Voltage-independent catecholamine release mediated by the activation of muscarinic receptors in guinea-pig adrenal glands.

1. The differences between the mechanisms of muscarinic and nicotinic receptor-mediated catecholamine secretion with respect to their dependence on voltage changes and extracellular Ca were examined using perfused adrenal glands of the guinea-pig. 2. Acetylcholine (ACh, 10(-6) to 10(-3) M) caused a dose-dependent increase in catecholamine secretion. The ED50 value for ACh was 7 x 10(-5) M. In the presence of atropine (10(-5) M), the dose-response curve for ACh was shifted to the right. Hexamethonium (5 x 10(-4) M) preferentially reduced the responses to higher concentrations of ACh (greater than 10(-5) M). Pilocarpine (5 x 10(-4) M) and nicotine (3 x 10(-5) M) also stimulated catecholamine release. 3. During perfusion with isotonic KCl solution, ACh and pilocarpine, but not nicotine, evoked catecholamine secretion. These responses were abolished by atropine (10(-6) M). Pilocarpine-stimulated catecholamine secretion was enhanced during perfusion with isotonic KCl solution. Under these conditions, hexamethonium (10(-3) M) significantly augmented ACh-evoked catecholamine release. 4. During perfusion with either Ca-free isotonic KCl or Ca-free Locke solution, ACh and pilocarpine caused a partial increase in catecholamine secretion whereas nicotine and high K solution (56 mM) did not. The responses to ACh and pilocarpine were completely inhibited by atropine but not by hexamethonium. 5. When guinea-pig adrenal glands were perfused with isotonic KCl solution containing 2.2 mM Ca which was subsequently removed and replaced with EGTA, ACh-induced catecholamine secretion was similar in magnitude to that observed during perfusion with Locke solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adenosine-mediated hypotension in in vivo guinea-pig: receptors involved and role of NO

1. Adenosine produced a biphasic lowering of the mean BP with a drastic bradycardic effect at the highest doses. The first phase hypotensive response was significantly reduced by the nitric oxide (NO) synthase inhibitor L-NAME. 2. The A(2a)/A(2b) agonist NECA produced hypotensive and bradycardic responses similar to those elicited by adenosine, which were not significantly modified by the A(2b) antagonist enprofylline. 3. The A(2a) agonist CGS 21680 did not significantly influence basal HR while induced a hypotensive response antagonized by the A(2a) selective antagonist ZM 241385, and reduced by both L-NAME and the guanylate cyclase inhibitor methylene blue. 4. The A(1) agonist R-PIA showed a dose-dependent decrease in BP with a drastic decrease in HR at the highest doses. The A(1) selective antagonist DPCPX significantly reduced the bradycardic activity and also the hypotensive responses obtained with the lowest doses while it increased those obtained with the highest ones. 5. The A(1)/A(3) agonist APNEA, in the presence of the xanthinic non-selective antagonist 8-pSPT, maintained a significant hypotensive, but not bradycardic, activity, not abolished by the histamine antagonist diphenhydramine. 6. The selective A(3) agonist IB-MECA revealed a weak hypotensive and bradycardic effect, but only at the highest doses. 7. In conclusion, in the systemic cardiovascular response to adenosine two major components may be relevant: an A(2a)- and NO-mediated hypotension, and a bradycardic effect with a consequent hypotension, via atypical A(1) receptors. Finally, an 8-pSPT-resistant hypotensive response not attributable to A(3) receptor-stimulation or to release of histamine by mastocytes or other immune cells was observed.     

Chlorphentermine-induced lipidosislike ultrastructural alterations in lungs and adrenal glands of several species

Prolonged administration of the anorectic drug chlorphentermine causes an accumulation of “foam cells” in pulmonary alveoli of guinea pigs, mice, and rabbits. Ultrastructurally, the “foam cells” correspond to enlarged alveolar macrophages, packed with lamellated cytoplasmic inclusions. Lamellar bodies of the same type also occur in increased numbers within nearly all other pulmonary cell types and in the cells of adrenal cortex of all three animal species. These cellular alterations are interpreted to result from an intralysosomal accumulation of phospholipids. In view of the present findings and of the bulk of experimental evidence from the literature, it is concluded that the presence of alveolar “foam cells” in animals treated with an amphiphilic drug is not an isolated occurrence, but rather an indication for a generalized phenomenon, which is believed to be due to a drug-induced phospholipidosis.     

