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Biomedical subjects

R Collu

Publications and source records attributed to R Collu.

At least 73 records · Page 4Linked to original sources
PubMed1982

Pubertal development: normal, precocious and delayed.

The present concepts on the neuroendocrine mechanisms which trigger pubertal development and modulate the progression towards sexual maturity have been reviewed. Essentially, puberty is presented as a continuum, the programming of which is initiated prenatally and which ends in adult life when all hormonal secretions become autoregulated. This continuum is dependent on a delicate equilibrium between CNS neurohormones (GnRH), neurotransmitters (biogenic amines), pituitary gonadotrophin (FSH, LH) secretion and the end-organ response (testis or ovary) through the activation of specific membrane receptors. The gonadal sex steroids (T, OE2) will activate specific cytoplasmic and nuclear receptors of target tissues and exert their biological action. Initially, the activity of the HPGA is manifested by nocturnal LH peaks, followed by increased gonadal secretion of T or OE2. Extremely sensitive to negative feedback by circulating androgen and/or oestrogen in prepuberty, an hypothalamic regulatory system called the gonadostat increases its threshold of sensitivity and eventually becomes autoregulated at a higher feedback level. Progressively, the hypothalamus becomes sensitive to positive feedback action of gonadal hormones, this phenomenon being important for the onset of ovulation. It is likely also that adrenal androgens play a permissive and supportive role in the onset and progression of pubertal development. Finally, full maturity is reached, with final adult height through fusion of the epiphysis, and fertility is achieved. The clinical manifestations of each developmental stage of puberty are described and abnormalities of sexual development reviewed. While over 90 per cent of cases of precocious pubertal development are idiopathic in girls, a space-occupying lesion in the hypothalamic-pituitary region is frequent in boys. Dissociated pubertal signs (premature adrenarche, pubarche, thelarche, menarche) are discussed, together with diagnosis and treatment of precocious puberty, whether it is idiopathic or occurring independently of the activation of the HPGA. In addition to delay of puberty on a constitutional basis, or related to chronic endocrine or non-endocrine diseases, the main clinical entities with gonadal insufficiency, primary (hypergonadotrophic) or secondary (hypogonadotrophic), are reviewed in boys and girls and their investigation and treatment discussed.

Adolescent↗
PubMed1982

Stress-induced testicular hyposensitivity to gonadotropin in rats. Role of the pituitary gland.

The time course of stress-induced testicular hyposensitivity to gonadotropins was studied in hypophysectomized or naloxone-treated rats exposed to various periods of immobilization. Blood was collected from a chronically indwelling intra-atrial catheter every hour for luteinizing hormone (LH) and testosterone (T) measurement. Eight hours of immobilization completely suppressed T secretion without significant effect on LH. Human chorionic gonadotropin (hCG, 5 IU/rat, i.m.) induced a marked increase in plasma T levels in normal control groups 3 h post-injection while in immobilized rats the response was completely abolished, even after only 30 min of stress. In hypophysectomized rats, as expected, plasma T levels were undetectable, but, contrary to results obtained in normal animals, hCG induced a similar increase of plasma T levels both in control and stressed rats. Immobilization stress failed to inhibit plasma T values in hypophysectomized rats pretreated for 4 days with human menopausal gonadotropin (hMG) + hCG, while it did so in similarly treated normal animals. Naloxone induced a rise of plasma LH and T levels in control rats, but did not antagonize the stress-induced fall of plasma T concentration. In all groups, steroid testicular content mimicked variations of plasma T values. In particular, in stressed animals the lack of accumulation of testicular 17-hydroxyprogesterone probably reflected a normal activity of 17-20 lyase. These results indicate that stress induces very rapidly a state of Leydig cell hyposensitivity to gonadotropins and a blockade of T biosynthesis. The causal relationship between the two effects is presently not clear but these events seem to be due to stress-induced release of an inhibitory factor of pituitary origin other that endorphin.

Adrenocorticotropic Hormone↗
PubMed1982

Biosynthesis of a putative gonadotropin receptor component by rat leydig cells: isolation of a radiolabeled acidic protein of 79,000 molecular weight by affinity chromatography.

