Biomedical subjects

M Viader

Publications and source records attributed to M Viader.

8 recordsLinked to original sources

PubMed1997

Melatonin concentration before and during testosterone replacement in primary hypogonadic men.

OBJECTIVE: To study circadian levels of melatonin in primary hypogonadic adult men before and after testosterone treatment. DESIGN AND METHODS: Circadian serum melatonin profiles were studied in six men with primary hypogonadism before and during testosterone substitution and compared with an age-matched control group (n = 6). RESULTS: Hypogonadal patients had higher plasma melatonin concentrations than the control group during day time (34.2 +/- 8.8 compared with 5.4 +/- 0.5 ng/l, means +/- SD; P < 0.005) and night-time (74.8 +/- 34.5 compared with 30.8 +/- 3.2 ng/l). A 3 months course of testosterone replacement treatment in the hypogonadal group was followed by a diminution of the amplified melatonin circadian rhythm, with lower mean values both during the day (34.2.8 +/- 8 compared with 12.7 +/- 2.45 ng/l, P < 0.001) and at night (74.8 +/- 34.5 compared with 41.5 +/- 13.5 ng/l, P < 0.01), and a decrease in the total area under the curve (958 +/- 318 compared with 475.5 +/- 222.9, P = 0.046). There was a significant negative correlation between melatonin (r = -0.69) and testosterone concentrations. CONCLUSIONS: These data indicate that diminished testosterone in male primary hypogonadism is associated with enhanced plasma levels of melatonin, and that testosterone substitution treatment induces a deamplification of the circadian rhythm of melatonin values in humans.

Adult↗

PubMed1996

Flow cytometry analysis of pituitary adenomas.

UNLABELLED: Using flow cytometry, DNA content and index, and/or proliferative capacity (measuring proliferating cell nuclear antigen PCNA) in operated pituitary tumors, control pituitaries obtained at necropsy, and experimental pituitary hyperplasia induced in rats were analyzed. Simultaneous measurement of cell ploidy and proliferation differentiated normal pituitary (diploid DNA index and negative PCNA) from pituitary hyperplasia (diploid DNA index with intensely positive PCNA, between 30 and 72% of cells). In the tumors 83% (19/ 23) were positive for PCNA (between 3 and 84%) and 73% (17/23) aneuploid; only 1 tumor was diploid and negative for PCNA. CONCLUSIONS: Differentiation between normal and abnormal (neoplastic or hyperplastic) pituitary is possible by flow cytometry, but in the adenomas no correlation with postoperative clinical outcome was observed.

Adenoma↗

PubMed1995

In vivo and in vitro flow cytometry comparative analysis of somatostatin-positive cells in the pineal gland of the neonatal rat.

Flow cytometry was used for comparative in vivo and in vitro analysis of cell populations staining positively for somatostatin. Experiments were carried out with pineals obtained from neonatal, 8- and 15-day-old rats. Pineal cells were obtained by dispersion with collagenase and then processed in a flow cytometer or maintained in culture for 1 or 2 weeks. Identification of somatostatin-immunopositive cell populations was performed using a polyclonal somatostatin antibody and confirmed by indirect immunostaining of cytospun smears with the avidin-biotin-peroxidase method. In vivo, the percentage of somatostatin-positive cells was 60.6 +/- 4% in neonatal pineals and declined to 22.2 +/- 11% in 15-day-old animals (p < 0.04). The density of peptide immunostaining decreased in 8-day-old animals but recovered to the neonate levels in 15 day-old animals; homogeneity in the immunopositive population increased with age. Maintenance in culture for 1 week resulted in an increase in positive somatostatin staining in animals of 8 and 15 days with no changes in neonates; however, after 2 weeks of culture, the percent of immunopositive cells decreased from 53.3 +/- 6 to 12.2 +/- 4% in the older animals and remained unchanged in neonates. We conclude that somatostatin is found in pinealocytes and shows a declining pattern during the perinatal period; this probably implies that the peptide plays a paracrine role important for cell differentiation in these young animals, since maximal cellularity and a high mitotic index occur within the first 3 days of life, and pineal cell differentiation is completed before the end of the third week of extrauterine life.

Age Factors↗

PubMed1993

Expression of somatostatin in rat pineal cells in culture.

The expression of somatostatin mRNA was investigated in rat pineal cells after 1 week in culture, using reverse transcription of mRNA into cDNA and the polymerase chain reaction. The positive expression in cultured pineal cells demonstrates the capacity of this gland to synthesize somatostatin in denervated cells. Thus, apart from the neural origin of pineal somatostatin, which has been described in detail in the bovine species, a parenchymal source is demonstrated.

Animals↗

PubMed1990

Immunoreactive somatostatin diurnal rhythms in rat pineal, retina and harderian gland: effects of sex, season, continuous darkness and estrous cycle.

