Epinephrine Stimulation Research Articles

Alveolar epithelial fluid clearance is mediated by endogenous catecholamines at birth in guinea pigs.

Transition from placental to pulmonary oxygenation at birth depends on a rapid removal of fetal lung fluid from the developing alveoli. Alveolar fluid clearance was examined in ventilated, anesthetized developing guinea pigs of the ages newborn, 2-d-old, 5-d-old, 30-d-old, and 60-d-old (adult). An isosmolar 5% albumin solution was instilled into the lungs of the guinea pigs; the guinea pigs were then studied for 1 h. Alveolar fluid clearance was measured from the increase in alveolar protein concentration as water was reabsorbed. Newborn guinea pigs had a very high alveolar fluid clearance rate that declined rapidly within the first 5 postnatal days towards adult levels. The high alveolar fluid clearance at birth was apparently mediated by the beta-adrenergic system as demonstrated by the elevated plasma epinephrine levels and the increased sensitivity to inhibition by the beta-adrenergic antagonist propranolol immediately after birth. Surprisingly, exogenous addition of epinephrine was not able to stimulate alveolar fluid clearance in the newborn lung, but exogenous epinephrine stimulation increased over time to adult levels. The elevated alveolar fluid clearance at birth was associated with a significantly greater amiloride sensitivity in the newborn guinea pig lung. Northern blot analysis of distal lung tissue as well as isolated alveolar epithelial type II cells showed and confirmed higher levels of the alpha-subunit of the epithelial sodium channel mRNA in the newborn lung that rapidly tapered off toward adult levels. In conclusion, these data demonstrate the importance of the beta-adrenergic system and amiloride-sensitive sodium transporting pathways for clearance of fetal lung fluid at birth.

Desensitization of β2-Adrenergic Receptors with Mutations of the Proposed G Protein-coupled Receptor Kinase Phosphorylation Sites

Tentative identification of the G protein-coupled receptor kinase 2 and 5 (GRK2 and GRK5) sites of phosphorylation of the beta2-adrenergic receptor (betaAR) was recently reported based on in vitro phosphorylation of recombinant receptor (Fredericks, Z. L., Pitcher, J. A., and Lefkowitz, R. J. (1996) J. Biol. Chem. 271, 13796-13803). Phosphorylated residues identified for GRK2 were threonine 384 and serines 396, 401, and 407. GRK5 phosphorylated these four residues as well as threonine 393 and serine 411. To determine if mutation of these sites altered desensitization, we have constructed betaARs in which the threonines and serines of the putative GRK2 and GRK5 sites were substituted with alanines. These constructs were further modified to eliminate the cAMP-dependent protein kinase (PKA) consensus sites. Mutants betaARs were transfected into HEK 293 cells, and standard kinetic parameters were measured following 10 microM epinephrine treatment of cells. The mutant and wild type (WT) receptors were all desensitized 89-94% after 5 min of 10 microM epinephrine stimulation and 96-98% after a 30-min pretreatment. There were no significant changes observed for any of the mutant betaARs relative to the WT in the extent of 10 microM epinephrine-induced internalization (77-82% after 30 min). Epinephrine treatment for 1 min induced a rapid increase in the phosphorylation of the GRK5 and PKA- mutant betaARs as well as the WT. We conclude that sites other than the GRK2 and GRK5 sites identified by in vitro phosphorylation are involved in mediating the major effects of the in vivo GRK-dependent desensitization of the betaAR.

Effects of age and food restriction on calcium signaling in parotid acinar cells of Fischer 344 rats.

