A low-salt diet facilitates Cl secretion in hen lower intestine

Abstract

The regulation of sodium and chloride transport in hen coprodeum by mineralocorticoids was investigated with isolated epithelia under short-circuit conditions. Unidirectional fluxes of Na and Cl were measured by isotopes and modulated by amiloride, theophylline and bumetanide. Hens were maintained either on low-NaCl diet (LS) or on high-NaCl diet (HS). Plasma aldosterone (PA) levels of these groups were measured with radioimmunoassay. A group of HS hens received injections of aldosterone on a 6-hr schedule before experiments. Another group of LS hens was resalinated, and experiments carried out on a 24-hr interval. Salt deprivation stimulated PA levels ninefold, compared to HS hens. Na absorption was stimulated according to previous reports. Electrogenic Cl secretion was elicited by theophylline and partially inhibited by bumetanide. Modulation of PA levels by diet, resalination or aldosterone injection changed the magnitude of electrogenic Cl secretion in parallel between 0.5 mueq/cm2.hr (HS) and 4 mueq/cm2.hr (LS), with pronounced alteration in tissue resistance. The results demonstrate a new action of aldosterone which besides stimulating Na absorption also directly or indirectly elicits Cl secretion. Evidence is presented for a hormonal adaptation of chloride transport in this epithelium. There was a morphological change of the apical plasma membrane and further experiments will have to clarify the exact cellular nature of this process.

Luminal morphology of the avian lower intestine: Evidence supporting the importance of retrograde peristalsis for water conservation

“…Although not statistically significant, the results of the present study showed a trend of a higher absolute surface area and packing density of microvilli in the house sparrow, especially in segments 2 to 5. These findings support the previously observed association of greater microvillar surface area and more dilute urine (Clauss et al, 1988;Brugger, 1991;Elbrønd et al, 1991;Ciccotti et al, 1993).…”

“…Generally, the more dilute the diet, the greater the surface area amplification due to villi and microvilli (Clauss et al, 1988;Dantzer et al, 1988;Brugger, 1991;Elbrønd et al, 1991;Ciccotti et al, 1993). Dietary changes causing an increase in microvilli abundance are associated with a 100-fold augmentation in the rate of NaCl flux across the epithelium .…”

Localization of sodium absorption and chloride secretion in an intestinal epithelium

“…The transepithelial potential difference (PD) was monitored with KCI agar bridges and calomel electrodes by a multichannel computer-controlled voltage-clamp unit. The tissues were continuously short circuited at different PDs through Ag/AgC] electrodes (Clauss et al, 1988). An IBM PC computer was connected to the voltage-clamp units and permitted time sharing, on-line control and data acquisition.…”

“…Unidirectional fluxes of sodium and chloride were measured with isotopes as described previously (Clauss et al, 1988).…”

“…In response to NaCl depletion, electrogenic sodium absorption increases 200-fold (Choshniak, Munck & Skadhauge, 1977) through induction of an amiloridesensitive sodium channel in the apical membrane (Clauss et al, 1987). Simultaneously a scattered cell population, which could be marked with the silver precipitation technique, appeared on the villi, and coincidentally, chloride secretion could be induced by secretagogues (Clauss, Dantzer & Skadhauge, 1988). Although silver precipitation successfully identified chloride transporting cells in amphibian skin (Willumsen & Larsen, 1986), the technique is indirect and is subject to artifacts.…”