Biomedical subjects

G R Davenport

Publications and source records attributed to G R Davenport.

At least 19 recordsLinked to original sources

PubMed1991

The in vitro effects of various lysosomotropic agents on the gut of Schistosoma mansoni schistosomula.

Cultured Schistosoma mansoni schistosomula of various ages were exposed to several lysosomotropic agents. Weak bases such as chloroquine, ammonium chloride, and acridine orange caused gut swelling upon protonation. The latter compound fluoresced a bright orange indicating the acidic nature of the gut contents. Hydrolysis of ingested L-amino acid methyl esters also resulted in gut swelling, indicating the nonpermeant nature of the resulting L-amino acids. Neither age nor feeding status influenced these swelling effects. Treatment of schistosomula with D-amino acid esters, free L-amino acids, or methanol had no effect. Thin-layer chromatographic analysis of worms treated with radiolabeled L-leucine methyl ester provided evidence that the ester was hydrolyzed. These results support the premise that the schistosome gut is an acidic compartment and is reminiscent of a secondary lysosome in its reaction to lysosomotropic agents.

Acridine Orange↗

PubMed1988

Characterization of matrix domains of the hamster acrosome.

In this study we describe the purification and the structural and biochemical properties of a detergent-stable complex of the hamster sperm acrosome. This complex consists of two distinct acrosomal matrix domains and a layer of electron-dense material, termed the acrosomal lamina, derived from the luminal surface of the outer acrosomal membrane. This complex has been isolated by centrifugation of detergent-extracted sperm suspensions on Percoll density gradients. The complex contains two major polypeptides of Mr 29,000 and Mr 22,000 and minor polypeptides of Mr 64,000-62,000, 56,000 and 35,000. Gelatin-containing sodium dodecyl sulfate-polyacrylamide gels demonstrate that bands of proteinase activity are not the major polypeptide components of the complex. These data demonstrate that the matrix of the acrosome is compartmentalized into domains of differing structural properties that occupy specific locations in the intact acrosome and that matrix components are physically associated with the outer acrosomal membrane. These data indicate that a structural framework is present within the acrosome and we speculate that it may be involved in sequestering hydrolases into specific spatial domains and could affect the temporal release of activity of selected hydrolases during the acrosome reaction.

Acrosome↗

PubMed1987

Outer acrosomal membrane of guinea pig spermatozoa: isolation and structural characterization.

We describe a protocol to isolate a highly enriched fraction of outer acrosomal membrane from guinea pig spermatozoa and present new data on the ultrastructure of this membrane domain. Cauda epididymal spermatozoa were suspended into a low ionic strength buffer and subjected to brief homogenization; this stripped the plasma membrane from the spermatozoa and severed the acrosomal apical segment from the spermatozoon. The crescent-shaped apical segments retained the outer acrosomal membrane and specific components of the acrosomal matrix. Enriched fractions of apical segments were isolated on discontinuous sucrose gradients and the outer acrosomal membrane purified by subsequent centrifugation onto Percoll density gradients. The isolated outer acrosomal membrane did not form vesicles, but instead rolled up into spiral sheets. Both thin section and negatively stained specimens revealed a paracrystalline arrangement of filaments associated with the luminal surface of the membrane. The isolated outer acrosomal membrane revealed a limited number of polypeptides by SDS-PAGE, and the polypeptide pattern was distinct from the plasma membrane fraction. The isolated acrosomal membranes possessed no ouabain sensitive Na+,K+-ATPase activity, whereas about 20% of the ATPase activity of the plasma membrane enriched fraction was inhibited by ouabain. The potential function of the structural differentiations of the outer acrosomal membrane in the membrane fusion events of the acrosome reaction is discussed.

Acrosome↗

PubMed1985

Effects of maternal administration of diethylstilbestrol and estradiol on the newborn guinea pig.

The subcutaneous injection of diethylstilbestrol (2.5 micrograms/day) into pregnant guinea pigs from the 28th or 40th day to term resulted in an accelerated tempo of differentiation of the genital tract of the female offspring at birth, as well as intense estrogenic stimulation. Estradiol (50 micrograms per day) injected over the same period caused insignificant estrogenic stimulation in the newborn. The normal embryogenesis of the genital tract is described and a pattern of caudocranial differentiation identified. The normal genital tract is described as a basis for the analysis of results in the newborn. Comparative studies in other animals are discussed.

Animals↗

PubMed1984

Endometrial prostaglandins and phospholipase activity related to implantation in rabbits: effects of dexamethasone.

