PubMed Health⌕ Search

Biomedical subjects

G J Marcus

Publications and source records attributed to G J Marcus.

At least 19 recordsLinked to original sources
PubMed1992

The effect of supercooling on the developmental capacity of mouse embryos.

The effect of supercooled storage (at subzero temperatures without ice formation) on compacted mouse morulae and early blastocysts was studied. The embryos were equilibrated with one of three storage solutions containing 1, 3, or 6% each of methanol and glycerol and cooled to -2, -5, -10, or -15 degrees C and stored for up to 24 h to assess the effect of subzero storage at different temperatures and concentrations of the permeating cryoprotectants on embryo survival. Early blastocysts showed substantially greater survival than morulae and, in general, survival of embryos of either stage increased with the concentration of cryoprotectant, while the proportion of embryos surviving decreased with decreasing storage temperature and with increased duration of storage.

Animals↗
PubMed1992

In vitro fertilization and development of frozen-thawed bovine oocytes.

Bovine oocytes were vitrified (V-oocytes) or frozen slowly (S-oocytes) at the germinal vesicle (GV) stage or after maturation in vitro (IVM) and their survival assessed morphologically and also by in vitro fertilization (IVF) and culture. The morphological survival of S-oocytes was 30.7% after freezing at the GV stage and 53.3% after IVM. The corresponding survival rates of V-oocytes were significantly lower, viz. 14.6 and 14.0%, respectively. The fertilization rate of S-oocytes frozen after IVM (51.0%) was lower than that of unfrozen controls (75.8%), but higher than after other treatments. Development continued in 16.0% of the fertilized S-oocytes, compared to 39.4% of control IVF zygotes and 1.6% developed into morulae or blastocysts (4.5% in controls). Only 0.8% of frozen-thawed GV stage oocytes and 4.6% of post-IVM V-oocytes cleaved after IVF and none formed morulae or blastocysts. Transfer of four embryos (two morulae and two blastocysts) derived from post-IVM S-oocytes into a recipient heifer resulted in pregnancy and the birth of twin calves.

Animals↗
PubMed1991

New thermal stress test to assess the viability of cryopreserved boar sperm.

A new, rapid, thermal stress test for assessing the viability of boar semen, requiring only 45 min of incubation at 42.5 degrees C, was developed and compared with a widely used stress test of 180 min incubation at 37 degrees C. The shorter procedure was found to have the same discriminatory ability as the standard test in assessing the effects of freezing conditions on the percentage of spermatozoa remaining motile. Neither test was able to show differences in the kinetic rating of motile sperm after freezing in relation to the glycerol concentration present during freezing. However, the new test had a greater ability to distinguish the effects of different concentrations of glycerol, over the range of 0 to 6%, and to reveal different degrees of acrosomal damage sustained during freezing. The longer procedure was unable to distinguish among glycerol concentrations from 0 to 4% with respect to acrosomal damage and produced an overall lower proportion of sperm having a normal apical ridge. The new thermal stress test thus has the advantages of greater sensitivity and more rapid execution over the test hitherto in widespread use.

Animals↗
PubMed1990

Activation of cumulus-free mouse oocytes.

Attempts were made to activate parthenogenetically oocytes from random-bred mice under conditions required for nuclear transfer, viz. in the absence of cumulus cells. Of the large number of stimulants previously described and presumed to be generally effective, only exposure to strontium ion (as a replacement for calcium ion in the medium), or to calcium ionophore, activated a substantial proportion of cumulus-free oocytes from TRf mice, a synthetic, random-bred strain. These stimuli were less effective in oocytes from random-bred ICR mice. The relevance of the findings to nuclear-transfer cloning attempts in mice is discussed.

Animals↗
PubMed1990

The synthesis and actions of steroids and prostaglandins during follicular maturation in the pig.

Our understanding of the synthesis and production of follicular steroids and prostaglandins (PG) in the pig is based largely on in-vitro studies with granulosa and theca interna tissues obtained from Graafian follicles at various stages of maturation. As the follicle enlarges before the LH surge, granulosa cells exhibit a decrease in FSH receptors and are less responsive to FSH in terms of cAMP production. Concurrently, there is an increase in granulosa and thecal cell LH receptors associated with an increase in responsiveness to LH and an increase in steroid production. Both granulosa and thecal cells produce oestrogen and progesterone, the rates of production being dependent on the stage of maturation of the follicle and substrate availability. Thecal cells are the principal source of androgens and control oestrogen synthesis by providing aromatizable substrate. After exposure to LH/hCG in vivo, both cell types lose the ability to produce oestrogen in vitro. These studies support the two-cell, two-gonadotrophin hypothesis of ovarian steroidogenesis. In vitro, granulosa and thecal cells exhibit an increased ability to produce PGE-2 and PGF-2 alpha after exposure to LH/hCG in vivo. Follicular PG production appears to be regulated by arachidonic acid availability and PG synthetase activity. In vivo, the follicular fluid concentrations of PGE-2 and PGF-2 alpha increase markedly at the time of ovulation. The increases in PG levels and ovulation can be blocked by indomethacin, an inhibitor of PG synthesis. These studies provide convincing evidence for an intrafollicular source of PGs and are consistent with the hypothesis that LH induces an increase in PG production that is essential for rupture of the follicle. Steroids act on the follicle through autocrine and paracrine mechanisms to modulate follicular growth and differentiation and to regulate steroidogenesis. PG actions on the follicle appear to be exerted via effects on contractile elements of the theca externa, blood vessels and on collagenolytic and other proteolytic enzymes.

