Measurement of electrical potentials of the human rectum and pelvic colon in normal and aldosterone-treated patients

A method is described which allows rapid measurement of the electrical potential difference across colonic mucosal epithelium to be carried out during routine sigmoidoscopy. The potential differences measured had a mean value of 25 mV (range 4 to 51 mV) in 27 subjects with normal bowel. Six hours after two intravenous injections of 0.5 mg aldosterone the potential difference had risen to 60 mV (range 37 to 101 mV). The time course of responses studied after a single injection of aldosterone showed that the potential allowance rose within four hours and had fallen again after 18 hours. Urinary sodium concentrations and sodium/potassium ratios fell after aldosterone injections, the time course of the changes being similar to that of the potential differences of the colon. Sodium concentration of stool fluid also fell. The concentration of chloride in the stool fluid was consistent with a passive distribution of chloride according to the electrochemical gradient, but that of potassium was considerably greater than expected from a passive distribution, suggesting that potassium is actively secreted into the lumen of the colon.

Transmural electrical potential difference of the human colon

The electrical potential across the human colon was measured by a technique which accurately reflects the true mucosa-to-serosa potential difference. Large negative mucosal potentials were recorded from all regions. The potential difference of the sigmoid colon was significantly greater than that of the rectum. The technique may have important applications to the further study of normal or abnormal colonic function.

The neglected interface: the biology of water as a liquid-gas system

Water, solutes and membranes have long been the subject of intensive research, and many excellent reviews have brought the major biological problems in focus, have discussed accomplishments, and have outlined unsolved problems. The most interesting results pertain to the role of membranes, whether ‘active’ or ‘passive’, which separate different solutions, in other words, membranes at a water–water inerface Liquid gas interfaces have receied less attention, and I therefore wish to review some biological problem which relate to such systems. I shall discuss a variety of phenomena which may have little in common, except that they all bear onthe transition of water between liquid and gas.

The effect of intraventricular injections of noradrenaline, 5-hydroxytryptamine, acetylcholine and tranylcypromine on the ox (Bos taurus) at different environmental temperatures

1. Noradrenaline, 5-hydroxytryptamine (5-HT), acetylcholine and tranylcypromine were injected or infused into the lateral ventricle of the ox. The effects of these drugs on heart and respiration rates, heat production, rectal, skin and hypothalamic temperatures and skin evaporative loss were measured when the animal was exposed to environmental temperatures ranging from -1 degrees C to +30 degrees C.2. Acetylcholine (0.001-2 mg) had no detectable effect on temperature regulation at 20 degrees C.3. In small doses (0.005-0.05 mg) 5-HT had no detectable effect. Larger doses (2-5 mg) given in a cold environment (-1 degrees C) also had no effect but the same doses given in warm environments (15-30 degrees C) caused increases in skin temperatures, skin evaporative loss and respiratory rate, and decreases in rectal and hypothalamic temperatures.4. Infusion of tranylcypromine (0.107 ml./min of a 1 in 50 solution) in a warm environment (20 degrees C) also caused a decrease in rectal temperature after a delay of 1-1(1/2) hr during which no effects were apparent.5. Noradrenaline (2 mg) had no effect on temperature regulation when injected into animals in a warm environment (30 degrees C). When injected (1 mg) into animals in a cold environment (-1 degrees C) shivering stopped and heat production and rectal and hypothalamic temperatures were decreased.6. It is concluded that intraventricular 5-HT and noradrenaline both cause a decrease in body temperature, and it is unlikely that central temperature regulation in the ox is mediated only by these two substances.

Fine-Structural Changes in Relation to Ion and Water Transport in the Rectal Papillae of the Blowfly, Calliphora

The fine structure of the epithelial cells of the rectal papillae in the blowfly, Calliphora erythrocephala Meig., has been investigated to elucidate the possible mechanism of reabsorption of water and ions from the rectal lumen. To observe the variations in the structure of the epithelium in response to the absorptive processes the material was taken (a) from flies at the various stages of their first oviposition cycle, and (b) from freshly emerged imagoes starved for 2 days and injected into the rectum with solutions of various tonicities. It has been found that the complex system of intercellular spaces, formed by a prolific infolding of the lateral plasma membrane of the cells, shows a direct response to the conditions of supposedly maximal and minimal transport of fluid. These spaces are (a) grossly distended in the flies injected with hypotonic media, (b) highly dilated under normal conditions, and (c) completely collapsed in fasting and starved flies. These observations have been discussed in the light of the available theories to explain the mechanism of water transport in biological tissues. It is proposed that the structural design of the rectal papillae favours the application of double-membrane theory to explain the reabsorption of water against osmotic gradients as a consequence of an active transport of solutes into enclosed spaces.

Some aspects of anal continence and defaecation

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