Pulmonary Alveolar Type II Cells Isolated from Rats: RELEASE OF PHOSPHATIDYLCHOLINE IN RESPONSE TO β-ADRENERGIC STIMULATION

It is unclear what factors control the secretion of pulmonary surface active material from alveolar type II cells in vivo. Other workers have suggested that cholinergic stimuli, adrenergic stimuli, and prostaglandins may all stimulate secretion. We isolated type II cells from the lungs of rats by treatment with elastase, discontinuous density centrifugation, and adherence in primary culture. beta-Adrenergic agonists, but not cholinergic agonists, caused an increase in the release of [(14)C]disaturated phosphatidylcholine, the major component of surface-active material, from type II cells in culture. The beta-adrenergic effect was stereo-selective, (-)-isoproterenol being 50 times more potent than (+)-isoproterenol. Terbutaline, 10 muM, a noncatecholamine beta-2 adrenergic agonist, caused a release of 2.0+/-0.5 (mean+/-SD) times the basal release of [(14)C]disaturated phosphatidylcholine in 3 h; the concentration of terbutaline causing half maximal stimulation was 800 nM. The terbutaline effect was blocked by propranolol, a beta-adrenergic antagonist (calculated K(d) = 6 nM), but not by phentolamine, an alpha-adrenergic antagonist. Isobutylmethylxanthine, a phosphodiesterase inhibitor, and 8-Br cyclic AMP, but not 8-Br cyclic guanosine monophosphate, also stimulated release. We conclude that type II cells secrete disaturated phosphatidylcholine in response to treatment with adrenergic stimulation.     

Changes in the density of beta adrenergic receptors in rat lymphocytes, heart and lung after chronic treatment with propranolol

Abrupt withdrawal after the chronic administration of propranolol results in clinical syndromes that suggest adrenergic hypersensitivity. Furthermore, propranolol administration has been shown to lead to an increase in the density of beta adrenergic receptors on human lymphocytes. The present studies were designed to assess the relevance of changes measured in lymphocytes to changes that may occur in solid tissues. Direct measurement of the density and properties of beta adrenergic receptors in membrane fragments was performed in vitro using the radioligand [125I]iodohydroxybenzylpindolol. Chronic infusion of propranolol by s.c. implanted osmotic minipumps generated sustained plasma concentrations of propranolol sufficient to cause chronic blockade of beta adrenergic receptors. Infusion of propranolol for 7 days resulted in significant increases in the density of beta adrenergic receptors in rat ventricles, lungs and lymphocytes. A computer-assisted graphic analysis of results obtained in studies with drugs selective for beta-1 or beta-2 receptors revealed increases in the densities of both beta-1 an beta-2 adrenergic receptors. These results are consistent with the hypothesis that change in beta adrenergic receptors on lymphocytes are qualitatively similar to alterations in beta adrenergic receptors in solid tissues not routinely accessible in humans. Increases in the densities of beta-1 and/or beta-2 adrenergic receptors in solid tissues may be related to some of the untoward effects observed in humans after abrupt discontinuation of propranolol administration.     

Prenatal exposure to propranolol via continuous maternal infusion: effects on physiological and biochemical processes mediated by beta adrenergic receptors in fetal and neonatal rat lung

During lung development, beta adrenergic receptors undergo transient coupling to enzymes and physiological processes which govern respiratory function and trophic responses to neural stimulation. To determine the role of endogenous catecholamines in mediating these processes, we examined the gestational and postnatal effects of chronic propranolol infusion (10 mg/kg/day) throughout fetal development. The effectiveness of receptor blockade in dam and fetus were confirmed through measurements of heart rate and enzymatic stimulatory responses to acute challenge with beta agonists (terbutaline to isoproterenol). Propranolol antagonized the ability of terbutaline to stimulate fetal lung fluid resorption and phosphatidic acid phosphatase, a key enzyme in surfactant synthesis. After birth, basal lung compliance and the compliance response to beta adrenergic stimulation were compromised in the neonates that had been exposed to propranolol before birth, despite the fact that direct receptor antagonism had disappeared by that time. After weaning, animals exposed to prenatal propranolol showed interference with basal activity of ornithine decarboxylase (an enzyme involved in transduction of neuronal and hormonal trophic stimuli) and its response to acute beta adrenergic challenge. These results suggest that endogenous fetal catecholamines participate in perinatal respiratory adaptation to air-breathing and help to program future cellular responsiveness to neuronal input.     