Diurnal profiles of the content of immunoreactive somatostatin (IRS) in the male and female rat pineal, Harderian gland and retina have been studied. Supplementary experiments have been performed to elucidate a possible effect of infradian cycles, namely estrous and seasonal cycles, and continuous dark on IRS concentration. Results demonstrate that the IRS content in the rat pineal gland, Harderian gland and retina is submitted to diurnal variations, but not under all studied conditions. A sexual dimorphism exists between male and female animals: male rats showed higher IRS content in pineal (103.8 +/- 4.7 vs 32.3 +/- 1.8 pg IRS/gland), but lower in retina (1,362.1 +/- 82.7 vs 2,176 +/- 102.2 +/- pg IRS/mg of protein) and Harderian gland (10.3 +/- 0.8 vs 30.6 +/- 3.5 pg IRS/mg of protein). Additionally, seasonal differences appeared: in male and female animals pineal IRS content was lower in spring than in November. This decrease also appeared in female retina IRS concentration. Estrous cycle did not seem to change IRS content in the three studied tissues. Finally, pineal IRS rhythm persisted after continuous dark for a week. These results demonstrate, in the rat, sexual differences in the IRS content of the various tissues studied and suggest a physiological role for somatostatin, possibly related to seasonal adaptation.

Animals↗

PubMed1989

Regional distribution of immunoreactive somatostatin in the bovine pineal gland.

Regional distribution of immunoreactive somatostatin (IRS) and melatonin were investigated in the bovine pineal gland. The total IRS and melatonin content ranged from 0.26 to 2.28 pmol, and from 19.4 to 42.7 pmol, respectively, per bovine pineal. Reverse phase liquid chromatography of pineal extracts demonstrated that more than 90% of IRS coeluted with synthetic somatostatin-14 and somatostatin-28. While the IRS content was shown to vary considerably throughout the gland, with a constant and marked maximal concentration at the proximal end of the pineal, the maximal melatonin concentration appeared in the central part of the gland, coinciding with the total protein distribution. The existence of the highest levels of pineal IRS near the habenular commissure, where the afferent fibers of the central pinealopetal innervation enter the gland, suggests that pineal somatostatin may be, at least in part, of neural origin.

Animals↗

PubMed1988

Rhythms in pineal immunoreactive somatostatin in the Syrian hamster, mouse, and gerbil.

Immunoreactive somatostatin (IRS) has been previously demonstrated in the pineal gland of different rodent species, and we observed a 24-hr rhythm in rats. Recent data suggest that the peptide may represent a neurotransmitter in the so-called peptidergic nerves of the central, pinealopetal innervation of the epiphysis, which may modulate the activity and secretion of the gland. We investigated whether 24-hr changes of pineal IRS content occurred in Syrian hamsters, gerbils, and mice. Adult males, kept in a 14:10 LD photoperiod, were decapitated at 4-hr intervals throughout a 24-hr period. Pineals and median eminences were analyzed for IRS by radioimmunoassay. No significant changes in the median eminence content of IRS with time was observed. As previously described in rats, a statistically significant rhythm of IRS was observed in the pineal of hamsters and mice, with a peak at 2000 hr (mice 51.7 +/- 5 pg/pineal; hamsters 26.3 +/- 4.6) and a nadir at 2400 hr (mice 30.8 +/- 1.4) or 0400 hr (hamsters 8.6 +/- 1). However, in the gerbil pineal IRS content remained unchanged throughout the period of study. Since the three species examined have very different melatonin cycles, it is suggested that the melatonin and IRS rhythms are unrelated and independently regulated events within the pineal gland.

Animals↗

PubMedDate not supplied

Identification of immunoreactive somatostatin in the rat harderian gland: regulation of its content by growth hormone, beta-adrenergic agonists and calcium channel blockers.

Immunoreactive somatostatin (IRS) was identified in the male rat Harderian gland (HG) by radioimmunoassay. Tissue was extracted and a displacement curve performed; there were no significant differences between values obtained with serial dilutions of extracted tissue and those from purified somatostatin standard used in the radioimmunoassay. Basal values of HG-IRS were found to be in the nanomolar range (10.8 +/- 3.5 ng IRS/mg protein). Hypophysectomy did not change the HG-IRS but, in vivo growth hormone (GH) treatment led to a dramatic increase (6-7-fold) in the levels of IRS in the HG. Isoproterenol, a beta-adrenergic agonist, when administered in vivo significantly decreased the HG-IRS content. The effect of two different calcium channel blockers on the isoproterenol-induced decrease of HG-IRS was studied; no changes were observed with nifedipine but verapamil, injected one hour after isoproterenol administration, prevented the drop in HG-IRS levels. These data demonstrate the existence of IRS in a new location, the rat Harderian gland, and support a classical endocrine regulation for its tissue concentration.

Animals↗