Erik Skadhauge

Plasma levels of arginine vasotocin, prolactin, aldosterone and corticosterone during prolonged dehydration in the domestic flowl: effect of dietary NaCl

Summary1.Three groups of White Plymouth Rock laying hens were adapted to three levels of dietary NaCl: low-NaCl food with tap water (LOW), high-NaCl food (1% NaCl w/w added) with tap water (HT), and high-NaCl food with 0.5% NaCl for drinking (HS). The birds were subjected to water deprivation (dehydration) for 18 days. Blood sampling was done at 2–4 day intervals. Plasma concentrations of arginine vasotocin (AVT), prolactin (PRL), aldosterone (ALDO) and corticosterone (CS) were determined by radioimmunoassay. Plasma osmolality, sodium, chloride, and potassium were also determined.2.In the normally hydrated hens fully adapted to the diets, there was a stepwise increase from LOW to HS in plasma osmolality (305, 315, 332 mOsm, for LOW, HT and HS, respectively), [Na+] (144, 153, 161 mM) and [Cl−] (109, 119, 127 mM) as well as in [AVT] (6, 14, 18 pg/ml) and [PRL] (16, 24, 34 ng/ml). Regressing [AVT] on osmolality gave a slope of 0.30 pg·ml−1/mOsm and a threshold of 273 mOsm. The slope of [PRL] on osmolality was 0.73 ng·ml−1/mOsm. The correlation coefficient of [AVT] and [PRL] was 0.67. LOW had high [ALDO] (165 pg/ml) which was suppressed to low levels in HT and HS (5–8 pg/ml), while [CS] was the same in all groups (0.9–1.1 ng/ml). Plasma [K+] was decreased in the high-NaCl groups (5.8 mM in LOW, 4.4 and 4.7 mM in HT and HS).

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

SummaryThe 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 μeq/cmau2 · hr (HS) and 4 μeq/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.

Osmotic and hormonal responses to heat and dehydration in the fowl

Summary1.This study reports on osmotic and hormonal responses to heat and dehydration in birds.2.Heat exposure did not affect the osmotic and hormonal status of normally hydrated fowls.3.Dehydration for 48 h (normothermia, ca. 13% body weight loss) significantly (P<0.001) increased plasma osmolality and concentrations of sodium and chloride, and consequently the plasma concentrations of the antidiuretic hormone (AVT) and prolactin. Additional heat exposure of the dehydrated fowls further accelerated these changes, together with significantly (P<0.01) increasing plasma aldosterone concentration.4.Upon recovery (30 min of drinking) the osmotic and hormonal responses were significantly (P<0.001) diminished.5.Body temperature was not significantly affected by dehydration, yet during heat exposure the dehydrated fowls were significantly hyperthermic (P<0.05) compared with normally hydrated heat exposed fowls.6.A significant overall correlation (r=0.43,P<0.02) between body temperature and plasma sodium-to-calcium ratio suggests this ratio to be involved in the control of the hypothalamic thermoregulatory set-point.7.The associated thermoregulatory, osmoregulatory and hormonal changes revealed in the present study, together with literature information, are integrated into a model summarizing the operating mechanisms in dehydrated heat exposed birds.

The antisecretory factors: inducible proteins which modulate secretion in the small intestine

1. Cholera toxin and glucose induce the synthesis of antisecretory factors (ASF) of isoelectric points 5.0 and 4.3, respectively, and of a molecular mass of ca 60,000. 2. ASF, in nanogram amounts, inhibit intestinal secretion induced by cholera toxin, Campylobacter toxin, E. coli heat-stable toxin, C. difficile toxin A, and Dinophysis toxin. 3. Intraspinal injection of cholera toxin and glucose induces the synthesis of pituitary ASF much more effectively than does either peroral or intranasal administration. 4. Cholera toxin and glucose seem to act synergistically while inducing ASF. 5. Vagotomy abolishes both the intestinal effects of ASF and the peroral, but not the intraspinal induction of pituitary ASF. 6. ASF has no effect on ion transport across isolated intestinal mucosa from either pig or hen. 7. The results suggest that both the induction and the intestinal effects of ASF are mediated via the central and intestinal nervous system.

