PubMed Health⌕ Search

Biomedical subjects

A G Byskov

Publications and source records attributed to A G Byskov.

At least 91 records · Page 5Linked to original sources
PubMed1981

Meiosis-inducing and meiosis-preventing substances in human male reproductive organs.

The initiation of meiosis is controlled by two substances, a meiosis-inducing substance (MIS) and a meiosis-preventing substance (MPS). These have been shown to be present in reproductive organs of both sexes of different mammals. In this investigation MIS and MPS were also shown to be present in man. MIS was found in fetal and adult epididymides and testes. MPS was obtained from the tests of one fetus, which was delivered by laparotomy. MPS could not be found in the testes of another fetus, which was aborted by prostaglandin F2 alpha and oxytocin. No or only weak MPS activity was detectable in the adult testis. This report indicates that continued spermatogenesis might be influenced by the MIS:MPS ratio. MPS was shown not to be species-specific. MIS and MPS activity have been evaluated by qualitative scoring of the different germ cell stages present in fetal gonads after culture in used media containing MIS or MPS.

Adult↗
PubMed1980

Temperature measurements of rabbit antral follicles.

The temperature of 40 antral follicles in 16 rabbits was measured by microthermoelectrodes and by thermovision during anaesthesia. The temperature in the follicles was 2.8 +/- 0.2 degree C lower than the core body temperature and 1.4 +/- 0.2 degree C lower than in the ovarian stroma. No differences were observed between the temperatures obtained from large and small antral follicles, and different conditions of measurement gave similar results.

Animals↗
PubMed1979

Induction of meiosis in fetal mouse testis in vitro by rete testis tissue from pubertal mice and bulls.

To test whether a meiosis-inducing substance (MIS) is responsible for the induction of meiosis in the testis at puberty, pubertal mouse rete testis was grown with (1) fetal undifferentiated mouse testis attached to the other side of a filter and (2) the used medium obtained from culture of the rete testis of a pubertal bull for 2 days. In both systems meiosis was induced in the fetal testis showing that MIS is not species specific. No meiosis-preventing effect was seen and it is concluded that meiosis in the testis is triggered at puberty as a result of the activity of the MIS concomitant with decreased activity of the meiosis-preventing substance.

Animals↗
PubMed1979

The morphology of fetal gonads of spontaneous mouse hermaphrodites.

The gonads of 107 spontaneous, chromosomal mosaic, day-15 fetal hermaphrodites derived from BALB/cWt strain male mice are described and photographs of seven gonads representative of the major types are presented. There were 16 ovaries, 15 testes, and 183 ovotestes. The ovotestes contained on the average more testicular tissue than ovarian, and the ovarian tissue was more frequently located at the gonad poles, particularly the craniad pole. There was no difference between left and right sides with regard to gonad type, but more pure gonads were found on the left than on the right side (21/10), Meioses were observed throughout the ovarian tissue and also in some testicular cords, particularly in the caudad pole of the gonad. Some meiotic figures contained sex vesicles. The significance of these findings is discussed in relation to several aspects of sex determination.

Animals↗
PubMed1978

Follicular growth in fetal and prepubertal ovaries of humans and other primates.

Follicular growth begins in the fetal ovary as soon as the first follicles are formed. Although orderly follicular growth is found in the fetal ovary, many of the early growing follicles show abnormalties. Follicles with irregular granulosa layers, with hypertrophied or with underdeveloped theca layers, are characteristic. Such follicles are rarely seen after birth. The ovary during childhood is an active organ in which follicular growth and follicular atresia normally take place. Follicles begin to grow at all ages, differentiate to preantral and antral follicles, but degenerate at various stages of their development before they reach pre-ovulatory sizes. Follicular growth in the fetus and children is dependent on hormones. Fetal gonadotrophins are necessary to ensure normal and sequential follicular growth before birth. During childhood a close correlation between follicle growth, hormone response and hormone production seems to exist. Certain diseases and treatment with cytotoxic agents or radiation to the abdomen influence ovarian development and follicular growth. Chromosome abnormalities, especially Turner's syndrome, trisomy 18 or 21, alter normal ovarian development by reducing the pool of available follicles and inhibiting follicular growth. Treatment with cytotoxic drugs inhibits follicular growth, while abdominal irradiation in childhood unless the ovaries are adequately shielded causes permanent damage by destroying the small follicles.

Abdominal Neoplasms↗
PubMed1978

Follicular development in ovaries of children with Down's syndrome.

Ovaries of children with Down's syndrome were examined histologically in order to determine in what way the ovarian development differed from the normal. Twenty-six specimens obtained at autopsy at various ages between birth and 14 1/2 years were available and compared with ovaries from normal children of similar ages. All ovaries from normal children were characterized by active follicle growth. The ovaries of the children with Down's syndrome, however, showed absence or retardation of follicle growth. Furthermore the number as well as the size of the antral follicles differed from those in the normal ovary. The decrease of the number of small follicles occurs earlier in life in the ovaries of children with Down's syndrome than in the control. The possible relationship between an abnormal ovarian growth pattern and hormonal imbalance is discussed.

Adolescent↗
PubMed1977

Influence of ovarian surface epithelium and rete ovarii on follicle formation.