Effects of adrenergic stimulation on ventilation in man

The mechanism by which catecholamines affect ventilation in man is not known. Ventilatory responses to catecholamines were observed in normal subjects before and after adrenergic receptor blockade. Intravenous infusions of norepinephrine and isoproterenol caused significant increases in minute volume and decreases in end-tidal P(Co2) which were blocked by the administration of propranolol, a beta adrenergic receptor blocker. The hyperventilatory response to hypoxia was not altered by propranolol.Intravenous infusion of phenylephrine caused a small but significant decrease in minute volume which was antagonized by phentolamine, an alpha adrenergic receptor blocker. Angiotensin, a nonadrenergic pressor agent, also decreased minute volume significantly.100% oxygen was administered to suppress arterial chemoreceptors. Increases in minute volume and decreases in arterial P(Co2) in response to norepinephrine and isoproterenol were blocked by breathing 100% oxygen. The decrease in minute volume during phenylephrine was not altered by 100% oxygen.THE RESULTS INDICATE THAT: (a) beta adrenergic receptors mediate the hyperventilatory response to norepinephrine and isoproterenol but not to hypoxia. (b) the pressor agents phenylephrine and angiotensin decrease ventilation, and (c) suppression of chemoreceptors blocks the ventilatory response to norepinephrine and isoproterenol but not to phenylephrine. Implications concerning the interaction of adrenergic receptors and chemoreceptors with respect to the hyperventilatory response to catecholamines are discussed.     

Effects of prolonged isoproterenol infusion on cardiac and vascular responses to adrenoceptor agonists

In vitro responses of cardiac and vascular smooth muscle to both adrenoceptor agonists and phosphodiesterase inhibitors were studied in tissues from either saline- or isoproterenol-infused rats. After chronic isoproterenol infusion the sigmoidal relationship between concentration of acutely administered isoproterenol and inotropic response of cardiac muscle was shifted to the right; the maximum response was decreased by approximately 40%. Inotropic responses were attenuated further by the beta adrenoceptor antagonist, propranolol. By contrast, quantitatively comparable inotropic responses to phenylephrine were not altered after isoproterenol infusion. However, they were blocked by the selective alpha adrenoceptor antagonist, prazosin, but were not affected by propranolol. Inotropic effects of the phosphodiesterase inhibitor, isobutylmethylxanthine, were comparable in tissues from either saline- or isoproterenol-infused rats. Similar results were obtained in vascular tissues. Portal veins and aortas from isoproterenol-infused rats were less responsive to the acute relaxant properties of the beta adrenoceptor agonists, isoproterenol and salbutamol. However, as in cardiac muscle, relaxant effects to phosphodiesterase inhibitors (isobutylmethylxanthine and papaverine) were not attenuated. In addition, contraction to norepinephrine was comparable in tissues from either saline- or isoproterenol-infused rats. These data indicate that isoproterenol infusion attenuates beta adrenoceptor-mediated responses of vascular and cardiac muscle to similar degrees but does not alter responses to either alpha adrenoceptor agonists or phosphodiesterase inhibitors.     

