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Biomedical subjects

P Osman

Publications and source records attributed to P Osman.

18 recordsLinked to original sources
PubMed1999

Erratum

The paper 'Interference of rheumatoid factor activity by aspartame, a dipeptide methyl ester' by Paul A. Ramsland, Bahereh F. Movafagh, Morris Reichlin and Allen B. Edmundson, J. Mol. Recognit. 1999; 12: 249--257, was published without the required colour plates. The publisher would like to apologise for this omission. The article is reprinted here in full. Please replace the previously published pages with those following. The electronic version of the article, including the colour plates, can be downloaded from the Wiley Interscience website at http://www.interscience.wiley.com. The plates have been included in the original paper, which appeared in Issue 4 of the journal.

Journal Article↗
PubMed1996

The phosphorus-31 spectra of dielectrophoretically reoriented tubules in the HII phase of DOPE.

31P electric field nuclear magnetic resonance measurements are described which assess the effect of electric field on the orientation of tubules comprising the HII phase of dioeleoylphosphatidylethanolamine. A model, based on dielectrophoretic effects, was used to predict that a field of 4 MV/m would change the orientation of the lipid tubules in a HII phase. The excitation pulse was biphasic to help discriminate electric field interactions with free ions or permanent dipoles from interactions with induced dipoles, as well as to control the problems of ohmic heating, electrolysis and polarisation associated with dc or unbalanced ac excitation voltages. Spectra consistent with irreversible electrorotation and with reversible and transient electrorotation were observed. No response to the electric field was seen in certain cases. The conditions for irreversible and reversible electrorotation and failure to rotate have been tabulated and are discussed. Finally, some simple models are considered, in order to calculate the energies involved, if the observed NMR spectra are interpreted as arising from lipid HII phase reorientations.

Electric Impedance↗
PubMed1994

The effect of pulsed electric fields on the phosphorus-31 spectra of lipid bilayers.

A technique is described for measuring the effect of electric fields on the conformation of lipid bilayer membranes by solid state nuclear magnetic resonance. An apparatus was devised to obtain spectra from samples of aligned phospholipid dispersions at varying electric field strengths up to 100 MV/m. Measurements were carried out on membranes made from dioleoylphosphatidylethanolamine and dioleoylphosphatidylcholine, which resulted in electric field induced phase changes. Calibration experiments were performed using bilayers formed from dimyristoylphosphatidylcholine with glycerol and with a nematic liquid crystal. An electric field induced change, from L alpha to HII, was also seen in a dimyristoylphosphatidylcholine/alamethicin bilayer.

Electricity↗
PubMed1993

Model of antral follicle dynamics during the 5-day cycle in rats based on measurement of antral follicle inflow.

Antral follicles were counted in ovaries from young adult Wistar rats, collected on the 5 days of the ovarian cycle. Follicles were classified as healthy, early atretic or late atretic and divided into five volume classes. From these data, a model was developed in which the inflow of healthy follicles into the various size classes was quantified. This model describes the follicle dynamics during a normal 5-day cycle. It was concluded that the stage of early atresia takes between 20 and 24 h. The inflow of follicles into the antral stage (volume > or = 100 x 10(5) microns2) was continuous but not constant. The highest inflow was found during pro-oestrus and oestrus, at about the time of the first and second FSH surge. The total inflow during each cycle was about 120 follicles of which only 10% ovulated. These ovulating follicles were recruited during the previous pro-oestrus and oestrus. Follicle selection took place in volume classes 1 and 2 (volume 100-350 x 10(5) microns3) during oestrus and dioestrus 1. At dioestrus 2, the follicles that will ovulate have been selected and can be recognized on the basis of their bigger size.

Animals↗
PubMed1986

Morphometric analysis of follicular dynamics in pregnant and pseudopregnant rats.

Morphometric analysis of the follicle population greater than or equal to 100 X 10(5) micron 3 or a mean diameter of greater than or equal to 275 micron and assessment of the rate of atresia in ovaries of pregnant and pseudopregnant rats revealed no evidence for the presence of rhythmic follicular maturation during the prolonged dioestrous period. During the first 4-5 days of the dioestrous period, follicles developed to preovulatory size (volume class 5, i.e. greater than or equal to 1000 X 10(5) micron 3 = diam. greater than or equal to 576 micron) reaching the normal number of ovulating follicles in cyclic animals in pregnant rats, but only half that number in pseudopregnant rats. These follicles collapsed on the 5th to 8th days of the dioestrous period and full numbers of preovulatory follicles were not found thereafter until the end of pregnancy and pseudopregnancy. Follicles of smaller sizes (classes 1-4: 100-999 X 10(5) micron 3), however, were present throughout the prolonged dioestrous period. The rate of atresia in the follicle population had increased by the 2nd day and remained from then on at 26.5 +/- 4.5% in the pregnant and 34.3 +/- 1.9% in the pseudopregnant rats. Atretic follicles in the advanced stages of atresia, mostly derived from follicles of classes 1-3, persisted and accumulated at the end of the dioestrous period. The continuous presence of follicles and the constant rate of atresia during the dioestrous period indicate continuous follicular replacements and refute the idea of follicular quiescence during pregnancy and pseudopregnancy. Copulation and electrical stimulation of the cervix seemed to reduce the formation of the new crop of follicles the next morning and the pool of small antral follicles normally maintained after oestrus in cyclic animals. Nevertheless, the smaller crop and pool of follicles seemed able to provide a sufficient number of preovulatory follicles at the end of pregnancy and a sufficient number of ovulations at the end of pseudopregnancy.

