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

The blood flow to the digestive organs of nine sheep was determined by the use of isotopically labelled microspheres before, during and at 2 h and 4 h after feeding. Within 3 min of the start of feeding, the blood flow to the salivary glands and to the smooth muscle of the rumen and reticulum increased three-fold. The blood flow to the epithelium of the rumen and reticulum also increased before any appreciable effect on ruminal fermentation could have occurred. This increase in flow was greater in absolute but smaller in relative terms than that to the muscle. At 2 h after feeding blood flow to the epithelium of the rumen and reticulum was two to four times greater than before food was taken, while the flow to the smooth muscle of these organs had fallen to the level found before feeding. In the more distal parts of the gastrointestinal tract, blood flow changes in response to feeding were less pronounced and, where they occurred at all, consisted of decreases at different times. Thus blood flow to the omasum decreased during feeding but recovered thereafter, while the flows to abomasum, duodenum and ileum were not changed during feeding but were significantly lower at 2 h and 4 h later. In the rest of the small intestine and in the large intestine there were no significant changes in flow during the period of observation, nor were there any changes in the blood flow to pancreas or spleen. However, the flow to the omental and mesenteric fat declined abruptly on feeding and reached its minimal value 2 h afterwards. These results are in marked contrast to those reported in other species in that the subepithelial capillary plexus of the reticulum and rumen was the only region contributing to the increased hepatic portal blood flow after feeding.

The appearance of glucose, pyruvate and lactate in fluid recirculated through the lumen of the ampulla and isthmus of the rabbit oviduct has been followed for 2 h in vivo. Each nutrient appeared in the lumen of the ampulla at approximately 1.8 times its rate in the lumen of the isthmus. The circumference of the mucosa lining the two regions was measured together with the distribution of ciliated and secretory cells. The surface area of the mucosa lining the ampulla was 343 mm2, and that lining the isthmus, 191 mm2. It is tentatively suggested that the capacity of the ampulla and isthmus to transport small molecules is a function of their respective mucosal surface areas.

Transport of leucine by the small intestine of obese (ob/ob) mice has been compared with that by intestine of lean controls at various stages in the development of the syndrome. At 10 weeks of age, when hyperphagia and hyperinsulinaemia are at their peak, transport (expressed per gram dry weight) of a physiological concentration of leucine (5 mM) by luminally perfused whole small intestine of obese mice was significantly lower both in vitro (-45%) and in vivo (-27%). Experiments involving fasting and long-term partial dietary restriction of obese mice suggested that the reduction in leucine transport was probably not a consequence of hyperphagia. The absence of any difference between lean and obese mice in the kinetics of unidirectional influx of leucine across the brush border contrasted with the findings from the luminal perfusion experiments. This discrepancy could indicate that the effect of the (ob/ob) genotype on leucine transport was at a stage in the process of transepithelial transport distal to the brush border, perhaps that of movement across the basolateral membrane.

The fluorescent compound chlorotetracycline (CTC) enters the mouse egg by a mechanism controlled by the oolemma. The intracellular distribution of CTC is non-uniform and during the early stages of uptake fluorescent patches are observed at the egg's surface probably close to the oolemma. Lanthanum blocks the entry of CTC into the egg's cytoplasm and in this condition the CTC remains at the surface of the egg; the labelled site is not the zona pellucida and is likely to be the outer surface of the oolemma. The results of this study of CTC uptake support the idea that this compound labels divalent (or trivalent) cations in the neighbourhood of cell membranes.

A simple and specific analytical method incorporating high performance (anion-exchange) liquid chromatography has been used to study the absorption and metabolism of some purine derivatives in an in vitro preparation of adult rat jejunum. When present in the lumen the purine bases guanine (4 X 10(-5)M), hypoxanthine or xanthine (10(-4)-3 X 10(-4)M) do not appear in the serosal secretions but the uric acid (UA) content of these secretions is increased. With UA in the intestinal lumen (10(-4)-3 X 10(-4)M) the serosal UA is increased, in some cases to a higher concentration than that in the lumen. With adenine in the lumen (10(-4)-10(-3)M) there is an increased appearance of UA and adenine also appears in the serosal secretions, but the concentration of adenine never exceeds that in the lumen. It is concluded that purines absorbed from the lumen are significantly metabolized to UA during translocation across rat jejunum. Negligible amounts of metabolites are found in the luminal solutions except for guanine which appears to be degraded in the lumen.