Adrenergic Modulation of Pancreatic Glucagon Secretion in Man

In order to characterize the influence of the adrenergic system on pancreatic glucagon secretion in man, changes in basal glucagon secretion during infusions of pure alpha and beta adrenergic agonists and their specific antagonists were studied. During infusion of isoproterenol (3 mug/min), a beta adrenergic agonist, plasma glucagon rose from a mean (+/-SE) basal level of 104+/-10 to 171+/-15 pg/ml, P < 0.0002. Concomitant infusion of propranolol (80 mug/min), a beta adrenergic antagonist, prevented the effects of isoproterenol, although propranolol itself had no effect on basal glucagon secretion. During infusion of methoxamine (0.5 mg/min), an alpha adrenergic agonist, plasma glucagon declined from a mean basal level of 122+/-15 to 75+/-17 pg/ml, P < 0.001. Infusion of phentolamine (0.5 mg/min), an alpha adrenergic antagonist, caused a rise in plasma glucagon from a mean basal level of 118+/-16 to 175+/-21 pg/ml, P < 0.0001. Concomitant infusion of methoxamine with phentolamine caused a reversal of the effects of phentolamine.The present studies thus confirm that catecholamines affect glucagon secretion in man and demonstrate that the pancreatic alpha cell possesses both alpha and beta adrenergic receptors. Beta adrenergic stimulation augments basal glucagon secretion, while alpha adrenergic stimulation diminishes basal glucagon secretion. Furthermore, since infusion of phentolamine, an alpha adrenergic antagonist, resulted in an elevation of basal plasma glucagon levels, there appears to be an inhibitory alpha adrenergic tone governing basal glucagon secretion. The above findings suggest that catecholamines may influence glucose homeostasis in man through their effects on both pancreatic alpha and beta cell function.     

Nonadrenergic effects of isoproterenol in dogs with hypoxic pulmonary vasoconstriction. Possible role of prostaglandins

To determine whether the pulmonary vasodilation produced by isoproterenol is mediated solely by its beta adrenergic effects, we studied the hemodynamic responses to isoproterenol in three groups of dogs with pulmonary vasoconstriction produced by continuous ventilation with 10% oxygen: (a) hypoxia alone, (b) hypoxia and propranolol 0.3 mg/kg i.v. bolus followed by an infusion of 5 micrograms/kg per min, and (c) hypoxia after pretreatment with an inhibitor of cyclooxygenase, either indomethacin or meclofenamate 5 mg/kg s.c. twice daily for 2 d prior to study. All groups had similar values for mean pulmonary artery pressure (PAPm) and pulmonary vascular resistance (PVR) during room air and hypoxic ventilation. Isoproterenol in doses of 0.0025, 0.005, and 0.05 micrograms/kg per min produced a dose-related decline in PAPm and PVR during hypoxia in group 1. Despite beta-blockade with propranolol (group 2), isoproterenol at all three doses significantly reduced PAPm and PVR. The responses to isoproterenol were comparable in the presence or absence of propranolol; at 0.05 micrograms/kg per min the effects of isoproterenol were blunted, but not abolished, by propranolol. Similar results were observed even when five times the dose of propranolol was given. Isoproterenol at all three doses had no effect, however, on PAPm and PVR in the cyclooxygenase inhibitor-pretreated group. These data suggest that the pulmonary vasodilator effects of isoproterenol are not mediated solely by pulmonary vascular beta adrenergic receptors, and that vasodilator prostaglandins may play a role in the responses to this drug.     

Pharmacodynamic Studies of Beta Adrenergic Antagonism Induced in Man by Propranolol and Practolol