Animals↗
PubMed1985

Rate and course of atresia during follicular development in the adult cyclic rat.

Ovarian follicles (greater than or equal to 100 X 10(5) microns 3 or a mean diameter of greater than or equal to 275 microns) in adult rats were classified as non-atretic and atretic during the oestrous cycle and recorded in 5 volume classes. The atretic follicles were also categorized in several stages according to the progress of atresia. The degeneration of the entire granulosa wall until the induced changes in the oocyte took at least 24 h. Another 24 h elapsed before the oocyte became denuded. Therefore the % of atretic follicles, i.e. follicles in all stages of atresia, could not be used as indicator for the rate of atresia. The atretic portion in the follicle population greater than or equal to 100 X 10(5) microns 3 increased from early dioestrus 1 to early dioestrus 3, reached a plateau during dioestrus 3 and pro-oestrus, and declined at late oestrus to the level of early dioestrus 1. The sudden decrease in number of atretic follicles after late pro-oestrus was caused by the discard of many atretic follicles in the advanced stages due to various deformities as revealed by histological observation. By using the % of atretic follicles in the earliest stage as indicator of atretic rate, two waves of atresia were found affecting the population of antral follicles during their growth, the first at dioestrus 1 amounting to 15-20% and then at dioestrus 3, affecting 35% of the population. The present study also shows the extension of atresia in the various volume classes of follicles during the oestrous cycle. A pool of approximately 7 follicles in the smallest volume class was maintained after ovulation, grew further in the next cycle with a new cohort of 20 follicles, and seemed to provide the required number of follicles destined to ovulate. This suggests that the follicles that ovulate were already present at an antral stage in the preceding cycle and needed two cycles for their growth to ovulation.

Animals↗
PubMed1985

Precocious ovulation induced by human chorionic gonadotrophin in the immature female rat: comparison of follicle growth induced by treatment with human chorionic gonadotrophin and by electrical stimulation of the hypothalamus.

Precocious first ovulation, preceded by an endogenous preovulatory LH surge, could be predictably induced in immature female rats by administering repeated injections of human chorionic gonadotrophin (hCG). Administration of a dose of 0.05-0.075 i.u. hCG, four times a day from day 28 to day 31 of age resulted in a highly constant ovulatory response: at 4.0 +/- 0.0 days after the start of treatment 7.7 +/- 0.3 (n = 15) ova were found. Use of a higher dose of hCG (0.1 i.u.) resulted in lower numbers of ova (5.6 +/- 0.4, n = 7; P less than 0.005) whereas use of a lower dose of hCG (0.025-0.038 i.u.) resulted in a less constant timing of the induced ovulation at 5.4 +/- 0.2 days after the start of treatment (n = 7; P less than 0.0005). In animals treated with the dose of 0.05-0.075 i.u. hCG, a positive correlation was found between body weight at the start of treatment and the number of ova released (r = 0.75, n = 25; P less than 0.001). Ovarian follicle dynamics were studied on the various days of hCG treatment (dose 0.05-0.075 i.u.) and compared with the follicle changes that take place after electrical stimulation of the hypothalamus, performed on day 28, a treatment known to result in first ovulation 4-5 days later. In both groups a decrease in the number of the smallest and the middle-sized antral follicles as compared with their respective controls was seen, whereas numbers of follicles in the largest, 'ovulatable' size classes gradually increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Compensatory ovulatory mechanisms operative after first ovulation in rats unilaterally ovariectomized prepubertally.

