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Biomedical subjects

J Pelletier

Publications and source records attributed to J Pelletier.

At least 199 records · Page 11Linked to original sources
PubMed1986

Contribution of increasing and decreasing daylength to the photoperiodic control of LH secretion in the Ile-de-France ram.

Sexually mature Ile-de-France rams were exposed to an 8-month light regimen in which the daily light increment and decrement were constant and equal to 7 min/day. Daylength therefore varied from 6 to 20 h. The animals were allotted to two groups of 12 rams each and submitted to the same light regimen but 4 months out of phase. Blood was collected every 40 min for 10 h, on 15 occasions at various intervals during the second light cycle. Plasma LH and on some occasions plasma testosterone concentrations were measured by radioimmunoassay. In both groups the number of LH pulses increased significantly as daylength increased from 11:40 to 20:00 h (P less than 0.01) but because their amplitude was low the mean plasma LH increase, although significant, was moderate. As daylength started to decrease (from 20:00 to 18:30 h), the frequency of LH pulses further increased (P less than 0.05) and the pulse amplitude doubled so that mean plasma LH values increased abruptly and remained high until the decreasing light photoperiod reached 11:40 h. Thereafter, the frequency and amplitude of LH pulses decreased and the mean plasma LH dropped to one-fourth of its maximal value. Mean plasma testosterone concentrations were low during most of the 8-month cycle but increased steeply when daylength decreased from 11:40 to 6:00 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

[Disjunction between the daily duration of light and the plasma level of prolactin under hyperlong days in rams].

Adult rams were submitted to an artificial light regime with increasing and decreasing daylengths between 6 and 20 hrs. over a period of 8 months. Blood samples occurred at different durations of daylengths for measuring plasma levels of prolactin. Levels were high for a daily duration of light of 14.20, 17 and 18.30 hrs. along the increasing light-phase and of 18.30 hrs. during the decreasing light-phase. On the other hand prolactin levels were low for short daylengths, but also for a daylength of 20 hrs. It clearly appears that hyperlong days (greater than 18 hrs.) do not stimulate (or do actively inhibit) the secretion of prolactin in ovines.

Animals↗
PubMed1985

Insertion mutagenesis to increase secondary structure within the 5' noncoding region of a eukaryotic mRNA reduces translational efficiency.

The thymidine kinase gene of herpes simplex virus 1 was mutated by inserting oligodeoxynucleotide linkers into the region of the gene corresponding to the 5' untranslated portion of the mRNA. These linkers, when transcribed into mRNA, might be expected to form hairpin loops and hence to increase the secondary structure of the 5' end of the mRNA. Thymidine kinase insertion derivatives were examined in vivo and in vitro to determine translational efficiency. For the in vivo studies, thymidine kinase insertion derivatives were transfected into thymidine kinase deficient L cells alone and together with a selectable dominant marker, or were assayed in the COS-1 transient expression system. For in vitro studies, thymidine kinase insertion derivatives were subcloned into pSP64. Capped transcripts were analyzed for their ability to bind ribosomes and translate in rabbit reticulocyte lysates and wheat-germ extracts. The results demonstrate that translation efficiency is decreased as the number of linkers is increased and support the view that excessive secondary structure at the 5' end of eukaryotic mRNA impedes translation.

Animals↗
PubMed1985

Differential efficiencies of in vitro translation of mouse c-myc transcripts differing in the 5' untranslated region.

We have studied the in vitro translational efficiencies of two murine c-myc transcripts synthesized in vitro that differ in the lengths of their 5' noncoding regions (448 and 83 nucleotides) and also in their 3' noncoding regions. When translated in a reticulocyte translation system, the shorter transcript was translated 10-fold more efficiently. These results are consistent with the hypothesis of Saito et al. [Saito, H., Hayday, A. C., Wiman, K., Hayward, W. S. & Tonegawa, S. (1983) Proc. Natl. Acad. Sci. USA 80, 7476-7480] that translation of full-length human c-myc mRNA is normally repressed, whereas in several Burkitt lymphomas that have deletions of the mRNA 5' noncoding region (resulting from translocation of the c-myc gene), translation of the c-myc mRNA is more efficient. Our results suggest that activation of murine c-myc expression by production of a more efficient mRNA might in some cases play a role in neoplastic transformation.

