Average Secretion Rate Research Articles

Beta-cell sensitivity to insulinotropic gut hormones is reduced after gastric bypass surgery

ObjectivePostprandial hyperinsulinaemia after Roux-en Y gastric bypass (GB) has been attributed to rapid nutrient flux from the gut, and an enhanced incretin effect. However, it is unclear whether surgery changes...

Integrated multiscale mathematical modeling of insulin secretion reveals the role of islet network integrity for proper oscillatory glucose-dose response

The integrated multiscale mathematical model we present in this paper is built on two of our previous ones: a model of electrical oscillation in β-cells connected to neighboring cells within a three-dimensional (3D) network, and a model of glucose-induced β-cell intracellular insulin granule trafficking and insulin secretion. In order to couple these two models, we assume that the rate at which primed and release-ready insulin granules fuse at the cell membrane increases with the intracellular calcium concentration. Moreover, by assuming that the fraction of free KATP-channels decreases with increasing glucose concentration, we take into account the effect of glucose dose on membrane potential and, indirectly via the effect on the potential, on intracellular calcium. Numerical analysis of our new model shows that a single step increase in glucose concentration yields the experimentally observed characteristic biphasic insulin release. We find that the biphasic response is typically oscillatory in nature for low and moderate glucose concentrations. The plateau fraction (the time that the β-cells spend in their active firing phase) increases with increasing glucose dose, as does the total insulin secretion. At high glucose concentrations, the oscillations tend to vanish due to a constantly elevated membrane potential of the β-cells. Our results also demonstrate how insulin secretion characteristics in various glucose protocols depend on the degree of β-cell loss, highlighting the potential impact from disease. In particular, both the secretory capacity (average insulin secretion rate per β-cell) and the oscillatory response diminish as the islet cell network becomes compromised.

Secretion Rates of Human Nasal Submucosal Glands from Patients with Chronic Rhinosinusitis or Cystic Fibrosis

A majority of patients with cystic fibrosis (CF) have chronic rhinosinusitis (CRS) and/or nasal polyps, both of which may be secondary to reduced fluid secretion from nasal submucosal glands. To determine whether decreased fluid secretion from nasal submucosal glands also occurs in patients without CF and with CRS. Inferior turbinates of the nasal cavity were harvested from controls, subjects with CRS, and subjects with CF (n = 5-7 per group). The secretion rates of the nasal submucosal glands of the three groups in response to carbachol and forskolin were measured by using time lapse digital imaging of mucus bubbles from single glands as they formed on the mucosal surface under oil. Carbachol-stimulated secretion rates were the following: controls, 1670 ± 381 pl·min(-1)·gland(-1); CRS, 965 ± 440 pl·min(-1)·gland(-1); and CF, 933 ± 588 pl·min(-1)·gland(-1) (p = 0.23, Kruskal-Wallis test). Forskolin-stimulated secretion rates were the following: controls, 229 ± 14 pl·min(-1)·gland(-1); CRS, 154 ± 48 pl·min(-1)·gland(-1); and CF, 22 ± 15 pl·min(-1)·gland(-1) (p = 0.008, Kruskal-Wallis test). The ratio of the average secretion rate induced by forskolin to that induced by carbachol was 13.7% in the controls, and 15.9% in CRS and 2.3% in CF groups. The only significant difference in this small study was decreased forskolin-stimulated secretion in subjects with CF relative to the other subjects. However, there was a trend toward reduced carbachol-stimulated secretion rates in subjects with CRS and with and without CF relative to controls. Additional studies are needed to determine if nasal submucosal gland hyposecretion occurs in CRS either as a contributor to or as a consequence of CRS pathogenesis.

Effect of Salt Stress on the Salt Secretion in <i>Aeluropus littoralis</i>

The effects of NaCl on the growth, the number of salt gland and salt secretion ofAeluropus littoraliswere studied at different NaCl concentrations. Results showed that with the increase of NaCl concentration, the growth ofAeluropus littoraliswas inhibited and MDA content increased gradually. With the increase of NaCl concentration, fresh weight, dry weight of single plant decreased, andA. littoralissalt secretion increased significantly. Salt gland density was significantly higher with the increase of NaCl concentration, and the total number of salt glands on the low surface was more than that on the upper surface. At the same time, the average secretion rates of individual salt glands increased. These showed that the salt glands could effectively secrete salt outside the body to keep normal physiological function.