Aldosterone effects on electrolyte transport of the lower intestine (coprodeum and colon) of the fowl (Gallus domesticus) in vitro

Abstract Hens were maintained on commercial (high-Na) poultry food or on a wheat and barley (WB; low-Na) diet. Stripped mucosae from coprodeum and colon were mounted in a Ussing chamber, and short-circuit current ( I sc ), electrical potential difference (PD), and tissue resistance were measured. Tissue responses to addition of amino acids and amiloride were assessed. Coprodeum from commercial-diet birds had near-zero I sc and PD. WB diet enhanced the average I sc to 201 μA/cm 2 and the PD to 33 mV. The I sc and PD were abolished by amiloride, but were not responsive to amino acids. Colon from commericial-diet birds had fairly high I sc (134 μA/cm 2 ) and PD (10 mV); I sc and PD were increased by amino acids (by 45%) and not affected byamiloride. WB diet augmented I sc to 379 μA/cm 2 and PD to 20 mV, abolished amino acid sensitivity, and induced almost complete sensitivity to amiloride. Birds maintained on WB diet had higher plasma aldosterone concentrations (9.6 pg/100 μl) than commercial-diet birds (5.8 pg/100 μl), but diet did not affect plasma corticosterone concentrations. In vivo injections of aldosterone (32–128 μg/kg body weight) into commercial-diet birds induced changes in I sc and PD of coprodeum and colon, and changes in amino acid and amiloride sensitivity of colon, resembling the changes associated with WB maintenance, but of generally lesser magnitude. It is concluded that aldosterone injections reproduced qualitatively all the effects of a low-Na diet.

Plasma concentrations of arginine vasotocin, prolactin, aldosterone and corticosterone in relation to oviposition and dietary NaNl in the domestic fowl

The osmolality and concentrations of Na, K, Cl and the hormones arginine vasotocin (AVT), prolactin, aldosterone and corticosterone were measured in plasma as functions of time in relation to oviposition, changing NaCl content of the diet, and feeding-inanition. AVT was significantly increased immediately after oviposition (but not during the hour before) with a calculated average value of 38.0 +/- 4.1 pg/ml at oviposition. A moderate increase in concentrations of prolactin and corticosterone were observed immediately after oviposition. Oviposition was not associated with detectable changes in plasma osmolality (and electrolyte concentrations) nor with the concentration of aldosterone. After a sudden change from a high NaCl diet to a low NaCl diet the plasma osmolality and concentrations of NaCl, AVT and prolactin reached new stable levels in 24 hr, whereas the plasma aldosterone concentration required more than 4 days to reach a steady level. After resalination plasma aldosterone was suppressed in less than 8 hr. Both osmolality and concentrations of AVT and prolactin showed transient overshoots during the first 24 hr. NaCl depletion resulted in a transient increase of corticosterone.

Time course of adaptation to low and high NaCl diets in the domestic fowl. Effects on electrolyte excretion and on plasma hormone levels (aldosterone, corticosterone and prolactin).

White Plymouth Rock fowls (2.5–5.5 kg, mostly laying hens) were maintained onlow NaCl treatment (L: balanced ration and distilled water; mean Na+ intakes 0.2–0.3 m-mole/kg bw.d depending on experiment) orhigh NaCl treatment (H: balanced ration with 1% w/w NaCl+0.5% w/v NaCl drink; mean Na+ intakes 10–13.5 m-mole/kg d). DuringNaCl depletion (birds adapted to H, then switched to L for 1, 2, 4 or 8d) plasma aldosterone concentrations rose hyperbolically (half time,t1/2, 2d) from 2.2±0.3 (SEM;n=7) to 16.9±4.1 (8) pg/100 μl by 8d; prolactin concentrations fell linearly from 25.0±2.3 (10) to 20.5±2.2 (8) ng/ml in the same time. Epithelial short-circuit currents plotted against plasma aldosterone concentrations during NaCl depletion indicate that coprodeum is less sensitive than rectum (colon) to this hormone. Followingresalination (birds adapted to L, then given 10ml 0.75M NaCl/kg orally 24, 16 or 8h before blood sampling), aldosterone concentrations fell from 25.8±1.5 (3) to 3.7±1.6 (3) pg/100 μl and prolactin concentrations rose from 13.8±2.0 (3) to 44.7 ±8.4 (3) ng/ml, both within 8h. Corticosterone concentrations rose briefly following NaCl depletion and resalination, probably due to non-specific “stress”.Electrolyte balance studies (birds adapted to H, then switched to L for 6d, andvice versa (repletion) showed an accumulated change of 12–13m-mole Na+/kg, lost during NaCl depletion (t1/2 0.5d, stabilised by 4–6d) and gained during NaCl repletion (t1/2 0.5d, stabilised by 2–3d); results were similar for Cl−; K+ lost during NaCl repletion stabilised by 2d (t1/2 0.5d) at 5m-mole/kg, but losses continued during depletion at 2.3 m-mole/kg·d through to 6d. It is concluded that the pace of lower intestinal adaptation to dietary Na+ levels is probably dictated by the pace of changing Na+ balance, via its effect(s) on plasma aldosterone (and possibly prolactin) concentrations, while differences in temporal patterns of adaptation by coprodeum and rectum to NaCl depletion depend on their differential sensitivities to aldosterone. Reciprocating plasma concentrations of aldosterone and prolactin during NaCl depletion-resalination suggest prolactin may be a candidate antagonist to aldosterone actions during states of high NaCl-intake. Changes in K+ balance during NaCl depletion-repletion can be explained in terms of linked K+−Na+ transport by the lower intestine.