In this study, we characterized alpha-adrenergic (alpha AR) and muscarinic induced [Ca2+]i changes in individual parotid acinar cells from male Fischer 344 rats (6-24 month-old) fed ad libitum (AL) or 60% ad libitum intake (FR). Cells were prepared by collagenase/hyaluronidase digestion. [Ca2+]i was measured by video image, fluorescent microscopy in single acinar cells loaded with FURA2. Neither age nor food restriction altered the peak [Ca2+]i achieved in response to carbachol (100 microM). Similar results were obtained for epinephrine (Epi = 100 microM) stimulation in 6- and 12-month-old animals. However, the peak [Ca2+]i response to Epi declined between 12 and 18 months in both dietary groups (e.g., AL: 12 months = 387 +/- 21 nM, 18 months = 253 +/- 10 nM; FR: 12 months = 430 +/- 22 nM, 18 months = 325 +/- 14 nM). The decline in response to Epi seen with age was less in FR than in AL animals at 18 months, but not at 24 months. In addition, db cAMP reduced the carbachol-stimulated [Ca2+]i response to levels comparable to those observed with epinephrine. The results support the view that calcium mobilization in parotid acinar cells from male Fischer 344 rats in response to alpha AR, but not to muscarinic, stimulation is impaired with age. Food restriction may slow down, but does not prevent, the functional decline. Furthermore, cAMP appears to modulate the muscarinic response.

Involvement of α2-adrenoceptors in mediating sympathetic excitation of injured dorsal root ganglion neurons in rats with spinal nerve ligation

The present study examined the effects of sympathetic stimulation on the activity of primary afferent neurons that had peripheral axons being injured previously by a spinal nerve ligation. About 22% of afferents with injured fibers that showed spontaneous discharge were excited by sympathetic stimulation or systemic injection of adrenaline. Most sympathetically-excited afferent neurons had axons that conducted in the A-fiber range. This sympathetically-evoked afferent excitation was not affected by cutting the spinal nerve at a place close to the dorsal root ganglion (DRG). Yohimbine, α 2-antagonist, suppressed sympathetically-evoked afferent excitation which was not affected by α 1-antagonist prazosin. Clonidine, α 2-agonist, exerted an excitatory effect, whereas α 1-agonist phenylephrine had no effect on the activity of afferents with injured fibers. No afferent fibers in control preparations responded to sympathetic stimulation. The results suggest that after a spinal nerve ligation, injured DRG neurons with fast-conducting fibers become sensitive to sympathetic activity via activation of α 2-adrenoceptors.

Granulocytopenia in Cohen syndrome.

Cohen syndrome is an autosomal recessive disorder characterized by mental retardation, microcephalia and typical craniofacial features, myopia and chorioretinal dystrophy. As some patients were reported to have leucopenia, we collected the haematological data of 26 Finnish Cohen patients. They all had experienced periods of isolated granulocytopenia from an early age. Granulocytopenia was mild to moderate, non-cyclic and never fatal. Most patients suffered from prolonged or repeated gingival or skin infections. We restudied 16 patients. Bone marrow examination revealed in all patients a normo- or hypercellular marrow, with a left-shifted granulopoiesis in 8/16 patients. The response to adrenaline stimulation was subnormal in 12/14 and to hydrocortisone in 8/16 patients, but administration of rhG-CSF caused granulocytosis in the three patients studied. No bone marrow malignancies were seen.

