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Biomedical subjects

A Lacroix

Publications and source records attributed to A Lacroix.

At least 109 records · Page 6Linked to original sources
PubMed1988

Long-term effects of pinealectomy on testicular function, luteinizing hormone-releasing hormone hypothalamic system, and plasma prolactin levels in the mink, a short-day breeder.

Experiments in minks, as in a number of other seasonal breeders, clearly demonstrate that the pineal gland is essential for the photoperiodic control of reproduction. While maintenance of pineal-intact minks under natural photoperiods results in a set of seasonally appropriate changes in testicular activity, pinealectomized minks undergo none of these changes but rather remain sexually inactive as under long-day conditions. Thus, the consequences of pinealectomy differ from one photoperiodic species to another, but the unifying feature is the organism's need for the pineal gland to respond appropriately to changes in day length. Although the precise mechanism by which the pineal regulates hypothalamic-pituitary gonadal function remains unknown, the results of the present study indicate that, in the mink, luteinizing hormone-releasing hormone axonal transport is affected by pinealectomy. Furthermore, our results suggest that the pineal does not act exclusively upon the neuroendocrine-gonadal system but also acts on other functions that are influenced by photoperiod. Pinealectomized minks left in natural conditions cannot adjust their prolactin secretion in response to either long or short photoperiods. Operated animals continued to have plasma prolactin variations but at irregular intervals and with no apparent relation to the time of the year. The data strengthen the hypothesis that melatonin may act at some point on the hypothalamic neuroendocrine systems, which regulate the two functions differently, and that melatonin is not an anti- or progonadal substance but rather a seasonal transducer.

Animals↗
PubMed1988

Enzymatic oxidation of all-trans retinal to retinoic acid in rat tissues.

The 100,000 x g supernatant (cytosolic) fraction of rat tissue homogenates catalyzes the oxidation of all-trans retinal to retinoic acid. Kidney, testis, and lung were the most active of the tissues examined. The presence of enzyme activity in liver and intestine could be detected only when a substrate concentration beyond the saturation point for retinal reductase was used. Spleen, brain, and plasma had no activity. Boiled supernatants did not catalyze the reaction. The enzymatic product was chemically and physically identified as retinoic acid. The cytosol of kidney tissue also catalyzed the conversion of retinol to retinoic acid. These data indicate that kidney tissue has the highest retinal oxidase activity and suggest that it may play a major role in the oxidative metabolism of retinol in the body.

Aldehyde Oxidoreductases↗
PubMed1987

Plasma levels of retinol in cancer patients supplemented with retinol.

Previous studies have indicated that plasma levels of retinol are decreased in some cancer patients and that lower levels of retinol could be associated with a poor response to chemotherapy. This pilot study was conducted to determine whether it is possible to increase plasma levels of retinol in cancer patients by supplementation with retinol. Plasma levels of retinol were measured by high-performance liquid chromatography in 46 patients treated with chemotherapy for various malignancies and in 43 control individuals; cancer patients were supplemented orally either with 25,000 or 50,000 IU of retinol daily during up to 3 months. Initial levels of retinol were lower in cancer patients than in the control group; the decrease was significant in women with liver metastases but not in men. Women supplemented with 25,000 IU had a significant increase of their retinol levels after 1 month but this effect was not maintained during continued supplementation; in women receiving 50,000 IU daily, a sustained increase in retinol level was maintained during the 3 months of supplementation. In men, a similar trend was produced by the supplementation but the increases were not significant. Retinol levels decreased to initial levels within 1 month of discontinuation of supplementation, indicating the need for continuous supplementation.

Adult↗
PubMed1986

Circadian participation in the photoregulation of testis activity and prolactin secretion in the mink, a short-day breeder.

It has been demonstrated that an endogenous mechanism is involved in photoperiodic time measurement in the mink, a short-day-breeding mannal. A study of testicular activity (testicular volume, plasma testosterone concentration) and plasma prolactin level was carried out in sexually resting minks (the experiment began in November). Groups of minks were kept in the natural photoperiod or subjected to different resonance light-dark (LD) cycles (LD 4:8, LD 4:20, LD 4:32, LD 4:44); an additional group of animals was reared in an ahemeral photoperiod (LD 4:16). A rapid increase of testicular activity was observed in control animals or those kept in LD 4:20 (T 24) and LD 4:44 (T 48). In the other groups of animals, those kept in LD 4:8 (T 12), LD 4:32 (T 36), and LD 4:16 (T 20), testicular function remained at rest. Prolactin secretion was, in contrast, stimulated in the groups kept in LD 4:8 (T 12). LD 4:32 (T 36), and LD 4:16 (T 20), and remained low in the groups kept in LD 4:20 (T 24) and LD 4:44 (T 48). These results show that the effects of the different photoperiodic regimens do not depend on the duration of the photophase, but rather on the period of the LD cycles. The LD cycles that allow an increase of testicular function are those that are inhibitory to reproduction in birds and long-day-breeding mammals. To explain these results, it is suggested that in the mink exposure to light during the circadian photosensitive phase induces inhibition of testicular activity and stimulation of prolactin secretion. To explain the opposite effects of a single photoperiod on testicular function and secretion of prolactin, the hypothesis has been advanced that, in the mink, long days might simultaneously inhibit hypothalamic luteinizing-hormone-releasing hormone (LH-RH) activity and prolactin-inhibiting factor (PIF) activity.