Ovarian steroid contents and serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured during the days after first ovulation in rats unilaterally ovariectomized in late prepuberty. In addition, follicle counts were made at second estrus and second metestrus. During the cycle following first ovulation, ovarian estradiol contents in unilaterally ovariectomized (ULO) rats were significantly increased as compared to intact rats on the day of metestrus, on diestrus 1 and on second estrus. Ovarian progesterone was significantly increased on the days of metestrus, on diestrus 1, second proestrus and second estrus, but no differences were seen in ovarian androgen contents. After ULO there was an indication of an augmented FSH surge at the first and the second ovulation. Follicle counts revealed that the total number of healthy as well as of atretic antral follicles on the day of second estrus was significantly increased after ULO, due to increased numbers of the smallest antral follicles. At second metestrus the number of larger antral follicles (350-500 micron 3) and the total number of healthy antral follicles was higher after ULO. It is concluded that the compensatory process after ULO involved increased recruitment of small antral follicles. Activities in the remaining ovary were not simply doubled but a new hormonal balance was established.

Animals↗
PubMed1982

Ovarian follicular development leading to first ovulation and accompanying gonadotrophin levels as studied in the unilaterally ovariectomized rat.

Ovarian follicular development was studied in the rat during a 15-day period preceding first ovulation. Ovaries were obtained by unilateral ovariectomy performed at various ages and the rats were allowed to live until the day after first ovulation. The timing of this ovulation was compared with that in unoperated, paired control rats of the same age. For estimation of gonadotrophin levels, blood was taken from the paired control rats at the time when experimental rats were unilaterally ovariectomized. There was no evidence that unilateral ovariectomy had any influence on the timing of first ovulation. Therefore the ovaries obtained could be dated in relation to first ovulation, and follicular growth during the final prepubertal period could thus be studied in a genuine developmental sequence. Results revealed that follicular growth leading to first ovulation starts at +/- 8 days before this ovulation; follicular processes taking place are comparable to those found during the adult 5-day cycle but proceed more slowly. Gonadotrophin concentrations accompanying the follicular dynamics and measured at 11.00 h, showed a clear tendency for FSH concentrations to decrease with increasing age, i.e. approaching first ovulation. Concentrations of LH did not show a definite pattern and were generally low, although in some individual rats relatively high LH values ( greater than 100 micrograms/l) were found in the period of 5-3 days before first ovulation.

Animals↗
PubMed1980

Ovulation from rat and hamster ovaries in vitro.

The ovaries of pro-oestrous rats (pubertal and adult) and hamsters were explanted in toto at various times after the preovulatory gonadotrophin surge to obtain endogenously stimulated ovaries. Subnormal numbers of ovulations from pubertal and adult rat ovaries were found when incubation was started during the period from 17:00 to 24:00 h on the day of pro-oestrus. Normal numbers of ovulations only occurred from rat ovaries in vitro when incubation was started at 01:00 h, i.e. when ovulation had already begun in vivo. In contrast, full ovulation from hamster ovaries was observed in vitro after incubation at 22:00 h and later, although the ovulatory process had not started in vivo. This difference in the ability of rat and hamster follicles to ovulate in vitro could be due to a different role of the accumulation of tissue fluid for the mechanism of ovulation.

Animals↗
PubMed1977

Ovarian changes during the first spontaneous ovulation in intact and indomethacin treated rats.

Ovarian events during first spontaneous ovulation were studied and compared with those during later ovulations in adult rats. During the period of ovulation, from 24.000 hours to 04.00 hours, the pubertal ovaries showed, probably because of disappearance of marked interstitial oedema, a decrease in weight not observed in the adult animals. The preovulatory follicles showed prior to ovulation a similar increase in size in the pubertal and the adult animals. However, in the pubertal animals follicles were smaller and showed characteristic structural features. A group of pubertal rats received indomethacin (2.5 mg/rat) at prooestrus. This treatment reduced the increase in ovarian weight normally developing in the period before onset of ovulation, 17.00 hours at 24.00 hours. Indomethacin caused furthermore a greater increase in size of the preovulatory follicles during this same period and led to ovulatory processes at which only few eggs left the ovaries, the majority either remaining trapped in the follicles or being released into the ovarian stroma.

Animals↗
PubMed1976

Effects of sodium pentobarbitone administration on gonadotrophin release, first ovulation and ovarian morphology in pubertal rats.

Pubertal female rats received sodium pentobarbitone (PB; 45 mg/kg body wt) at various hours on the day of first pro-oestrus. Maximal blockade of ovulation, in about 60% of the rats, occurred after PB treatment at 12.00, 13.00 and 14.00 h. The number of small antral follicles (100-499 X 10(5) mum3) was reduced 1 day after PB treatment in both blocked and ovulating rats. In the ovaries of non-ovulating rats signs of stimulation by LH such as dispersion of cumulus cells, oocyte maturation and early luteinization were sometimes present; in ovulating rats cystic corpora lutea with entrapped ova were found in addition to normal corpora lutea. Gonadotrophin measurements after PB treatment (14.00 h) in pubertal and adult rats showed (at 17.00 h) reduced levels of both LH and FSH, these levels being lower in the adults. Gonadotrophin levels of blocked and ovulating pubertal rats overlapped. In PB-treated, pubertal rats in which ovulation was postponed by 1 day, vaginal oestrus was prolonged by 1 day and the subsequent dioestrus by 2 days. The pubertal rat is thus less sensitive to PB treatment than the adult. PB treatment of the younger animal influences not only the ovulatory process but also follicular growth and, presumably, the length of the approaching cycle.