Evidence for the shuttle model for G Sα activation of adenylyl cyclase

Knowledge of the nature of the interaction between the stimulatory G protein (G s) and the adenylyl cyclase catalytic unit (C) is essential for interpreting the effects of G s mutations and expression levels on cellular response to a wide variety of hormones, drugs, and neurotransmitters. It has been proposed that ß-adrenergic receptor activation of adenylyl cyclase occurs either by a two-step “shuttle” mechanism where the receptor activates G s independently of cyclase followed by G sα activation of cyclase independent of the receptor; or the receptor activates a “precoupled” G s—C complex in a single step. Simulations of the two models revealed that the two forms of activation are distinguishable by the effect of G s levels on epinephrine-stimulated EC 50 values for cyclase activation; specifically, the shuttle model predicts an increased potency of epinephrine stimulation as levels of G sα increase. To address this problem, S49 cyc − cells were stably transfected with the gene for G sα long regulated by the MMTV LTR promoter, which allowed for an induction of G sα long expression levels over a 40-fold range by incubation of the cells for various times with 5 μM dexamethasone. Expression of G sα was strongly correlated to the appearance of GTP shifts in the competitive binding of epinephrine with [ 125I]iodocyanopindolol to the β-adrenergic receptors and epinephrine-stimulated adenylyl cyclase activity. Most importantly, high expression of G sα resulted in lower EC 50 values for epinephrine and prostaglandin E 1 stimulation of adenylyl cyclase activity. The decrease in EC 50 did not occur as a result of a change in β 2-adrenergic receptor, G iα, Gβα, or adenylyl cyclase levels. These novel findings demonstrate that a change in the level of a protein downstream of a plasma membrane receptor can influence hormone potency. We explain these results by using kinetic arguments to suggest that some fraction of hormone-activated adenylyl cyclase occurs via a shuttle mechanism, and not a purely precoupled mechanism.

DTTX30, a combined thromboxane receptor antagonist and thromboxane synthetase inhibitor, prevents coronary thrombosis in anesthetized dogs.

Combined thromboxane A2 receptor blockade and thromboxane synthetase inhibition facilitates local prostacyclin production at the site of platelet activation thereby providing a potent antithrombotic effect. The efficacy of DTTX30, a combined thromboxane A2 receptor blocker-thromboxane synthetase inhibitor, in inhibiting recurrent coronary thrombosis was evaluated in vivo using a canine model of unstable angina pectoris. Pentobarbital-anesthetized dogs (total of 25) were used in which acute damage of the proximal left circumflex coronary artery, together with mechanical stenosis, produced an occlusive thrombosis. When the platelet plug was removed by rubbing the vessel, the occlusion returned reproducibly for at least 2 hours in control studies. To evaluate the antithrombotic efficacy of DTTX30, a reproducible pattern of occlusive coronary thrombi was first established over a period of one hour. Thereafter, DTTX30 (0.12 mg/kg i.v. bolus plus 0.29 mg/kg/hr), acetylsalicylic acid (ASA, 5 mg/kg, i.v. bolus), vapiprost (1.0 mg/kg i.v. bolus plus 1.0 mg/kg/ hr), or vehicle was administered and observations continued for one additional hour. At the end of the one hour observation period, epinephrine (0.3 microgram/kg/min i.v.) was infused (with continued DTTX30, vapiprost or vehicle infusion) and observations were continued for an additional 30 min. DTTX30 eliminated the recurrent arterial thrombus formation in all dogs without significant systemic or left ventricular hemodynamic effects. Infusion of epinephrine to further provoke thrombus formation produced a significant enhancement of left ventricular pressure development (LV dP/dt) and arterial diastolic and systolic pressures but failed to initiate thrombus formation. DTTX30 inhibited fully collagen-induced platelet aggregation ex vivo and produced an approximate 3-fold prolongation of the sublingual bleeding time. ASA eliminated thrombus formation in 4 of 5 dogs, but the additional prothrombotic stimulus of epinephrine infusion produced recurrent thrombus formation in all dogs. Collagen-induced platelet aggregation ex vivo was inhibited by acetylsalicylic acid, but sublingual bleeding time was unaffected. Vapiprost inhibited arterial thrombus formation in all dogs, but thrombus formation returned with the addition of epinephrine. There was a tendency for prolonged bleeding times with vapiprost administration and collagen-induced platelet aggregation ex vivo was effectively inhibited. These studied indicate that the combined inhibition of the thromboxane A2 receptor together with inhibition of thromboxane synthetase provides superior antithrombotic activity in vivo than does thromboxane A2 receptor blockade alone (vapiprost) or inhibition of cyclooxygenase (ASA). Thrombus formation even with the additional stimulation of epinephrine was inhibited by DTTX30 but neither vapiprost nor ASA was effective in this setting.

