Drug-Induced Changes in Blood Pressure Lead to Changes in Extracellular Concentrations of Epinephrine, Dihydroxyphenylacetic Acid, and 5-Hydroxyindoleacetic Acid in the Rostral Ventrolateral Medulla of the Rat

Neurochemical changes in the extracellular fluid of the rostral ventrolateral medulla (RVLM) were produced by changes in arterial blood pressure. Blood pressure was raised or lowered with systemic infusions of phenylephrine or nitroprusside and neurochemicals were recovered from RVLM by in vivo microdialysis. A dialysis probe 300 microns in diameter and 500 microns in length was stereotaxically implanted in the RVLM of the urethane-anesthetized rat. Sterile physiological Ringer's solution was perfused at a rate of 1.5 microliter/min. The perfusate was collected under ice-cold conditions every 15 min for the assay of epinephrine, dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA), ascorbic acid, and uric acid. After stable baseline neurochemical concentrations were achieved, animals were infused with phenylephrine or nitroprusside intravenously to raise or lower the blood pressure. Increasing blood pressure 50 mm Hg above the baseline value by phenylephrine led to a significant reduction in heart rate and a reduction in extracellular epinephrine and DOPAC concentrations. The 5-HIAA concentration was increased during the hypertensive drug infusion. There were no changes in the concentrations of ascorbic acid or uric acid. Hypotension produced by nitroprusside (-20 mm Hg) led to neurochemical changes which were the reciprocal of those seen during hypertension. During hypotension, heart rate increased as did the extracellular fluid epinephrine concentration. The 5-HIAA concentration fell with hypotension and remained depressed following the nitroprusside infusion. Ascorbic acid and uric acid concentrations did not change during hypotension but ascorbic acid did increase after the nitroprusside infusion stopped. These data provide direct evidence that epinephrine release in RVLM is linked to changes in systemic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Central effects of DN1417, a novel TRH analog, on plasma glucose and catecholamines in conscious rats

Intracerebroventricular (icv) injection of DN1417 (0.3, 3 and 30 nmol/rat), a TRH analog, resulted in a dose-related increase in plasma glucose, epinephrine and norepinephrine levels in conscious male rats. The effects of DN1417 were more potent and longer-lasting than those of TRH on a molar basis. Intravenous injection of DN1417 (30 nmol/rat) did not change plasma glucose, epinephrine and norepinephrine levels. Pretreatment with hexamethonium (1.5 mg/100 g body wt, iv, 2 min before) inhibited plasma glucose, epinephrine and norepinephrine responses to DN1417 (3 nmol/rat, icv). DN1417 did not change plasma glucose, epinephrine and norepinephrine levels in rats after total adrenalectomy. In the animals pretreated with cysteamine (30 mg/100 g body wt, sc, 4 h before), basal plasma glucose, epinephrine and norepinephrine levels were raised, and exaggerated responses of plasma glucose, epinephrine and norepinephrine to DN1417 (3 nmol/rat, icv) were obtained. These results indicate that DN1417 has a potent and long-lasting effect in the central nervous system in stimulating the secretion of catecholamines through the autonomic nervous system, which is associated with an elevation of plasma glucose and that endogenous hypothalamic somatostatin may inhibit the action of DN1417.     

EFFECTS OF PRE- OR POSTNATAL DEXAMETHASONE, ADRENOCORTICOTROPHIC HORMONE AND ENVIRONMENTAL STRESS ON PHENYLETHANOLAMINE N-METHYLTRANSFERASE ACTIVITY AND CATECHOLAMINES IN SYMPATHETIC GANGLIA OF NEONATAL RATS

