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The rate of active H § secretion (JH) across the luminal cell membrane of the turtle bladder decreases linearly with the chemical (ApH) or electrical potential gradient (A~) against which secretion occurs. To examine the control Of JH from the cell side of the pump, acid-base changes were imposed on the cellular compartment by increasing serosal [HCO~]

A B S T R A C T Acidification of the luminal solution by the isolated turtle bladder involves H+ secretion by a pump at the luminal membrane. The OH-dissociated in this process reacts with CO2 and forms HCO-which moves passively out of the cell across the serosal cell membrane. In the present study, this exit step for HCO3 was inhibited by serosal addition of the disulfonic stilbene, SITS, an agent which is thought to bind to a transport protein at the serosal cell membrane. 90 min after serosal addition of 0.5 mM SITS, H+ secretion decreased by > 80%. In contrast, luminal addition of SITS had no effect. During inhibition of H+ secretion by serosal SITS, overall cell pH, measured by the 5,5-dimethyl-2,3-oxazolidinedione method, increased from 7.48+0.03 to 7.61+0.02. This increase of0. 13+0.02 pH U was associated with a much larger regional pH increase as judged from the decrement in the attainable pH gradient across the epithelium. After serosal SITS, this gradient was reduced from 2.88+0.06 to 2.09±0.11 pH U. In the absence of evidence for increased H+ permeability or a change in the force of the H+ pump, the gradient decrement of 0.79±0.08 U reflects a similar pH increment on the cytoplasmic side of the pump.SITS inhibits the exit of bicarbonate across the serosal cell membrane and, thereby, creates a compartment of high alkalinity in series with the pump.

The defect in urinary acidification induced by amphotericin B (AMB) was further characterized in turtle bladder. Since AMB has been shown to increase the hydrogen ion (H+) permeability of this epithelium in the absence of exogenous bicarbonate ions (HCO3-), we explored the permeability characteristics in the presence of imposed bicarbonate ion gradients, comparable to those occurring in vivo. With mucosal (M) pH lowered to the point of zero net hydrogen ion secretion, the transepithelial flow of bicarbonate ions (JHCO3) from serosa (S) to M was 0.91 +/- .06 y mole/hr in response to a 20 mM HCO3- gradient. After AMB addition to M, back diffusion of hydrogen ions from M to S (-JH) increased from zero to 0.36+/-0.05 micronmole/hr, whereas bicarbonate ion transport from S to M (JHCO3) failed to increase (0.91+/-0.06 before and 0.82+/-0.09 micronmole/hr after AMB). In contrast to M addition, S addition of AMB had no effect on either -JH or JHCO3. The defect in urinary acidification induced by AMB is characterized by a large increase in the permeability for hydrogen ions rather than that for bicarbonate ions and depends on direct exposure of the luminal cell membrane to AMB. The permeability increase is cation selective, not only for hydrogen ions but also, as shown previously, for potassium ions, and to a lesser extent, for sodium ions. The results are consistent with the formation by AMB of aqueous half pores in the luminal membrane. Although the passive permeabilities for bicarbonate and chloride ions are not affected primarily, they may increase after prolonged exposure, probably as a results of paracellular leaks that are not specific for AMB.

Bicarbonate is transferred across the serosal (S) membrane of the epithelial cells of the turtle bladder in two directions. Cellular HCO3- generated behind the H+ pump moves this membrane into the serosal solution. This efflux of HCO3- is inhibited by SITS (4-isothiocyano-4'-acetamido-2,2'-disulfonic stilbene). When HCO3- is added to the serosal solution it is transported across the epithelium in exchange for absorbed Cl-. This secretory HCO3- flow traverses the serosal cell membrane in the opposite direction. In this study the effects of serosal addition of 5 x 10(-4) M SITS on HCO3- secretion and Cl- absorption were examined. The rate of H+ secretion was brought to zero by an opposing pH gradient, and 20 mM HCO3- was added to S. HCO3- secretion, measured by pH stat titration, was equivalent to the increase in M leads to S Cl- flux after HCO3- addition. Neither the S leads to M flux of HCO3- nor the M leads to S flux of Cl- were affected by SITS. In the absence of electrochemical gradients, net Cl- absorption was observed only in the presence of HCO3- in the media; under such conditions, unidirectional and net fluxes of Cl- were not altered by serosal or mucosal SITS. H+ secretion, however, measured simultaneously as the short-circuit current in ouabain-treated bladders decreased markedly after serosal SITS. The inhibition of the efflux of HCO3- in series with the H+ pump and the failure of SITS to affect HCO3- secretion and Cl- absorption suggest that the epithelium contains at least two types of transport systems for bicarbonate in the serosal membrane.