Animals↗
PubMed1989

Continuous live-dead discrimination of ram sperm during freezing.

Use of the dye amaranth (Color Index 16185) as a supravital stain for ram sperm is described. At a concentration of 0.4% in diluted semen, the dye was completely excluded by motile sperm and had no effect on sperm motility. The nuclei of immotile sperm were stained pink by amaranth. The decrease in sperm motility during 24-h storage at 5 degrees C was accompanied by a corresponding increase in stained sperm nuclei. The presence of the dye during freezing had no effect on sperm cryosurvival but tended to reduce sperm motility during post-thaw incubation. Insemination of ewes with fresh semen containing amaranth or with semen frozen in the presence of amaranth resulted in pregnancies in 7/10 ewes in each group, compared to 6/9 in the case of ewes inseminated with fresh semen without dye.

Amaranth Dye↗
PubMed1988

Estradiol assay by microtitre plate enzyme immunoassay.

Development of a simple enzyme linked immunosorbent assay (ELISA) for estradiol in serum extracts is described. The assay involves use of a 96-well microtitre plate, designed for immunoassay, as the support for a purified, high-titre antiserum, raised against estradiol-6(O)-carboxymethyloxime linked to bovine serum albumin, and using horseradish peroxidase-labelled estradiol-6-(O)-carboxymethyloxime as the labelled species, with 2,2'-azino-bis-(3-ethylbenzthiazoline sulfonic acid) diammonium salt (ABTS) as the chromogenic substrate. The assay characteristics rival those of radio- or chemiluminescence immunoassays for estradiol.

Cross Reactions↗
PubMed1987

Photoperiod entrainment of testosterone, luteinizing hormone, follicle-stimulating hormone, and prolactin cycles in rams in relation to testis size and semen quality.

Adult rams were exposed to photoperiod treatments over 2 years to study the influence of light regimes on pituitary-testicular activity and semen quality. Initially, all rams (12 per group) were exposed to 3 months of long days (16L:8D). Group 1 was then exposed to a regime of continuous short days (8L:16D) and Groups 2, 3, and 4 were exposed to 4 months of short days alternated with 1, 2, or 4 months, respectively, of long days. Every 2 weeks, serum hormone levels and scrotal circumference were determined and semen quality was evaluated. Regular cycles in pituitary and testicular activities corresponding to the period of the lighting regime resulted in Groups 2, 3, and 4, but not in Group 1. In general, the change from long days to short days induced increases in follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone levels, scrotal size and sperm numbers and a decrease in prolactin. The reverse occurred after subsequent exposure to long days. After 4 months of long days, testicular regression was complete, but when long-day exposure was reduced, less regression occurred. With continuous exposure to short days, FSH and testosterone remained above basal levels, prolactin levels were depressed, scrotal size remained near the maximum, and elevated numbers of motile sperm were sustained.

Animals↗
PubMed1986

The effect of thawing velocity on survival and acrosomal integrity of ram spermatozoa frozen at optimal and suboptimal rates in straws.

The effect of various thawing velocities on the motility and acrosomal maintenance of ram spermatozoa frozen at 20 degrees C/min (optimal) or 2 degrees C/min (suboptimal) was studied. The freeze-thaw motility and the percentage of intact acrosomes of spermatozoa frozen at 20 degrees C/min increased progressively with the thawing velocity. In semen frozen at 2 degrees C/min, motility of spermatozoa and the percentage of intact acrosomes declined drastically when the thawing velocity obtained in air at 20 degrees C was increased by thawing in water at 20 degrees C. Thawing at higher temperatures markedly increased both motility and acrosomal preservation, but the best results with semen frozen at 2 degrees C/min were lower than those obtained with semen frozen at 20 degrees C/min. The optimal freeze-thaw conditions for semen protected by 4% glycerol were freezing at 20 degrees C/min and thawing in water at 60 or 80 degrees C for 8 or 5 sec, respectively. Semen collected from rams exposed to a decreasing photoperiod exhibited higher motility after freezing and thawing than those exposed to an increasing photoperiod. However, there was no effect on acrosomal preservation after freezing at 20 degrees C/min.

Acrosome↗
PubMed1986

Use of enzyme-linked immunosorbent assay for measurement of bovine serum and milk progesterone without extraction.

An enzyme immunoassay for progesterone, using horseradish peroxidase as the label, was adapted for direct measurement of progesterone in serum or milk. Values obtained by direct measurement are highly correlated with values measured in extracts and are usable for convenient, rapid, accurate monitoring of the reproductive status of dairy cows. The assay is sensitive (ca. 1 pg), rapidly performed (3.5 h), and allows 92% accuracy in assessment of pregnancy status by direct measurement of progesterone in paired milk samples collected at breeding and 21 d later.

