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Biomedical subjects

K Blackburn

Publications and source records attributed to K Blackburn.

29 records · Page 2Linked to original sources
PubMed1990

Nickel inhibits endothelin-induced contractions of vascular smooth muscle.

Endothelin (ET)-induced contractions of vascular smooth muscle (VSM) are dependent on extracellular Ca2+ yet display only partial sensitivity to L-type Ca2+ antagonists. The purpose of this study was to evaluate the effect of nickel (Ni2+), a Ca2+ channel antagonist with clearly documented differential potency toward L- vs. T-type Ca2+ currents on ET-mediated contractions in VSM. Treatment of rings of left anterior descending porcine coronary artery (LAD) with Ni2+ produced a profound dose-dependent inhibition of isometric force development in response to porcine ET (ET-1). At a concentration of 360 microM, Ni2+ exerted a significant inhibitory effect on contracture in response to doses of ET-1 ranging from 3 to 100 nM. In contrast, the same concentration of Ni2+ failed to significantly affect peak force development in response to KCl depolarization (5-77 mM) or to phenylephrine (0.3-30 mM). In addition, 360 microM Ni2+ significantly inhibited the contractile response of rat aorta to 10 nM ET-1. We conclude that ET-1 activates a Ni2(+)-sensitive process in VSM which may signal an additional Ca2+ influx pathway that appears to be functionally distinct from the L-type Ca2+ channel.

Animals↗
PubMed1989

Can implanted cyst pieces of Echinococcus granulosus regenerate?

Small piece of ovine hydatid cysts devoid of brood capsules and protoscoleces, and half or quarter pieces of secondary sterile murine cysts of equine origin failed, over a six-month period, to regenerate when passaged into the peritoneal cavity of BALB/c mice. The majority of similar pieces placed in microdiffusion chambers prior to insertion into mice also failed to regenerate, suggesting that the passage of cyst pieces may not be totally reliable in the assessment of the viability of germinal layer tissue after chemotherapy.

Animals↗
PubMed1988

The peritrophic membrane of the female sandfly Phlebotomus papatasi.

The ultrastructure of the peritrophic membrane of the female sandfly Phlebotomus papatasi has been studied at various times after blood meals. The membrane begins to form within four hours of the blood meal with the secretion by the entire midgut epithelium of an electron-dense amorphous material. Subsequently, the membrane is stabilized and strengthened by the production of a layer of irregular chitinous microfibres, the whole membrane then forming a complete and resilient sac apparently unaffected by boiling 9 M potassium hydroxide. The membrane appears redundant 48 hours after the blood meal and fragments, possibly as a result of chitinase activity. The membrane's main functions are probably the prevention of clogging of the microvillous brush border by the blood meal and the confinement of large proteins, particularly serum trypsin inhibitors, to the endoperitrophic space while allowing sandfly proteases access to the blood meal periphery. Blood is not required to stimulate membrane production. Saline taken by blood feeding into the midgut also stimulates membrane formation. Phlebotomus papatasi females may lack an efficient anticoagulant, at least in the midgut, as blood meals frequently include fibrin clots.

Animals↗
PubMed1986

Evaluation of the reproductive toxicology of 2,4,6-trichlorophenol in male and female rats.

The toxicity of chlorinated organic compounds which may be generated as a by-product of drinking water chlorination has been an issue of increasing concern. Relatively few data are available concerning their reproductive toxicity. The present study was designed to evaluate the reproductive effects of one of these compounds, 2,4,6-trichlorophenol (TCP), in male and female rats. Adult males were treated with either 0, 100, 500, or 1000 mg/kg of TCP (po) for 10 weeks, at which time semen evaluations were conducted on ejaculates recovered from the genital tract of receptive females. Fertility was assessed in the 0- and 1000-mg/kg groups. Females were treated with identical doses for 2 weeks prior to pregnancy then throughout gestation. Dams were allowed to litter and pup development was monitored until Day 42 postpartum. TCP had no effect on any sperm parameter or male fertility. Treatment of females with 1000 mg/kg of TCP produced gross maternal toxicity as reflected in increased lethality and decreased weight gains in the dams. However, no treatment-related differences were seen in litter sizes or pup survival. Male and female birth weights were significantly depressed in the 500- and 1000-mg/kg groups; these differences disappeared by Day 4 postpartum, suggesting that they were a reflection of maternal toxicity. To this extent, the reproductive processes of male and female rats do not appear to be a primary target for the effects of TCP.