The Leydig cells of the testis are known to possess high affinity receptors for luteinizing hormone and human chorionic gonadotropin (hCG), but no information concerning the synthesis of these receptors is available yet. In order to investigate this question, we have purified crude rat interstitial cell preparations on discontinuous Percoll gradients, and Leydig cells recovered from fractions demonstrating maximum testosterone production and hCG binding capacity were incubated for 17 h in a culture medium containing [35S]methionine. Radioactive proteins solubilized with Triton X-100 were submitted to affinity chromatography on a resin consisting of hCG covalently linked to agarose. Proteins bound to the column were analyzed by two-dimensional gel electrophoresis. Autoradiography of the gel revealed a major protein (molecular weight: 79,000; pI 4.5) whose binding to the resin could be greatly diminished by an excess of hCG. The electrophoretic properties of this protein are similar to those of previously isolated gonadotropin receptor components.

Animals↗
PubMed1981

Lack of tolerance to long-term neuroleptic treatment in dopamine tuberoinfundibular system.

The plasma prolactin (PRL) levels of 35 chronic schizophrenic patients undergoing long-term maintenance treatment with neuroleptic drugs were measured before and after either neuroleptic withdrawal or a switch to a fixed dose of chlorpromazine 900 mg/day. In both men and women there tended to be a significant correlation between the initial log plasma PRL level while on neuroleptic maintenance treatment and the dosage received converted to chlorpromazine equivalents. Neuroleptic withdrawal in ech of 19 cases was followed by a decline in PRL plasma levels. Switching to chlorpromazine 900 mg/day (16 cases) produced either increases or decreases in PRL plasma levels that were significantly correlated with the change in neuroleptic dosage converted to chlorpromazine equivalents. Thus there was no evidence of tolerance to the PRL-elevating effect of neuroleptics in these patients who had been treated for many years with neuroleptics.

Adult↗
PubMed1981

Sodium-dependent interaction of benzamides with dopamine receptors in rat and dog anterior pituitary glands.

Sulpiride and other benzamides' displacement of [3H]-spiroperidol binding to rat and dog anterior pituitary dopaminergic receptors was found to be selectively sodium dependent, while typical neuroleptic activity was not influenced by NaCl. These results indicate the existence in the anterior pituitary of a subpopulation of dopaminergic receptors with which benzamides interact.

Animals↗
PubMed1981

Circulating LH, FSH, prolactin, testosterone, delta 4-androstenedione, dehydroepiandrosterone sulfate and cortisol levels in the fetus in late gestation and in newborn male and female lambs.

Gonadotropins, prolactin (PRL), testosterone (T), delta 4-androstenedione, dehydroepiandrosterone sulfate and cortisol (F) levels were determined from 14 days before birth to term in 3 female and 3 male ovine fetuses with a chronically implanted venous catheter, and in the same animals from birth to 72 h of age. In both sexes, plasma gonadotropins and androgens were low throughout the period of study while plasma F increased with gestational age. After birth, plasma gonadotropins and PRL tended to increase progressively with time while PRL concentrations were significantly higher in female than in male lambs. F and T concentrations decreased significantly within the first 12 and 6 h of postnatal life. Higher T values were again observed at 36 h in male lambs. These data indicate that the fetal hypothalamic-pituitary-gonadal axis is relatively quiescent in the last 14 days of gestation but is activated within the first 72 h after birth.

Aging↗
PubMed1981

Perinatal activity of the hypothalamic-pituitary-gonadal axis in the lamb. III. LH, testosterone and prolactin secretory pattern in newborn lambs.

Crossbred male and female lambs from Suffolk rams and Dorset-Finnish ewes born in January and February were studied at 1, 3, 7, 21 and 28 days of age and female lambs at 14 days. Ultradian variations in plasma luteinizing hormone (LH), prolactin (PRL) and testosterone were studied at 30-min intervals during a 4-hour period. In female lambs LH secretory peaks were observed at 7 days of age the amplitude of LH peaks increasing 8-fold between 7 and 14 days and 2-fold between 21 and 28 days. The number of secretory peaks also increased with age. Ultradian variations in PRL were observed from 1 day of age, the amplitude of the PRL peaks increasing also with age. In male lambs, LH and testosterone peaks were observed at 3 days of age, the testosterone peak being preceded by or concomitant with LH peaks. The amplitude of LH peaks increased with age together with basal testosterone levels although the amplitude of testosterone peaks was unchanged. This study demonstrates pulsatile secretion of LH and PRL in lambs of both sexes and of testosterone in male lambs in the first week of postnatal life. In addition, since the ovine testis is responsive to endogenous gonadotropic stimulation at this period, it is suggested that the hypothalamic-pituitary-gonadal axis is already operative at this age. It can be concluded that the hypothalamic activity concerned with pulsatile LH and prolactin secretion is present very early in the lamb neonate.