Animals↗
PubMed1985

A simple enzyme-linked immunosorbent assay for testosterone.

A new, enzyme-linked, immunosorbent assay for testosterone is described. The assay uses horseradish peroxidase coupled to testosterone as the tracer and offers the same sensitivity and reliability but greater convenience than radioimmunoassay. The assay is also simpler and more rapidly completed than previously described assays for testosterone.

Androgens↗
PubMed1985

Differential production of steroids by dispersed granulosa and theca interna cells from developing preovulatory follicles of pigs.

Dispersed granulosa and theca interna cells were recovered from follicles of prepubertal gilts at 36, 72 and 108 h after treatment with 750 i.u. PMSG, followed 72 h later with 500 i.u. hCG to stimulate follicular growth and ovulation. In the absence of aromatizable substrate, theca interna cells produced substantially more oestrogen than did granulosa cells. Oestrogen production was increased markedly in the presence of androstenedione and testosterone in granulosa cells but only to a limited extent in theca interna cells. The ability of both cellular compartments to produce oestrogen increased up to 72 h with androstenedione being the preferred substrate. Oestrogen production by the two cell types incubated together was greater than the sum produced when incubated alone. Theca interna cells were the principal source of androgen, predominantly androstenedione. Thecal androgen production increased with follicular development and was enhanced by addition of pregnenolone or by LH 36 and 72 h after PMSG treatment. The ability of granulosa and thecal cells to produce progesterone increased with follicular development and addition of pregnenolone. After exposure of developing follicles to hCG in vivo, both cell types lost their ability to produce oestrogen. Thecal cells continued to produce androgen and progesterone but no longer responded to LH in vitro. These studies indicate that several functional changes in the steroidogenic abilities of the granulosa and theca interna compartments occur during follicular maturation.

Androstenedione↗
PubMed1984

Enzymatic dissociation of ovarian and uterine tissues.

A method is described for the preparation of high yields of viable, dissociated cells from porcine theca interna and corpus luteum and from human and bovine endometrium. The tissues were dissociated by incubation at 37 degrees C in a mixture of 0.5% collagenase, 0.1% hyaluronidase and 0.1% pronase in balanced salt solution containing 1% chicken serum. This procedure consistently provided high yields of structurally and metabolically intact dispersed cells after a digestion period of 60 min. The procedure is superior to methods previously reported in the literature.

Animals↗
PubMed1982

Influence of sperm number and seminal plasma on fertility of progestagen-treated sheep in confinement.

Progestagen-impregnated vaginal sponges + PMSG were used to synchronize oestrus in crossbred adult ewes which were inseminated 56 h after sponge removal with 0.5 ml diluted semen containing 400, 200, 100, 50 or 25 x 10(6) spermatozoa per insemination. The diluent was skim milk-citrate or pooled seminal plasma. There was no difference in reproductive performance due to the insemination medium. Fertility (no. of ewes lambing) after insemination of 400 or 200 x 10(6) spermatozoa was 68% and was similar to that observed after natural service at progestagen-induced oestrus. When less than or equal to 100 x 10(6) spermatozoa were inseminated, fertility fell markedly and the number of lambs per ewe inseminated decreased. A decrease in litter size also occurred. The data indicate that insemination of 200 x 10(6) spermatozoa, i.e. less than 10% of the number in a single ram ejaculate, allows normal conception rates in progestagen-treated ewes.

Animals↗
PubMed1979

Cholesterol biosynthesis and progesterone production by chorionic cells of the early sheep conceptus in vitro.

Dissociated trophoblast cells from the chorion of the 21-day sheep conceptus were shown to produce progesterone in vitro. Evidence that this represented synthesis de novo was provided by the prolonged production of progesterone in the absence of added precursor steroids. Radioactive cholesterol was isolated after incubation of dispersed chorionic cells with acetate-1-14C.

Acetates↗
PubMed1979

Metabolism of progesterone by chorionic cells of the early sheep conceptus in vitro.

Progesterone-4-14C was extensively metabolized during incubation with dispersed trophoblast prepared from chorionic membranes of the 21-day sheep conceptus. Of the metabolites formed, 17, 20 alpha-dihydroxypregn-4-en-3-one, 20 alpha-hydroxypregn-4-en-3-one, 20 beta-hydroxypregn-4-en-3-one, 5 alpha-pregnane-3 alpha, 17,20 alpha-triol, 5 beta-pregnane-3 alpha, 17,20 alpha-triol, 5 beta-pregnane-3 alpha,20 alpha-diol, 3 beta-hydroxy-5 alpha-pregnan-20-one, 3 alpha-hydroxy-5 beta-pregnan-20-one, 20 beta-hydroxy-5 beta-pregnan-3-one, 5 alpha-pregnane-3,20-dione and 5 beta-pregnane-3,20-dione were identified. These findings indicate that the sheep conceptus acquires extensive steroid metabolizing capability very early in pregnancy.

Animals↗