Summary.In normal fasting ducks, a somatostatin infusion (800ng/kg/min for 30min) elicited a prompt inhibition of insulin secretion, plasma levels falling from 140 _+ 20 to 20 + 6 pg Eq/ml as observed in mammals. -However plasma glucagon-likeimmunoreactivity shown to be decreased in mammals by somatostatin was sharply increased from a mean basal level of 1.46 + 0.13 ng Eq/ml to 6.61 + 0.77 ng Eq/ml. This effect was not mediated via inhibition of growth hormone secretion since it was also observed in hypophysectomised ducks. Despite the fall in plasma insulin and rise in GLI observed with somatostatin infusion in intact birds, plasma glucose concentrations were lower than with control saline infusion. [5,14,22] and it has been shown that somatostatin simultaneously inhibits insulin and glucagon secretion; moreover somatostatin appears to be one of the most effective A cell suppressants known [22]. Key words:In birds, it has been shown that the somatostatin producing D cells are particularly numerous in the islets of the pigeon pancreas [20] and very high somatostatin concentrations have been measured in the chicken pancreas [25]. As the duck appears to be an interesting species for studies on pancreatic hormone regulation [17,18] the present study was undertaken to explore the response of pancreatic hormones to somatostatin infusion in ducks. Materials and Methods AnimalsExperiments were performed on male Peking ducks 3 to 6 months old (2 to 2.5 kg), maintained on a normal diet with fowl pellets and tap water ad libitum. HypophysectomyRemoval of the pituitary was performed under local anaesthesia (1% xylocaine, Bellon) according to Benoit's technique [1]. These animals were used for experiments 4 to 10 days after operation. Completeness of hypophysectomy was checked by plasma growth hormone determination. InfusionsAfter an overnight fast the conscious ducks, normal or hypophysectomised, were tied to a board.Somatostatin was dissolved in 0.154 mol/l saline and administered intravenously as a bolus of 800 ng/kg immediately followed by a sustained infusion of 800 ng/kg/min for 30 minutes through a cathether inserted into a leg vein. As controls, normal or hypophysectomised ducks received 0.154 mol/1 saline infusions. Blood SamplingBlood samples were collected from a catheter inserted into a wing vein immediately before infusion (zero time) and at selected intervals thereafter.Blood samples kept on ice were centrifuged at 4 ~ and plasma stored at -20 ~ until the time of assay. Plasma DeterminationsPlasma glucose concentration was measured with a Technicon autoanalyser using a ferricyanide reagent [11] after dialysis of plasma.

1. Selected organ-ablation experiments were performed in dogs in an attempt to identify the source of the natriuretic hormone postulated to participate in the natriuresis of blood volume expansion. 2. An isolated dog kidney perfused with blood from the femoral artery of deoxycorticosterone-loaded dogs subjected to acute volume expansion with equilibrated blood served as the bioassay system for the natriuretic factor. Four groups were studied after the following procedures: group I, no ablation; group II, thyroparathyroidectomy; group III, hypophysectomy; group IV, adrenalectomy. 3. In all groups, the administration of equilibrated blood promoted a significant increase in sodium chloride excretion in the isolated kidney. The natriuresis was unrelated to changes in glomerular filtration rate, renal blood flow, renal arterial pressure, plasma protein concentration or packed cell volume. In the absence of volume expansion, sodium chloride excretion in the isolated kidney did not change or decreased. 4. These results argue against the thyroid, parathyroid, adrenal and pituitary glands as the source of natriuretic hormone.

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