Biomedical subjects

J W Knight

Publications and source records attributed to J W Knight.

At least 55 records · Page 3Linked to original sources

PubMed1991

Effects of pregnenolone, cyclic adenosine monophosphate, and human chorionic gonadotropin on in vitro progesterone and estrone synthesis by the porcine placenta and endometrium.

Two experiments were conducted to determine the effects of pregnenolone (P5), cyclic adenosine monophosphate (cAMP), and human chorionic gonadotropin (hCG) on porcine placental and endometrial production of progesterone (P4) and estrone (E1) in vitro at days 30, 60 and 90 of gestation. Placental P4 production increased between days 30 and 90 and was enhanced by the addition of P5. A further increase in placental P4 production occurred at days 30 and 90 due to cAMP supplementation. Addition of hCG failed to increase placental P4 production at any day. Placental E1 production in vitro was biphasic and mimicked the pattern seen in maternal plasma and fetal fluids. Placental E1 production in P5-supplemented medium was enhanced by the addition of cAMP at day 90. However, hCG supplementation reduced placental E1 production at day 90. Endometrial P4 and E1 production were similar to those of the placenta at day 30 of gestation. However, unlike placental steroidogenesis, endometrial hormone production remained relatively constant over the 3 days of gestation examined. Supplemental P5 enhanced endometrial P4 and E1 production. The overall magnitude of response to supplementation was considerably less in endometrial vs placental tissue. We conclude that both porcine placental and endometrial tissues are steroidogenically competent but that placenta is the far more active and responsive tissue. The mechanism controlling placental steroidogenesis apparently does not involve LH/hCG tropic stimulation, but cAMP is an effective intracellular second messenger.

Animals↗

PubMed1991

Nutritional factors and antimicrobials on development of infective larvae of subperiodic Brugia malayi (Nematoda: Filarioidea) in Anopheles quadrimaculatus and Aedes aegypti (Diptera: Culicidae).

The effects of nutritional factors and antimicrobials on the development of infective larvae of subperiodic Brugia malayi in susceptible Anopheles quadrimaculatus Say and Aedes aegypti (L.) were investigated. Larvae of both species of mosquitoes were reared on brewers yeast or a 1:1 brewers yeast-liver powder mixture. After emergence, one-half of the adults from each rearing condition were maintained on a 10% sucrose solution and the other half on a 10% sucrose solution containing 0.1% p-aminobenzoic acid (PABA). Females of both species of mosquitoes that fed on B. malayi-infected jirds showed a significant increase in the ineffective rate and intensity of infectiveness when the mosquito larvae were reared on the brewers yeast-liver powder diet. The addition of 0.1% PABA to the adult diet increased numbers of infective larvae of B. malayi that developed in Ae. aegypti but not in An. quadrimaculatus. The intensity of infectiveness of B. malayi was significantly greater when An. quadrimaculatus females were provided with a second blood meal from an uninfected jird and when females of both species were maintained on different concentrations of an antimicrobial solution.

4-Aminobenzoic Acid↗

PubMed1991

Effects of medium alterations on in vitro development of Brugia malayi larvae in cultured mosquito thoraces.

A recent study showed that 1-day-old, intracellularly lodged larvae of Brugia species develop in vitro to the infective third-stage larvae (L3) in excised thoraces of susceptible mosquitoes in the diphasic insect tissue culture medium containing a nutrient agar base overlaid with a 1:1 mixture of Schneider's Drosophila medium and Grace's insect cell culture medium supplemented with 20% fetal bovine serum (FBS) and antimicrobial agents. In the present investigation, the diphasic culture medium was used to evaluate the effects of medium alterations on the development of 1-day-old, intracellularly lodged larvae of subperiodic Brugia malayi in excised thoraces of Aedes aegypti to the L3. One-day-old larvae developed to the L3 in medium without nutrient agar base, at pH 7.0 and pH 7.5, in Hanks' balanced salt solution (HBSS) and in HBSS supplemented with bovine albumin fraction-V (BAF-V). These larvae also developed in the absence of FBS in the overlay medium, in overlay medium containing 5-20% FBS, in medium components obtained from different sources, in serum free Sf-900 (GIBCO) medium, and when FBS is replaced by BAF-V in the overlay medium. The percentage of L3 was not increased substantially in infected excised thoraces of mosquitoes when nutrient supplements, such as folic acid, p-aminobenzoic acid, glucose, lipid concentrate, hemin, or reduced glutathione, were added to the overlay medium containing BAF-V. These results suggested that 1-day-old, intracellularly lodged larvae developed to the L3 in infected excised thoraces of mosquitoes at almost the same rate as in intact mosquito, when excised thoraces were maintained alive under optimal conditions in a culture medium.

