Nature of the intestinal slow wave waxing and waning zone

Abstract

SUNY, Syracuse, New York. n.s.wong. From the Surgical Service, VA Hospital and Univererty of California, San Francisco. Intestinal slow waves (also called BER or pace-setter potentials) are responsible for the phasic, sometimes rhythmical contractions of the small intestine, and are also involved in peristaltic contractions. I the cat, and perhaps in other species well, the frequency of slow waves recorded in situ decreases ahorally in step-wise fashion, resulting in frequency plateaus which are separated by short zones (l-3 cm) of waxjnq and waning (Diamant and Bortoff, Am. J. Physiol. 216:301, 1969). The purpose of this study as to describe in detail the nature of the axing and waning (W and W) zone. Volume recordings were obtained from isolated segments of cat jejunum, using an array of eight recording electrodes, each separated from the next by 3 mm. It as found that slow waves propagate across the W and W zone during its waxing period, but the propagation velocity gradually diminishes ending in propagation failure. This is followed imediately by qeneration of slow waves at a slightly lower frequency by a pacemaker oscillator located just distal to the point of failure. Toward the end of the waning period one or two slow waves generated by this oscillator sometimes propagate in a retrograde direction; this phenomenon has been recorded both in vitro and in viva. Eventually the mire orad pacemaker again takes over and the W and W zone begins the waning phase of the cycle. The overall result is that there is one slow wave less per W and W cycle in the distal plateau, than in the proximal one. Thus, except for the activation of a more distal pacemaker the process resembles the Wenckebach phenomenon in the heart. The mechanical consequences of W and W zones are that propulsive contractions can cross the zone during its waning period, but are blocked during the waxing period. Thus, the W and W zones serve to regulate intestinal transit. (This work as supported in part by Grant AM 06958 from the Nat. Inst. of Arth. Met. and Diq. Dis.) We investigated pancreatic secretion in Syria” golden hamsters. Male hamsters (100-150 g) were fasted and anesthetized with urethane. The c-o” bile-pancreatic duct was cannulated near the duodenum, and ligated at the liver hilum to exclude bile from the collection. Basal samples of unstimulated juice were collected for up to one hour, and then secretin (GIli) was give” IV a bolus (0.09 to 17.7 U/Kg body weight). These experiments provided information on dose response to secretin, flow rates, and chloride and bicarbonate production. Another group of animals was stimulated by a single maximal dose of secretin (2 U/Kg body weight). These experiments provided information about [HCO -1 and [protein] in juice. Samples were weighed an a analyzed for chloride, bicarbonate and total protein content. Results: A secretin dose of 2 U/Kg body weight produced a maximal secretory response. [HCO -1 varied inversely with [Cl-] and appeared to exchange 2 or chloride with a ratio of 1.15:1 (bicarbonate:chloridel. At high flow rates, maximal [HCO -1 was 117+4.0 mEq/l and minimal [Cl-] was 28.4+2.0 mEq31, but [HC03-I decreased and [CJ-] increased at flow rates greater than 1.5x10 ul/min/g body weight. Pancreatic juice [HC03-] varied inversely with protein concentration. These results suggested that secretin stimulated secretion arises from two independent sources of different composition. One is protein rich with a high [Cl-]; the other is low in chloride and protein and has a high [HC03-1. Admixture of varying amounts of these fluids, well a rate limited exchange diffusion of the major anions both account for the observed characteristics of pancreatic secretion in the hamster.