The pharmacodynamic activities of two beta adrenergic antagonists, propranolol and practolol, were compared in eight hypertensive patients. The activity of each antagonist was established in relation to its blood concentration at maximal and submaximal adrenergic blockade defined by inhibition of exercise tachycardia. Maximal inhibition of exercise tachycardia was comparable with both drugs and averaged 74+/-7% of the control value during drug treatment. This inhibition was achieved with a blood concentration of 2.5+/-0.4 mug/ml practolol and 0.10+/-0.08 mug/ml propranolol. The antagonist activities of these drugs against adrenergic stimulation with isoproterenol infusion indicated a much greater relative potency of propranolol against this stimulus, and in vivo estimates of PA(2) values differed by more than 600-fold. Relative antagonist activity of practolol during isoproterenol stimulation was equivalent both at cardiac (inotropic and chronotropic) and at vascular adrenergic receptors, whereas greater antagonist activity of propranolol was observed at vascular receptors than at cardiac receptors. Thus, the activity of practolol was not limited to cardiac receptors as previously suggested. Practolol did not reduce cardiac output at any dose level and the effect on resting blood pressure was small. Both practolol and propranolol had much greater hypotensive activity during exercise. These studies have defined the differing pharmacodynamic activities on the cardiovascular system of two effective beta adrenergic receptor antagonists and have established the blood levels of these antagonists necessary to achieve effective adrenergic blockade.     

In vivo cardiovascular responses to isoproterenol, dopamine and tyramine after prolonged infusion of isoproterenol

Effects of prolonged in vivo infusion of isoproterenol on acute cardiovascular responses to isoproterenol, dopamine and tyramine were studied in pithed rats. Isoproterenol infusion resulted in a significant decrease in control values for maximum left ventricular dP/dt; heart rate and left ventricular systolic blood pressure were not altered. This treatment also depleted both atrial and ventricular stores of norepinephrine and caused cardiac hypertrophy. Isoproterenol infusion resulted in a desensitization of drug-induced cardiovascular responses. The acute in vivo effects of isoproterenol on maximum left ventricular dP/dt, heart rate and left ventricular systolic blood pressure responses to isoproterenol were severely attenuated. The ED50 for maximum left ventricular dP/dt was increased 36-fold and maximal responses were reduced by half; changes in heart rate occurred in a parallel fashion. By contrast, ED50 values for inotropic responses to tyramine and dopamine were increased 14- and 4-fold, respectively, whereas increases in heart rate were blunted. Tyramine and dopamine-mediated increases in heart rate were completely attenuated by desensitization; chronotropic effects were again evident after pretreatment with the selective alpha-1 blocker prazosin. In addition, prazosin blocked the inotropic responses to tyramine and dopamine after desensitization and this antagonism was only slightly enhanced by addition of propranolol (prazosin + propranolol); propranolol alone was ineffective. These results are consistent with the down-regulation of beta adrenoceptors after prolonged exposure to catecholamines and indicate that under such conditions the alpha-mediated cardiovascular responses may be unmasked. Compared to pure beta agonists, agents with a degree of alpha-1 activity might be superior inotropes in heart failure patients who characteristically present with depleted stores of myocardial norepinephrine and minimal beta adrenoceptor reserve.     

Role of the alpha agonist activity of dobutamine in mediating cardiac output: effects of prolonged isoproterenol infusion

Hemodynamic activities of dobutamine enantiomers were studied in either control rats or those infused with isoproterenol (400 micrograms/kg/hr) for 4 days. In control animals prazosin attenuated the effects of (+/-)-dobutamine on cardiac output by approximately 50%; remaining activity was blocked by propranolol. After isoproterenol infusion (+/-)-dobutamine was less efficacious and the blocking effects of prazosin were greater than 90%. Isoproterenol infusion had no effect on (-)-dobutamine-mediated (alpha-1 adrenoceptor agonist) increases in cardiac output and these actions were blocked by prazosin. By contrast, compared to (+/-)- and (-)-dobutamine, effects of (+)-dobutamine (beta adrenoceptor agonist) on cardiac output were modest, not altered by prazosin and were blocked by propranolol; (+)-dobutamine was inactive after isoproterenol infusion. (-)-Dobutamine increased systemic vascular resistance in both control and isoproterenol infused rats, whereas (+)-dobutamine was inactive. (+/-)-Dobutamine increased systemic vascular resistance only in isoproterenol-infused rats. All increases in systemic vascular resistance were blocked by prazosin. Neither (+/-)- nor (+)-dobutamine significantly altered stroke volume. By contrast, (-)-dobutamine resulted in prazosin-sensitive increases in stroke volume in both control and isoproterenol-infused rats. In control animals, (+/-)-, (+)- and (-)-dobutamine increased heart rate in a dose-dependent manner; chronotropic effects of (-)-dobutamine were less than those of either (+/-)- or (+)-dobutamine. Chronotropic effects were not demonstrable in isoproterenol-infused animals. These data support the notion that in control rats cardiac output may be increased by either alpha or beta adrenoceptor stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Noradrenergic denervation alters serotonin2-mediated behavior but not serotonin2 receptor number in rats: modulatory role of beta adrenergic receptors