The anti-inflammatory steroid, dexamethasone, was demonstrated to have an antifertility effect in rabbits when administered systemically on Days 5-7 of pregnancy. The effects of this agent on prostaglandin (PG) concentrations and phospholipase activity in endometrium were determined. Using a highly specific and sensitive gas chromatography-mass spectometry (GC-MS) method, it was established that PGF2 alpha, PGE2 and 6-keto-PGF1 alpha concentrations are all significantly elevated in implant site endometrium relative to nonimplant regions on Day 7 postcoitus (p.c.). Although these levels were strikingly lowered in indomethacin-treated females, the administration of dexamethasone altered the balance between the various PGs but did not reduce tissue levels greatly. Determinations of PG levels in uterine venous plasma likewise demonstrated that neither synthesis nor release of PGs had been drastically curtailed by dexamethasone treatment. Endometrial phospholipase activity was determined on Days 6, 7 and 8 of pregnancy. Enzyme activity was elevated on Day 7 relative to the other days and implant site activity was significantly greater than nonimplant region activity on both Days 6 and 7. Treatment with either dexamethasone or indomethacin reduced the Day 7 activity to baseline levels and obliterated the differential between implant and nonimplant regions. The dexamethasone effect appears to be mediated by induction of a transferable inhibitory factor. Thus, while indomethacin and dexamethasone have similar effects on pregnancy when present during the implantation period, their respective mechanisms of action may be different. Even though dexamethasone inhibits endometrial phospholipase activity, this is not attended by inhibition of PG generation.

6-Ketoprostaglandin F1 alpha↗

PubMed1979

Symplasma formation and decidualization in the pseudopregnant rabbit after intraluminal instillation of tricaprylin.

A pure neutral triglyceride, tricaprylin, was injected (Day 0) into isolated segments of the uterus of rabbits in which pseudopregnancy had been induced by i.v. injection of hCG 6 days before. The animals were killed in groups of 3 on Days 1, 2, 3, 4 and 6. Saline, simple ligation of the uterus or uterine trauma were used as control treatments in other uterine segments in the same animals. Extensive symplasma formation in the uterine epithelium of the tricaprylin-treated segments was observed on Days 2 and 3; this had degenerated by Day 4 and was absent by Day 6. Decidualization of the stroma began on Days 3 and 4 and was absent by Day 6. The symplasma formed earlier on the antimesometrial side than it did laterally or mesometrially. Decidualization was maximal mesometrially, intermediate laterally, and absent antimesometrially. Ligation with saline and trauma, but not ligation alone, produced symplasma formation. Decidualization occurred after trauma but not after saline injection or ligation alone.

Animals↗

PubMed1977

Deciduogenic effect of prostaglandins in the pseudopregnant rabbit.

Intrauterine implants made of Silastic or wax and containing various additives, including prostaglandins (PGs), were used to characterize some of the factors involved in deciduogenesis in rabbits. Implants were inserted into uteri on Day 6 of pseudopregnancy and the response was assessed by light microscopy on Day 10. The surface area of decidual tissue in histological sections was employed as an index of the degree of decidualization obtained. PGE-2, PGF-2alpha and arachidonic acid each elicited a prominent decidual response, PGE-2 being most potent. Implants which released histamine or oestradiol-17beta had a very slight decidualizing effect in some females. Control implants and implants releasing dibutyryl cyclic-AMP had no deciduogenic influence. All implants, regardless of additive content, induced a symplasmic transformation of the uterine surface epithelium. It is concluded that PGs and the distension caused by the implant may be involved in deciduogenesis in the rabbit.

Animals↗

PubMed1975

Energy-dependent calcium uptake activity of microsomes from the aorta of normal and hypertensive rats.

Energy-dependent calcium uptake activity of microsomes isolated from the rat aorta has been characterized. The microsomes consist of smooth membrane vesicles which in the presence of MG-ATP as an energy source continuously sequester calcium over a 60-min period. This calcium uptake is greatly stimulated by oxalate anion which serves as a calcium trapping agent. Unlike the calcium uptake of mitochondria this uptake is not inhibited by sodium azide. Sucrose density gradient analysis of the microsomal calcium uptake suggests that the system is associated with the sarcoplasmic reticulum. In presence of 5 mM Mg-ATP and 20 muM calcium approximately 38 nmol of calcium per mg of microsomal protein are taken up in 20 min. In the absence of ATP, less than 2 nmol of calcium per mg of protein are taken up in the first 2 min with no further uptake of calcium in subsequent time periods. When calcium uptake activity is plotted against calcium or ATP concentration of the medium, half maximal activity is calculated for 24.3 muM calcium and for 1.6 mM ATP. The calcium uptake characteristics of the rat aorta microsomes are compatible with a postulated role in the relaxation of the vascular smooth muscle and the provision of an intracellular calcium store for muscle contraction. Aorta microsomes from SHR rats (a genetic strain that is spontaneously hypertensive) have a significantly reduced uptake when compared with the corresponding nonhypertensive control strain. The level of calcium and ATP for half maximal activity of the rat aorta microsomal calcium uptake system is approximately the same in the SHR and the control strain. The rate of release of calcium from rat aorta microsomes is apparently identical in SHR strain and control. The calcium uptake activity of kidney and liver microsomes isolated from the SHR strain and control. The calcium uptake activity of kidney and liver microsomes isolated from the SHR rat appears to be identical to that found in the control strain.

Adenosine Triphosphate↗

PubMed1973