Desensitization of human adipose tissue to adrenaline stimulation studied by microdialysis.

1. Desensitization of fat cell lipolysis to catecholamine exposure has been studied extensively in vitro but only to a small extent in human adipose tissue in vivo. 2. We measured interstitial glycerol concentrations by microdialysis in subcutaneous, abdominal adipose tissue in healthy humans during intravenous adrenaline infusion for three 35 min periods with 30 min breaks in between. Local blood flow, interstitial adrenaline and arterial glycerol concentrations were also measured. Adrenaline was infused to result in either a high, a low and a high arterial concentration (5.8, 3.1 and 5.6 nM, respectively) or a low, a high and a low concentration (2.5, 4.6 and 2.6 nM, respectively) in order to examine both desensitization and the dose dependency of adipose tissue lipolysis to adrenaline. 3. Adipose tissue lipolysis was calculated and was found to vary directly with arterial adrenaline concentration. However, lipolytic responses to adrenaline decreased markedly during repeated stimulation at a given concentration. Further, arterial glycerol and free fatty acid concentrations varied directly with arterial adrenaline concentrations and showed reduced responses upon repeated exposure. 4. The increase in adipose tissue blood flow in response to adrenaline was also reduced by prior adrenaline exposure, but no consistent desensitization could be demonstrated for whole-body energy expenditure, blood pressure and heart rate. 5. In the basal state, arterial plasma and interstitial adrenaline concentrations did not differ. During perturbations of arterial adrenaline concentrations, changes in interstitial concentrations were highly reproducible but smaller than changes in arterial concentrations. 6. In conclusion, in vivo adrenaline-mediated adipose tissue lipolysis and blood flow increments are desensitized by prior adrenaline exposure.

INTERSTITIAL ADENOSINE AND FUNCTION IN RAT HEART IN VIVO: EFFECTS OF ADRENALINE AND 8‐CYCLOPENTYL‐1,3‐DIMETHYLXANTHINE

1. Left ventricular interstitial adenosine and cardiac function were studied in open chest rats during adrenaline stimulation and P1-purinoceptor antagonism with 8-cyclopentyl-1,3-dimethylxanthine (8-CPT). 2. Cardiac microdialysate adenosine concentration was 0.10 +/- 0.01 mumol/L (n = 24) under basal conditions, giving an estimated interstitial adenosine concentration of 0.27 mumol/L. Stimulation with 3.2 and 8.0 micrograms/kg per min adrenaline increased the rate-pressure product (heart rate x systolic blood pressure) by 72 and 157%, respectively, and increased dialysate adenosine to 0.26 +/- 0.04 and 0.65 +/- 0.11 mumol/L (n = 12), respectively (interstitial concentrations of approximately 0.70 and 1.76 mumol/L). 3. Treatment with 60 micrograms/kg per min 8-CPT did not alter basal adenosine concentrations, but potentiated elevations in dialysate adenosine during infusion of 3.2 and 8.0 micrograms/kg per min adrenaline to 0.54 +/- 0.10 and 1.30 +/- 0.22 mumol/L, respectively (n = 12). Basal function and the response to 8.0 micrograms/kg per min adrenaline were unaltered by 8-CPT, whereas elevations in heart rate and rate-pressure product during stimulation with 3.2 micrograms/kg per min adrenaline were enhanced by 8-CPT (by up to 30%). 4. Studies in isolated hearts confirmed the inhibitory potency of 8-CPT at A1 vs A2 P1-purinoceptors (e.g. pK(B) of 7.7 +/- 0.2 and 6.4 +/- 0.1 for 5'-N-ethyl carboxamidoadenosine-mediated bradycardia and vasodilatation, respectively; n = 6). Studies in intact animals verified effective A1 blockade by 60 micrograms/kg per min 8-CPT, but also revealed some inhibition of A2-mediated responses. 5. In conclusion, the data show that cardiac interstitial adenosine levels exist within a physiologically active range in vivo and increase dose-dependently during graded adrenaline stimulation. Adenosine receptor antagonism enhances elevations in interstitial adenosine and modifies functional responses to moderate, but not high, doses of adrenaline. Whether 8-CPT-dependent elevations in interstitial adenosine are due to A1 inhibition vs inhibition of A2-mediated vasodilatation requires further investigation.