Recent behavioral evidence suggests that enhancement of noradrenergic neurotransmission may alter the functional sensitivity of serotonin2 (5-HT2) receptors in the central nervous system. The present studies have examined the effects of two types of noradrenergic denervation [neurotoxic: via N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) treatment; and pharmacologic: via chronic beta adrenergic receptor blockade] on the 5-HT2-mediated head shake response and cortical beta adrenergic and 5-HT2 receptor number in the rat. No changes in quipazine-induced head shakes were observed 3 days after DSP4 lesion. However, the frequency of head shakes was significantly enhanced 10 days after DSP4 treatment in the presence of a 39% up-regulation of beta adrenergic receptors. Pretreatment with propranolol 10 days after DSP4 lesion selectively antagonized the enhancement of the behavioral response to quipazine without altering base-line response rate, whereas pretreatment with the 5-HT2 antagonist ketanserin totally blocked head shakes in both control and DSP4-treated rats. Pharmacologic denervation achieved by continuous (14 day) administration of the beta adrenergic antagonist propranolol also resulted in a potentiation of the head shake response (274% of control) and an upregulation of beta adrenergic receptors (44%). Conversely, continuous treatment with the beta adrenergic agonist clenbuterol resulted in a marked reduction in head shakes (36% of control) with a concomitant 29% down-regulation of beta adrenergic receptors. 5-HT2 receptor binding was not modified by either DSP4 lesion or continuous administration of beta adrenergic agonists or antagonists. These studies demonstrate that changes in cortical beta adrenergic receptor density may modify 5-HT2-mediated behavior in a manner that is independent of changes in 5-HT2 receptor number.     

In vivo regulation of secretion of bronchiolar Clara cells in rats.

We used ultrastructural morphometric methods to study the in vivo regulation of secretion in bronchiolar Clara cells of rats. The Clara cells studied were located in airways with an internal diameter of 0.21 +/- 0.06 mm (mean +/- SD) at a transpulmonary pressure of 20 cm H2O. We found that pilocarpine caused a 50% decrease in the volume density of secretory granules of Clara cells in 60 min and that atropine blocked this effect. Isoproterenol produced a similar fall in volume density and this was blocked by propranolol. Propranolol also blocked the effect of pilocarpine. The fall in volume density of the secretory granules produced by pilocarpine and by isoproterenol occurred without any change in the surface-to-volume ratio of the granules. This indicates the change in volume density reflected a decrease in number rather than in size of the secretory granules. The observation that propranolol blocks the secretory response to pilocarpine as well as the response to isoproterenol suggests a dual in series cholinergic adrenergic regulation of secretion in bronchiolar Clara cells in rats.     

Psychopharmacological consequences of activation of beta adrenergic receptors by SOM-1122

