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Biomedical subjects

J A Elliott

Publications and source records attributed to J A Elliott.

108 records · Page 6Linked to original sources
PubMed1976

Circadian rhythms and photoperiodic time measurement in mammals.

Many mammalian species display seasonal breeding patterns correlated with annual cycles of change in the physiology and morphology of the reproductive system. Such annual reproductive cycles are often photoperiodically controlled (i.e, the annual change in day length determines when reproductive activity begins and when it ends within the annual cycle). Photoperiodic control of seasonally appropriate changes in reproductive activity is dependent on an endogenous time measuring process. Among mammals the physiological basis of photoperiodic time measurement has been studied most extensively in the golden hamster. Studies with this species indicate that photoperiodic time measurement is executed by the circadian system. The time measuring process depends on a circadian oscillation of responsiveness to light with properties similar to those of the hypothetical rhythm originally proposed by Bünning to explain photoperiodic phenomena in plants. The available evidence strongly suggests the participation of the pineal gland and the suprachiasmatic nucleus (SCN) in the photoperiodic regulation of mammalian reproductive cycles. However, little is known regarding concrete physiological mechanisms, and the extent to which the SCN and the pineal gland may participate in the time measuring process per se remains to be determined.

Animals↗
PubMed1975

The effect of pregnancy on the control of lipolysis in fat cells isolated from human adipose tissue.

1. Lipolysis has been estimated by measuring the release of glycerol in isolated adipose tissue cells obtained from women in early prognancy, late pregnancy and 1 - 3 days post partum and from non-pregnant women. 2. Adipocytes of women at the end of pregnancy exhibited higher rates of lipolysis in response to adrenaline (1.5 - 15 muM) plus phentolamine (13 muM) than those of non-pregnant women or those in early pregnancy. 3. Lipolysis in response to adrenaline plus phentolamine in fat cells from women 1 - 3 days post partum was reduced compared to that at the end of gestation but was enhanced relative to that in the non-pregnant or early pregnant state. 4. Basal lipolysis also tended to be greatest at term. 5. Under conditions where the production of cyclic AMP was not rate limiting for the stimulation of lipolysis, that is in the presence of dibutyryl cyclic AMP (1 mM) or adrenaline (15 muM) plus phentolamine (13 muM) plus caffeine (1 mM), the release of glycerol in cells from women at term and in the puerperium was greater than that in women in the non-pregnant or early pregnant state. 6. Cell levels of cyclic AMP rose after incubation with adrenaline (6 muM) plus phentolamine or adrenaline (15 muM) plus phentolamine plus caffeine (1 mM) but were similar in all four groups of women. 7. It is concluded that the observed enhancement of lipolysis demonstrated in fat cells from women at the end of pregnancy reflects an increase in hormone-sensitive lipase activity rather than a modification of hormone receptor site sensitivity or of the rates of synthesis or breakdown of cyclic AMP. 8. This increase in adipose tissue lipolysis at the end of gestation could contribute to the reported rise in plasma nonesterified fatty acids in the final weeks of pregnancy.

Adipose Tissue↗
PubMed1975

A comparison of gas-liquid chromatography and a titration method for the determination of plasma non-esterified fatty add levels during pregnancy.

The level of plasma non-esterified fatty acids (NEFA) was measured by gas-liquid chromatography (GLC) and a titration method in 194 samples collected during pregnancy and from four days to 24 weeks post partum. Both techniques indicated a similar pattern of changes in plasma NEFA associated with pregnancy. The titration estimates of NEFA level were usually greater than those measured by GLC, and there was some suggestion that the disparity between the methods was increased at the end of pregnancy and was reduced at six weeks after delivery.

