Hydrogen ion transport in the rabbit esophagus

The lumen of the rabbit esophagus was perfused in vivo with solutions (one solution per esophagus) containing 0-160 mM HCl by a constant circulation technique for 5 h. During the 1st h, net H+ flux out of the lumen (efflux) was minimal at H+ concentrations of 80 mM or less, but increased linearly with increase in luminal H+ concentrations above 80 mM. After 3 h, the net H+ efflux increased proprtionately to increasing H+ concentrations above a threshold of 20 mM. At the 5th h a linear relationship between net H+ efflux and luminal concentration was seen at all concentrations. Histological damage accompanied increase in H+ efflux and correlated with luminal acid concentrations and duration of exposure. We conclude that the rabbit esophageal mucosa is essentially impermeable to H+ below a threshold concentration of 80 mM for up to 1 h of exposure. When exposure is prolonged, this threshold steadily decreases with time. The occurrence of passive H+ diffusion above threshold concentrations most probably results from an increase in mucosal permeability, possibly an initiating event in the genesis of esophagitis.

The vagus, the duodenal brake, and gastric emptying

It has been suggested that an intact vagal supply is essential for the normal function of the recptors in the duodenum and proximal small bowel, which influence the rate of gastric emptying. This paper reports the effect of vagal denervation on gastric emptying and also examines the site and mode of action of receptors in the proximal small bowel. It has been demonstrated in the dog that most, if not all, the receptors controlling gastric emptying lie in the proximal 50 cm of the small bowel. Following truncal vagotomy the emptying time of each instillation increased significantly and the differential rate of emptying of different instillations remained unchanged. The proximal 50 cm of small bowel was capable to differentiating between different instillates even after selective extragastric vagotomy, in which the duodenum was vagally denervated and, therefore, duodenal braking receptors function independently of vagal innervation.

Mechanisms of acid disposal in canine duodenum

Distal duodenal pouches chronically excluded from the intestinal stream were perfused in seven awake dogs by a constant-circulation technique using isomolar solutions containing 60-120 mM HCl. The rate of disappearance of hydrogen ions (H+) and net ion movements was measured. In all experiments there was a loss of H+ from the perfusate accompanied by a gain of sodium (Na+), potassium (K+) and chloride (Cl-), together with an increase in volume and a decrease in osmolality. The magnitude of this H+ loss was a function of instillate [H+]. The H+ lost by neutralization was separated from that lost by diffusion by calculations based on the assumption that the observed changes in somolality were the result of neutralization by bicarbonate (HCO3-). The bulk of the acid (67%) was lost by neutralization, the remainder back-diffusing in a one-to-one exchange for diffusable Na+. This ability to dispose of acid decreased with increasing age of the pouches due to a diminished volume of HCO3- secretion, the magnitude lost by backdiffusion remaining unchanged.

Studies on the absorption and distribution of doxycycline in normal patients and in patients with severely impaired renal function

Doxycycline, a recently synthesized analogue of tetracycline, was given to 16 patients with normal renal function and to 14 patients with severely impaired renal function. Serum concentrations in the two groups following a single dose were followed after absorption. The rate of clearance from the plasma following a single dose did not differ significantly in the two groups despite low urinary concentrations in patients with renal failure. No accumulation of doxycycline occurred in the serum of three normal patients or of nine patients with renal failure when treated with either 200 mg. daily or 200 mg. initially followed by 100 mg. daily for up to 15 days.