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Biomedical subjects

D A Jenner

Publications and source records attributed to D A Jenner.

At least 37 records · Page 2Linked to original sources
PubMed1987

Environmental temperature and blood pressure in 9-year-old Australian children.

Relationships between blood pressure (BP) and environmental temperature were investigated as part of a broader study of constitutional and environmental determinants of BP in a sample of 1037 9-year-old Australian children. A Dinamap semi-automatic device was used to obtain three BP readings for each child. Average systolic blood pressure (SBP) and diastolic blood pressure (DBP) differed according to month of examination, with higher levels in the colder months. Negative relationships were observed between BP and temperature on the measurement day; computed regression equations indicated that a rise in maximum daily temperature of 10 degrees C was associated with falls of 5-7 mmHg in SBP and DBP. The relationships were independent of age, weight, height, socio-economic status and heart rate (HR). The results emphasize the importance of taking environmental temperatures into account in epidemiological studies of BP.

Anthropometry↗
PubMed1986

Relaxation and stress management in the treatment of essential hypertension.

Thirty-two male and female hypertensives, 34 to 65 yr of age, systolic blood pressure (SBP) less than 200 mmHg and diastolic blood pressure (DBP) between 90 and 109 mmHg, were randomly allocated to receive either relaxation and stress management (experimental condition) or mild physical exercise (control condition). Half the participants were taking antihypertensive drugs, which were constant for six months prior to the study and controlled during the study. Outcome measures included various measures of blood pressure in the clinic and at home, cardiovascular responsiveness, moods and 24-hr urinary adrenaline and noradrenaline. The study schedule consisted of 3-months baseline, 10 weeks treatment and 3-months follow-up. Relaxation was superior to the control procedure in reducing blood pressure as assessed by nurses blind to the participants' treatment at post-treatment for DBP and at follow-up for DBP and SBP.

Adult↗
PubMed1985

Determination of cortisol and cortisone in urine using high-performance liquid chromatography with UV detection.

The application of reversed-phase gradient high-performance liquid chromatography with UV detection to the determination of cortisol and cortisone in 24-h urine samples is described. The method employs Sep-pak C18 cartridges for the part-purification and concentration of the corticosteroids, with sample enrichment at the head of an HPLC pre-column and separation using water/acetonitrile gradient. The internal standard is 6alpha-methylprednisolone. Measurement of both cortisone and cortisol provides further information on adrenocortical function. 24-hour excretion rate data from normal subjects are reported.

Journal Article↗
PubMed1983

Encapsulation of drugs in intact erythrocytes: an intravenous delivery system.

A number of drugs and the plasma antiprotease alpha 1-antitrypsin has been encapsulated in intact erythrocytes after hypotonic swelling, using a technique designed to preserve the viability of the cells. By labelling the cells with fluorescein isothiocyanate it has been shown that the cells survive exceptionally well when returned to the animal's circulation. Cell survival has been demonstrated in the rat, rabbit and guinea-pig. With encapsulation of cortisol-21-phosphate and methotrexate it was found that blood levels of the drug were maintained for a longer period than when the free drug was administered. Cortisol-21-phosphate was hydrolysed enzymatically by acid phosphatase located primarily in the erythrocyte membrane. An in vitro test involving the interaction or erythrocytes with phagocytes was developed to determine the viability or erythrocytes after being subjected to the encapsulation process. Preparations which did not interact with phagocytes survived when returned to the animal's circulation. The encapsulation procedure increased the fragility of the cell membrane compared to that of normal cells as measured by the leakage of haemoglobin after thermal treatment but it was found that encapsulated cortisol-21-phosphate in cells actually stabilized the membrane. The electrical charge on the membrane of encapsulating cells was the same as that of the normal cells. The charge on reformed ghosts was lower than that of normal cells. Reformed ghosts were rapidly removed when introduced into the circulation. The encapsulation procedure and its possible applications are discussed.

Animals↗
PubMed1982

Estimation of sympathetic activity in essential hypertension.

The estimation of sympathetic nervous activity by measurement of plasma norepinephrine (NE) concentration assumes a constant relation between this and the synaptic cleft concentration. This assumption would be incorrect if the clearance of plasma NE could be varied without affecting its removal from the synaptic cleft, so we compared the clearance of plasma NE in mild hypertensives and normal subjects by measurement of its plasma concentration during a 0.5-hr infusion at 0.07 microgram/kg/min; there were no differences. The simultaneous infusion of isoproterenol, 0.02 microgram/kg/min, led to an increase in heart rate and NE clearance. There was partial inhibition of catechol-O-methyltransferase by a single oral dose of alpha-methyldopa, 250 mg, which reduced the clearance of both catecholamines (CAs) by about 20%. After the end of the infusions containing isoproterenol, the tachycardia persisted for more than 1 hr and declined more slowly in the hypertensives than the normals. In contrast, plasma concentrations of both CAs returned to basal values within a few minutes. The persistent tachycardia may be due to rerelease of isoproterenol into the synaptic cleft, since stimulation of sympathetic activity by assumption of the erect posture was associated with an exaggerated increase in heart rate (by 48/min after infusion and 23/min before infusion). The study therefore suggests that synaptic cleft and plasma CA concentrations can be independently manipulated and the relation between them may be different in hypertensive patients and normal control subjects.

Blood Pressure↗
PubMed1982

Blunted sympathoadrenal response to exercise in asthmatic subjects.