Rat respiratory muscles underwent considerable changes in histochemical fibre type profile in response to hypo- and hyperthyroidism. Hypothyroidism increased the proportion of type 1 slow oxidative fibres in diaphragm and to a lesser extent in intercostal muscles. Hyperthyroidism resulted in a decreased proportion of type 1 fibres in both diaphragm and intercostals. These changes were broadly comparable to those reported previously in rat limb muscles. In normal rat respiratory muscles, the type 1 fibres were characterized by very high levels of beta-hydroxybutyrate dehydrogenase which was thought to contribute to the fatigue-resistance of these muscles. The type 2B fast glycolytic fibres, and to a lesser extent type 2A fast oxidative fibres, contained high levels of mitochondrial alpha-glycerophosphate dehydrogenase, an enzyme known to be specifically affected in dysthyroid states. The implications of the observed changes in fibre type profile with respect to the oxidative metabolism of rat respiratory muscles are discussed.

The fluorescent compound chlorotetracycline (CTC) enters the cells of the cockroach salivary gland. The acinar peripheral cells and the non-secretory duct cells become preferentially labelled by CTC. Microscopic examination of the intracellular distribution of CTC indicates that this compound labels the highly folded apical plasma membranes of the peripheral cells and the deep infolds of the basal plasma membranes of the non-secretory duct cells. Lanthanum blocks the entry of CTC into all of the gland cells and in this condition the CTC labels the basal surfaces of the acini and ducts. The results of this investigation support the idea that CTC labels calcium ions in the vicinity of plasma membranes.

Botulinum toxin (BoTx) was injected into the muscles of one leg in mice causing local paralysis. Black widow spider venom (b.w.s.v.) was then injected into the paralysed muscles 3 or 15 d later. In both groups b.w.s.v. destroyed the nerve terminals poisoned by BoTx. In the 15 d group axonal sprouts, which had former due to the block of neuromuscular transmission by BoTx, were also destroyed. Within a few days the motor nerve terminal regenerated and the muscles recovered from paralysis at a faster rate than after BoTx alone. Recovery seemed to begin earlier in muscles where axonal sprouting was already advanced when b.w.s.v. was injected. The normal pattern of innervation was re-established in both groups, which was in marked contrast with muscles after BoTx alone where numerous sprouts and many ectopic end-plates had formed.

In humans and in carnivores the motor activity of the colon was separated into various types based on records of the intraluminal pressure. However, little is actually known about the physiological significance of the various pressure waves. The aim of the present investigation was to clarify the basic pattern of colonic motility in a herbivorous species. Motility of the proximal colon was studied by strain gauge transducer records combined either with fluoroscopy or by direct visual observation in conscious and anaesthetized rabbits. In the proximal colon three types of contraction were found: (1) high frequency repetitive contractions, (2) low frequency rises of the base line, and (3) monophasic progressive waves. The frequency of the repetitive contractions was 13.8 contractions/min at the oral site and 16.3 contractions/min at the aboral site of the proximal colon. The mean duration of the repetitive contractions was 3.2 +/- 1 s. They coincided with orally migrating (1-2 mm/s) shallow annular constrictions which represented haustral activity. The low frequency rises of the base line (mean duration 13 +/- 47 s) were associated with aborally migrating (7 mm/min) deep annular constrictions representing segmental activity. The monophasic progressive waves represented peristaltic contractions. The mean durations of the monophasic waves 5.5 +/- 1.2 s (period of hard faeces formation), and 9.7 +/- 2.8 s (period of soft faeces formation), the average rates of progression were 3.2 +/- 1.2 cm/s (period of hard faeces production), and 1.3 +/- 0.6 cm/s (period of soft faeces production). The results proved that the colonic motility of rabbits consisted of a complex motor pattern. The present classification was similar but not identical with that described in carnivores and man. Further comparative studies on other mammals are necessary to decide whether the motor activity of the colon is comparable between various species.