Animals↗
PubMed1985

Identification of a new polypeptide coded by reovirus gene S1.

The reovirus S1 gene has recently been shown potentially to encode two polypeptides (from two overlapping reading frames) having predicted molecular weights of 49,071 and 16,143 (Nagata et al., Nucleic Acids Res. 12:8699-8710, 1984; Bassel-Duby et al., Nature [London], in press). The larger polypeptide is reovirus protein sigma 1, but synthesis of the smaller polypeptide has not been described to date. A truncated clone of the S1 gene in which the first ATG is deleted was expressed in an in vitro protein synthesis system to yield a approximately 13-kilodalton polypeptide, as determined from migration on sodium dodecyl sulfate-polyacrylamide gels. A polypeptide with a similar migration pattern on sodium dodecyl sulfate-polyacrylamide gels was present in reovirus-infected cells and absent from mock-infected cells. Comparative tryptic peptide analysis of the 13-kilodalton polypeptides produced in vivo and in vitro showed them to be identical. Thus, the s1 mRNA of reovirus type 3 is apparently bicistronic, and we suggest that the approximately 13-kilodalton polypeptide be called sigma s (standing for sigma small).

Genes, Viral↗
PubMed1985

Photochemical cross-linking of cap binding proteins to eucaryotic mRNAs: effect of mRNA 5' secondary structure.

We used UV light-induced cross-linking to study the interactions of cap binding proteins with the 5' cap structure of eucaryotic mRNAs. Thymidine kinase gene (herpes simplex virus type 1) transcripts prepared in vitro using the SP6 RNA polymerase transcription system were capped and methylated posttranscriptionally with [alpha-32P]GTP and S-adenosyl-L-methionine to yield cap-labeled transcripts. Irradiation of capped transcripts with crude rabbit reticulocyte initiation factors in the presence of ATP-Mg2+ resulted in the cap-specific cross-linking of two polypeptides with molecular masses of 24 and 80 kilodaltons (kDa). The cross-linking characteristics of these polypeptides resemble those of the cap-binding proteins previously detected by a chemical cross-linking assay (N. Sonenberg, D. Guertin, D. Cleveland, and H. Trachsel, Cell 27:563-572, 1981). However, the relative efficiency of the cross-linking of these two polypeptides to the cap structure was different from that in previous studies, and there was no detectable cross-linking of the previously described 50-kDa polypeptide. In addition, we present data indicating that the insertion of secondary structure into the 5' noncoding region of tk mRNA, 6 nucleotides from the cap structure, decreases the cap-specific cross-linking of the 80-kDa but not the 24-kDa polypeptide. In contrast, the insertion of secondary structure 37 nucleotides from the cap structure had no significant effect on the cross-linking of either the 24- or the 80-kDa cap-specific polypeptide. These results demonstrate that the position of mRNA 5'-proximal secondary structure relative to the cap structure can influence the cap-specific interaction between the mRNA and a translation initiation factor.

Animals↗
PubMed1985

Oestradiol binding to nuclei of anterior pituitary cells of the ram.

The methodology to fully characterise nuclear receptor for oestradiol-17 beta (E2) in the ram pituitary has been investigated. Purified nuclei, clean under the electron microscope, were obtained from 2.4 M sucrose ultracentrifugation and were extracted for 2 h at 0 degrees C with 0.6 M NaCl. After centrifugation, the supernatant was incubated with [3H]E2 with or without a 100-fold excess of unlabelled E2. The main results were: the specific binding was maximum at 20 degrees C in 2-3 h and remained constant up to 19 h without significant metabolism; an incubation temperature of 25 degrees C reduces the binding, while at 0 degrees C maximum binding was attained at a much slower rate; the binding was linearly related to the dose of nuclear proteins; the binding was not affected by DNase and RNase but was suppressed by trypsin, pronase or a temperature of 56 degrees C; binding was specific for oestrogens; preincubation of cytosol with [3H]E2 and then coincubation with nuclei showed an uptake of the [3H]E2 receptor complex by nuclei; such a transfer was inhibited if cytosol was previously heated; after a prelabelled cytosol-nuclei coincubation, a specific binding peak was found in the nuclear extract submitted to sucrose gradient sedimentation (4.1S); in vivo injection of 100 micrograms E2 resulted in a sharp increase in nuclear receptor numbers 30 and 60 min later, with a concomitant drop in cytosolic receptor numbers. These results indicate that E2 can bind to pituitary nuclei in the ram.