Transformation of Althaea officinalis L. by Agrobacterium rhizogenes for the production of transgenic roots expressing the anti-HIV microbicide cyanovirin-N

The marshmallow plant (Althaea officinalis L.) has been used for centuries in medicine and other applications. Valuable secondary metabolites have previously been identified in Agrobacterium rhizogenes-generated transgenic 'hairy' roots in this species. In the present study, transgenic roots were produced in A. officinalis using A. rhizogenes. In addition to wild-type lines, roots expressing the anti-human immunodeficiency virus microbicide candidate, cyanovirin-N (CV-N), were generated. Wild-type and CV-N root lines were transferred to liquid culture and increased in mass by 49 and 19 % respectively over a 7 day culture period. In the latter, the concentration of CV-N present in the root tissue was 2.4 μg/g fresh weight, with an average secretion rate into the growth medium of 0.02 μg/ml/24 h. A. officinalis transgenic roots may therefore in the future be used not only as a source of therapeutic secondary metabolites, but also as an expression system for the production of recombinant pharmaceuticals.

Model for Glucagon Secretion by Pancreatic α-Cells

Glucagon hormone is synthesized and released by pancreatic α-cells, one of the islet-cell types. This hormone, along with insulin, maintains blood glucose levels within the physiological range. Glucose stimulates glucagon release at low concentrations (hypoglycemia). However, the mechanisms involved in this secretion are still not completely clear. Here, using experimental calcium time series obtained in mouse pancreatic islets at low and high glucose conditions, we propose a glucagon secretion model for α-cells. Our model takes into account that the resupply of releasable granules is not only controlled by cytoplasmic , as in other neuroendocrine and endocrine cells, but also by the level of extracellular glucose. We found that, although calcium oscillations are highly variable, the average secretion rates predicted by the model fall into the range of values reported in the literature, for both stimulated and non-stimulated conditions. For low glucose levels, the model predicts that there would be a well-controlled number of releasable granules refilled slowly from a large reserve pool, probably to ensure a secretion rate that could last for several minutes. Studying the α-cell response to the addition of insulin at low glucose, we observe that the presence of insulin reduces glucagon release by decreasing the islet level. This observation is in line with previous work reporting that dynamics, mainly frequency, is altered by insulin [1]. Thus, the present results emphasize the main role played by and glucose in the control of glucagon secretion by α-cells. Our modeling approach also shows that calcium oscillations potentiate glucagon secretion as compared to constant levels of this cellular messenger. Altogether, the model sheds new light on the subcellular mechanisms involved in α-cell exocytosis, and provides a quantitative predictive tool for studying glucagon secretion modulators in physiological and pathological conditions.

Endothelin-1 and angiotensin II secretion at different lengths of endothelial cell monolayer in the view of tensile stress accumulation in the upper endothelial cell membrane

Theoretical analysis and experimental observations have shown that tensile stress inside an endothelial cell membrane is capable of growing in the direction opposite to blood flow and can accumulate to a level that is three or more orders of magnitude higher than flow-induced shear stress on the membrane surface. This phenomenon is called cell membrane tension accumulation (CMTA). We hypothesize that correlation may exist between the endothelial cell monolayer length or CMTA and secretory function of endothelial cells. To verify this hypothesis, a paired experimental study was devised to measure the secretion of endothelin (ET-1) and angiotensin II (Ang II) by two monolayers of cultured human glomerular vascular endothelial cell (HGVEC) monolayers subjected an identical steady shear stress. After replicate cultured HGVEC monolayer with two kinds of length of 6 cm and 10 cm were subjected to the same steady laminar shear stress of 0.45 N/m 2 for 24 h, the average secretion rates of ET-1 and Ang II in 6 cm long increased l.7- and 0.5-fold ( n=26, P<0.00l) over 10 cm long, respectively. Over 10 h of exposure to 0.65 N/m 2, the average secretion rate of both ET-1 and Ang II by HGVEC monolayer of 6 cm in length exceeded 0.5-fold ( n=26, P<0.0001) over 10 cm in length. All these demonstrated that the close relationship may exist between length of endothelial cell monolayer and secretion of ET-1 and Ang II by endothelial cells, indicating the possible existence of the cumulative effect of the tensile stress in the upper endothelial cell membrane under the shear flow field.