N-substituted imidazolines and ethylenediamines and their action on alpha- and beta-adrenergic receptors

A series of N-substituted imidazolines and ethylenediamines were synthesized and examined for their activity in alpha- and beta-adrenergic systems. The length of the intermediate side chain between the catechol and imidazoline ring or the amine of the ethylenediamine segment was shown to affect the adrenergic activity. N-[2-(3,4-Dihydroxyphenyl)ethyl]imidazoline hydrochloride (2) and N-[2-(3,4-dihydroxyphenyl)ethyl]ethylenediamine dihydrochloride (4), both with two methylene groups between the catechol and amine segment, were found to be somewhat selective for alpha 2-adrenergic receptors while 1-(3,4-dihydroxybenzyl)imidazoline hydrochloride (1) and N-2-(3,4-dihydroxybenzyl)ethylenediamine dihydrochloride (3), both with one methylene group between the catechol and amine segment, were more selective for alpha1-adrenergic receptors in a pithed rat model. Of the four compounds examined, only compound 2 showed significant direct activity on beta1- and beta2-adrenergic receptors.     

Alpha 1- and beta-adrenergic and muscarinic cholinergic receptors in guinea-pig nasal mucosa

The alpha 1- and beta-adrenergic and muscarinic cholinergic receptors in guinea-pig nasal mucosa were measured for the first time by direct binding techniques using [3H]prazosin, [3H]dihydroalprenolol ([3H]DHA) and [3H]quinuclidinyl benzilate ([3H]QNB). The maximum binding capacities of [3H]prazosin, [3H]DHA and [3H]QNB in guinea-pig nasal mucosa were 20.1, 42.3, 159 fmol/mg protein, respectively. The dissociation constants of [3H]prazosin, [3H]DHA and [3H]QNB in guinea-pig nasal mucosa were 0.37, 0.77 and 1.5 nM, respectively. After the removal of the superior cervical ganglion in the guinea-pig, the number of alpha 1-adrenergic receptors was increased in the nasal mucosa while the number of beta-adrenergic and muscarinic receptors remained unchanged. Thus, alpha 1-adrenergic receptors are probably postsynaptic receptors in the target cells of sympathetic nerves, while beta receptors relate to the circulating catecholamines.     

Reduced number of alpha- and beta-adrenergic receptors in the myocardium of rats exposed to tobacco smoke

The concentration of alpha- and beta-adrenergic receptors--as measured by specific [3H]WB-4101 and (-)-[3H]dihydroalprenolol binding--was diminished by 60% below control values in the hearts of rats exposed to tobacco smoke. These changes in receptor numbers took place almost immediately after tobacco smoke exposure and were rapidly reversible after termination of the exposure. The dissociation constant, KD, for [3H]WB-4101 was identical in exposed (KD = 0.34 +/- 0.09 nM) and control (KD = 0.35 +/- 0.07 nM) hearts but was significantly different in the case of (-)-[3H]dihydroalprenolol binding (exposed, KD = 2.83 +/- 0.30 mM vs. control KD = 5.22 +/- 0.61 nM). For beta-receptor binding there was no significant difference between exposed and control animals in the Ki values for (-)-epinephrine, (-)-norepinephrine, (-)-alprenolol, (+/-)-propranolol or timolol. (-)-Isoproterenol, however, was found to bind with lower affinity in exposed compared with control hearts. For alpha-receptor binding there was no significant difference between control and 'smoked' animals in the Ki values for (-)-epinephrine, (-0)-norepinephrine or phentolamine. The decrease in alpha- and beta-adrenergic receptor concentration may be related to the phenomenon of receptor desensitization resulting from a release of catecholamines in rats exposed to tobacco smoke.     

