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Biomedical subjects

R D Purves

Publications and source records attributed to R D Purves.

At least 37 records · Page 2Linked to original sources
PubMed1986

Body sodium in rats: response to DOCA, adrenalectomy, changes in salt intake, and a salt load.

Body Na was studied by an isotope method in rats on Na-free diet plus a choice of H2O and 0.5% or 0.1% NaCl. Two groups (1 on 0.5%, 1 on 0.1% NaCl) had Silastic deoxycorticosterone acetate (DOCA) implants, two similar groups were sham operated, and a fifth group (on 0.5% NaCl) underwent adrenalectomy (ADX). Saline consumption increased in DOCA-treated and ADX rats. Body Na was increased by DOCA and by drinking 0.5% NaCl compared with 0.1% NaCl. Body Na after intraperitoneal NaCl loading (which raised body Na 8-10%) and withdrawal of NaCl drinking fluids was analyzed by use of the model y = Ae-a(t-d) + Be-bt, where y is body Na at time t and d is delay before fast rate constant a is established; d was greater on the lower Na intake. Rate constant a was not reduced by chronic DOCA treatment. Coefficient B of the slow exponential, representing the basal level to which body Na falls on zero Na intake, and equivalent to Hollenberg's "set-point," was higher in DOCA-treated rats. This analysis makes use of Hollenberg's set-point concept, but the findings suggest that the set-point is related to mineralocorticoid activity and is thus presumably variable.

Adrenalectomy↗
PubMed1985

Effects of DOCA and salt intake on body sodium, fluid intake, blood pressure and excretion of a sodium load in rats.

Body sodium was measured repeatedly by a whole-body counting method (22Na) in control and deoxycorticosterone acetate (DOCA)-treated Wistar rats taking a sodium-free pelleted diet and drinking a choice of H2O and either 0.5% NaCl or 0.1% NaCl (n = 11 per group, four groups). Body sodium was higher in DOCA-treated than in control rats and higher in rats on 0.5% NaCl than in those on 0.1% NaCl. These differences persisted even when all sodium intake was stopped. An intraperitoneal NaCl load was excreted at least as rapidly by the DOCA-treated as by the control rats. Commencement of excretion was slower in the rats on 0.1% NaCl than in those on 0.5% NaCl. It is concluded that DOCA raises the basal level of body sodium but does not slow down the excretion of sodium in the body in excess of the basal level.

Animals↗
PubMed1984

Mechanical hypothesis of sperm penetration.

Sperm have generally been supposed to penetrate the zona pellucida surrounding the mammalian egg with the aid of a protease, acrosin. Difficulties associated with this view are discussed and an alternative, mechanical hypothesis introduced. The calculated force exerted by individual sperm is too small to permit the rupture of any but the weakest of secondary chemical bonds. Mechanical progress through the zona must rely on stress relaxation in a viscoelastic medium. The known properties of the zona appear to be consistent with such a mechanism of penetration.

Acrosin↗
PubMed1980

The mechanics of pulling a glass micropipette.

The pulling of micropipette electrodes from glass tubing has been treated as a problem of viscous flow coupled with the Newtonian dynamics of the pulling apparatus. Analytical solutions are given from which the taper profile, tip diameter, and pulling time can be obtained. The physical principles of operation of micropipette pullers are discussed.

Glass↗
PubMed1979

The physics of iontophoretic pipettes.

A theoretical study has been made of the release of drugs from iontophoretic pipettes. The chief predictions are: (1) in the steady state, release becomes linear with current and independent of pipette geometry when the ejecting voltage exceeds approximately 100 mV; (2) release rises relatively slowly during an ejecting pulse to approach its steady state value. At the end of the pulse, release falls abruptly. This asymmetry of the release curve is greatly accentuated by the prior application of a retaining current. It provides an explanation for the characteristic time course of response commonly seen when drugs are applied iontophoretically to central neurones: (3) the above effects occur on a time scale which depends strongly on the geometry of the pipette. Release from pipettes of large tip diameter and nearly cylindrical bore, such as those generally used in the central nervous system, should be thousands of times slower than from pepettes of small tip diameter and larger taper angle. Experimental observations of the release of an ionized fluorescent compound quantitatively confirm prediction (1) and qualitatively confirm predictions (2) and (3).

Electricity↗
PubMed1978

Synaptic delay in the heart: an ionophoretic study.

1. Neurotransmitters were applied ionophoretically to spontaneously beating clusters of ventricular muscle cells cultured from neonatal rats. 2. Acetylcholine or its analogue carbachol produced hyperpolarization and decreased the rate of spontaneous beating. These responses had minimum latencies of about 250 msec and total durations of 6-12 sec. 3. Noradrenaline, adrenaline or isoprenaline increased the rate of spontaneous beating. The minimum latency for this effect was 3-6 sec. Following a single brief pulse the rate remained elevated for 2 min or more. 4. Chronotropic responses of intact atria from adult rats to stimulation of the autonomic nerves were of similar time course to responses of the cultured muscle cells. 5. Calculations based on the theory of diffusion showed that access of drugs to their receptors could not be rate-limiting for the observed responses, unless a diffusion barrier of rather special properties was postulated. A number of other explanations for the long latencies have been ruled out; these are most likely to be due to some physical or chemical process occurring in or under the cell membrane. 6. Attempts to mimic responses to catecholamines by intracellular application of cyclic AMP were unsuccessful, perhaps because the release of nucleotide from the pipettes was insufficient. A theoretical treatment suggests that ionophoretic efflux of anions might be greatly diminished by the opposing electro-osmotic flux.

Acetylcholine↗
PubMed1977

Differentiation of electrical and contractile properties of slow and fast muscle fibres.

1. The development of the electrical and contractile properties of slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) muscles of the chick was studied. 2. At the earliest ages studied (14-16 days of incubation), the membrane resistance was similar in both muscles. Subsequently the membrane resistance of PLD decreased, and that of ALD increased. Electrical differentiation continued after hatching. 3. The contractile speeds of ALD and PLD muscles were similar in embryos at 14-16 days of incubation, and suddenly differentiated at 17-18 days. Unlike the electrical properties, contractile speeds changed little after hatching. 4. It is suggested that the different electrical properties of the membrane of the two types of muscle fibre develop as a result of the particular type of excitation imposed by their nerves.

Action Potentials↗
PubMed1976

Specificity of innervation of iris musculature by sympathetic nerve fibres in tissue culture.

Irides from 3-5 day old rats have been grown 1-3 mm from superior cervical or lumbar paravertebral sympathetic ganglia in modified Rose chambers. The two muscles of the iris received distinctly different innervation patterns in vitro, and these were similar to those seen in vivo. Varicose, adrenergic fibres were consistently associated with the dilator pupillae rather than with the sphincter pupillae while excitatory, cholinergic junctions developed between the nerve fibres and the muscle cells of the spincter but not the dilator. There was a lack of specificity shown by the sympathetic neurons during this innervation. Fibres from lumbar ganglia formed plexuses within the dilator similar to those formed by superior cervical fibres, and sympathetic, cholinergic fibres were able to substitute for the normal parasympathetic, cholinergic fibres in the sphincter.

Animals↗