Animals↗
PubMed1975

Levels of follicle-stimulating hormone, luteinizing hormone, oestradiol-17 beta and progesterone, and follicular growth in the pseudopregnant rat.

Throughout a period of pseudopregnancy the peripheral blood levels of progesterone, oestradiol-17 beta, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), as well as the size-distribution of ovarian antral follicles were estimated in the rat. The progesterone concentrations, as measured by a competitive protein-binding technique, exceeded metoestrous values (25 ng/ml plasma) from day 3 of pseudopregnancy onwards. The highest levels were found on days 6 and 8 (91 ng/ml). From day 8 onwards the levels decreased gradually but were still above metoestrous values on the day of pro-oestrus after pseudopregnancy. Concentrations of oestradiol-17 beta, as measured by radioimmunoassay, were within the range of those at metoestrus (about 5 pg/ml plasma) until day 10. Thereafter levels increased to a value of 57 pg/ml. Concentrations of FSH, measured by radioimmunoassay, were within the range of metoestrous values until day 10 (about 100 ngNIAMD-rat-FSH RP-1/ml serum), but declined to a level of 33 ng/ml on day 12. Concentrations of LH, measured by radioimmunoassay, were generally within the wide range of metoestrous values (9-60 ng NIAMD-rat-LH RP-1/ml serum), but concentrations found on days 4, 8 and 10 were significantly lower than those found on preceding or subsequent days. Histological determination of the number of follicles present in various volume-classes, showed an increase in antral follicles on days 1 and 2, comparable to the increase observed during metoestrus and dioestrus 1 of the normal cycle. There was no change in the follicles between days 3 and 10 and they resembled those of early dioestrus. Preovulatory growth had occurred by day 12. Injection of human chorionic gonadotrophin (HCG) on days 2, 4 or 6 showed that ovulation could be induced only in some of the larger follicles. On the basis of these results it is suggested that during pseudopregnancy the high progesterone levels present result in a decreased plasma LH level which is insufficient to cause full maturation of the follicles and to stimulate oestrogen secretion to the levels required for induction of an ovulatory surge of LH release.

Animals↗
PubMed1975

Preovulatory changes in the ovaries during the first spontaneous pro-oestrus in the rat.

Events in the ovaries during the first spontaneous pro-oestrus were compared with those in the adult rat. The occurrence of first spontaneous pro-oestrus was determined from vaginal smears after surgical opening of the vagina. Pubertal rats showed a remarkable increase in ovarian weight from 10.00 to 15.00 h on the day of pro-oestrus, which was absent in the adults. They also showed an earlier and more pronounced interstitial oedema. Dispersion of cumulus cells, resumption of meiosis and ovulation also occurred slightly earlier in pubertal rats. A distinct difference was found in the growth rate of follicles of ovulatory size, i.e. follicles of larger than or equal to 500 X 10(5) mum3. At the first pro-oestrus these follicles showed a slower and less pronounced increase in size from 10.00 to 17.00 h compared with the adult follicles at this time, although this disparity was made up by a marked increase in growth from 17.00 to 24.00 h. The development of a new crop of follicles progressed similarly in the pubertal and adult animals. Follicular atresia seemed to progress more rapidly from 10.00 to 15.00 h in the pubertal animals compared with adults but from 15.00 h onwards no further differences were observed. The possible causal factors underlying the observed differences between the pubertal and adult animal are discussed.

Animals↗
PubMedDate not supplied

The ion channel switch biosensor.

A biosensor technology is described which provides a direct measurement for functional molecular interactions, at the surface of a tethered bilayer membrane, through the electrical transduction of chemically modified ion-channels. High sensitivity of analyte detection is achieved due to the large flux of ions transmitted through the ion channel. The biomimetic sensor surface allows the molecular recognition to be measured in complex biological matrices (such as blood and sera) without compromising sensitivity. We have used the sensor for activity and concentration measurements for a range of analytes, which include bacteria, DNA, proteins and drugs. We have a quantitative model for the biosensor performance which is described by three-dimensional molecular interactions with the membrane surface and two-dimensional molecular interactions within the tethered bilayer.

Biosensing Techniques↗