Lung uptake and antianaphylactic effects of KWD 2131 (a beta-adrenergic agonist) in perfused guinea-pig lungs

The lung uptake and modulating effects of KWD 2131 [1-(3,5-dihydroxyphenyl)-2-(1,1-dimethyl-2-hydroxyethyl) amino ethanol], a beta-adrenergic agonist, on pulmonary perfusion flow and histamine release from anaphylactic guinea-pig lungs were studied using an isolated perfused lung model. The lung extraction ratio, as calculated from the concentration of drug in the inflowing and outflowing medium in single pass studies was less than 0.05 at steady state which was achieved within 3 min. after start of drug infusion. Statistically significant protection to antigen elicited reduction in perfusion flow and inhibition of histamine release were obtained at the inflowing concentration 1.5 x 10(-6) mol/l but not at 1.5 x 10(-7) mol/l. The observed inhibition of the anaphylactic decrease in the perfusion flow can partly be explained by the decreased histamine release.     

The role of adrenal and pineal glands on the hypothalamo-pituitary axis in adult male rats

Although there have been reports on the effects of adrenal and pineal gland secretions on the hypothalamus and the pituitary, the maintenance of rhythmicity by these glands has not been reported so far. The present data deals with the alterations in the periodicity of hypothalamo-pituitary axis after the surgical removal of either adrenal, gonad or pineal in adult male rats. The data indicated an alteration in the 24 hour pattern of hypothalamic content of LHRH after adrenalectomy, castration or pinealectomy. In adrenalectomy group, the in vitro responsiveness of pituitary decreased at 0600 h and 100 h as compared to the intact rats, resulting in a low amplitude of LH circadian rhythm. The pituitaries of pinealectomized rats showed increased sensitivity at 1000 h and 1800 h which resulted in two peak LH concentration at those time intervals. Further, pinealectomized rats showed a selective five fold increase over 24 hr in serum FSH concentration as compared to intact rats suggesting dissociation in the release of FSH and LH.     

The role of alpha- and beta-adrenergic effects in the action of adrenaline on renal lithium elimination in adrenalectomized rats.

Repeated s.c. injections of L-adrenaline (4 X 0.5 mg/kg body weight) increased the urinary clearance of lithium in intact rats and in adrenalectomized animals. Adrenaline also increased the fractional excretion of lithium in adrenalectomized rats; an effect that was prevented by repeated s.c. injections of the alpha-adrenergic blocking agent phentolamine (4 X 1 mg/kg body weight). When administered alone, propranolol and phentolamine decreased the urinary clearance of lithium in adrenalectomized rats. The drug-induced changes in the urinary clearance of lithium were not directly related to the effects of the drugs on the urinary elimination of sodium, potassium, creatine and water. The results suggest that the action of adrenaline on renal lithium elimination in adrenalectomized rats might be mediated by alpha-adrenergic receptors.     

The functional role of the alpha-1 adrenergic receptors in cerebral blood flow regulation

Cerebral vasculature is richly innervated by the α-1 adrenergic receptors similar to that of the peripheral vasculature. However, the functional role of the α-1adrenergic receptors in cerebral blood flow (CBF) regulation is yet to be established. The traditional thinking being that during normotension and normocapnia sympathetic neural activity does not play a significant role in CBF regulation. Reports in the past have stated that catecholamines do not penetrate the blood brain barrier (BBB) and therefore only influence cerebral vessels from outside the BBB and hence, have a limited role in CBF regulation. However, with the advent of dynamic measurement techniques, beat-to-beat CBF assessment can be done during dynamic changes in arterial blood pressure. Several studies in the recent years have reported a functional role of the α-1adrenergic receptors in CBF regulation. This review focuses on the recent developments on the role of the sympathetic nervous system, specifically that of the α-1 adrenergic receptors in CBF regulation.     

Differential roles of the adrenal gland in the suppression of morphine antinociceptive tolerance development by alpha- and beta-adrenergic blockers.