Shear-Induced Changes in Endothelin-1 Secretion of Microvascular Endothelial Cells

Human glomerular microvascular endothelial cell (HGMEC) culture monolayers were maintained in static culture as controls or subjected to steady laminar shear stress of 0.5, 1.0, or 1.5 N/m2. Over 25 h of shear, the cumulative secretion of ET-1 was 705.4 pg/cm2 in the control, 820.7 pg/cm2 at 0.5 N/m2, 1063.2 pg/cm2 at 1.0 N/m2, and 644.7 pg/cm2 at 1.5 N/m2. The average ET-1 secretion rate for the HGMEC monolayers exposed to 0.5, 1.0, or 1.5 N/m2 of shear stress was 32.83 ± 2.01 pg/cm2·h, 42.53 ± 3.74 pg/cm2·h, and 25.79 ± 1.29 pg/cm2·h, respectively. The average ET-1 secretion rate of the static controls was 28.22 ± 3.11 pg/cm2·h. The results showed that low shear stress (0.5 N/m2) elevated and high shear stress (1.5 N/m2) suppressed secretion of ET-1, while an intermediate level of shear stress (1.0 N/m2) led to the maximum secretion of ET-1, and furthermore, ET-1 secretion varied with the duration of shear in a nonlinear fashion, and the logistic equations may be used to describe relationship between the duration of shear and the ET-1 secretion. The major secretion period of ET-1 occurred between 5.3 and 22.3 h, with the peak secretion rate occurring at approximately 10.7–15.2 h. Our findings showed also that the major secretion period and peak secretion rate of HGMECs varied with the level of shear stress. Thus, the response of cultured human microvascular endothelial cells to shear stress differed from that of large-vessel endothelial cell cultures in terms of ET-1 secretion. In addition to the level of shear stress, the duration of shear is an important determinant in ET-1 secretion. Consequently, the heterogeneity of vascular endothelial cells and the duration of shear should both be considered in future research on the secretion of vascular endothelial cell cultures.

Regulation of endothelin-1 production in cultured rat vascular smooth muscle cells.

Endothelin-1 (ET-1) is secreted from all rat vascular smooth muscle cells (VSMCs) examined, in addition to endothelial cells (ECs). An average secretion rate of ET-1 from rat VSMCs was determined to be 10% that excreted from ECs. We examined the effects of 22 substances on ET-1 secretion from VSMCs and compared them with those from ECs. Transforming growth factor-beta1 (TGF-beta), acidic and basic fibroblast growth factors, epidermal growth factor, angiotensin II, and adrenaline stimulated ET-1 secretion from VSMCs, whereas forskolin, thrombin, and platelet-derived growth factor-BB reduced it. Only TGF-beta and phorbol ester elicited consistent effects on ET-1 secretion from VSMCs and ECs. Regulation of ET-1 and adrenomedullin secretion from VSMCs was distinctly different. These data suggest that ET- 1 production in VSMCs is regulated by a mechanism separate from that in ECs and from adrenomedullin production in VSMCs. Chromatographic analysis showed immunoreactive ET-1 secreted from VSMCs was mainly composed of big ET- 1, whereas approximately 90% of that from ECs was ET-1. By TGF-beta stimulation of VSMCs, the ratio of big ET-1 to ET-1 was further increased. Because big ET-1 is converted into ET-1 only on the surface of the ECs in the culture system, big ET-1 secreted from the VSMCs may function as a mediator transmitting a signal from VSMCs to ECs in vivo.

Pharmacoydnamics of Beta-Blocker Modulation of Aqueous Humor Production

A conscious rabbit model with microdialysis sampling of endogenous aqueous humor ascorbate was developed in order to assess the pharmacodynamics of beta-blocker modulation of aqueous humor production. CMA/20 microdialysis probes were implanted in the anterior chamber of each eye of rabbits (n =6). After a 2 week recovery period, an i.v. bolus of14C-ascorbate (20 μCi) was administered. Blood samples and aqueous humor microdialysis probe effluent were collected and analysed for endogenous and14C-ascorbate to estimate the basal rate of ascorbate blood to aqueous humor secretion (Ro). After a 1 hr washout, each rabbit received a series of three doses of3H-propranolol (750–3000 μ g, 16.5 μCi mg−1) every 60 min into the lower cul-de-sac of each eye. Probe effluent was analysed for endogenous ascorbate and3H-propranolol; ascorbate and propranolol in the iris/ciliary body, vitreous and aqueous was determined at the end of the experiment. Nonlinear least-squares regression analysis of the concentration-time profiles for aqueous humor ascorbate was performed to estimate the change in aqueous humor flow. The average basal aqueous humor ascorbate secretion rate was ∼48 μg hr−1. Propranolol (1500 μg) produced significant increases in aqueous humor ascorbate, this observation is consistent with a reduction in aqueous humor production (∼47%). Analysis of intraocular tissue ascorbate indicated that propranolol inhibited ascorbate secretion at the 3000 μg dose, the highest dose examined in this study; this inhibition was not observed at the 750 μg or 1500 μg doses. Changes in aqueous humor production precipitated by the administration of beta-adrenergic antagonists can be estimated by measuring changes in aqueous humor ascorbate concentrations in the conscious rabbit. Microdialysis sampling of aqueous humor for endogenous ascorbate provides a relevant analytic tool to estimate modulatory effects of anti-glaucoma drugs on aqueous humor production.