Animals↗
PubMed1985

Changes in pulsatile LH secretion after ovariectomy in Ile-de-France ewes in two seasons.

Two experiments were conducted in Ile-de-France ewes to study changes in pulsatile LH secretion in ewes ovariectomized during anoestrus or during the midluteal phase of the oestrous cycle. In Exp. 1, blood samples were taken every 20 min for 12 h the day before ovariectomy (Day 0). After ovariectomy, samples were taken every 10 min for 6 h (10 ewes per group), on Days 1, 3, 7 and 15. In Exp. 2 samples were taken every 10 min for 6 h (10 ewes per group) on Days 7, 15, 30, 60, 90, 120, 150 and 180 after ovariectomy. Further samples were taken (5 ewes per group) at 9 and 12 months after ovariectomy. There were significant interactions between season and day of sampling for the interval between LH pulses in both experiments. LH pulse frequency increased within 1 day of ovariectomy and the increase was more rapid during the breeding season. There were clear seasonal differences in pulse frequency in Exp. 2. Compared with ewes ovariectomized in anoestrus, pulse frequency was significantly higher for ewes ovariectomized in the breeding season, from Day 7 until Day 120. Once pulse frequency had increased in ewes about the time of the normal breeding season, pulse frequency remained high and subsequent seasonal changes were greatly reduced. Pulse amplitude increased immediately after ovariectomy to reach a maximum on Day 7 and there were no differences between season of ovariectomy in the initial changes in amplitude. In Exp. 2, changes in amplitude followed changes in pulse interval and there was a significant interaction between season and day of sampling. There were no significant effects of season on nadir LH concentrations which increased throughout the duration of the experiments. These results show that, in ovariectomized ewes, LH pulse frequency observed on a given day depends on time after ovariectomy, season at the time of sampling and on previous exposure of ewes to stimulatory effects of season. The direct effects of season on LH pulse frequency and seasonal changes in sensitivity to steroid feedback may contribute to control of the breeding season and their relative contributions to the beginning and end of the breeding season may differ.

Animals↗
PubMed1985

Gonadotrophin release in ovariectomized ewes fed different amounts of coumestrol.

Three experiments were conducted to study changes in pulsatile secretion of LH and FSH during the breeding season or anoestrus in ovariectomized Ile-de-France ewes fed different amounts of the phyto-oestrogen coumestrol. In Exp. 1, conducted during the breeding season, ewes (3-4 per group) were fed lucerne supplying 4, 18 or 30 mg coumestrol per ewe per day for 15 days. Experiments 2 and 3 were conducted during seasonal anoestrus. In Exp. 2, ewes (4 per group) were fed lucerne supplying coumestrol concentrations ranging from 4 to 38 mg/ewe/day for 15 days. In Exp. 3, ewes (10 per group) were fed lucerne supplying 14 or 125 mg coumestrol/ewe/day for 15 days. During the breeding season, an increased concentration of coumestrol in the diet significantly decreased the amplitude of LH pulses. There were no effects on LH pulse frequency or on FSH concentrations. During seasonal anoestrus, there were no significant effects on LH pulse frequency, or amplitude and no significant effect on FSH concentration. These results show that high concentrations of coumestrol in lucerne diets would not explain seasonal variation in LH pulse frequency in ovariectomized ewes. However, lucerne diets with increased coumestrol concentrations can influence LH release during the breeding season.

Anestrus↗
PubMed1985

Relationship of testosterone pulses to androgen binding in the pituitary of rams.