SOM-1122 was found to be a high-affinity, partial agonist for beta adrenergic receptors. SOM-1122 inhibited the binding of [125I]iodopindolol to membranes prepared from rat cerebral cortex and cerebellum. GTP regulated the binding of SOM-1122 by increasing the Hill coefficient in both tissues and reducing the affinity of the receptor for SOM-1122 in the cerebellum. SOM-1122 increased the concentration of cyclic AMP in slices of rat cerebral cortex in a dose-dependent manner; this effect was antagonized by propranolol. Two lines of evidence suggested that SOM-1122 was centrally active after peripheral administration. First, SOM-1122 inhibited the binding of [125I]iodopindolol in vivo in a dose-dependent manner. Second, after chronic infusion with SOM-1122 for 7 days, the density of beta adrenergic receptors in the cerebellum was reduced; receptor density also was reduced 18 hr after acute administration of SOM-1122, although to a lesser extent. SOM-1122 was found to be behaviorally active. It reduced locomotor activity and reduced response rate under a multiple fixed-interval, fixed-ratio schedule in a dose-dependent manner. SOM-1122 also reduced response rate and increased reinforcement rate under a differential-reinforcement-of-low-rate schedule. These behavioral actions of SOM-1122 appeared to be due to an interaction of the agonist with beta adrenergic receptors, as they were antagonized by propranolol. The behavioral changes produced by stimulation of beta adrenergic receptors with SOM-1122 were generally similar to those caused by other centrally acting beta adrenergic agonists and by antidepressant drugs.     

Selective desensitization of cardiac beta adrenoceptors by prolonged in vivo infusion of catecholamines in rats

The effects of prolonged in vivo infusion of isoproterenol (400 micrograms/kg/hr) or norepinephrine (200 micrograms/kg/hr) from a minipump on the physiological reactivity and binding properties of cardiac beta and alpha-1 adrenoceptors were tested in rats. Infusion of either catecholamine significantly reduced the in vitro inotropic and chronotropic potency of isoproterenol in isolated left and right atria, respectively; desensitization was near maximal as early as after 2 hr of infusion. No significant change in the density of [3H]dihydroalprenolol-labeled beta receptors was evident at this time point in either atrial or ventricular tissue, although isoproterenol did decrease binding site density after 7 days of infusion. There was no change in the binding affinity or physiological blocking potency of dihydroalprenolol after isoproterenol infusion. The inotropic potency of phenylephrine in the presence of dihydroalprenolol was unaffected by infusion of either isoproterenol or norepinephrine and methoxamine failed to increase right atrial rate either in control or in isoproterenol-infused rats. There was also no change in the density and affinity of [3H]prazosin binding sites after isoproterenol infusion. These results indicate selective desensitization of cardiac beta receptors without changes in alpha-1 receptors by prolonged in vivo stimulation with catecholamines. This reaction pattern is different from the well documented effects of hypothyroidism, which include decreased sensitivity of cardiac beta and increased sensitivity of cardiac alpha-1 receptor-mediated responses in rats. Thus, the mechanisms responsible for altered receptor function in the two conditions appear to be different.     

Mechanism of isoproterenol-induced desensitization of tracheal smooth muscle.

Isolated rat tracheal smooth muscle became considerably less sensitive to the relaxing action of isoproterenol after being incubated with 5 x 10(-6) M isoproterenol for 30 minutes. Pretreatment of the tissue with propranolol, but not with methylprednisolone, clearly reduced the isoproterenol-induced desensitization. This suggested that propranolol by occupying the beta adrenergic receptor prevented isoproterenol from binding to this receptor, thereby preventing the isoproterenol-induced desensitization. Furthermore, an isoproterenol-desensitized tracheal preparation exhibited a diminished sensitivity to other beta agonists, but not to the spasmolytic actions of D600, hydralazine, sodium nitrite and aminophylline. These results suggested that the beta receptor is specifically involved in the desensitization induced by isoproterenol. A highly desensitized tissue could always be made to undergo complete relaxation by exposing it to sufficiently high concentrations of isoproterenol. Thus, there appeared to be no positive indication of a very large change in the apparent intrinsic activity of the isoproterenol in the desensitized tissue. However, the dissociation constant for the propranolol-beta receptor complex in the desensitized tissue was shown to be 180-fold larger than that in the normal tissue. These findings provide strong evidence that one demonstrable cellular change that occurs in the desensitized tissue is a pronounced reduction in the affinity of the beta receptors for isoproterenol.     