Animals↗
PubMed1985

[Teaching of diabetics: evaluation of the questions put to patients by health care personnel and the usefulness of a pedagogic analysis].

In order to be fully therapeutic diabetes education should allow the patient to understand the mechanisms of the illness as well as the steps to be taken to achieve optimal treatment. In the course of their classes health care personnel ask diabetic patients questions with the intention of encouraging their participation. An education specialist has analysed the use of these questions: their number, their type and their functions' were noted. A) By type of question we refer to the various answers possible. Two groups can be distinguished: 1) limited number of answers possible as the result of a closed question, 2) multiple answers possible as the result of an open question. B) By function of question we refer to the cognitive effect a question may have on the patient. Again two categories can be described. In the first case numbers, terminology or facts learnt by heart; this being the result of questions of simple knowledge. In the second case, the establishment of relationships between facts as well as the solving of problem situations are encouraged by questions of understanding. The study shows that health care personnel tend to put forward closed rather than open questions. Regarding the function of the question most of them aim at simple repetition. Few activate the thinking process. As a result of the pedagogical training our team received concerning the use of questions in patient education an increase in the number of open questions and of questions of understanding was noted. These questions encourage the thinking process and the solving of problems encountered by the patient in the treatment of his/her diabetes.

Diabetes Mellitus↗
PubMed1984

Modulation of glucocorticoid receptors by mitogenic stimuli, glucocorticoids and retinoids in normal human cultured T cells.

Human T lymphocytes can be maintained in cell culture by the addition of conditioned medium (CM) containing a T cell growth factor (TCGF). This system provides an opportunity to study the presence and modulation of glucocorticoid receptors (GR) by various factors in these cells. GR were present in T cells grown from each of 22 normal individuals; the binding capacity (mean = 3851 +/- 2880 sites/cell) and affinity (Kd = 7.4 X 10(-9)) were similar in rested cultured T cells (CTC) to those reported in peripheral blood T lymphocytes. Treatment of rested CTC with stimuli such as phytohemagglutinin (PHA), CM, or 12-O-tetradecanoylphorbol-13-acetate (TPA) results in a mean increase in GR binding capacity of 3.1-, 3.2- or 2.4-fold respectively without modification of binding affinity. Using an exchange assay to measure occupied and unoccupied GR, we examined the effects of cortisol on its own receptor. Treatment of rested CTC with 10(-7) M cortisol for 24 h decreased GR by more than 50%. Cortisol treatment also blocked the induction of GR by PHA and CM. Since retinoids have been shown to modulate the immune response and to alter the effects of PHA and phorbol esters on lymphocytes, we examined their effects on GR. Retinol decreased GR activity in CTC but only at concentrations which inhibit cell growth. It is concluded that GR activity in human T cells can be modulated by several important factors involved in lymphocyte function.

Cells, Cultured↗
PubMed1984

Seasonal reproductive endocrine profiles in two wild mammals: the red fox (Vulpes vulpes L.) and the European badger (Meles meles L.) considered as short-day mammals.

The annual cycle of the testicular function (testis and epididymis weights and plasma testosterone levels) were considered in relation to seasonal variations in plasma LH and prolactin concentrations in two wild European mammals: the badger and the fox. Phase relationships were established between the annual prolactin cycles and daylight duration. The influence of castration on the seasonal variations in plasma LH levels was also studied. The resumption of activity in the testicular function occurs during autumn for both species. The reproduction period begins in winter but it is over by the beginning of spring for the fox whereas for the badger it lasts until early summer. In the same way, the annual cycle of the gonadotrophic function which, in the fox, presents only one maximum at the end of autumn, is bimodal in the badger with one maximum in January and a second in June. On the other hand, both species have a similar annual prolactin cycle, which shows an increase from the winter solstice onwards, in synchronization with the increase in daily light duration. The highest prolactin levels are measured in spring followed by a decrease during summer. This result calls into question the role played by prolactin in the regulation of the testicular function in as far as the two species have an annual reproductive cycle of the 'short-day' type (onset of activity occurring before the winter solstice) but show seasonal prolactin variations similar to those described for 'long-day' species.

Animals↗
PubMed1984

Cytoplasmic retinoic acid-binding protein in retinoic acid-resistant human breast cancer sublines.

Two sublines resistant to the growth-inhibitory effects of retinoic acid (RA) have been isolated from the parental Hs578T wild-type (W.T.) human breast cancer cell line. These sublines (Hs578T-R-1 and Hs578T-R-2) have been growing normally in 10 microM RA during more than 18 months, and their RA-resistant phenotype has remained stable after the removal of RA. The resistance is specific for RA, since their growth is still inhibited by retinol. The intracellular incorporation of [3H]RA is not deficient in the RA-resistant sublines. Cytoplasmic RA-binding protein (cRABP) is present in Hs578T-R-1 and in Hs578T-R-2 and is not different in terms of maximum binding capacity or binding affinity from cRABP in Hs578T (W.T.). These results indicate that RA resistance in these sublines is not secondary to a defect of RA uptake or of binding of RA to cRABP; the resistance may result from a defect distal to binding to cRABP, or alternatively, cRABP may not mediate this effect of RA.

Binding, Competitive↗