The effects of testosterone on cytosol and nuclear androgen receptors of ram pituitary were examined in two experiments. In Exp. I, 500 micrograms testosterone were injected intravenously and groups of 4 rams were slaughtered at 0, 15, 30, 45, 90 and 360 min after injection. Cytosolic receptor concentration decreased from 21 +/- 0.9 to 6 +/- 0.9 fmol/mg protein 30 min after the testosterone injection (P less than 0.001), and then returned towards the preinjection level after 90 min. The pattern of nuclear receptor concentration was the opposite; a maximal increase (12 +/- 3.5 to 32 +/- 5.7 fmol/mg protein) was observed 30 min after injection (P less than 0.001), followed by a progressive but incomplete decrease by 360 min. In Exp. II, blood was collected every 20 min for 17 h in three successive series, each of 12 rams, which were then slaughtered. Plasma LH and testosterone concentrations were measured by radioimmunoassay. No changes were observed in cytosol receptor concentration, but nuclear receptor concentration was negatively correlated with the interval elapsed since the beginning of the last testosterone pulse (r = -0.62; P less than 0.001). The highest values for nuclear receptor concentrations were observed at an interval equal to or less than 120 min. These results indicate that natural pulses are associated with androgen binding particularly in the pituitary nuclei.

Animals↗
PubMed1985

Plasma prolactin, LH, FSH and estrogen excretion patterns in gilts during sexual development.

Plasma prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay in groups of eight gilts sampled every 20 min for 6 h at about 2-wk intervals between 15 and 192 d of age. The PRL levels were high at 15 and 28 d, declined at 40 d just after weaning and then rose slowly until 192 d of age. The number of LH pulses during 6 h was higher between 83 and 125 d than at the other periods. Magnitude of LH pulses was highest at 15 d, constant from 54 to 125 d, fell at 137 d and remained low until 192 d. Plasma FSH was high from 15 to 125 d, with a maximum at 54 d. It declined slowly until 168 d and did not change thereafter. Estrogen excretion was estimated from urine excretion of estrone (E1; conjugated plus nonconjugated E1) per 24 h from 40 d until puberty in three gilts and at 156 and 174 d in two other animals. The E1 excretion increased with age and four levels were described before peak values with the onset of first estrus. The first increase in E1 excretion occurred between 68 and 110 d, when antral follicles appeared in the ovaries. It was subsequent to the highest levels of FSH and concomitant with the increased frequency of LH pulses. The drop in levels of both gonadotropins after 125 d probably corresponded to the development of the negative feedback as a result of greater ovarian activity in these gilts.

Aging↗
PubMed1985

[Light entrainment and stimulation of the secretion of prolactin in rams].

Light entrainment and stimulation of PRL release were studied in rams submitted to artificial light regimes: In a first experiment four groups of animals were submitted to light regimes with a period of 6, 4, 3 or 2 months respectively (T6 to T2 groups) and amplitude of 8-16 h of daylength. In all four groups PRL level was significantly correlated with daylength (r greater than 0.51; P less than 0.01). However in July, when temperatures were indeed high, an additional PRL increase was observed in the T6, T4 and T3 groups, although the role of temperature appears debatable. In a second experiment, animals were exposed daily to 8 hrs. of light given in two photofractions. The first fraction of 7 hrs. began at the same time as "dawn", and the second of 1 hr ended at the same time as "dusk" of the T6 group in the first experiment which served as control group. Correlation of plasma prolactin in rams receiving 8 h light in one or two photofractions was highly significant (r = 0.66; P less than 0.001). This suggests that rams measured daylength between two limits considered as "dawn" and "dusk" even if lights were turned off during part of this interval.

Animals↗
PubMed1985

[Partial abolition of seasonal variations of testicular weight in rams by decreasing the photoperiod].