Concomitant treatment with phentolamine, an alpha-blocker, or with propranolol, a beta-blocker, suppressed the development of morphine tolerance in sham-operated (Sham) mice. In adrenalectomized (ADX) mice, daily morphine developed tolerance as well as in the Sham group, and concurrent phentolamine suppressed the development of tolerance, whereas such suppression by propranolol was abolished. Supplemental treatment of ADX mice with dexamethasone did not restore the suppressive effect of propranolol. These results suggest that different mechanisms underlie the prevention of tolerance development by alpha- and beta-blockers, and that adrenal cortex does not seem to participate in the suppression by beta-blockers.     

A possible role for beta-adrenergic receptors in the expression of audiogenic seizures

DBA/2 mice are genetically prone to audiogenic seizures and, when compared with seizure resistant C57BL/6 mice, were found to have an increased density of beta-adrenergic receptors in their midbrain at the age of peak seizure susceptibility. Propranolol, a beta-receptor blocking agent, attenuated all stages of the seizure syndrome. However, a comparison of the effects of its d- and l-isomers suggested that propranolol's anticonvulsant activity was due to its local anesthetic-like action. Pindolol, a more potent beta blocker that is at least 100 times less potent than propranolol with respect to local anesthetic-like activity, produced anticonvulsant effects in approximately the same systemic dose range as propranolol. This indicates that pindolol's anticonvulsant activity could be due to beta blockade and, taken together, these data suggest that beta-adrenergic receptors may play a role in the expression of audiogenic seizures in these animals.     

Inhibitory effects of cortical steroids and adrenocorticotropic hormone on catecholamine secretion in guinea-pig perfused adrenal glands

1 We investigated the effects of exogenously applied steroids and endogenously released cortisol on catecholamine (CA) secretion induced by cholinergic agonists in perfused guinea-pig adrenal glands. 2 Acetylcholine (ACh) and electrical stimulation induced CA secretion, which was reversibly inhibited by cortisol. Adrenocorticotropic hormone (ACTH) increased the concentration of cortisol in the perfusion effluent and partly inhibited the secretory response to ACh. 3 Cortisol or aldosterone dose-dependently inhibited secretory responses to nicotine and muscarine. These inhibitory effects were not antagonized by mifepristone and spironolactone, respective cortisol and aldosterone receptor blockers. 4 Dexamethasone, cortisone, corticosterone, 11-deoxycortisol, 11-deoxycorticosterone, prednisolone and cholesterol inhibited nicotine-evoked CA secretion. The secretory response to muscarine was inhibited by these compounds except for dexamethasone and prednisolone. 5 Dexamethasone, cortisol and aldosterone had no effect on CA secretion induced by high KCl. 6 These results suggest that steroids affect nicotinic and muscarinic ACh receptor-mediated responses through distinct mechanisms, and that cortisol released from the adrenal cortex inhibits CA secretion from the adrenal medulla.     

Characterization of alpha- and beta-adrenergic receptors in membranes prepared from the rabbit iris before and after development of supersensitivity.

α-Adrenergic and β-adrenergic receptors were studied by measuring the binding of [³H]dihydroergocryptine and [³H]dihydroalprenolol, respectively, to membranes prepared from homo-genized rabbit irides. The binding of [³H]dihydroergocryptine appears to be specific for α-adrenergic receptors as adrenergic agents displace this radioligand with the following order of potency: phentolamine > epinephrine ? norepinephrine ? isoproterenol = propranolol. The binding of [³H]dihydroalprenolol appears to be specific for β-adrenergic receptors as adrenergic agents displace this radioligand with the following order of potency: propranolol ? isoproterenol ? epinephrine > norepinephrine ? phentolamine. Several weeks after removal of the superior cervical ganglion, when all the adrenergic nerves to the tissue have degenerated, membranes prepared from denervated irides have an increased density of β-adrenergic receptors with no increase in the density of α-adrenergic receptors. A small decrease in the total number of α-adrenergic receptors probably occurs, which is due to the loss of pre-junctional receptors. The affinities of the receptors do not change. These findings suggest that unlike skeletal muscle, the supersensitivity that occurs in smooth muscle is not due to an increase in the population of receptors governing contraction. However, the change in population of β-adrenergic receptors is consistent with the hypothesis that, as in other tissues, the level of cyclic AMP modulates the density of the β-adrenergic receptor.     

