Steady-state sodium absorption and chloride secretion of colon and coprodeum, and plasma levels of osmoregulatory hormones in hens in relation to sodium intake

Abstract

The plasma levels of four osmoregulatory hormones and their target ion-transport systems in the lower intestines of the domestic fowl were determined in order to elucidate their interrelationship and their setpoints in relation to NaCl intake. White Plymouth Rock hens were adapted to six intake levels of NaCl (0.20 +/- 0.02-24.7 +/- 1.9 mmoles Na+.kg bw-1.day-1) for 6 weeks. The Na+ absorption and the Cl- secretion of colon and coprodeum were characterized in vitro by the effects of hexoses, amino acids, amiloride, and theophylline on the short-circuit current (SCC) and electrical potential difference (PD). The NaCl-conserving system of the adult chicken is set at low intake levels of NaCl as the 80% range (quantized by non-linear, logistic regression analyses) of the change in the plasma [ALDO], the amiloride-inhibitable Na+ absorption of coprodeum and colon (delta SCC), occurred from 0.18 to 2.3, from 0.9 to 4.3, and from 1.2 to 7.3 mmoles Na+.kg bw-1.day-1, respectively. These results demonstrate that the amiloride-inhibitable Na+ absorption of coprodeum is more closely linked to plasma [ALDO] than that of colon. The aminoacid-Na+ coabsorption of colon increased over exactly the same range of Na+ intake as the colonic amiloride-inhibitable Na+ absorption decreased, whereas the hexose-Na+ coabsorption increased at higher levels of Na+ coabsorption increased at higher levels of Na+ intake, from 2 to 11 mmoles Na+.kg bw-1.day-1. Both these Na+ absorption types had reached their maximums at 24.7 mmoles Na+.kg bw-1.day-1, whereas the plasma [AVT] and plasma [PRL], although significantly increased, apparently had not; their 80% range of change occurred from 9.9 to 99 mmoles Na+.kg bw-1.day-1, and the main changes in plasma osmolality were predicted to occur from 5.4 to 107 mmoles Na+.kg bw-1.day-1. These results suggest that these colonic and hormonal variables conserve osmotically-free water and operate at high NaCl intake. The theophylline-induced colonic Cl- secretion did not change with NaCl intake, whereas the stimulation of SCC in coprodeum decreased with increasing NaCl intake: the main change occurred between 0 and 3.2 mmoles Na+.kg bw-1.day-1. Thus, all ion-transport capacity (although the nature of the Na+ transport changes). It is suggested that hormones defending the extracellular volume and composition are regulated close to zero input and output of both NaCl and water, regardless of whether they are NaCl conserving or free-water conserving.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological adaptations to induced changes in transepithelial sodium transport in chicken lower intestine (coprodeum): a study of resalination, aldosterone stimulation, and epithelial turnover

“…The response of brush cells to resalination and aldosterone stimulation is very quick and occurs within 1-2 days. It can be concluded that the changes are closely related to measured variations in sodium transport (as observed in this study) and plasma-aldosterone level, as shown by Arnason et al (1986), Arnason and Skadhauge (1991), Thomas and Skadhauge (1982), and Skadhauge et al (1983).…”

“…Plasma concentrations of Na + , Cl -, and K + , measured in previous studies (Thomas and Skadhauge 1982;Skadhauge et al 1983;Arnason et al 1986;Arnason and Skadhauge 1991) and in this study of aldosterone stimulation, expressed a slight temporary interruption of homeostasis, which seemed to be reestablished within the experimental period. In the present study, development of the dome-like cell apices, most pronounced after 2-3 days of resalination and 2-4 days of aldosterone stimulation, might reflect this temporary interruption of homeostasis.…”

“…Hens adapt and stabilize osmotically, hormonally, and morphologically to the specific and permanent dietary conditions (Choshniak et al 1977;Lyngdorf-Henriksen et al 1978;Bindslev 1979;Eldrup et al 1979Eldrup et al , 1980Thomas and Skadhauge 1982;Clauss et al 1984Arnason et al 1986;Mayhew et al 1990Mayhew et al , 1992aElbrønd et al 1991). The adaptations are mainly regulated by the mineralocorticoid aldosterone (Thomas et al 1979(Thomas et al , 1980Skadhauge et al 1983Skadhauge et al , 1984, as the plasma-aldosterone level is significantly higher in low-NaCl hens than in high-NaCl hens (Bindslev et al 1982;Skadhauge et al 1983;Arnason et al 1986;Arnason and Skadhauge 1991).…”

Effects of resalination on intestinal glucose transport in chickens adapted to low Na+ intakes

“…1); high-Na¤ fed birds have a low serum aldosterone concentration, as previously described ( Arnason & Skadhauge, 1991;Garriga et al 1999a). When animals that had been maintained for 14 days in the low-Na¤ diet (L14d group) were resalinated, the serum aldosterone concentration returned to the values characteristic of the highNa¤ condition within 4 h of the oral NaCl dose (R4h group).…”

Effect of dehydration on apical Na + -H + exchange activity and Na + -dependent sugar transport in brush-border membrane vesicles isolated from chick intestine

“…However, both dehydration ( [2] and current results) and Na + depletion [19] increase plasma aldosterone levels. Since it has been reported that the plasma arginine vasotocin (AVT) level is increased by dehydration [2] and decreased by Na + depletion [1], AVT could be the regulator of intestinal Na + -dependent sugar transport. We have not been able to measure plasma AVT levels in the chicken.…”