Quarterly journal of experimental physiology (Cambridge, England)最新文献

The numbers of myelinated and non-myelinated nerve fibres in the spinal roots of one strain of mouse have been counted from electron micrographs and the accuracy of counting procedures assessed. Non-myelinated nerve fibres are present in the ventral roots at all levels though the largest number are found inthe thoracic and L1, L5, L6 and S1 ventral roots. The number is very small in L2, L3, and L4 ventral roots which are those supplying the hind limb. Fibre diameter histograms were obtained from measurements of cross sectional area for myelinated and non-myelinated fibres in L1 and L4 ventral roots. The relationship of myelin thickness to axon diameter shows that to a near approximation the myelin thickness is 1/5 to 1/4 the axon diameter. A measure of circularity was calculated, the ratio of the measured cross-sectional area to the area calculated from the measured perimeter assuming the fibre to be circular, and plotted against the axon perimeter fo L1 and L4 ventral root myelinated fibres, This showed a tendency for larger fibres to be less circular than smaller fibres.

Feeding rats a highly palatable 'cafeteria' diet resulted in a two-fold increase in interscapular brown adipose tissue (b.a.t.) mass after only 3 d on the diet. No significant difference in DNA content of b.a.t. was noted between control and cafeteria-fed rats at this time but DNA content was elevated 2-3-fold in the latter group by day 30, and incorporation rates of tritiated thymidine into DNA were elevated in these animals after 5, 15 and 30 d of cafeteria feeding. A doubling of specific GDP (per mg protein) to b.a.t. mitochondria was seen in cafeteria-fed rats on days 3, 15 and 30 and total GDP binding in the interscapular depot was increased by 3-4-fold. Injection of the animals with noradrenaline (25 micrograms/100 g body weight) 1 h before killing caused 180 and 430% increases in b.a.t. mitochondrial GDP binding in control and cafeteria-fed rats respectively. Linear Scatchard plots of binding data obtained from 15 d control and cafeteria groups indicated a single class of receptor, with the same affinity for GDP in all animals, but the maximum number of binding sites was markedly elevated in cafeteria rats and was increased further after treatment with noradrenaline 1 h prior to sacrifice. When cafeteria-fed rats were returned to stock diet alone the differences in b.a.t. mass and GDP binding diminished but after 10 d brown fat mass and noradrenaline-stimulated GDP binding were still significantly higher than control levels. These data provide further evidence for the involvement of b.a.t. and its mitochondrial proton conductance pathway in diet-induced changes in thermogenic capacity.

Bile flow, during feeding and fasting, was studied in three ponies in which catheters, maintained in the bile duct over 1-2 months, drained all bile continuously. During experiments bile was returned to the small intestine, via a second catheter, by means of a small pump which also measured bile flow rates. The mean +/- S.E. of the mean rate of bile flow in fed ponies with an intact enterohepatic circulation of bile salts was 1.33 +/- 0.10 ml/kg . h, n = 13; mean +/- S.E. of the mean concentration of bilirubin in bile was 10.82 +/- 0.91 mg/dl, n = 13. The effect on bile flow and bilirubin excretion in bile of a standard feed lasting 2 h was compared with that of an intraduodenal or intravascular 2 h infusion of glucose (50 g/h) before and after a short period of fasting (approximately 2 d). Prior to the fast, bile flow and bilirubin excretion in bile rose by 38.5 and 39.0% respectively following a feed. Glucose infused intravascularly or intraduodenally did not alter bilirubin excretion. Following a two day fast, bilirubin excretion in bile rose 72.7% to 136.5% following feeding and 65.2% to 120.3% when glucose was infused either intravascularly or intraduodenally. A correlation between plasma glucose and bilirubin excretion in bile was observed when the pony was fed or glucose infused intraduodenally. When glucose was infused intravascularly a correlation was only observed in a single experiment in which glucose was infused over 10 h at the lower rate of 24 g/h. It appears that an infusion of glucose can mimic the effects of a feed on bilirubin excretion in bile following a short fast, but not preceding it.

There is a positive linear relation between the vascular flow rate and the magnitudes of the unidirectional fluxes of Na in either direction in the steady state across the small intestine of the frog. Both unidirectional Na fluxes increase to the same extent with an increase in vascular flow so there is no apparent effect of flow on net Na movement. Raising the vascular flow rate in individual experiments increases the lumen-blood Na flux proportionately, but reducing the flow from an initially high value reduces the lumen-blood flux only slowly at first then more rapidly. The unidirectional Na fluxes increase linearly as the lumen flow rate is increased. In the colon increasing the vascular flow rate also increases the lumen-blood Na flux but changing the vascular flow rate has little effect on the blood-lumen flux, the net absorption of Na is invariably increased as the vascular flow increases. Using 14C-labelled sucrose as a marker for the extracellular space of the small intestine, it can be shown that the increases in Na flux found with increased vascular flow rates are associated with an increase in this sucrose space. An increase in sucrose space, therefore, seems to enhance the accessibility of the low resistance, paracellular pathways for Na to and from the blood across the epithelium.