Signal Transduction Pathways for Serotonin as an Intestinal Secretagogue

This review presents a signal transduction pathways for serotonin (5-hydroxytryptamine, 5-HT) as an intestinal secretagogue and some recently published related findings. 5-HT is a secretagogue in the small and large intestine of all studied species including pig and man. 5-HT mediates intestinal secretion through activation of at least the epithelial 5-HT2, and neuronal 5-HT3, and 5-HT4 receptors in the submucosal plexus, including a reflex arc. 5-HT activates both a cholinergic and a non-cholinergic pathway in its secretory response. Intracellular mediators include at least eicosanoids (prostaglandin E2), calcium, phosphoinositols (1,4,5-inositol trisphosphate) and maybe nitric oxide and cyclic nucleotides. Pig small intestine appears to be an appropriate model for the human small intestine with respect to the signal transduction pathways for 5-HT as an intestinal secretagogue. Species and segmental differences in the signal transduction pathways for 5-HT as an intestinal secretagogues are discussed together with related news on 5-HT receptors, 5-HT antagonists in clinical use, the enteric nervous system, and intracellular mediators.

Ruminal transport and metabolism of short-chain fatty acids (SCFA) in vitro: effect of SCFA chain length and pH.

The unidirectional transport and metabolism of 14C-labeled acetate, propionate and butyrate across the isolated bovine rumen epithelium was measured in vitro by the Ussing chamber technique. There was a significant, but relatively small, net secretion of acetate and propionate, and a large and significant net absorption of butyrate. The results demonstrate that the mucosal-serosal (MS) pathway for short-chain fatty acids (SCFA) is different from the serosal-mucosal (SM) pathway, and that butyrate is treated differently from acetate and propionate by the epithelium. The results support that the main route for epithelial SCFA transport is transcellular. The correlation between SCFA lipophility and the flux rate was positive but weak at both pH 7.3 and 6.0. Decreasing pH increased all SCFA fluxes significantly, but not proportionally to the increase of protonized SCFA in the bathing solution. There was a significant and apparently non-competitive interaction between the transport of acetate, propionate and butyrate. It seems that mediated transport mechanisms must be involved in epithelial SCFA transport in the bovine rumen, but the data do not exclude that passive diffusion could account for a significant part of the flux. The metabolism of SCFA in the Ussing chamber system was considerable, and there was a clear preference for excretion of CO2 from this metabolism to the mucosal side, while side preference for non-CO2 metabolite excretion was not studied. Of the propionate and butyrate transported in the MS direction, 78 and 95% was metabolised, while only 37 and 38% was metabolised in the SM direction (acetate metabolism could not be measured). There was, however, no simple relation between the degree of metabolism and the transport rate or the transport asymmetry of the SCFA.

Caecal water and electrolyte absorption and the effects of acetate and glucose, in dehydrated, low-NaCl diet hens

SummaryIn vivo electrolyte transport and water absorption from the caeca of dehydrated, low-NaCl diet hens are reported. In the absence of luminal glucose or acetate, net electrolyte transport rates and water absorption are small. When physiological concentrations of acetate (40 mM) are included in the perfusate, Na+ transport and water absorption increase significantly (P<0.01): 38±7 μeqNa+/caecum kg·h and 256±33 μl H2O/caecum · kg · h.A similar increase in water absorption occurs with the inclusion of 15 mM glucose in the perfusate (219±30 μl H2O/caecum · kg · h), however both net Na+ and Cl− absorption increase: 28±6 μeq Na+/caecum · kg · h and 21±5 μeq Cl−/caecum kg · h.These pronounced increases in electrolyte and water absorption are not accompanied by any significant increase in transmural potential difference.The data presented establish caeca as important sites in the recuperation of water and electrolytes in dehydrated, low-NaCl diet hens.