Six asthmatic subjects and six matched controls performed a standardized exercise test in which resting and post-exercise blood samples were assayed radioenzymatically for catecholamines. Plasma adrenaline one minute after exercise rose over threefold in the controls whereas in the asthmatic subjects there was no increase. Plasma noradrenaline increased to five times the basal concentration in the controls, but to less than half this level in the asthmatic subjects. These results agree with a recent study (Barnes et al. 1981) and suggest there is a marked abnormality of the sympathoadrenal response to exercise in asthmatic subjects.

Adult↗
PubMed1981

Increased sensitivity and accuracy of phaeochromocytoma diagnosis achieved by use of plasma-adrenaline estimations and a pentolinium-suppression test.

26 patients with suspected phaeochromocytoma underwent selective venous sampling: a tumour was identified and removed in 18.4 of these patients did not have sustained hypertension, and the only persistent abnormality was an elevated plasma-adrenaline level. The increased plasma-catecholamine concentrations in the tumour patients were not suppressed by pentolinium 2.5 mg i.v., whereas the levels in the 8 non-tumour patients were lowered to the normal range. Calculations based on the arteriovenous differences of adrenaline and noradrenaline suggest that adrenal medullary secretion contributed less than 2% of circulating noradrenaline in the non-tumour patients. Plasma-adrenaline, however, is derived almost entirely from the adrenal gland, and its estimation appears superior to that of noradrenaline in the detection of a small adrenal phaeochromocytoma.

Adrenal Gland Neoplasms↗
PubMed1981

Novel double-isotope technique for enzymatic assay of catecholamines, permitting high precision, sensitivity and plasma sample capacity.

1. A novel use of a double-isotope method is described which allows radioenzymatic assays to combine precision and sensitivity. 2. In the catechol O-methyltransferase assay separate portions of each plasma sample are incubated with either S-[3H]- or S-[14C]-adenosyl-L-methionine. Standards of noradrenaline and adrenaline are added to the latter portions and are thus converted into standards of [14C]metadrenalines. These are added to the 3H-labelled portions after the incubation, where they function as tracers. 3. The final recovery of 14C radioactivity corrects for (a) the efficiency of methylation in the plasma sample concerned and (b) the recovery of metadrenalines during the extraction procedures. 4. The 3H/14C ratio is constant in each assay for a given catecholamine concentration and is determined for samples to which standards of noradrenaline and adrenaline are added to the 3H- (as well as the 14C-) labelled portions before the initial incubation. 5. The sensitivity of the assay is increased by using high specific radioactivity S-[3H]adenosyl-L-methionine (60--85 Ci/mmol), and low backgrounds are maintained by catecholamine depletion in vivo in the rats use for enzyme preparation. 6. Both catecholamines (1.5 pg/ml; 10 pmol/l) may be detected; the coefficients of variation are 3.0 and 3.2% for noradrenaline and adrenaline respectively (intra-assay) and 4.6 and 5.0% (inter-assay).

Animals↗
PubMed1976

Studies on low-dose oral contraceptives: cervical mucus and plasma hormone changes in relation to circulating D-norgestrel and 17alpha ethynyl-estradiol concentrations.

A study was undertaken to determine the effects of a low-dose oral contraceptive comprising 150 mug of D-norgestrel and 30 mug of 17alpha-ethynyl estradiol (Microgynon) on the plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), 17BETA-ESTRADIOL, AND PROGESTERONE AND ON THE PHYSICAl properties of cervical mucus. Samples of blood and cervical mucus were obtained from three women during a treated cycle and the immediately-following "withdrawal" cycle. Specific radioimmunoassay methods were used to determine LH, FSH, 17beta-estradiol, and progesterone levels in treated and withdrawal cycles, and D-norgestrel and 17alpha-ethynyl estradiol in samples obtained during treated cycles. The concentration of synthetic steroids was also measured in blood samples obtained before and 1 hour after ingestion of the contraceptive to determine the maximal daily variation. The results indicated that the contraceptive action of this combined low-dose oral contraceptive is mediated through suppression of ovulation and by rendering the cervical mucus impenetrable to sperm. Plasma FSH levels appeared to be one of the most sensitive indices of suppression. Determination of D-norgestrel and 17alpha-ethynyl estradiol showed that 3 to 4 days were required to reach maximal plasma levels and that daily fluctuations were considerable. Withdrawal of the pill resulted in an immediate return to ovulatory cycles in all three subjects studied.

Biological Clocks↗
PubMed1976

Plasma hormone levels and the incidence of carcinogen-induced mammary tumours in two strains of rat.

The incidence of mammary tumours developing after administration of the carcinogen DMBA (at 50 days of age) has been determined in 2 strains of Sprague-Dawley rat. Untreated animals of each strain were exsanguinated in dioestrus at a time corresponding to the early post-carcinogen stage (at 70 days of age) and the plasma concentrations of prolactin, oestradiol-17B and progesterone were measured by radioimmunoassay. In an inbred strain of rats, tumour-induction rate was 6-4% and plasma prolactin concentration was 2-5 x lower than that found in a random-bred strain with a tumour-induction rate of 41-6%. No difference was found between the 2 strains in the level of either ovarian hormone. It is concluded that the difference between these strains in mammary gland susceptibility to DMBA may be related to plasma prolactin concentration, but it is unlikely to be determined by the ovarian hormones.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1975

Ileocaecal tuberculosis.

This report is of a single case of ileocaecal tuberculosis presenting as subacute bowel obstruction, with clinical features suggesting an inflammatory cause. The diagnosis of tuberculosis was made at operation although tuberculosis was suspected beforehand. Treatment consisted of triple therapy only and appeared to be successful in so far as loss of symptoms resulted.

Adult↗