Abstract— Injections of dexamethasone (0.1 mg/kg/day, s.c.) on the first 2–3 days of life increased the phenylethanolamine- N -methyltransferase (PNMT) activity and epinephrine content of the superior cervical ganglion (SCG) and stellate ganglion of neonatal rats; the dopamine content was unaltered while norepinephrine was slightly reduced in these ganglia. Dexamethasone did not alter the PNMT activity or epinephrine content of the salivary glands or heart. The PNMT activity and epinephrine content of the SCG remained elevated for 10–14 days. Pretreatment with 6-hydroxydopamine did not alter the dexamethasone effects.
Injections of adrenocorticotrophic hormone (ACTH) (25 munits/rat twice a day) or exposure to a cold stress (4°C, 3 times a day) on the first 2–3 days of life, elevated the plasma concentration of corticosterone, and also increased the PNMT activity and epinephrine content in SCG of neonatal rats. Injecting pregnant rats with dexamethasone or ACTH, or exposing them to cold or restraint stress on the last 3 days of gestation increased the PNMT activity and epinephrine content in the SCG of their pups. These results indicate that the actions of dexamethasone on neonatal sympathetic ganglia may be mimicked by increasing the plasma concentration of endogenous adrenocortical steroids.     

Mechanism of stimulation of DNA synthesis induced by epinephrine in primary culture of adult rat hepatocytes

Addition of epinephrine to primary cultured adult rat hepatocytes stimulated their DNA synthesis dose-dependently, especially in presence of insulin and epidermal growth factor. This effect of epinephrine was strongly inhibited by an alpha 1-antagonist, prazosin, but not by a beta-antagonist, propranolol, and was also slightly inhibited by an alpha 2-antagonist, yohinbin. These results indicate that the stimulation of DNA synthesis of hepatocytes by epinephrine is mediated predominantly by an alpha 1-action. 12-o-Tetradecanoylphorbol-13-acetate (TPA) or Ca2+-ionophore A-23187 stimulated DNA synthesis of Swiss 3T3 cells, but did not induce DNA synthesis of hepatocytes either singly or in combination. The fact that pretreatment of hepatocytes with TPA caused down-regulation of the stimulatory effect of epinephrine on DNA synthesis of hepatocytes within 15 min suggested that the effect of epinephrine on hepatocytes is mediated by its alpha 1 receptor and that TPA activated protein kinase c in the hepatocytes. Addition of dibutyryl cGMP did not induce DNA synthesis of hepatocytes. Therefore, the alpha 1-action of epinephrine that induce stimulation of DNA synthesis of primary cultured adult rat hepatocytes was apparently not mediated by either activation of phospholipid-dependent protein kinase or Ca2+ mobilization. Possible alternative mechanism was discussed.     

Alanine and glutamine synthesis and release from skeletal muscle. IV. beta-Adrenergic inhibition of amino acid release.

Alanine and glutamine formation and release were studied using the intact epitrochlaris preparation of rat skeletal muscle. Epinephrine reduced the release of alanine and glutamine in a concentration-dependent manner. Measurable inhibition was observed at 10(-9) M epinephrine, and maximal inhibition was obtained at 10(-5) M. Norepinephrine also reduced alanine and glutamine formation and release but the concentration required for maximal inhibition was approximately 100-fold greater than for epinephrine. Isoproterenol (beta agonist), but not phenylephrine (alpha agonist), reproduced the effects of epinephrine, and propranolol (beta antagonist), but not phentolamine (alpha antagonist), blocked the effect of the catecholamine. N6,O2'-Dibutyryl adenosine 3':5'-monophosphate reproduced the effects of epinephrine and theophylline potentiated the effect of submaximal concentrations of the hormone. Glucagon and prostaglandin E2 had no observable effect on amino acid release. Insulin did not modify the inhibition of alanine and glutamine release produced by epinephrine. Alanine and glutamine formation from added precursor amino acids was unaffected by epinephrine or cyclic adenosine 3':5'-monophosphate. Epinephrine reduced alanine formation in muscles obtained from diabetic rats or animals treated with thyroxine or cortisone. These findings indicate that physiological levels of catecholamines reduce alanine and glutamine formation and release from skeletal muscle. This effect is mediated by a beta-adrenergic receptor and the adenylate cyclase system and can be accounted for by an inhibition of muscle protein degradation.     