Goats were milked hourly with the aid of oxytocin at different stages of lactation. Udder volume and milk yield were also measured. The marked variation between goats in the time after parturition at which peak milk yield is attained and in the rate of decline after peak is illustrated. Hourly milking had a stimulatory effect on the rate of milk secretion in early lactation (before peak) and in declining lactation (after peak), in both cases at previous milk yields of 1.1 - 1.48 g/ml udder volume . d. There was no stimulatory effect of hourly milking on milk yield at or near peak lactation (yield before the experiment greater than 1.48 g/ml volume . d) or in late lactation (less than 1.1 g/ml . d). The responses of milk yield to hourly milking are discussed in relation to the factors which limit the rate of secretion. In particular, it is concluded that a stimulatory response indicates that before the experiment the rate of secretion could not have been limited directly by the arterial supply of one or more substrates for milk synthesis. It is stressed that the results were obtained under one dietary regime only.

Fifty percent of a population of thirty weanling rats were fed a vitamin A-deficient diet. The remaining 50% were fed a control diet. In comparison with the control group, the rate of growth started to slow down in the vitamin A-deficient animals around day 33. Single unit recordings were made from sensory nerve fibres supplying slowly adapting type I cutaneous mechanoreceptors (touch corpuscles). Touch corpuscles were stimulated repetitively with low force mechanical stimuli. Receptors in vitamin A-deficient animals showed clearly reduced nervous responses compared with receptors in control animals. Most receptors remained responsive even after prolonged repetitive stimulation.

The capacity of ischaemic myocardium to respond to the inotropic stimulus of tachycardia was investigated in open-chest anaesthetized dogs following ligation of a branch of the anterior descending coronary artery. In two areas of the left ventricular surface (ischaemic and non-ischaemic), local coronary blood flow was measured by thermistors and isometric contractile force was recorded with strain gauge arches. NADH redox state was measured simultaneously in both regions using a two-channel surface fluorometer. It was found that ligation was followed by an immediate fall in local coronary blood flow to the ischaemic region, accompanied by a sharp elevation in NADH redox level. Local contractile force in the ischaemic region was also reduced. The non-ischaemic region showed little or no change following occlusion. Response to heart rate elevation before ligation was increased work, elevation of NADH redox levels, and increased coronary flow. Following ligation, this response was attenuated in the ischaemic region, but not abolished. It is concluded that ischaemic myocardium retains the capacity for inotropic response even when intracellular O2 levels are low.

The relationship between the concentration of phosphate in plasma and parotid saliva was studied in six conscious sheep and a goat, either intact or thyroparathyroidectomized (t.x.p.t.x.), under conditions designed to minimize marked fluctuations in flow rate of saliva. A linear relationship between acutely induced changes in plasma phosphate concentration and the phosphate level in saliva has been demonstrated in both intact and t.x.p.t.x. animals. Dietary phosphorus depletion caused adaptation of salivary phosphate concentration so that less was secreted at a given concentration of plasma phosphate. Attention is drawn to the similarity between this phenomenon and that already described for the proximal renal tubule. Parathyroid hormone (PTH) was shown to reduce the salivary phosphate concentration with little or no effect on phosphataemia. The administration of 1,25-dihydroxycholecalciferol (1,25(OH)2CC) also caused a reduction in salivary phosphate concentration despite hyperphosphataemia and hypercalcaemia. It is suggested that salivary phosphate concentration can be influenced directly by the concurrent level of plasma phosphate but that this relationship can be modified by the circulating concentration of 1,25(OH)2CC and indirectly by PTH via increased production of 1,25(OH)2CC.

Outflow obstruction of the submandibular duct, for a short period during parasympathetic secretion, caused an increase in glandular permeability to horseradish peroxidase. Higher frequencies of parasympathetic nerve stimulation during the obstructive period induced greater increases in the permeability. It is likely that the intraluminal distensions had disrupted some tight junctions and so permitted a greater paracellular leakiness. The damage tended to induce ballooning between striated ductal cells, similar to the appearances observed by Emmelin, Garrett & Gjörstrup (1977 a) when sympathetic secretion was accompanied by myoepithelial contraction against a raised outflow pressure. The present results have been compared with experimental data from other workers and give support to the idea that tight junctions can behave in a sieve-like manner towards the back-diffusion of molecules across them. This work indicates that there is a great need for care in permeability studies. It is possible that some permeability changes observed by other workers may have been the consequences of physical damage between cells. Our findings reinforce the need for morphological assessment of the glands after permeability experiments. In man it is likely that naturally occurring or artificially induced obstructive events may at times create similar permeability changes and these may enable protective substances to pass from the blood to the saliva. This affords possible explanation for such phenomena as the therapeutic value that often accrues from sialography and the efficacy of many different antibiotics in obstructive sialadenitis, despite the fact that most antibiotics do not normally permeate to the saliva.