Interactions between large and small bovine luteal cells in a sequential perifusion co-culture system.

The objectives of this experiment were to study large and small luteal cell interactions and examine the effect of arachidonic acid (AA) on progesterone production by separated bovine luteal cells. Corpora lutea collected from Holstein cows (n = 5) on d 12 of the estrous cycle were dispersed, and small (SLC) and large (LLC) luteal cells were separated by unit gravity sedimentation and flow cytometry. Cells were incubated at 37 degrees C in separate perifusion chambers with a modified Ham's F-12-HEPES medium and aerated with 95% O2:5% CO2. The flow rate of medium was 100 microL/min, and fractions were collected at 30-min intervals for 4 h. Luteal cells were arranged in tandem so that medium from the first cell type would pass through the chamber containing the second cell type. Luteal cells were arranged so that medium flowed from 1) SLC to SLC, 2) LLC to LLC, 3) SLC to LLC, 4) LLC to SLC, 5) SLC to LLC, 6) LLC to SLC; medium for arrangements 5 and 6 contained 10 microM AA. Cells in arrangements 5 and 6 were perifused for 30 min before AA was added. Progesterone was measured with an enzymeimmunoassay. The LLC to LLC arrangement had a greater (P < .05) average progesterone secretion rate than all other cell arrangements, and the SLC to SLC arrangement had the least progesterone secretion rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride inhibits arginine vasopressin-induced decrease in fetal lung liquid secretion

The effects of arginine vasopressin (AVP) and amiloride were studied in 16 unanesthetized fetal sheep (129-135 days of age) with indwelling catheters. Secretion was measured by an impermeant tracer technique. Control fetuses showed no change in lung liquid secretion over a 5-h period with an average secretion rate of 3.6 +/- 0.31 ml.kg-1.h-1. Infusion of AVP (23.4 +/- 2.23 mU.kg-1.min-1) in seven fetuses (134-140 days of age) produced significant decreases (from control) in the secretion rate over a 5-h period: the secretion rate decreased by 68% in the last hour. Amiloride placed in the lung liquid during infusion of AVP, but after AVP effects had taken place, reversed the AVP-induced decrease in lung liquid secretion. AVP in conjunction with other hormones that are elevated during the stress of birth (epinephrine and cortisol) may be important in the removal of lung fluid at birth.

Involvement of endothelium-derived relaxing factor in the pressure control of renin secretion from isolated perfused kidney.

Using isolated rat kidneys perfused at controlled pressure, we examined a potential role of endothelium-derived relaxing factor (EDRF) in the pressure control of renin secretion. We found that stimulation of EDRF release by acetylcholine (1 mumol/liter) increased mean perfusate flow rates from 15.0 +/- 0.5 to 18.0 +/- 0.5 ml/min per g and average renin secretion rates from 3.5 +/- 0.5 to 16.0 +/- 2.0 ng angiotensin I/h per min per g at a perfusion pressure of 100 mmHg (mean +/- SEM, n = 6). Those effects of acetylcholine were significantly reduced during inhibition of EDRF formation with NG-nitro-L-arginine (100 mumol/liter), but they were not affected with the cyclooxygenase inhibitor indomethacin (10 mumol/liter). Lowering of the perfusion pressure from 100 mmHg to 40 mmHg resulted in an increase of average renin secretion rates from 3.5 +/- 0.5 to 79 +/- 12 ng AngI/h per min per g under control conditions (n = 8), and to 171 +/- 20 ng AngI/h per min per g in the presence of 10 mumol/liter acetylcholine (n = 3). The rise of renin secretion in response to a reduction of the renal artery pressure was markedly attenuated with inhibitors of EDRF formation such as NG-nitro-L-arginine (100 mumol/liter) and related compounds. During inhibition of EDRF formation, addition of sodium nitroprusside (10 mumol/liter) increased mean perfusate flow rates from 12.0 +/- 0.5 to 23.0 +/- 2.0 ml/min per g and average renin secretion rates from 2.0 +/- 0.5 to 18.0 +/- 1.5 ng AngI/h per min per g at 100 mmHg (n = 5). Lowering of the perfusion pressure from 100 mmHg to 40 mmHg under those conditions increased average renin secretion rates to 220 +/- 14 ng AngI/h per min per g (n = 5). Taken together, our findings suggest that EDRF and related activators of soluble guanylate cyclase stimulate renin secretion from isolated kidneys, predominantly at lower perfusion pressure. Moreover, pressure control of renin secretion appears to require the tonical stimulation by intrarenal EDRF.