Adrenaline activates oxidative phosphorylation of rat liver mitochondria through alpha 1-receptors

We studied the effects and mode of action of epinephrine on the oxidative phosphorylation of rat liver mitochondria. With either succinate or beta-hydroxybutyrate as substrate, i.v. injection of 1.5 microgram/100 g epinephrine increased the respiratory rates by 30-40% in state 3 (with ADP), and by 20-30% in state 4 (after ADP phosphorylation), so that the respiratory control ratio (state 3/state 4) changed little. The respiratory stimulation by epinephrine was maximal 20 minutes after its injection. The action of epinephrine on mitochondria was blocked by pretreatment of the animals with the alpha 1-antagonist prazosin but not by treatment with the beta-antagonist propranolol. I. v. injection of 10 micrograms/100 g phenylephrine evoked the same mitochondrial response as epinephrine. I. v. administration of 50 micrograms/100 g dibutyryl cyclic AMP enhanced glycaemia but did not affect mitochondrial respiration. Epinephrine therefore has an alpha 1-type of action on mitochondrial oxidative phosphorylation.     

Comparison of the effects of CRF and stress on levels of pituitary cyclic AMP and plasma ACTH in vivo

We have previously reported that acute stress increases levels of rat pituitary cyclic AMP in vivo. The present study was conducted to test the hypothesis that stress-induced increases in pituitary cyclic AMP in vivo were mediated via CRF. We compared the effects of various stressors with the effects of CRF or epinephrine administration on pituitary cyclic AMP and plasma ACTH responses in vivo. Stressors, epinephrine or CRF increased levels of pituitary cyclic AMP. Pituitary cyclic AMP response to either immobilization or CRF was much greater at light onset than at lights off in rats maintained on at 12 hr light: 12 hr dark lighting regimen. In rats with pituitary stalk transections, footshock did not increase levels of pituitary cyclic AMP, suggesting that some factor of central origin was required for this stress response. Exogenous CRF administration did increase levels of pituitary cyclic AMP in stalk-transected rats, while epinephrine increased levels in sham-operated but not in stalk-transected rats. Antisera to CRF markedly decreased pituitary cyclic AMP response to exogenous CRF administered 6 min following antisera and partially attenuated pituitary cyclic AMP response to forced running. Taken as a whole these data support a major role for CRF in the pituitary cyclic AMP response to stress.     

Epinephrine inhibits insulin-stimulated muscle glucose transport.

We recently demonstrated that epinephrine could inhibit the activation by insulin of insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol 3-kinase (PI3-kinase) in skeletal muscle (Hunt DG, Zhenping D, and Ivy JL. J Appl Physiol 92: 1285-1292, 2002). Activation of PI3-kinase is recognized as an essential step in the activation of muscle glucose transport by insulin. We therefore investigated the effect of epinephrine on insulin-stimulated glucose transport in both fast-twitch (epitrochlearis) and slow-twitch (soleus) muscle of the rat by using an isolated muscle preparation. Glucose transport was significantly increased in the epitrochlearis and soleus when incubated in 50 and 100 microU/ml insulin, respectively. Activation of glucose transport by 50 microU/ml insulin was inhibited by 24 nM epinephrine in both muscle types. This inhibition of glucose transport by epinephrine was accompanied by suppression of IRS-1-associated PI3-kinase activation. However, when muscles were incubated in 100 microU/ml insulin, 24 nM epinephrine was unable to inhibit IRS-1-associated PI3-kinase activation or glucose transport. Even when epinephrine concentration was increased to 500 nM, no attenuating effect was observed on glucose transport. Results of this study indicate that epinephrine is capable of inhibiting glucose transport activated by a moderate, but not a high, physiological insulin concentration. The inhibition of glucose transport by epinephrine appears to involve the inhibition of IRS-1-associated PI3-kinase activation.     