The Adrenergic Control of Lower Esophageal Sphincter Function: AN EXPERIMENTAL MODEL OF DENERVATION SUPERSENSITIVITY

To evaluate the adrenergic regulation of lower esophageal sphincter (LES) function, LES pressure, LES relaxation during swallowing, and blood pressure were measured in the anesthetized opossum, Didelphis virginiana, during intravenous administration of alpha and beta adrenergic agonists and antagonists. Studies were done in controls and animals adrenergically denervated with 6-hydroxydopamine. Alpha adrenergic agonists (norepinephrine, phenylephrine) increased LES pressure and blood pressure, whereas a beta adrenergic agonist (isoproterenol) decreased both pressures. Alpha adrenergic antagonism (phentolamine) reduced basal LES pressure by 38.3+/-3.8% (mean +/-SEM) (P < 0.001). Beta adrenergic antagonism (propranolol) had no significant effect on either basal LES pressure or percent of LES relaxation with swallowing. After adrenergic denervation with 6-hydroxydopamine, basal LES pressure was reduced by 22.5+/-5.3% (P < 0.025) but LES relaxation during swallowing was unaltered. In denervated animals, both LES pressure and blood pressure dose response curves showed characteristics of denervation supersensitivity to alpha but not to beta adrenergic agonists. These studies suggest: (a) a significant portion of basal LES pressure is dependent upon alpha adrenergic stimulation; (b) LES relaxation during swallowing is not an adrenergically mediated response; (c) the LES pressure response to alpha adrenergic agonists after 6-hydroxydopamine may serve as a model of denervation supersensitivity in the gastrointestinal tract.     

Adrenergic regulation of glycogenolysis in rat liver after cholestasis. Modulation of the balance between alpha 1 and beta 2 receptors.

The effects of extrahepatic cholestasis upon adrenergic regulation of glycogenolysis and upon the numbers of adrenoceptors in rat liver were studied using isolated hepatocytes and plasma membranes, respectively. A 60% decrease in the number of alpha 1 adrenoceptors (285 vs. 680 fmol/mg protein) and a simultaneous 2.7-fold increase in the number of beta adrenergic sites (67 vs. 25 fmol/mg protein) were observed beginning 36 h after bile flow obstruction and persisted for at least 68 h. The reciprocal modification of the numbers of alpha 1 and beta adrenoceptors was accompanied by a change in the manner of stimulation of glycogen phosphorylase by catecholamines in hepatocytes; originally alpha 1 adrenergic in normal rats (phenylephrine Ka = 0.9 microM, isoproterenol Ka = 7.1 microM), the stimulation became predominantly beta adrenergic in cholestatic animals (phenylephrine Ka = 3.7 microM, isoproterenol Ka = 0.06 microM). In normal rats, activation of the enzyme by epinephrine was inhibited by the alpha blocker phentolamine, without inhibition by the beta blocker propranolol. In contrast, propranolol was more effective than phentolamine in cholestatic rat hepatocytes. Modification of the regulation of glycogenolysis after cholestasis did not seem to be secondary to an alteration in the metabolism of thyroid hormones or in the action of glucocorticoids. However, cholestasis provoked a 10-fold increase in the number of hepatic mitoses and in the incorporation of thymidine into liver DNA of cholestatic animals. Similar changes were observed in regenerating livers, following two-thirds hepatectomy. We propose that the changes following extrahepatic cholestasis might, as well, be explained by a regenerative process.     

Pineal beta adrenergic receptor: correlation of binding of 3H-l-alprenolol with stimulation of adenylate cyclase.