Identification of the molecular basis for phosphorylase hypersensitivity in cultured diabetic cardiomyocytes.

The focus of this study was to identify the molecular basis for the hypersensitive response of glycogen phosphorylase activation to epinephrine stimulation in alloxan diabetic-derived cardiomyocytes. Cyclic AMP levels were found not to be significantly different between normal and diabetic-derived cells while cGMP concentrations were found consistently to be significantly lower in diabetic-derived cells than in normal cells. Treatment with cyclic GMP analogues did not affect phosphorylase activation by epinephrine in normal cardiomyocytes whereas, IBMX, a nonselective phosphodiesterase inhibitor, had a significant effect on basal and agonist-stimulated phosphorylase activity in both normal and diabetic-derived cardiomyocytes. Differences in the time course for the rate of decay of phosphorylase a from agonist-stimulated to basal levels were observed between normal and diabetic cells. After 3 h in primary culture, phosphorylase a activity returned to basal levels more quickly in normal than in diabetic-derived cells while after 24 h in culture, the time for phosphorylase a decay was not significantly different between normal and diabetic myocytes and was longer than the 3 h response. After 3 h response. After 3 h in primary culture, no significant difference in phosphorylase kinase activity was observed between normal and diabetic-derived cells exposed to epinephrine whereas, after 24 h in culture, phosphorylase kinase activity was significantly decreased in diabetic cells under basal and agonist-stimulation conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluid and protein secretion from ferret submandibular and parotid glands in response to sympathetic nerve stimulation or administration of sympathomimetics.

Electrical stimulation of the sympathetic innervation evoked secretion of submandibular and parotid saliva. By changing the mode of stimulation from a continuous to an intermittent one the fluid response increased and glandular blood flow improved. The volumes from the submandibular glands were larger than those from the parotid glands and further, the protein concentration of submandibular saliva was higher than that of parotid saliva. Adrenaline, isoprenaline and phenylephrine evoked larger fluid responses from submandibular than from parotid glands. However, the fluid response was small compared to the parasympathetic one. Substance P-evoked saliva was used as carrier for protein released by sympathetic nerve stimulation or administration of adrenaline and isoprenaline. In vitro tissues of submandibular and parotid glands responded to adrenaline with a dose-dependent release of protein. Taken together, the analytical pharmacology performed in vivo and in vitro, and including the antagonists phentolamine, dihydroergotamine, propranolol and metoprolol, showed that in submandibular glands, alpha(alpha 1)adrenoceptors were predominantly involved in fluid secretion and beta(beta 1)-adrenoceptors predominantly involved in protein secretion. In parotid glands, fluid secretion seemed solely to depend on alpha(alpha 1)-adrenoceptors, while beta(beta 1)-adrenoceptors seemed almost solely involved in protein secretion.

Epinephrine test and plasma elastase as diagnostic tools in a patient with CD3+ large granular lymphocyte proliferation

Large granular lymphocytes (LGL) proliferation is characterized by expansion of cytotoxic lymphocytes and associated with neutropenia. In a case of CD3+ LGL-proliferation the epinephrine stimulation test (EST) induced a striking elevation of CD3+, CD8+, CD57+ LGL in peripheral blood from 2.7 x 10(9)/l to 20 x 10(9)/l and might be an additional diagnostic tool in patients with normal or low absolute numbers of circulating LGL. After treatment with steroids, plasma elastase--a marker of neutrophil destruction--decreased from 162 to 40 micrograms/l (normal < 47 micrograms/l) which correlated well with a simultaneous increase in peripheral neutrophil counts from 0.14 to 1.0 x 10(9)/l. This finding supports the hypothesis that neutropenia in CD3+ LGL proliferation is due to neutrophil destruction, possibly mediated by LGL.