4-Aminobenzoic Acid↗

PubMed1990

In vitro release of progesterone and estrone by the porcine placenta throughout gestation.

In vitro release of progesterone (P4) and estrone (E1) by the porcine placenta was characterized at 12 days of gestation between d 20 and 110. Placental P4 rose linearly from d 25 to 40, plateaued between d 40 and 50, continued to increase to a peak concentration at d 100, then decreased sharply to d 110. Placental E1 decreased abruptly from d 30 to a nadir at d 40, then increased continuously from d 70 to peak values at d 110. This biphasic pattern for E1 mimicked the pattern observed in allantoic fluid and maternal plasma pools. Only trace amounts of testosterone (T) were measured at d 20, 50, 60, and 100, suggesting rapid aromatization of C19 steroids to estrogens. The results of this in vitro study indicate that the porcine placenta collected throughout gestation can release large quantities of P4, although the lack of an increase in systemic P4 suggests that under in vivo conditions P4 is utilized and/or metabolized within the uterus.

Allantois↗

PubMed1990

Susceptibility of Anopheles quadrimaculatus (Diptera: Culicidae) to subperiodic Brugia malayi and Brugia pahangi (Nematoda: Filarioidea) adapted to nude mice and jirds.

Anopheles quadrimaculatus and Aedes aegypti (Black-eyed Liverpool strain) were fed on jirds and nude mice (jird-jird infection, jird-mouse infection, and mouse-jird infection) infected with subperiodic Brugia malayi and B. pahangi. Microfilariae of B. malayi from jird-mouse and mouse-jird infections developed normally in An. quadrimaculatus, whereas those from jird-jird infections did not develop. Microfilariae of both species from jirds and nude mice developed normally in Ae. aegypti and those of B. pahangi developed normally in An. quadrimaculatus. It is suggested that microfilariae from nude mice are modified physiologically, immunologically, or both so that they can develop in refractory An. quadrimaculatus, thus indicating that susceptibility and refractoriness of An. quadrimaculatus to B. malayi also is influenced by factors relating to the vertebrate host in addition to mosquito genetic factors.

Aedes↗

PubMed1990

Uptake and clearance rates of biotin in pig plasma following biotin injections.

Nine crossbred gilts were surgically fitted with indwelling anterior vena cava cannulae, and randomly assigned to receive intramuscular injections of either 2.2 micrograms biotin/kg body wt, 6.6 micrograms biotin/kg body wt or a sham dose of carrier medium. Plasma biotin concentrations (PBC) were determined from blood samples taken at 39 time points during a 73 h period. There were no time differences (P less than .05) in PBC for the sham injected gilts suggesting no diurnal variation in PBC. The sham injected gilts had an overall mean PBC of 42.5 ng/dl. Following biotin injection, PBC increased and peaked at 4 h (66.7 ng/dl) and 6 h (90.9 ng/dl), respectively for gilts receiving low and high levels of biotin. These increases in PBC resulted in treatment differences (P less than .05) in PBC from 4 h to 10 h post-injection. Biotin uptake and clearance rates were calculated using exponential curves. Uptake rates (% increase PBC/h) were 16.5 and 15.9% and clearance rates (% decrease PBC/h) were 5.7 and 2.8%, respectively, for gilts receiving low and high levels of biotin. Clearance rate, expressed as the amount of biotin cleared per hour, was similar (2 to 3 ng/dl) for both biotin treatments.

Animal Nutritional Physiological Phenomena↗

PubMed1989

Chronic pruritic eruption in patients with acquired immunodeficiency syndrome associated with increased antibody titers to mosquito salivary gland antigens.

Five of seven patients with acquired immunodeficiency syndrome (AIDS) who had pruritus and a chronic, nonspecific-appearing skin eruption had increased antibody titers to antigens in the salivary glands of Aedes taeniorhynchus, a salt marsh mosquito common to South Florida. We hypothesize that the pruritus and skin lesions in patients with AIDS represent a form of chronic "recall" reaction. Increased antibody titers to mosquito salivary gland antigens may be a consequence of nonspecific B cell activation, a feature of AIDS.

Acquired Immunodeficiency Syndrome↗

PubMed1989

Intracellular melanization in the mosquito Anopheles quadrimaculatus (Diptera: Culicidae) against the filarial nematodes, Brugia spp. (Nematoda: Filarioidea).

