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Biomedical subjects

T Bennett

Publications and source records attributed to T Bennett.

At least 343 records · Page 19Linked to original sources
PubMed1978

Corticosteroid involvement in the changes in noradrenergic responsiveness of tissues from rats made hypertensive by short-term isolation.

1 The responses to noradrenaline and to noradrenergic nerve stimulation of spontaneously beating right atria, electrically driven left atria and vasa deferentia taken from rats made hypertensive by short-term isolation have been compared with the responses of tissues from normotensive, group-housed animals.2 Adrenocortical activity of isolated animals was assessed by plasma corticosterone determinations and measurement of adrenal weights.3 The hearts of the isolated animals were weighed and the myocardial contents of water, sodium, potassium and calcium were measured.4 Spontaneously beating right atria from isolated animals showed a lower resting rate, no difference in the response to nerve stimulation but a greater sensitivity to noradrenaline compared to atria from group-housed animals.5 Vasa deferentia from isolated animals showed a decreased maximal response to noradrenaline, but no change in noradrenaline sensitivity or in the response to transmural stimulation.6 There were indications of hyperactivity of the adrenals throughout a 5 week period of isolation, manifest as elevated plasma corticosteroid levels and increased adrenal weights.7 Myocardial levels of sodium and calcium were elevated at the same time as the tissue level of potassium was reduced, but heart weights did not significantly change.8 It is possible that adrenal steroid action caused the changes in tissue ionic balance. These ionic disturbances may have been responsible for some of the changes in tissue sensitivity found in the isolated hypertensive animals.

Adrenal Cortex Hormones↗
PubMed1978

Reversal of 6-hydroxydopamine-induced hypotension in the rat without activation of the renin-angiotensin system.

1. Male Wistar rats were housed individually in glass metabolic cages for 5 days during which time their food and water intakes reached plateau levels and they developed a significant systolic arterial hypertension. 2. After the initial 5-day period, systolic blood pressure and water and electrolyte balances were measured for 4 days before and 7 days after I.P. injection of 6-hydroxydopamine (100 mg/kg). In a separate experiment, plasma renin activity and glomerular filtration rate were measured 1 and 3 days after injection of 6-hydroxydopamine. Haematocrit, plasma volume, osmolality and plasma concentrations of glucose, sodium, potassium and protein were also measured at intervals after treatment. 3. Systolic blood pressure fell within 24 hr after treatment with 6-hydroxydopamine but was restored to pretreatment levels within 7 days. There was also a transient fall in glomerular filtration rate. 4. Plasma volume was significantly expanded on the first day after treatment and there was a fall in haemotocrit together with changes in plasma constituents indicative of a haemodilution, although plasma glucose levels were elevated. 5. There was a significant water retention on the third, fourth and fifth days after treatment but this was not accompanied by any measurable sodium retention and could not be attributed to renal compensation. Furthermore, plasma renin activity showed no significant change following 6-hydroxydopamine treatment. 6. It is suggested that the return of systolic blood pressure to pre-treatment levels was chiefly due to the return of vasoconstrictor function. The changes in plasma composition and volume were probably due to a fall in capillary hydrostatic pressure and an increase in the osmolality of extracellular fluid due to the elevated glucose levels.

Animals↗
PubMed1978

Assessment of methods for estimating autonomic nervous control of the heart in patients with diabetes mellitus.

A comparison of the cardiac responses to a variety of maneuvers that modify cardiac vagal tone was made in nondiabetic and diabetic subjects. We concluded that assessment of heart rate variability by reference to standard deviation of R-R intervals is unhelpful; that a single deep breath is a more potent stimulus for heart rate change than repeated deep breaths in diabetic subjects; and that measurement of this response together with the bradycardia evoked by the Valsalva maneuver obviate the need to perform invasive investigations, such as the estimation of baroreflex sensitivity, or tedious procedures, such as apneic face immersion. In a small number of subjects, heart responses to lower body, negative pressure provided information not forthcoming from other tests.