Animals↗
PubMed1981

Perinatal activity of the hypothalamic-pituitary-gonadal axis in the lamb. IV. Testicular responsiveness to hCG from 1 through 28 days of life.

Previous studies in this laboratory have shown the existence of an early postnatal activation of the hypothalamic-pituitary-gonadal axis (HPGA) in the male lamb which was present at 2 and 4 weeks of age. In order to define more precisely the time sequence of HPGA activity, we have studied the in vivo and in vitro testicular responsiveness to human chorionic gonadotropin (hCG) of the immature lamb at 1, 3, 7, 14, 21 and 28 days of life. Plasma testosterone (T) increments (delta) after hCG were lower in 1-day-old animals than in other age groups. Testicular concentrations of T, dehydroepiandrosterone and 17-hydroxyprogesterone increased from 1 to 14 days. Testicular 17, 20 lyase activity rose significantly with age but was not influenced by hCG. hCG and dibutyryl cyclic AMP increased significantly the T production by enriched interstitial cell preparation at 1, 3, and 7 days, the greatest response being found at 7 days. hCG also increased significantly the T production at 14 days. These data suggest that the lamb testis has the capacity to respond to hCG in vivo and to various stimuli vitro from the 1st day of life and that the response reaches a plateau from 2 to 4 weeks after birth.

Androstenedione↗
PubMed1981

Effects of chronic intermittent immobilization stress on rat testicular androgenic function.

In rats, chronic intermittent immobilization stress induced a drastic fall in the plasma concentration and testicular content of testosterone (T) without detectable changes in plasma LH values. In vitro basal T production by interstitial cell-enriched preparations from stressed rats and the responses to hCG, dibutyryl cAMP, or choleratoxin were suppressed, while cAMP production was not modified. The increase in plasma T concentrations in control animals was identical after the in vivo injection of 5, 10, or 50 IU hCG, while stressed rats failed to respond to 5 IU, but showed a response similar to that of control animals with 10 and 50 IU. These results suggest that chronic intermittent immobilization stress decreases Leydig cell sensitivity to gonadotropins.

Animals↗
PubMed1980

Sodium-dependent interaction of benzamides with dopamine receptors.

Sulpiride and other benzamide (BM)-displacing activity on [3H]-spiroperidol ([3H]SPIR) binding by rat striatal dopaminergic receptors was found to be uniquely sodium-dependent, while classical neuroleptic (NL) activity was not influenced by NaCl. These results suggest the existence of at least two populations of striatal dopaminergic receptors, sodium-dependent and sodium-independent, through which BM and NL respectively interact.

Animals↗
PubMed1980

Perinatal activity of the hypothalamic-pituitary-gonadal axis in the lamb. II. In vitro testicular response to human chorionic gonadotropin and choleratoxin in the first 2 months of life.

Testicular response to human chorionic gonadotropin (hCG) was studied in male lambs. Adenosine 3':5'-cyclic monophosphate (cAMP), testosterone (T), delta 4-androstenedione and 17 alpha-hydroxyprogesterone content and cAMP and T production by dispersed interstitial cells were assessed in control and hCG-pretreated animals. Plasma T levels increased after hCG at 1, 4 and 8 weeks. Increments in the testicular content of cAMP, delta 4-androstenedione, and T were greater at 8 weeks and that of 17 alpha-hydroxyprogesterone and 125I-hCG binding to dispersed interstitial cells were identical at all ages. cAMP and T production by dispersed interstitial cells from nonstimulated animals and the response to hCG and choleratoxin were similar in all lambs. In contrast, cAMP and T production were higher at 1 week only in animals pretreated with hCG in vivo. These data are compatible with hCG-induced desensitization at 4 and 8 weeks.

Androstenedione↗