Intracellular melanization responses to developing larvae of Brugia species (B. malayi (Buckley), B. pahangi (Buckley and Edeson), and B. patei (Buckley, Nelson, and Heisch] in the thoracic muscle fibers of eight strains of Anopheles quadrimaculatus Say were first observed 48 to 72 h after an infective blood meal. Three to 4 d later, large numbers of melanized first-stage larvae were found within the thoracic muscle fibers. These intracellular responses were in addition to the extracellular responses to microfilariae and microfilarial sheaths of B. pahangi in the abdominal hemocoel of An. quadrimaculatus described in literature. Simultaneously, normal development of larvae of the three Brugia species also was observed in all eight strains of An. quadrimaculatus. Comparisons of melanized first-stage larvae and normally developing larvae of the three Brugia species in the thoracic muscle fibers of the eight strains of An. quadrimaculatus showed that there were distinct variations in numbers of melanized and developing larvae and percentage of females with melanized and developing larvae in different strains. Numbers of melanized first-stage larvae reflected the extent of refractoriness of An. quadrimaculatus strains. Fully melanized larvae showed no abnormalities in parasite organelles, indicating that refractoriness is due to an enhanced ability of the host to recognize the living parasite. Further comparison among the strains suggested that the mutants, Yellow Larvae and Vero Beach Colony were significantly more susceptible, and Red Stripe was the most refractory to all three Brugia species. Thus, the gene(s) controlling susceptibility and refractoriness to all three Brugia species probably occurs on the same autosomal chromosome as the mutations in these strains. The significance of intracellular melanization of filarial larvae is discussed with reference to the melanization responses to different parasites in other mosquitoes.

Animals↗

PubMed1989

Long-term liquid storage of porcine spermatozoa separated using a discontinuous bovine serum albumin gradient.

Two experiments were conducted to determine efficacy of a discontinuous bovine serum albumin (BSA) gradient for isolating viable porcine spermatozoa more tolerant to 5-d liquid storage in Beltsville Thawing Solution (BTS) at 15 degrees C. The gradient, contained in a 500-ml separatory funnel, consisted of 4% BSA (60 ml) over 10% BSA (60 ml). Spermatozoa were extended in 26 ml of BTS, layered on top of the gradient, and allowed to migrate through the BSA. The quality of spermatozoa separated by the gradient varied among boars. However, populations of spermatozoa isolated from the bottom 30 ml of the gradient (Fraction 4) consistently contained a high percentage of spermatozoa with acrosomes possessing normal apical ridges (NAR; 89.6%) and progressively motile spermatozoa (MOT; 84.0%), as well as spermatozoa with high velocity (VEL; 336.5 mu/s). Increasing sperm migration time, but not gradient temperature, increased the number of spermatozoa recovered in Fraction 4, but it did not reduce quality of the separated spermatozoa. Spermatozoa isolated in Fraction 4 had greater NAR, MOT and VEL after 5-d storage in BTS than did unseparated spermatozoa. Boar spermatozoa isolated on a discontinuous BSA gradient were more tolerant to storage at 15 degrees C than were unseparated spermatozoa. Such a population may be desirable for use in artificial insemination programs.

Acrosome↗

PubMed1989

Mosquito salivary gland antigens identified by circulating human antibodies.

Salivary glands were removed from female mosquitoes of laboratory-reared strains of species common to southern Florida. Protein antigens were isolated from homogenates of these glands by denaturing electrophoresis and transferred to nitrocellulose for immunoblotting with serum samples obtained from human volunteers. A spectrum of antigens with a wide range of molecular weights (14 to 126 kilodaltons) were identified by antibodies in human serum for each species. Both species-unique and species-shared antigens were present. The results of these studies indicate that the humoral response to mosquito bite is complex, with a multitude of antigens provoking antibody responses. Since each individual has his or her own unique exposure history to mosquitoes, it seems unlikely that desensitization to a specific immunogen will confer protection in clinical situations in which multiple exposures to a variety of mosquito species occur.

Animals↗

PubMed1988

Further characterization of refractoriness in Aedes aegypti (L.) to infection by Dirofilaria immitis (Leidy).

Factors which control the expression of the refractory or susceptible condition to infection with Dirofilaria immitis in the mosquito. Aedes aegypti, were investigated using three protocols. (1) Microfilariae and prelarvae were injected into the hemocoel of susceptible A. aegypti. Some microfilariae and prelarvae developed to the L1 larval stage but they failed to complete development to the infective stage. (2) Enema of microfilariae and prelarvae from infected susceptible and refractory donor females were given into the midgut of uninfected susceptible and refractory recipient females. The results indicate that the conditions which inhibit the initiation of development are present in the Malpighian tubules and not in the midgut of the refractory mosquitoes. (3) Transplants of infected Malpighian tubules from susceptible and refractory donor females were made into the abdominal hemocoel of uninfected susceptible and refractory recipient females. The results showed that the refractory condition depends on the genetic makeup of the donor, not the recipient, mosquito. The above results taken as a whole indicate that the factors which control refractoriness are not present in the midgut but are present in the Malpighian tubule cells of refractory A. aegypti.