Effects of hypoxia on vertebrate blood vessels

Hypoxia contracts mammalian respiratory vessels and increases vascular resistance in respiratory tissues of many vertebrates. In systemic vessels these responses vary, hypoxia relaxes mammalian vessels and contracts systemic arteries from cyclostomes. It has been proposed that hypoxic vasoconstriction in cyclostome systemic arteries is the antecedent to mammalian hypoxic pulmonary vasoconstriction, however, phylogenetic characterization of hypoxic responses is lacking. In this study, we characterized the hypoxic response of isolated systemic and respiratory vessels from a variety of vertebrates using standard myography. Pre-gill/respiratory (ventral aorta, afferent branchial artery, pulmonary artery) and post-gill/systemic (dorsal and thoracic aortas, efferent branchial artery) from lamprey (Petromyzon marinus), sandbar shark (Carcharhinus plumbeus), yellowfin tuna (Thunnus albacares), American bullfrog (Rana catesbeiana), American alligator (Alligator mississippiensis), Pekin duck (Anas platyrhynchos domesticus), chicken (Gallus domesticus) and rat (Rattus norvegicus) were exposed to hypoxia at rest or during pre-stimulation (elevated extracellular potassium, epinephrine or norepinephrine). Hypoxia produced a relaxation or transient contraction followed by relaxation in all pre-gill vessels, except for contraction in lamprey, and vasoconstriction or tri-phasic constriction-dilation-constriction in all pulmonary vessels. Hypoxia contracted systemic vessels from all animals except shark and rat and in pre-contracted rat aortas it produced a transient contraction followed by relaxation. These results show that while the classic "systemic hypoxic vasodilation and pulmonary hypoxic vasoconstriction" may occur in the microcirculation, the hypoxic response of the vertebrate macrocirculation is quite variable. These findings also suggest that hypoxic vasoconstriction is a phylogenetically ancient response.     

Physiological mechanisms contributing to increased interleukin-1 secretion

Interleukin-1 (IL-1) is a monocyte-derived polypeptide that mediates many host defense adaptations to environmental and infectious stresses. This investigation was intended to characterize further IL-1 activity found in human plasma following exercise (3) and to identify physiological initiators of IL-1 secretion. IL-1 activity was measured by the ability of plasma fractions to stimulate lymphocyte proliferation. This activity appeared in plasma several hours after exercise on a cycle ergometer (1 h at 60% of aerobic capacity, n = 8 subjects) and was neutralized with a specific antiserum to human IL-1. The hypothesis that IL-1 release from monocytes was initiated by phagocytosis of material from cells damaged by exercise was tested. The increase in IL-1 activity did not correlate significantly (r = 0.55) with creatine kinase activity, a marker for release of intracellular proteins into the circulation, and IL-1 secretion by monocytes was not stimulated by incubation with red blood cell lysates in vitro. Thus the stimulus for IL-1 secretion did not appear to be related to a scavenging function of monocytes. The possibility that IL-1 secretion may be mediated by stress hormones associated with exercise was examined. IL-1 secretion by monocytes was increased up to 48 +/- 18% (P less than 0.01) by addition of physiological concentrations of epinephrine in vitro. Low concentrations of hydrocortisone (1 ng/ml) also augmented IL-1 secretion by 58 +/- 20%. Higher concentrations in the physiological range had no effect, and combinations of epinephrine and hydrocortisone suppressed IL-1 secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Depletion of epinephrine in rat hypothalamus by a dopamine agonist,pergolide

The i.p. injection of pergolide mesylate, a dopamine agonist, at doses of 0.3–0.6 mg/kg led to a decrease in epinephrine concentration in rat hypothalamus. After a 0.6 mg/kg dose of pergolide mesylate, epinephrine concentration in hypothalamus decreased within 2 hr, reached a minimum concentration at about 8 hrs, and then returned toward control values. Norepinephrine N-methyltransferase activity was not decreased after pergolide injection in vivo nor was it inhibited by pergolide added in vitro at concentrations as high as 10^–3 M. Higher i.p. doses of less potent dopamine agonists, apomorphine (10 mg/kg) and lergotrile (3 mg/kg), also decreased epinephrine concentration in hypothalamus. The pergolideinduced decrease in hypothalamic epinephrine concentration was prevented by pretreatment with haloperidol or spiperone., antagonists of dopamine receptors. Activation of dopamine receptors appears to result in a decrease in epinephrine concentration in rat brain, possibly due to, enhanced release of epinephrine.     