α2 Adrenergic Receptor Subtypes Expressed in Chinese Hamster Ovary Cells Activate Differentially Mitogen-activated Protein Kinase by a p21ras Independent Pathway

Epinephrine stimulation of rat alpha 2D, alpha 2B, and alpha 2C adrenergic receptor subtypes, expressed stably in Chinese hamster ovary (CHO) cells, caused a rapid, transient activation of mitogen-activated protein kinase (MAPK), with subtype-specific different efficiencies. The order of activation was CHO-2B approximately CHO-2D much greater than CHO-2C. Pertussis toxin blocked the stimulation of MAPK enzymatic activity and the parallel MAPK phosphorylation, demonstrating that these responses are mediated by pertussis toxin-sensitive Gi proteins. Contrary to what has been reported for the alpha 2A subtype expressed in rat-1 fibroblasts, epinephrine did not cause any detectable activation of p21ras in the CHO transfectants. Furthermore, combined application of epinephrine and phorbol myristate acetate had a potent cooperative but not additive effect in clones CHO-2D and CHO-2B but not in CHO-2C, suggesting that protein kinase C is probably differently involved in the signaling by the three alpha 2 receptor subtypes. These results show that in CHO cells, the different alpha 2 adrenergic receptor subtypes utilize differential pathways to activate MAPK in a p21ras-independent way.

Enhanced Vascular Plasminogen Activator (t-PA) Release by Epinephrine in Aged Rats

Adrenergic stimulation induces an acute fibrinolytic response in the vascular wall and can play an important role in limiting thrombus growth. The incidence of thrombotic disease increases with age. As many adrenergic functions are affected by aging, the vascular response to adrenergic stimulation was studied in young (3 +/- 1 months) and aged (18 +/- 3 months) rats, using an experimental model of vascular perfusion. Five min epinephrine (EPI) infusion (0.15-25 microM) induced a dose-dependent increase in tissue-type plasminogen activator (t-PA) release and in perfusion pressure, in both young and aged rats. In the latter, however, the basal activity of t-PA was significantly higher than in young animals (0.22 +/- 0.02 vs 0.13 +/- 0.01 U/ml; means +/- SE; p < 0.01, n = 40) and EPI infusion induced a significantly higher increase in t-PA activity (0.78 +/- 0.06 vs 0.47 +/- 0.08 U/ml, p < 0.01, for 6.25 microM EPI). The response was characterized by a delayed onset. In contrast, the increase in the perfusion pressure by EPI was significantly lower in aged that in young rats, its basal levels being normal. To evaluate whether the increased vascular response of t-PA was peculiar for adrenergic stimulation, we infused platelet activating factor (PAF), an inducer of t-PA release, not related to catecholamines. PAF, during five-minute infusion induced a rapid and dose-dependent (100-1250 pM) increase in t-PA release, to the same extent in both young and aged rats. In conclusion, basal t-PA secretion was increased in aged rats probably as a response of vascular endothelium to chronic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of stimulation of phosphoinositide hydrolysis by alpha 1-adrenergic agonists in adult rat hearts.