Aedes↗

PubMed1988

Isolation of a population of intact, highly-motile porcine spermatozoa using a discontinuous bovine serum albumin gradient.

This study was conducted to determine the efficacy of isolating intact, highly-motile porcine spermatozoa using a discontinuous bovine serum albumin (BSA) gradient. Either 0.25, 0.5, 1, 2.5 or 5x10(9) spermatozoa extended to 26 ml with Kiev extender were layered on a discontinuous BSA gradient (4% BSA over 10% BSA) contained within a 500-ml separatory funnel. After 1 h of sperm migration at 23 degrees C, four 30-ml aliquots designated Fractions 1, 2, 3, 4 and Fraction T were collected from the bottom of the funnel. Fraction 4 was the bottom fraction and Fraction T was the remnant of the applied sample. For all concentrations of applied spermatozoa, the percentage of progressively motile spermatozoa was greater in Fraction 4 than in Fractions T or 1 (P<0.05). Fraction 4 contained a greater (P<0.05) proportion of spermatozoa with normal apical ridge acrosomes than Fraction T. Regardless of the concentration of spermatozoa applied, Fraction 4 contained more than 90% of progressively motile spermatozoa and spermatozoa possessing normal apical ridge acrosomes. The percentage of applied cells recovered in Fraction 4 decreased as the concentration of spermatozoa applied to the gradient increased.

Journal Article↗

PubMed1988

Circulating antibody detection in human serum to mosquito salivary gland proteins by the avidin-biotin-peroxidase technique.

Serum was collected from individuals with little, average, or extensive exposure to mosquito bites for determination of the presence of circulating antibodies to mosquito salivary gland proteins. Intensity of exposure was determined by mosquito-bite and exposure history. Sections cut through the thorax of four different species of mosquitoes, locally prevalent in South Florida, were exposed to serum and developed for antibody binding with the use of the avidin-biotin-peroxidase immunohistochemical technique. In subjects with histories of little or average exposure to mosquitoes, binding was observed that appeared to be species-specific; in subjects with extensive exposures, little antibody binding to salivary gland was noted. We hypothesize that suppression of the humoral immune response is an adaptive mechanism in response to significant exposures of mosquito salivary gland antigens.

Animals↗

PubMed1987

Effect of chlortetracycline supplementation during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival and fetal development in gilts.

A total of 166 crossbred gilts weighing approximately 87 +/- 1 kg was limit-fed (2.5 kg/d) a corn-soybean meal gestation diet containing either 0 or 220 ppm of chlortetracycline (CTC) from 157 +/- 1 d of age until 15 d after breeding. These gilts were slaughtered at 31 +/- 1 or 71 d +/- 1 d of gestation for evaluation of reproductive performance. Age (190 +/- 3 d vs 195 +/- 3 d) and body weights (106 +/- 2 kg vs 106 +/- 2 kg) at puberty were similar for control and CTC-fed gilts, respectively. Although not significant (P > 0.05), ovulation rate was higher in CTC-fed than in control gilts as assessed at both 31 d (14.2 +/- 0.7 vs 12.9 +/- 0.9, P = 0.31) and 71 d (13.9 +/- 0.6 vs 12.4 +/- 0.5, P = 0.10) of gestation. There was an increase (P = 0.04) in the number of live embryos for CTC-fed gilts at 31 d (12.1 +/- 0.7 vs 9.7 +/- 0.7) but not at 71 d (10.0 +/- 1.1 vs 9.6 +/- 1.0) of gestation. The mean uterine length, placental length, placental weight, fetal length, fetal weight, and allantoic fluid volumes were similar between the control and CTC-fed gilts. Results indicated that feeding CTC during prebreeding and early gestation did not influence the proportion or age of gilts at puberty. However, CTC feeding may have influenced a trend to-ward an increased ovulation rate and increased number of live embryos in gilts.

Journal Article↗

PubMed1986

Relationship between estrone sulfate in plasma and litter size at farrowing for sows and gilts.