Adolescent↗
PubMed1978

Factors affecting the development of isolation-induced hypertension in rats.

Rats were housed either individually in separate metabolic cages or in pairs in two connecting metabolic cages and systolic blood pressure was measured before and after a 5 day period over which the animals were left undisturbed. After the 5 day period isolated rats were hypertensive whereas paired rats were not. A further study compared the Na+, K+ and water balances of pairs of normotensive rats with those of isolated rats over the 5 days during which the latter became hypertensive. There was no evidence of any renal Na+ and water retention in isolated, hypertensive rats and thus it is unlikely that mineralocorticoids could have caused a plasma volume expansion and thereby contributed to the hypertension.

Animals↗
PubMed1978

The effect of peripherally administered 6-hydroxydopamine on food and water intake in rats.

The effect of peripheral administration of a single dose of 6-hydroxydopamine (6-OHDA; 100 mg/kg i.p.) on ingestive behaviours in adult rats has been studied. Individual food and water intakes were measured daily for a period of 7 days following treatment. Most animals became hypophagic for up to 72 hours and hypodipsic for up to 24 hours. The possibility that peripherally administered 6-OHDA may enter the CSF by means of the circum-ventricular organs and thereby exert central behavioural effects is discussed.

Animals↗
PubMed1977

Assessment of vagal control of the heart in diabetes. Measures of R-R interval variation under different conditions.

R-R intervals and R-R interval variation were measured in 2 selected groups of diabetic subjects; 1 group was selected because vagal control of the heart appeared normal, the other group was selected because they lacked vagal control of the heart. The means of the R-R intervals for the 2 groups were not significantly different under various conditions (sleeping, lying, during deep breathing, sitting, standing, and during upright activity). The standard deviations of the R-R intervals for the 2 groups were only significantly different during deep breathing and upright activity. It is suggested that cardiac vagal function is not reliably assessed by measurement of R-R interval variation during quiet standing, but useful information may be obtained during deep breathing.

Diabetes Mellitus↗
PubMed1977

The integrity of the noradrenergic innervation of the cardiovascular system in genetically dystrophic hamsters.

Noradrenergic nerves in dystrophic hamsters did not differ, in fluorescence morphology, from those in control hamsters. The responses to noradrenergic nerve stimulation and the sensitivity to noradrenaline of right atria and hepatic portal veins were similar in control and dystrophic animals. The contractility of left atria and their maximal responses to noradrenaline or noradrenergic nerve stimulation at 4 Hz were depressed relative to control. This reduction in inotropic responsiveness may be due to disturbances of excitation-contraction coupling.

Adrenergic Fibers↗
PubMed1977

Mycobacterium bovis infection in baboons (Papio papio).

Two tuberculin-positive baboons in a primate colony were found to have grossly visible tuberculous lesions in the liver, spleen, lung, and mediastinal lymph nodes on necropsy. Results of histopathologic examination of the tissues showed granulomas with Langhans giant cells. An acid-fast organism was isolated from tissues of each baboon; the isolates were identified as Mycobacterium bovis by being negative for niacin production and nitrate reduction and by their susceptibility to thiophen-2-carbosylic acid hydrazide and to 5% glycerol.

Animals↗
PubMed1977

The effects of short-term isolation on systolic blood pressure and heart rate in rats.

The effect of short-term isolation on the systolic blood pressure and heart rate of rats has been studied. Five days continuous isolation in glass metabolic cages caused systolic arterial hypertension in all animals. Isolation in standard cages for this time period caused hypertension, but only in 55% of the animals. Both forms of isolation caused an initial tachycardia. Handling and contact with other animals for 1 hr daily prevented the development of hypertension in some animals but did not alter the blood pressure once the hypertension had developed. Group-housing of animals after a 3 week period of isolation restored blood pressure to control levels within 24 hr. It is possible that stress imposed by isolation activated the sympatho-adrenal system and thereby caused these changes.

Animals↗