The coupling of the pharmacologically defined alpha 1A- and alpha 1B-adrenoceptors to the hydrolysis of phospho[3H]inositides (PI) was investigated in ventricular myocytes freshly isolated from adult rat hearts. The alpha 1-adrenoceptor population in the heart was characterized by competitive binding experiments using [3H]prazosin and the alpha 1A-adrenoceptor-selective antagonist 5-methyl urapidil. It was heterogeneous with approximately 25% being pharmacologically of the alpha 1A-adrenoceptor subtype and 75% being of the alpha 1B-adrenoceptor subtype. Epinephrine, norepinephrine, or phenylephrine stimulated PI hydrolysis in the presence or absence of propranolol. The greatest stimulation (7-fold) was with epinephrine. The half-maximum effective concentrations for agonists were approximately 0.5-3.5 and 0.2 microM in the absence and presence of propranolol, respectively. The inhibition by 5-methyl urapidil of the stimulation of PI hydrolysis by a fixed concentration of epinephrine fitted a two-site competition curve. The distribution between high-affinity (25%) and low-affinity (75%) sites suggested that both the alpha 1A- and alpha 1B-adrenoceptors were coupled to PI hydrolysis in proportion to their relative abundance. Equally, the stimulation of PI hydrolysis by epinephrine in the presence of a fixed concentration of 5-methyl urapidil was biphasic. In addition, chloroethylclonidine, an irreversible inhibitor of the alpha 1B-adrenoceptor, inhibited the epinephrine stimulation of PI hydrolysis by 35%. We conclude that the pharmacologically defined alpha 1A- and alpha 1B-adrenoceptor subtypes are both coupled to PI hydrolysis in the ventricular myocyte.

Hormonal stimulation of hepatocyte metabolism in rainbow trout following an acute handling stress

Abstract In juvenile rainbow trout subjected to a 3-min handling stress, plasma cortisol and lactate concentrations showed an initial rapid rise, but returned to near-resting levels after 1 and 3 hr post-stress, respectively. Plasma glucose concentration showed a more gradual increase and was higher than the pre-stress level at 3 and 6 hr post-stress. No significant differences in hepatocyte glycogen content, total glucose production and alanine oxidation after stress were apparent from those of the pre-stress values; alanine gluconeogenesis increased at 3 hr post-stress, but not at any other time periods. Hepatocyte responsiveness to epinephrine (1 hr post-stress) and glucagon stimulation of total glucose production was abolished after stress, while hepatocyte responsiveness to insulin stimulation increased at 3 and 6 hr post-stress. Hepatocyte response to hormonal stimulation of alanine oxidation was also modified by acute stress, but there was no hormonal effect on alanine gluconeogenesis after stress. The results show that acute handling stress alters hepatocyte responsiveness to hormonal stimulation in rainbow trout. The changes are indicative of a control mechanism that may be partly responsible for conserving hepatic glycogen in stressed fish.

Postpartum hypophagia in primiparous sows: II. Effects of feeding level during gestation and exogenous insulin on lactation feed intake, glucose tolerance, and epinephrine-stimulated release of nonesterified fatty acids and glucose.

The objectives of this experiment were 1) to determine whether allowing sows ad libitum access to feed from d 60 of gestation affects glucose tolerance and 2) to determine whether exogenous insulin increases feed intake by preventing mobilization of nonesterified fatty acids (NEFA). Sixty crossbred sows were assigned to one of two feeding regimens during gestation, either a standard level of feed (SL; 1.85 kg/d) or allowed ad libitum access to feed (AL). Sows also received an injection of either .75 IU of insulin/kg BW or saline daily during the first 7 d of lactation. Exogenous insulin increased ADFI at d 7 of lactation (P = .07) and increased total feed intake at d 7 and 14 of lactation (P = .09). Total feed intake during d 0 to 21 was not affected by insulin treatment. Compared with the SL sows, the AL sows were less tolerant of glucose infusion (1 g of glucose/kg BW, i.v.) on d 1 of lactation (P < .01). Baseline and peak concentrations of insulin were not affected by feeding level during gestation (P = .4). Baseline and peak concentrations of NEFA were greater in AL sows than in SL sows (P < .001) and were not affected by insulin treatment (P = .39). Release of NEFA after epinephrine stimulation was greater in AL sows than in SL sows (P < .05). The data indicate that the reduced feed intake during lactation exhibited by sows that are overfed during gestation may be caused by insulin resistance. Exogenous insulin seems to increase feed intake by reducing plasma glucose rather than be affecting plasma NEFA.