A positive association (P < 0.01) was detected between estrone sulfate (ES) concentrations in maternal plasma at Day 30 of pregnancy and litter size at parturition in swine. This relationship was best described by a fifth order regression equation (R(2) = 0.5) which indicated that as ES increased from 1 to 7.5 ng/ml on Day 30, litter size increased from 0 (nonpregnant) to 18 piglets farrowed. Day of sampling (P < 0.02), month (P < 0.04) and parity (P < 0.08) were major sources of variation in the model. This indicated that effects of environmental factors such as heat stress, which influence conception rate and embryonic survival, are reflected in changes in maternal ES. Also, larger litter size associated with parous sows is reflected in increased ES in maternal plasma. We conclude that measurement of ES early in gestation may be useful in reproductive management to identify nonpregnant gilts and sows as well as those with small litters.

Journal Article↗

PubMed1986

Experimental vertical transmission of Saint Louis encephalitis virus by Florida mosquitoes.

Vertical transmission of St. Louis encephalitis (SLE) virus to F1 larval progeny was demonstrated in 8 species of mosquitoes which occur in Florida: Culex quinquefasciatus, Cx. nigripalpus, Cx. salinarius, Cx. restuans, Cx. opisthopus, Anopheles quadrimaculatus, An. albimanus, and Aedes taeniorhynchus. Relatively high rates of such transmission were observed in Ae. taeniorhynchus and vertical transmission to F1 adult progeny and venereal transmission from males to females also were demonstrated with this species. Larval rearing temperature affected transstadial transmission of the virus in Ae. taeniorhynchus, especially to the adult stage. Such transmission was observed with a larval rearing temperature of 18 degrees C but not at 27 degrees C. Because of the abundance and distribution of Ae. taeniorhynchus in Florida, and the relatively high rates of vertical transmission of SLE virus observed in the present experiments, this mosquito species warrants further investigation as a possible overwintering host for the virus in that locality.

Aedes↗

PubMed1985

Supplemental biotin for swine. I. Influence on feedlot performance, plasma biotin and toe lesions in developing gilts.

Three trials, utilizing a total of 240 crossbred gilts, were conducted to study the influence of 0 (NB) or 220 (SB) microgram supplemental biotin/kg of diet on feedlot performance, plasma biotin and development of toe lesions in developing gilts. Corn-soybean meal diets were fed from weaning to 92 kg body weight. Gilts were housed on expanded-metal floors to 50 kg body weight and on partially slatted concrete floors until completion of the trials. Feedlot performance, hair and structural soundness scores were not different (P greater than .10) between NB and SB gilts. Plasma biotin (PB) levels were elevated (P less than .01) when supplemental biotin was included in the diet. Gilts consuming SB diets had fewer (P less than .01) toe lesions/gilt and lower (P less than .01) toe lesion severity scores/gilt compared with gilts fed NB diets. Heel-horn erosion and heel cracks were the most frequent toe lesions observed. Fewer gilts (P less than .01) developed side-wall toe cracks when fed SB diets. Supplemental biotin reduced the frequency of individual toes containing heel-horn erosion (P less than .10), heel cracks (P less than .05) and side-wall toe cracks (P less than .05) with the severity of these lesions not affected (P greater than .10) by supplemental biotin. These results suggest that biotin levels in corn-soybean meal diets are adequate for feedlot performance, and that supplemental biotin can improve hoof integrity, but will not prevent toe lesions.

Animals↗

PubMed1985

Supplemental biotin for swine. II. Influence of supplementation to corn- and wheat-based diets on reproductive performance and various biochemical criteria of sows during four parities.

Data from 116 females previously fed a corn-soybean basal diet with 0 or 220 micrograms supplemental biotin/kg during growth and development were used to study the influence of 0 (NB) or 440 (SB) micrograms of supplemental biotin/kg to corn-(C) or wheat-(W) based diets for gilts and sows housed in total confinement. Reproductive performance through four parities (total of 245 litters) and various sow and pig biochemical criteria were evaluated. Females fed W diets were older (P less than .07) at first estrus, farrowed litters that were lighter weight (P less than .01) at birth and that contained fewer (P less than .05) total and live pigs compared with females fed C diets. Biotin supplementation did not significantly influence (P greater than .10) farrowing and lactation performance; however, after the first parity, total and live pigs/litter at farrowing tended to be larger for SB females. Conception rate at first estrus postpartum was increased (P less than .07) by 9% and the average weaning to estrus interval was reduced (P less than .05) from 14.5 to 10.2 d with SB. Biotin supplementation increased (P less than .001) the biotin content of sow plasma, milk and liver, while sow liver pyruvate carboxylase activity was not altered (P greater than .10). Pigs farrowed by SB females had three- and fivefold higher (P less than .001) levels of plasma biotin at birth and 14 d of age, respectively; however, liver biotin levels at birth were not different (P greater than .10) for pigs from NB and SB females.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