction in length of the body and mobilization of body tissue was established. The mobilization was slow until shortly before sexual maturation and then rapid, most pronounced in females. Lampreys hypophysectomized in January, before sexual maturation, continued the slow reduction in length and often survived for a long time after the normal controls had died. Some of the lampreys operated in March, during sexual maturation, continued the rapid reduction in length and died in the same period as control lampreys, whereas others stopped the rapid reduction in length and survived for a long time. It is suggested that starvation may be a major cause of natural death after spawning, and that hypophysectomized lampreys survive because of a slower depletion of body tissue as apparent from the slower rate of reduction in length. The concentration of glucose in blood was about 30 mg/100 ml in hypophysectomized and in immature lampreys. After sexual maturation in normal lampreys the values rose significantly, especially in females. Growth of the ovary was accelerated during sexual maturation, and a conspicuous granular layer consisting of big, well-separated cells laden with mucopolysaccharide developed in the vegetative end of the egg. This layer did not develop in females hypophysectomized before sexual maturation. In females hypophysectomized in March, the cells of the granular layer formed a continuous layer at death in those females in which ovulation had not taken place. It is suggested that the granular layer is involved in the process of ovulation. Spermiation and ovulation never occurred in lampreys hypophysectomized in January. In males operated in March spermiation occurred in all, but sometimes with a considerable delay and accompanied by only slightly developed secondary sex characteristics. In females hypophysectomized in March only one-third ovulated, and always shortly after the operation. Secondary sex characteristics never developed in lampreys hypophysectomized in January. In males hypophysectomized in March, their development stopped or regressed. In females hypophysectomized in March, they continued to develop for some time.

Effects of Testosterone and oestradiol on gonadectomized and intact male and female river lampreys (Lampetra fluviatilis (L.) Gray)

Abstract Pellets of testosterone (25 mg) or oestradiol-17β (25 mg) were implanted into adult gonadectomized or intact male or female river lampreys before the period of sexual maturation. Testosterone induced male secondary sex characters in gonadectomized males and intact females, and oestradiol-17β induced female sex characters in gonadectomized females and intact males. The homologous sex hormones administered to intact males and females did not accelerate the appearance of secondary sex characters except for growth of the urogenital papilla in the male. The heterologous sex hormones caused a range of effects from inhibition of certain normal changes to stimulation of characters characteristic of the other sex. There was no marked inhibition of spermiation and ovulation, and no convincing signs of a negative feedback between sex hormones and gonadotropin secretion. Oestradiol released from the implanted pellets was found to act on untreated males kept in the same tank, so oestradiol can be transferred via the water from one lamprey to another. The intestinal hypertrophy observed after gonadectomy was not counteracted by sex hormones. Oestradiol in several lampreys increased the survival beyond the time of natural death after spawning of untreated lampreys. During the period of prolonged survival the rate of reduction in length of the body was slowed down.

Effect of gonadectomy and hypophysectomy on plasma steroid levels in male and female lampreys (Lampetra fluviatilis, L.)

Testosterone, estradiol, and dehydroepiandrosterone (T, E2, and DHA) were measured by RIA in plasma samples from three groups of sexually immature male and female (male, female) river lampreys: (I) intact, (II) gonadectomized, or (III) with pro- and mesoadenohypophysis removed (hypophysectomized). T levels were around 0.1 ng/ml in both I male and I female and increased significantly in all operated groups, especially in II male, to 1.2 ng/ml. E2 levels were between 0.7 and 1 ng/ml in I male and I female and were significantly elevated only in II male to 2.0 ng/ml. DHA levels showed significant decreases, from around 0.9 ng/ml in I male and I female, in both operated groups. It is suggested that T and E2 are secreted from a nongonadal source in both sexes and then converted to biologically active sex hormones in the gonads. Therefore T and E2 do not decrease, and may even accumulate, in the blood after gonadectomy. Since extirpation of the pro- and mesoadenohypophysis was not followed by a decrease in T and E2, their secretion may be stimulated by a hormone from another part of the pituitary such as the metaadenohypophysis.