The effects of furosemide and bumetanide on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 61 +/- 3 days of gestation were supported in vitro for 3 h, and lung liquid secretion rates were measured by a dye dilution technique based on Blue Dextran 2000. Ten preparations that had received no treatment showed an average secretion rate of 1.12 +/- 0.28 mL.kg-1 body weight.h-1 during the first hour, and there were no significant changes over the following 2 h. In studies of 54 fetal lungs, furosemide, bumetanide, control ethanol carrier, or saline alone were placed in the supporting medium during the middle hour of the 3-h incubations (ABA design). Furosemide at 10(-3) M reduced secretion 83.4 +/- 16.8%; at 10(-4) and 10(-5) M it produced smaller reductions. Bumetanide at 10(-3) M usually produced reabsorption (129.9 +/- 23.0% reduction), at 10(-4) M it reduced secretion 30.9 +/- 11.8%, but at 10(-5) M it was ineffective. Control carrier and saline were without effect. The ability of the loop diuretics to produce reabsorption of fluid in some preparations suggests the unmasking of an active reabsorptive process. The results also suggest that lung liquid secretion in the fetal guinea pig, as in the sheep, is dependent on a Na+ and Cl- cotransport system.

Fluid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs (54-67 days of gestation) were supported in vitro, and lung liquid secretion rates were measured by a dye-dilution technique. The average secretion rate in the first hour was 2.14 +/- 0.08 (SE) mL x kg-1 body weight.h-1 (0.21 +/- 0.01 mL/h) (n = 450); this was comparable to intact preparations. In an independent study of 30 lungs, secretion continued unchanged for 3 h, with no significant change in fluid composition. Between 54 days and term, production appeared to fall in terms of millilitres per kilogram per hour. The following agents were placed in the supporting saline during the middle hour of incubation. (i) Sodium iodoacetate: at 10(-4) M this produced a fall in secretion (fall, succeeding hours; 55.4 +/- 23.0 and 64.9 +/- 17.5%; n = 6); at 10(-3) M it stopped secretion (fall, succeeding hours; 87.2 +/- 10.3 and 100%, n = 6). (ii) Ouabain: at 10(-5) M there was no change in production (n = 6); at 10(-4) M, four preparations were unaffected, two reduced production. (iii) Epinephrine (10(-7) M) produced a significant fall in production in all cases (n = 6); in four preparations secretion reduced (average fall, 64.4 +/- 10.8%); in two preparations there was reabsorption (average rate, -1.03 mL.kg-1.h-1). This extends the effect of epinephrine to the guinea pig, and suggests that the in vitro preparation is a useful model for studies of the fetal lung.

Estimation of pituitary secretion rate during the reproductive cycle of sheep

SUMMARYA technique has been developed for the measurement of pituitary hormone secretion rates in conscious sheep. The technique involves the continuous and simultaneous sampling of blood from the carotid artery and jugular vein and the measurement of cephalic blood flow by an indicator dilution technique. Veno-arterial differences in hormone concentrations multiplied by cephalic blood flow gave average secretion rates which were measured after single or repeated large doses of luteinizing hormone releasing hormone (LHRH) and thyrotrophin-releasing hormone (TRH) at various times in the reproductive cycle.