Continuing development of acid pump inhibitors: site of action of pantoprazole.

Both receptor antagonists and acid pump inhibitors are clinically useful suppressants of acid secretion. The latter class of drugs, the substituted benzimidazoles, inhibit acid secretion more effectively and, therefore, provide superior symptom relief and healing in all acid-related diseases. The H2-receptor antagonists competitively block the action of histamine on the H2-receptors of parietal cells. This histamine is released from enterochromaffin-like cells (ECL cells) due to gastrin, acetylcholine or epinephrine stimulation. In addition, parietal cells have M3-receptors which can function independently of H2-receptors. Hence, there is no single common pathway for parietal cell stimulation. Stimulation of acid secretion by parietal cells requires activation of the acid pump, the gastric H+,K(+)-ATPase. The target site for the benzimidazoles is the activated gastric H+,K(+)-ATPase, and, in particular, the cysteines of the pump that are exposed to the acid space of the secretory canaliculus of the parietal cells. Pantoprazole in its protonated form selectively reacts with cysteines present in both the fifth and sixth membrane segments of the ATPase, explaining its mechanism of inhibiting proton transport by this enzyme.

Adrenaline stimulated cyclic adenosine monophosphate response in leucocytes is reduced after prolonged physical activity combined with sleep and energy deprivation.

The mechanism for adrenergic desensitisation during physical stress was studied by measuring [125I] cyanopindolol ([125I]CYP) binding sites and the adrenaline stimulated cyclic adenosine monophosphate (cAMP) responses in peripheral blood leucocytes from ten male cadets during a 5-day military training course. The cadets had physical activities around the clock corresponding to a daily energy consumption of about 40,000 kJ but with an intake of only 2,000 kJ, and only 1-3 h of sleep in the 5 days. During the course, the maximal cAMP response to adrenaline stimulation was reduced to about 45% in granulocytes and to 52% in mononuclear cells, and the half maximal response was obtained only at 5-10 times higher adrenaline concentrations than in the control experiment. The binding sites for [125I]-CYP in mononuclear cells increased during the course. However, [125I]-CYP measured not only surface receptors but also intracellular receptors and might even have represented other binding sites. In conclusion, this study showed that decreased cAMP response to adrenergic stimulation would seem to be one of the mechanisms behind adrenergic desensitisation during stress.

Segmental differences in short-chain fatty acid transport in rabbit colon: effect of pH and Na.

Short-chain fatty acids (SCFAs) are the predominant luminal anion in the mammalian colon. Although they are rapidly absorbed in vivo, little is known about the mechanisms of transepithelial transport in vitro. Previous studies have suggested that SCFA transport may be linked to Na absorption or an anion exchange mechanism. We compared the transport of propionate under short-circuit conditions in rabbit proximal and distal colon to determine whether there were segmental differences, how SCFAs may be linked to either Na absorption or anion transport, and whether SCFAs, as weak electrolytes, may be affected by transepithelial pH gradients. In distal colon, propionate transport was not significantly altered by stimulation of electrogenic Na absorption, epinephrine or Cl removal. However, a modest transepithelial pH gradient (luminal 6.8/serosal 7.4) stimulated propionate absorption. In proximal colon, propionate transport was significantly altered by maneuvers that either stimulated (lowered [Na] in the bathing media) or inhibited (theophylline) apical Na-H exchange. Neither Cl removal, nor the anion exchange inhibitor DIDS, nor a transepithelial bicarbonate gradient, altered propionate transport. A transepithelial pH gradient inhibited propionate secretion, but not in a manner entirely consistent with the effect of pH on the distribution of a weak electrolyte. These results suggest that there is significant segmental heterogeneity in colonic SCFA transport; that transepithelial propionate fluxes are altered by changes in pH or electroneutral Na absorption (Na-H exchange), but not by chloride removal, bicarbonate gradients or electrogenic Na absorption. Regulation of SCFA transport may be an important factor in the physiology of colonic fluid balance.