Animals↗
PubMed1985

The development of young infants' ability to detect stimuli in the nasal visual field.

We compared infants' ability to detect single lines of varying width in the temporal and nasal visual fields. The smallest lines detected by 1-month-olds at 20 degrees in the nasal visual field were more than eight times wider than those detected at 30 degrees in the temporal visual field. In contrast, 2-month-olds detected smaller lines at 20 degrees in the nasal visual field than at 30 degrees in the temporal visual field. Converging evidence suggests that the observed improvement between 1 and 2 months in detection in the nasal visual field reflects the maturation of a projection from the retina through the visual cortex to the superior colliculus.

Eye Movements↗
PubMed1985

Novel methods for the estimation of acceptable daily intake.

This paper describes two general methods for estimating ADIs that circumvent some of the limitations inherent in current approaches. The first method is based on a graphic presentation of toxicity data and is also shown to be useful for estimating acceptable intakes for durations of toxicant exposure other than the entire lifetime. The second method uses dose-response or dose-effect data to calculate lower CLs on the dose rate associated with specified response or effect levels. These approaches should lead to firmer, better established ADIs through increased use of the entire spectrum of toxicity data.

Animals↗
PubMed1984

An evaluation of the copulatory, endocrinologic, and spermatotoxic effects of carbon disulfide in the rat.

The present study was undertaken to evaluate the endocrinologic and spermatogenic effects of carbon disulfide (CS2) exposure in the rat. Adult, male rats were exposed to either 600 ppm CS2 or filtered air for 6 hr/day for 5 days/week for 10 weeks. One week prior to exposure and then at Weeks 1, 4, 7, and 10, males were placed with ovariectomized, hormonally primed females, and copulatory behaviors were scored. Fifteen minutes postcopulation, the female was killed and the ejaculate was recovered from the excised uterine tract along with the semen plug. Sperm counts, sperm motility, and morphology were determined. A blood sample was obtained for analyses of testosterone, follicle-stimulating (FSH), and luteinizing hormone (LH). At the end of the 10th week, five animals in each group were challenged with either human chorionic gonadotropin (HCG, 50 IU/animal, iv) or gonadotropin-releasing hormone (GnRH, 100 ng/animal, iv), and the testosterone or gonadotropin responses were monitored over time. Animals were subsequently killed with one epididymis and testis processed for histology and a sperm count determined from the other epididymis. Analysis revealed that CS2 exposure produced significant alterations in copulatory behavior and a decrease in ejaculated sperm counts by the fourth and seventh weeks of exposure, respectively. No endocrinologic alterations were observed. Moreover, caudal epididymal sperm counts were not depressed and the testes appeared histologically normal. These data suggest that CS2 does not exert a direct effect on the testes, but rather may interfere with the processes regulating sperm transport and ejaculation.

Animals↗
PubMed1984

Effects of trichloroethylene exposure on male reproductive function in rats.

The present study was designed to evaluate the influences of trichloroethylene (TCE) on the reproductive system of male rats. In addition, information was obtained on the distribution and metabolism of TCE. At 100 days of age, male rats were allowed to copulate with ovariectomized, hormonally primed females and copulatory behaviors scored. Fifteen minutes post-ejaculation, females were sacrificed and ejaculate and semen plug recovered from the uterus and vagina for evaluation. These data served as a pre-exposure baseline for each animal. TCE exposure was then initiated with animals intubated with either 0, 10, 100, or 1000 mg/kg of TCE (10 males/group) for 5 days/week for 6 weeks. Copulatory behaviors and semen evaluations were conducted at Weeks 1 and 5 as well as 4 weeks post-exposure. Three males/group were sacrificed at the end of the sixth week of exposure and levels of TCE and its metabolites measured in various organs and blood. The remaining animals were sacrificed at the end of Week 10. TCE-related effects were seen primarily in the 1000 mg/kg group as reduced body weight gain, elevated liver/body weight ratios, and impaired copulatory behavior. However, the copulatory performance of the "affected" males had returned to normal by the fifth week of exposure. Although TCE and its metabolites concentrated to a significant extent in the male reproductive organs, semen evaluations failed to reveal any indices of spermatotoxicity. The initial alterations in copulatory behavior may be attributed to the narcotic properties of TCE. Tolerance to this pharmacological effect may explain the absence of these effects by the fifth week of exposure.

Animals↗