Under moderate latitudes all breeds of rams undergo seasonal variations in testicular weight with a maximum during summer under decreasing daylength ([1]-[4]). Similarly, in rams submitted to a 6-month artificial light regime [5] or to an alternation of long (16L:8D) and short (8L:16D) days [6] an increase in testicular weight occurred following a decrease in daylength and vice versa. However this effect is transitory, a phenomenon which can be referred as photorefractoriness. In the present study the influence of the period of the light cycle on variation in testicular weight in the ram was investigated. 4 groups of 6 adults Ile-de-France rams were submitted to artificial light cycles where the daylength varied between 8-16 hrs. and the period (T) was 6, 4, 3, or 2 months respectively (Groups T6, T4, T3, and T2). Testicular volume was measured fortnightly using an orchidometer, Variations in testicular volume were submitted to harmonic regression analysis following the model y(t)=mu + a sin(2(pi t/tau) + phi). Cyclic changes in testicular volume were seen with each light cycle, at least in groups T6, T4, and T3 (Fig.). Analysis (Table) showed that: (1) the coefficient of determination R2 was high in the groups (2) mean testicular volume has increased from 258 to 294 cm3 when the period of the light cycle decreased from 6 to 2 months; (3) conversely, the amplitude decreased from 66.5 to 26.5 cm3 as the period decreased; (4) maximal testicular volumes (mean plus amplitude) were similar in all groups (range: T4, 312,5-T6,324 cm3) while minima (mean less amplitude) differed significantly (P<0.000,1) between groups (range: T6 and T4 about 190, T2 267.5 cm3) and (50 th computed periods of testicular volumes cycles were almost identical to the imposed light cycles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Variations in the plasma levels of gonadotrophin and testosterone and in Leydig and Sertoli cell populations between birth and adulthood in Romanov lambs born in spring or autumn.

Plasma gonadotrophin and testosterone levels during the prepuberal period have been compared in spring and autumn-born Romanov lambs; the somatic and germ cell populations of these lambs have also been compared at birth and at adulthood. At 1 and 3 months of age, the number of LH pulses per hour and mean plasma LH levels were significantly higher in spring than in autumn lambs. In adults, no such differences were observed. Similarly, at 1 and 3 months of age, the number of testosterone pulses per hour was higher in spring than in autumn animals. In the prepuberal period, the ratio of the levels of mean plasma testosterone to LH was higher in autumn than in spring lambs. The highest ratio was observed in adults but there was no variation according the season of birth. At 1 month of age, mean plasma FSH levels were higher in autumn than in spring lambs; this difference did not persist later on. Despite these endocrinological differences, testis weight, total Sertoli and Leydig cell numbers per testis, total number of gonocytes per testis at birth and daily production of round spermatids per testis in adult rams were similar in spring and autumn-born animals.

Animals↗
PubMed1984

A comparison of the changes in LH, FSH and testosterone in spring-born ram lambs of two different breeds.

LH, FSH and testosterone variations were compared during the prepubertal period in Romanov and Ile-de-France ram lambs born in the spring. Mean plasma LH levels increased significantly between the 1st and 8th week of age in the Romanov and between the 1st and 12th week of age in the Ile-de-France. At 1 month of age, the number of LH and testosterone pulses per hour was higher in Romanov than in Ile-de-France lambs. The mean plasma testosterone levels, higher in the Romanov, increased from 1 week of age onwards. Mean plasma FSH levels increased from the first neonatal week till the 8th week in the Romanov and till the 12th week in the Ile-de-France. The levels of FSH did not differ significantly between the two breeds. The higher and earlier secretion of LH and production of testosterone in the Romanov might be a cause of its better reproductive performance.

Age Factors↗
PubMed1984

Changes in photoperiod and nutrition and their effect on testicular growth of rams.

Groups of 6 Ile-de-France rams were housed in light-proof rooms and subjected in a factorial design to two light regimens, 180 degrees out of phase, and two levels of protein in their diets. The daily duration of daylight was varied sinusoidally to produce 6-month years with 'winters' of 8 h light and 'summers' of 16 h light. The diets were formulated to supply 50% above or 25% below maintenance requirements in protein. Testicular diameter and volume increased with decreasing light and decreased with increasing light but the diet had no effect. The frequency of LH pulses was measured monthly and was high (3/12 h per ram) when the daylight was being reduced and low (1/12 h per ram) when it was increased. At the extremes of the duration of dark or light the frequency of pulses was around 1.6/12 h per ram, regardless of the duration of light. The two diets had no effect on testicular dimensions but rams fed the 'high' protein diet had a total of 175 LH pulses, which was significantly higher (P less than 0.05) than the 131 pulses recorded from rams on the 'low' protein diet. It is concluded that, in these '6-month years', decreasing light stimulates LH pulsatility and testicular growth and increasing light is inhibitory. Pulsatility of LH appears to be influenced by the protein level in the diet.

Animal Nutritional Physiological Phenomena↗