Early follicle development has been studied in mouse ovaries grafted to immunologically incompetent hosts. Early follicular formation and growth is apparently dependent on the presence of the rete ovarii: the surface epithelium does not seem to play a decisive role. This was shown in transplantation studies of fetal gonads which had been divided into parts with and without the rete ovarii. None of the rete-depleted ovaries exhibited normal follicular differentiation regardless of the presence or absence of the surface epithelium, whereas follicles developed normally in all the implants containing the rete system.

Animals↗
PubMed1976

Induction of meiosis in fetal mouse testis in vitro.

Fetal mouse testes and ovaries with their urogenital connections were cultured singly or in pairs on Nuclepore filters. When a testis in which the sex was not yet morphologically detectable was cultured together with older ovaries containing germ cells which were progressing through the meiotic prophase, the male germ cells were triggered to enter meiosis. When older fetal testes in which the testicular cords have developed were cultured together with ovaries of the same age with germ cells in meiosis, the oocytes were prevented from reaching diplotene stage. It was concluded that the fetal male and female gonads secrete diffusable substances which influence germ cell differentiation. The male gonad secretes a "meiosis-preventing substance" (MPS) which can arrest the female germ cells within the meiotic prophase. The female gonad secretes a "meiosis-inducing substance" (MIS) which can trigger the nondifferentiated male germ cells to enter meiosis.

Animals↗
PubMed1976

Follicular atresia in the infant human ovary.

The pattern of follicular atresia was studied in nine ovaries from children between the ages 3 months and 8 years. Atretic follicles were found among follicles at all stages of development. The percentage of follicles with signs of atresia became larger as the size of the follicles increased. Only 2% of small follicles (Type 3b) showed signs of atresia, while all follicles greater than 1 mm in diameter (Type 8) were atretic. In follicles of Type 5 and larger, four stages of atresia, which represent consecutive stages of a single atretic process, were defined. The beginning of atresia was characterized by the presence of pyknotic granulosa cells. As atresia progressed, the granulosa layer disappeared, the oocyte became necrotic, the follicle collapsed and the theca cells became hypertrophied. The oocyte can degenerate in several ways: it can be penetrated by cells, the nucleus can become pyknotic or it may complete meiotic prophase. It is suggested that the last event is only possible after the oocyte has reached its full size and has completed RNA synthesis.

Child↗
PubMed1976

Protein composition in the fluid of individual bovine follicles.

The proteins in follicular fluid from individual and pooled bovine follicles were studied by gel chromatography and quantitative immunoelectrophoresis. The mean protein concentration was 86-4% of serum; very large proteins were present in only low concentrations. A minimum of 40 individual proteins was distinguished in follicular fluid, and 15 of these proteins were quantitated. A correlation between molecular weight and follicular fluid: serum concentration ratio was found. Fluid from individual follicles differed only in the relative concentrations of small and large proteins. An exception to this was IgG which was occasionally, but never in healthy growing follicles, present in concetrations above 150% of serum. Healthy growing, preovulatory and atretic follicles had higher, and cystic follicles mostly lower, concentrations of small proteins than serum. The concentration of alpha2-macroglobulin in healthy growing follicles never exceeded 16% of serum. The concentration of large proteins in follicular fluid increased with increasing follicle size. Attempts to detect proteins specific to follicular fluid by immunizing rabbits with pooled follicular samples and the follicular fluid proteins not bound by anti-bovine antiserum resulted in production of antibodies against fibrinogen and its split products D+E only.

Albumins↗
PubMed1975

The role of the rete ovarii in meiosis and follicle formation in the cat, mink and ferret.

Ovarian morphology was studied from the inception of meiosis in the cat, mink and ferret. It was shown that "open connections", allowing cellular contact, existed between the intra-ovarian rete cords and the groups of germ cells as well as between the surface epithelium and the germ cells. The germ cells in the innermost part of the cortex and lying in contact with the rete cells were those which were the first to enter meiotic prophase. Later, the more peripheral oogonia transformed to oocytes. The first follicular formations occurred at the innermost part of the cortex. The granulosa cell layers were in open connection with the intra-ovarian rete cords. In the mink and ferret, a certain part of the rete system at the hilus differentiated into the hilar rete body. In all animals, the extra-ovarian rete cells were actively secreting. It is proposed that the rete system interacts with the cortex, initiating the start of meiosis and that the rete cells as well as cells of the surface epithelium contribute to the granulosa cell layer.

Animals↗
PubMed1975

Follicular growth: the basic event in the mouse and human ovary.

Follicular growth is described as a continuum. It goes on at all times, at all ages, uninterrupted by pregnancy or other periods of non-ovulation. A distinction is made between the continuum at the beginning of follicular growth and events concerning the cyclicity at the end of follicular growth, i.e. ovulation. Follicles grow sequentially. Also large follicles continue to grow until they become atretic or ovulate. No evidence for a pool of large follicles held in reserve could be found. Examination of the effect of PMSG on the growth of large follicles showed that this hormone provented the degeneration of large follicles, thus allowing more follicles to grow further. As in the mouse, follicular growth occurs during human infancy and is the normal event during childhood. Ovaries without signs of follicular growth are uncommin in the child and are apparently connected with certain systemic diseases.

Aging↗