3H-l-Alprenolol, a potent competitive beta adrenergic antagonist, binds to sites in rat pineal gland membranes. The properties of these binding sites were compared to those of the receptors which mediate the beta adrenergic activation of pineal adenylate cyclase. Both sites are highly stereospecific. The l-stereoisomers of alprenolol and propranolol were at least two orders of magnitude more potent than the d-stereoisomers in inhibiting isoproterenol-stimulated adenylate cyclase or 3H-l-alprenolol binding. The dissociation constants (Kd) of the l-stereoisomers of both alprenolol and propranolol were 10 to 22 nM as determined by competition for binding sites or by inhibition of isoproternol-stimulated adenylate cyclase. Beta adrenergic agonists which stimulated adenylate cyclase also competitively inhibited the binding of 3H-l-alprenolol. They showed the same order of potency (isoproterenol greater than norepinephrine greater than or equal to epinephrine) and the same individual affinities in the two systems. Alpha adrenergic blockers were ineffective in inhibiting either adenylate cyclase stimulation or 3H-l-alprenolol binding. Isoproternol stimulation of adenylate cyclase acrivity, and 3H-l-alprenolol binding, were rapid and rapidly reversible. The 3H-l-alprenolol binding sites were saturable and bound 0.6 pmol of ligand per mg of added protein. The data suggest that the binding of 3H-l-alprenolol occurs at sites indistinguishable from the pineal beta adrenergic receptor.     

Effects of Adrenergic Receptor Activation and Blockade on the Systolic Preejection Period, Heart Rate, and Arterial Pressure in Man

We have investigated the possibility that alterations in the duration of the systolic preejection period can be used to estimate adrenergic influences on the human left ventricle. The preejection period was determined from high speed, simultaneous recordings of the phonocardiogram, carotid pulse tracing, and electrocardiogram. The preejection period was shortened by isoproterenol, epinephrine, and moderate doses of norepinephrine—all of which activate beta adrenergic receptors—and by cedilanid-D. It was unaltered by changes in heart rate induced by atropine and right atrial electrical pacing. Beta adrenergic receptor blockade by propranolol abolished the shortening effects of the three catecholamines but did not inhibit that due to cedilanid-D. Vasoconstriction, both alpha adrenergic (epinephrine and norepinephrine after propranolol) and nonadrenergic (angiotensin), prolonged the preejection period. Most of the shortening of the preejection period by beta adrenergic receptor activating agents and cedilanid-D and all of the prolongation accompanying pharmacologic vasoconstriction occurred after the onset of the first heart sound, thereby excluding changes in electrical-mechanical delay as a major factor in the observed preejection period responses. Shortening of the preejection period by beta adrenergic activity induced with isoproterenol was dose-related. Increasing doses of propranolol produced parallel shifts to the right in the isoproterenol dose-response curve.     

Phosphatidic acid phosphatase in neonatal rat lung: effects of prenatal dexamethasone or terbutaline treatment on basal activity and on responsiveness to beta adrenergic stimulation

Phosphatidic acid phosphatase (PAPase) is a key enzyme in the synthesis of lung surfactant. This study compares the effects of prenatal exposure (gestational days 17, 18 and 19) to two drugs which enhance surfactant synthesis: dexamethasone (0.2 mg/kg) and terbutaline (2 or 10 mg/kg). Maternal dexamethasone treatment did not cause an initial stimulation of lung PAPase but did eventually evoke a small increase after the 1st postnatal week. The effect was selective in that brain PAPase activity was generally unaffected; liver PAPase was stimulated during the early neonatal period only. Dexamethasone also prolonged the developmental period of peak reactivity of lung PAPase to beta developmental period of peak reactivity of lung PAPase to beta adrenergic stimulation (tested with acute isoproterenol challenge), which ordinarily accompanies genesis of alveoli in the 2nd to 3rd postnatal week. Significant growth retardation was present even at this low dose of dexamethasone. In contrast, maternal administration of the beta adrenergic agonist, terbutaline, resulted in a large increase in basal enzyme activity in the lung during the immediate perinatal period and enhanced the responsiveness to isoproterenol challenge. The effect of terbutaline was accompanied by little or no growth impairment. Thus, although prenatal administration of either glucocorticoids or beta adrenergic agonists can enhance lung PAPase activity and reactivity to stimulation, the two classes of drugs differ substantially in time course of effect and in the propensity to retard growth.