Effect of Prostaglandins on Hepatic Cyclic Nucleotide Concentration,Carbohydrate and Lipid Metabolism

The effects of exogenous prostaglandin E₁ (PGE₁) or prostaglandin E₂ (PGE₂) were studied in the isolated perfused rat liver and in the intact canine liver in order to determine the possible physiological role of prostaglandins on hepatic carbohydrate and lipid metabolism. The data indicate that PGE₁ and PGE₂ did not stimulate cyclic AMP (cAMP) and cyclic GMP (cGMP) concentrations in intact dog liver and PGE₁ failed to stimulate cAMP or cGMP in fed or fasted perfused rat liver. PGE₁ did not promote hyperglycemia, glycogenolysis, lipolysis, or prevent epinephrine-induced hyperglycemia in the isolated perfused rat liver. Other known glycogenolytic agents including glucagon and epinephrine increased cAMP and glycogenolysis in the same perfusion system. This study does not support a physiologic role for PGE₁ on hepatic glycogenolysis or lipolysis. If PGE₁ subsequently is found to influence other metabolic parameters such as lipogenesis, gluconeogenesis, ureogenesis or amino acid transport in isolated perfused liver, such alterations would probably occur independent of changes in cyclic nucleotide activity.     

Functional Significance of Vertebrate lntegumental Pigmentation

SYNOPSIS Pigment cells and their synthesized products play animportant functional role in the skin of most all vertebrates,from cyclostomes to man Both dermal and epidermal pigment cellsfunction in physiological and morphological color changes andprovide the cellular basis for vertebrate pigment patterns anddifferences in racial coloration Epidermal melanization is ofparticular importance in homeotherms in the regulation of seasonalpelage and feather color changes In addition, melanin pigmentation may have a photoprotective function, influence vitaminD synthesis in the skin protect or influence neivous systemfunction, affect heat absorption and consenition, play an intracellularhomeostatic role in the skin and (by leucocytic transport) elsewherein the bodv and provide a structural element to the integumentA consideration of the comparative evolution of the vertebratelntegumental pigmental) system may be necessary for a pioperinterpretation of the supposed roles ot melanin and other lntegumentalpigments     

Immunohistochemical localization of epidermal growth factor in rat and man

Epidermal growth factor (EGF) is a peptide which stimulates cell mitotic activity and differentiation, has a cytoprotective effect on the gastroduodenal mucosa, and inhibits gastric acid secretion. The immunohistochemical localization of EGF in the Brunner's glands and the submandibular glands is well documented. The localization of EGF in other tissues is still unclarified. In the present study, the immunohistochemical localization of EGF in tissues from rat, man and a 20 week human fetus were investigated. In man and rat, immunoreaction was found in the submandibular glands, the serous glands of the nasal cavity, Brunner's glands of the duodenum, the Paneth cells of the small intestine, and the tubular cells of the kidney. In the fetus EGF was found in the kidney and in the intestinal Paneth cells. Antisera raised against rat submandibular EGF did not recognize EGF in human tissues, whereas antisera against human urinary EGF worked in rat as well as man. EGF was found only in cells with an exocrine function.     

Thyroid hormones in cyclostomes and fish and their role in regulation of intermediary metabolism

1. Experimental data obtained in cyclostomes and fish concerning the plasma levels of thyroxine and tri-iodothyronine as well as their influence on intermediary metabolism of lipids, carbohydrates, and proteins are reviewed. 2. The information dealing with the physiological role of thyroid hormones in regulation of metabolic processes seems to be scarce in cyclostomes and controversial in fishes. 3. Nevertheless, the data covered in the review support the generalization that thyroid hormones, probably along with some other hormones, exert a regulatory action on the metabolic processes already on the lower stage of the evolution of poikilothermic vertebrates.     

Effect of homocysteine, cysteine, and their derivatives on the platelet link of hemostasis system

The influence of homocysteine, homocysteine thiolactone, cysteine and their derivatives on activation and aggregation of human platelets was investigated using the model systems in vitro. It was established that homocysteine and cysteine increased platelet aggregation induced by ADP, epinephrine, or collagen. Their action began in a range of concentrations such as their physiological blood levels (10 microM) and was increasing with the rise of their concentrations. Cysteine increased ADP-induced platelet aggregation, hardly any affect on epinephrine-induced platelet aggregation and depressed collagen-induced platelet aggregation in the highest concentration (1000 microM). Their disulfides and thioethers did not influence platelet aggregation.     