Adrenergic Receptors Regulationof Insulin Secretion due to 12-O-Tetradecanoyl phorbol-13-acetate

A possible role for the activation of protein kinase C and adenylate cyclase in the regulation of insulin secretion by monolayer islet B cells of neonatal rats was examined in a perifusion system. Stimulation of 60 min of 16.7 mM glucose secreted a first component of insulin for the first 10-min period. In the presence of 200 nM 12-O-tetradecanoyl phorbol-13-acetate(TPA), a protein kinase C activator, however, the same dose of glucose significantly increased cAMP accumulation in medium and dramatically enhanced a second component of insulin secretion in which the average secretion rate was 1.81 +/- 0.25 of insulin for the first 10-min period. In the presence of 200 nM 12-O-tetradecanoyl phorbol-13-acetate(TPA), a protein kinase C activator, however, the same dose of glucose significantly increased cAMP accumulation in medium and dramatically enhanced a second component of insulin secretion in which the average secretion rate was 1.81 +/- 0.25 of insulin for the first 10-min period. In the presence of 200 nM 12-O-tetradecanoyl phorbol-13-acetate(TPA), a protein kinase C activator, however, the same dose of glucose significantly increased cAMP accumulation in medium and dramatically enhanced a second component of insulin secretion in which the average secretion rate was 1.81 +/- 0.25 ng/ml/min for the 10-30 min (second phase IIa) and 3.39 +/- 0.18 ng/ml/min for the 30-60 min (second phase IIb) respectively. Addition of 10 microM epinephrine significantly decreased the medium cAMP content and abolished the sustained second-phase secretion, resulting in a monophasic response of approximately the same magnitude as evoked by 16.7 mM glucose alone. In contrast, joint addition of 10 microM epinephrine and 10 microM phentolamine, which activates adenylate cyclase, exerted a more pronounced increase in cAMP accumulation and the second component of insulin secretion than in the presence of TPA; the average secretion rates were 3.62 +/- 0.38 and 6.44 +/- 0.35 ng/ml/min respectively for the second phase IIa and IIb. However, no antagonistic effect of propranolol (10 microM) was found. Likewise, either phenylephrine (10 microM) or clonidine (1 microM) inhibited enhancement of insulin secretion that a combination of glucose with TPA caused, and alpha 1-adrenergic blockade of 10 microM prazosin was weak as compared to the blockade of yohimbine at the same concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Free amino acids in human palatine gland secretions

Human palatine gland saliva (HPS) was collected from young adult subjects (mean age 22 yr) of both sexes by gentle mechanical stimulation. The HPS contained 9–13 of the common amino acids within the range of 2—850 nmol/ml, but most samples had low or no concentrations of arginine, tryptophan and proline. Methionine and cysteine were not reliably detected. The molar ratios of most amino acids varied between subjects, but the ratio of leucine to isoleucine was remarkably constant (mean ± SD = 1.86 ± 0.28; n = 28). The minimum average secretion rate of HPS, using gentle mechanical stimulation, was estimated to be about 25 mg/min (wet weight).

Serum free fed batch production of IgM

Fed batch cultivation of a murine hybridoma secreting IgM in a serum free medium was successfully attempted. Cell growth and IgM productivity remained high for over a month, and compared well to a similar fed batch culture in medium supplemented with 10% fetal calf serum. The average specific secretion rates of antibody in both media were the same. Sufficient inoculum cell density was crucial to the establishment of a viable culture in serum free medium for the cell line, NS6.3, used.

Stimulation of Bile-Pancreatic Zinc, Protein and Carboxypeptidase Secretion in Response to Various Proteins in the Rat

The objective of this study was to determine the rate of bile-pancreatic secretion of zinc, protein and carboxypeptidase (CP) in response to three different dietary proteins, egg white (EW), soy protein isolate (SPI) and casein. The infusion of protein into the duodenum stimulated a significant increase in the secretion rate of zinc, protein and CP in bile-pancreatic juice. There was a high degree of correlation between the concentration of zinc and enzyme activity (CPA and CPB) in bilepancreatic juice indicating that zinc in bile-pancreatic juice is associated with CP activity. The average secretion rate of zinc, protein and CP during the 1-h period after infusion of protein was significantly greater after SPI infusion than after casein. The bile-pancreatic secretion rate of protein, zinc and CPB in response to EW infusion was consistently intermediate between SPI and casein and did not differ statistically from either. Only CPA secretion rate was significantly greater after EW than after casein. Differences in protein digestibility appear to account for the greater pancreatic response to SPI, and this factor may be important in understanding the effect of protein source on zinc bioavailability.