Hormonal regulation of electrolyte and water transport in the colon

Investigation of the effect of verapamil on the regional absorption of sofosbuvir from rabbit intestine in situ

PURPOSE

Sofosbuvir, a nucleotide antiviral drug, is a Biopharmaceutics Classification System (BCS) class III prodrug suffering from limited intestinal absorption due to its high hydrophilicity and low intestinal permeability. This research aims to investigate the luminal stability of Sofosbuvir, the influence of anatomical site on its intestinal absorption and the effects of verapamil on such absorption.

METHOD

The study utilized in situ rabbit intestinal perfusion technique to examine absorption of Sofosbuvir from duodenum, jejunum, ileum and ascending colon. This was conducted both with and without verapamil.

RESULTS

The luminal stability study showed that Sofosbuvir was subjected to premature degradation with varying fractions degraded from the different intestinal segments. The in situ perfusion data showed incomplete absorption of Sofosbuvir from small and large intestinal segments. The recorded values of the absorptive clearance per unit length (Pe.A/L) of Sofosbuvir were 0.026, 0.0075, 0.0026, & 0.054 ml/min.cm for duodenum, jejunum, ileum, and ascending colon, respectively. The Pe.A/L values were ordered as colon > duodenum > jejunum > ileum. This is the opposite rank of P-gp content in the different intestinal segments. The recorded values of the length required for complete Sofosbuvir absorption (L95%) were 29.58, 128.47, 949.2 and, 13.63 cm for duodenum, jejunum, ileum, and ascending colon, respectively. Co-perfusion with verapamil significantly increased Pe.A/L and reduced the L95% of Sofosbuvir from both jejunum and ileum (P-value < 0.05).

CONCLUSION

The results indicated that the absorptive clearance of Sofosbuvir was site dependent and associated with the content of P-glycoprotein, in addition to the expected drug interactions that can occur in polymedicated hepatitis C virus (HCV) infected patients.

Er Shen Wan extract reduces diarrhea and regulates AQP 4 and NHE 3 in a rat model of spleen-kidney Yang deficiency-induced diarrhea

INTRODUCTION

Er Shen Wan (ESW), a traditional Chinese medicinal formula comprised of Psoraleae Fructus (Babchi seeds, from Psoralea corylifolia Linn.) and Myristicae Semen (Nutmeg, from Myristica fragrans Houtt.), is widely used to treat spleen-kidney Yang deficiency (SKYD)-induced diarrhea. Previous studies have demonstrated preliminarily that the petroleum ether extract of ESW (ESWP) exhibits significant anti-diarrheal activity. The present study aimed to evaluate the anti-diarrhea activity of ESWP and to explore the underlying mechanisms with respect to fluid metabolism in a rat model of SKYD-induced diarrhea.

MATERIALS AND METHODS

A high-performance liquid chromatography-diode array detector (HPLC-DAD) approach was developed and validated for qualitative and quantitative analyses of the main constituents of ESWP. SKYD model rats were established and treated with an effective dose (3.5?g/kg) of the extract for two weeks. Anti-diarrheal activity and stool properties were observed. After the experiment, the appearance and histology of the intestines were evaluated. Serum levels of neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) were also determined. Furthermore, to characterize the regulation of aquaporin-4 (AQP 4) and Na⁺/H⁺ exchanger isoform 3 (NHE 3) in the colon, quantitative real-time RT-PCR (qRT-PCR), immunohistochemistry (IHC) and Western blotting (WB) were employed to detect mRNA and protein expression levels.

RESULTS

In the rat models, oral ESWP administration significantly reduced the diarrhea score and the number and weight of wet stools. Jejunal and ileac histological damage was impeded, and the histology score decreased. Serum VIP levels were significantly decreased, in contrast to NPY levels. In addition, AQP 4 and NHE 3 expression levels increased significantly.

CONCLUSIONS

These results showed that ESWP's anti-diarrheal effect might at least partially involve the regulation of hormones intimately involved in maintaining fluid and electrolyte levels, as well as by increasing AQP 4 and NHE 3 expression levels and enhancing the absorption of Na⁺ and water.

Water handling in the human distal colon in vitro: role of Na+, Cl- and HCO3-

The minute by minute net water movement (Jw) was measured, in the human distal colon in vitro, simultaneously with the transepithelial potential difference (PD) and short circuit current (SCC) with the following results: (1) An absorptive Jw (+0.36 +/- 0.04 microliters/(min.cm2)) was observed, in 21 cases, when the colon was mounted between two identical standard salines (Na+ 140, Cl- 110, HCO3- 25 mequiv./L) and in the presence of a hydrostatic pressure gradient (delta P) of 13 cm of H2O (mucosal side positive). (2) This absorptive Jw was a linear function of the applied delta P or the imposed osmotic transepithelial gradient (Phydr = 0.22 +/- 0.03 cm/s; Posm = 0.0020 +/- 0.005 cm/s; n = 6). (3) A fraction of this Jw was independent of the presence of any hydrostatic, osmotic or chemical gradient while associated with a serosal side positive and partially amiloride sensitive PD (11.3 +/- 1.8 mV). (4) Both Jw and PD were dependent on the presence of Na+ in the incubating media. (5) Replacement of Cl- by SO(4)2- did not change the absorptive Jw, but increased the observed PD and the transepithelial resistance. (6) HCO3- removal strongly reduced the SCC and PD together with an important increase in Jw. Unexpectedly, other 9 colon fragments spontaneously showed a secretory Jw when mounted between two identical standard salines (-0.55 +/- 0.11 microliters/(min.cm2). In these experiments it was observed that: (7) The tissue moved water against the imposed delta P (13 cm of H2O), while the associated PD (+11.9 +/- 2.1 mV) was similar to the one observed in absorptive fragments. (8) As in the case of absorptive preparations, PD, SCC and the transport associated Jw fell to zero in the absence of Na+. (9) When SO(4)2- replaced Cl-, secretory Jw reversed to absorptive Jw, together with an increase in PD and resistance. In both absorptive and secretory preparations it was finally observed that: (10) norepinephrine (5 x 10(-6) M) decreased SCC and increased the absorptive Jw in a tightly parallel manner (half-times for each response: SCC = 11.4 +/- 2.1 min; Jw = 11.4 +/- 2.0 min, n = 4) and (11) 8-Br cyclic AMP (10(-3) M) increased SCC while simultaneously decreasing the absorptive Jw. It is concluded that the observed Jw in the distal human colon in vitro results from the complex addition of osmotic, hydrostatic and transport associated driving forces. The transport-associated Jw has absorptive and secretory components.(ABSTRACT TRUNCATED AT 400 WORDS)

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

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.