Suppression of triglyceride secretion by epinephrine in isolated rat hepatocytes

The effect of epinephrine on triglyceride synthesis and secretion was examined in isolated rat hepatocytes. Epinephrine potently inhibited triglyceride secretion but did not affect cellular triglyceride content or the rate of incorporation of radiolabelled glycerol into cell triglyceride. The inhibitory effect of epinephrine was abolished by inclusion of the alpha-adrenergic antagonist prazosin but not the beta-antagonist propranolol.     

Cardiac adrenoceptors at low temperature: what is the experimental evidence for the adrenoceptor interconversion hypothesis?

Isolated heart preparations of frog and rat were used to test the validity of the adrenoceptor interconversion hypothesis. This hypothesis claims that low temperature converts the inotropic beta-adrenoceptors in isolated frog and rat heart to alpha-adrenoceptors. The present results do not support the adrenoceptor interconversion hypothesis. In the isolated frog ventricle, lowering the temperature from 24 C to 14 C did not significantly alter the inotropic potency of the sympathomimetic drugs isoprenaline, epinephrine, and phenylephrine and did not reduce the potency of the beta-adrenoceptor blocking drug propranolol as an epinephrine antagonist. In the isolated rat left atrium, lowering the temperature from 31 C to 17-19 C did not significantly change the inotropic potency of isoprenaline, norepinephrine and phenylephrine, did not diminish the potency of propranolol, and did not increase the potency of the alpha-adrenoceptor blocking drug phentolamine.--Benfey, B. G. Cardiac adrenoceptors at low temperature; what is the experimental evidence for the adrenoceptor interconversion hypothesis?     

Free and conjugated plasma catecholamines, DOPA and 3-O-methyldopa in humans and in various animal species

The aim of the present study was to determine the extent to which plasma catecholamines are conjugated in different animals compared to man and how widespread is the presence of dihydroxyphenylalanine (DOPA) and 3-methoxy-4-hydroxyphenylalanine (3-OMD) in plasma among the different animal species. Free and conjugated norepinephrine, epinephrine, and dopamine were measured in plasma in humans and in several animal species (dog, rat, Gunn rat, cat, rabbit, guinea pig, African green monkey, young pig, calf, and one American black bear) using HPLC with electrochemical detection. The same technique was used to measure free and conjugated DOPA and 3-OMD in plasma of man, dog, rat, Gunn rat, calf, and American black bear. Human plasma contains the highest concentration of total (free and conjugated) catecholamines (46.1 pmole/ml), while low concentrations (below 15 pmole/ml) were observed in unstressed rats, calves, cats, and young pigs. In man, 95.3% of total plasma catecholamines were conjugated. The extent to which plasma catecholamines were conjugated varied greatly between animal species. The conjugated fraction expressed as percentages of the total catecholamines is lowest in the young pig (4.7%) and highest in the bear (100%). Conjugated dopamine was present in the plasma of all species, varying between 3% of the total catecholamine pool in young pig to 90% in dog. Conjugated norepinephrine was also present in plasma of all species except in unstressed rats with access to food. Conjugated epinephrine was detected only in cat and rat. Free DOPA and 3-OMD were present in plasma of all tested species with especially high levels of 3-OMD being present in dog. Conjugated DOPA and 3-OMD were not consistently found in any species. Our results indicate that man, dog, bear, and African green monkey are particularly good catecholamine conjugators and that young pig, guinea pig, rabbit, and calf are poor conjugators.     

Brain insulin receptors in the evolution of vertebrates

Studies have been made on 125I-insulin binding for brain membranes from cyclostomes (the lamprey Lampetra fluviatilis), fish (pink salmon Oncorhynchus gorbuscha) and mammals (rats). The species studied differed by the level of binding (the highest in the rat and the lowest in the lamprey), which was due mainly to differences in the number of binding sites per membrane protein. Qualitative properties of the receptors in the species studied were found to be very similar. All three types of the receptors were capable of differentiating between the insulins from pig, pink salmon and lamprey, all of them binding porcine insulin more readily than the salmon one and the latter better than the insulin from the lamprey. It means that these insulins reacted not to the species specific properties of the hormone, but to biological activity of the insulin. The data obtained indicate that functionally mature insulin receptor may be found already in the brain of cyclostomes and that in the course of animal evolution from cyclostomes to mammals functional properties of this receptor did not undergo any significant changes.