Fatty Acids, Nonesterified↗
PubMed1975

The interaction of castration and photoperiod in the regulation of hypophyseal and serum gonadotropin levels in male golden hamsters.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in intact and castrate adult male hamsters maintained on photostimulatory (LD 14:10) and non-photostimulatory (LD 6:18) light:dark cycles to assess the interaction of photic stimuli and gonadal hormones on pituitary gonadotropin release. Immunoreactive serum LH and FSH levels increased 1.6- and 8-fold respectively, within 3 days after photostimulated hamsters were castrated. In contrast, castration failed to alter serum LH concentration and had only a slight, if any, effect on FSH concentration in hamsters exposed to nonstimulatory photoperiods that induced testicular atrophy. In a second experiment, male hamsters previously maintained on LD 14:10 were castrated, transferred with intact animals to LD 6:18, and killed periodically over 60 days. In intact animals, pituitary content and serum levels of LH and FSH declined substantially during exposure to the non-stimulatory LD 6:18 cycle. In castrated animals, serum LH and FSH levels which had increased 2- and 8-fold in response to the castration eventually declined to about the levels found in the intact initial control animals. In contrast to serum gonadotropins, the increased hypophyseal content of LH and FSH following castration was not reduced during exposure to LD 6:18. Exposure to nonstimulatory photoperiods does not alter the increased hypophyseal LH and FSH content observed after castration. However, our results indicate that exposure to short days renders the hypothalamic-hypophyseal neuroendocrine system governing gonadotropin release relatively insensitive to gonadal steroid hormone feedback.

Animals↗
PubMed1972

Regulation of testis function in golden hamsters: a circadian clock measures photoperiodic time.

The photoperiodic testicular response of adult golden hamsters was examined by the use of a 6-hour light period coupled with dark periods of 18, 30, 42, and 54 hours. Cycle lengths of 24 and 48 hours resulted in testicular regression, whereas testicular weight was maintained by cycle lengths of 36 and 60 hours. Our data demonstrate a circadian rhythm of sensitivity to the effects of light on the photoperiodic testicular response of the hamster. The position of light relative to the circadian system (as measured by the locomotor rhythm) is critical in the response.

Animals↗
PubMed1970

Continuous-flow ultracentrifugation of canine distemper virus and infectious canine hepatitis virus.

The use of a Spinco L-4 zonal centrifuge with the B-XVI continuous-flow rotor for the purification of canine distemper and infectious canine hepatitis viruses is described. Up to 68 liters of virus was processed at one time. Infectious canine hepatitis virus was found to band at 39% sucrose and canine distemper virus banded between 32 and 48% sucrose. The virus was concentrated 10-fold, and the purity of the virus, as measured by protein concentration, was increased by 99%.

Adenoviruses, Canine↗
PubMedDate not supplied

Herbicide and nutrient transport from an irrigation district into the South Saskatchewan River.

Pesticides and nutrients can be transported from treated agricultural land in irrigation runoff and thus can affect the quality of receiving waters. A 3-yr study was carried out to assess possible detrimental effects on the downstream water quality of the South Saskatchewan River due to herbicide and plant nutrient inputs via drainage water from an irrigation district. Automated water samplers and flow monitors were used to intensively sample the drainage water and to monitor daily flows in two major drainage ditches, which drained approximately 40% of the flood-irrigated land within the irrigation district. Over three years, there were no detectable inputs of ethalfluralin into the river and those of trifluralin were less than 0.002% of the amount applied to flood-irrigated fields. Inputs of MCPA, bromoxynil, dicamba and mecoprop were 0.06% or less of the amounts applied, whereas that for clopyralid was 0.31%. The relatively higher input (1.4%) of 2,4-D to the river was probably due its presence in the irrigation water. Corresponding inputs of P (as total P) and N (as nitrate plus ammonia) were 2.2 and 1.9% of applied fertilizer, respectively. Due to dilution of the drainage water in the river, maximum daily herbicide (with the exception of 2,4-D) and nutrient loadings to the river would not have resulted in significant concentration increases in the river water. There was no consistent remedial effect on herbicides entering the river due to passage of the drainage water through a natural wetland. In contrast, a considerable portion of the nutrients entering the river originated from the wetland.

Agriculture↗
PubMedDate not supplied

Effectiveness of pneumococcal polysaccharide vaccine for preschool-age children with chronic disease.

To estimate the effectiveness of pneumococcal polysaccharide vaccine, we serotyped isolates submitted to the Pneumococcal Sentinel Surveillance System from 1984 to 1996 from 48 vaccinated and 125 unvaccinated children 2 to 5 years of age. Effectiveness against invasive disease caused by serotypes included in the vaccine was 63%. Effectiveness against serotypes in the polysaccharide vaccine but not in a proposed seven-valent protein conjugate vaccine was 94%.

Bacterial Vaccines↗