The occurrence of postsynaptic alpha- and beta-adrenoceptors in the guinea-pig gall bladder.

1 Guinea-pig gall bladder strips were contracted by (-)-noradrenaline, 10(-5) M, and by field stimulation at 5 Hz (in the absence or presence of 10(-6) M atropine) and relaxed to 10(-5) M (-)-isoprenaline. (-)-Adrenaline, 10(-5) M, predominantly contracted, but sometimes relaxed, this preparation. 2 In the presence of 10(-6) M phentolamine, contractions to (-)-noradrenaline and to (-)-adrenaline were reversed to relaxations. The relaxations produced by (-)-isoprenaline were unaltered. In the presence of 10(-6) M propranolol, contractions to (-)-noradrenaline increased in magnitude, relaxations to (-)-adrenaline were reversed to contractions, and relaxations to (-)-isoprenaline were abolished. These results demonstrate the presence of postsynaptic alpha-adrenoceptors which mediate contractions, and postsynaptic beta-adrenoceptors which initiate relaxations, in the guinea-pig gall bladder. 3 The contractile responses to continuous field stimulation for 5 min at 5 Hz in Krebs solution alone were reduced in magnitude by propranolol, 10(-6) M. In the presence of 10(-6) M atropine (added to eliminate the cholinergic component of the response), propranolol, 10(-6) M, had no effect on responses to stimulation at 5 Hz. Thus propranolol reduced the response to cholinergic stimulation in this tissue; the basis of this effect is unclear. In the absence or presence of atropine (10(-6) M), the responses to 5 Hz were smaller in magnitude in the presence than absence of phentolamine, 10(-6) M. This suggests that the responses to field stimulation of the guinea-pig gall bladder may, in part, be due to the release of endogenous noradrenaline which acts at postsynaptic alpha-adrenoceptors.     

Tolerance to sympathomimetic bronchodilators in guinea-pig isolated lungs following chronic administration in vivo.

1. The inactivation of prostaglandin E2 by the rabbit lung was estimated in vivo by comparing its depressor potency following intravenous and intra-aortic injections, and in vitro by measuring the rate of disappearance of smooth muscle stimulating activity when the prostaglandin was incubated with high speed supernatant fractions from lung homogenates. 2. The ability of the lung to inactivate prostaglandin E2 in vivo increased gradually throughout pregnancy, and then decreased rapidly during the three days post-partum. 3. An increased lung inactivation was also seen in pseudopregnant (day 12) rabbits, and in non-pregnant rabbits treated with progesterone for 12 days. A further increase occurred when progesterone treatment was prolonged to 26 days. 4. Treatment with oestradiol monobenzoate or cortisol for 12 days, and deprivation of ovarian hormones for 14-17 days by ovariectomy, were without effect on the lung inactivation of prostaglandin E2. 5. The in vitro experiments revealed a striking increased in the activity of lung prostaglandin metabolizing enzymes during pregnancy. 6. The results are discussed in relation to the hormonal changes occurring during pregnancy, and it is suggested than an enhanced lung inactivation of prostaglandins might have an important protective function at this time.     

Antagonism of aminoglutethimide and adrenocorticotropic hormone (ACTH) studied on slices of adrenal glands of the guinea-pig

Aminoglutethimide at concentrations from 0.1 to 5 nM is able to inhibit the cortisol release elicited by adrenocorticotropic hormone (ACTH) (from 2.5 to 50 ng/ml) in guinea-pig adrenal cortex slices. The antagonism is a non-competitive one (in a Lineweaver-Burk plot), whereas other drugs (morphine, endorphin, indomethacin, etc.) inhibit ACTH competitively. This is in agreement with the known mechanism of action of aminoglutethimide, which inhibits the synthesis of cortisol by blocking reactions of enzymes such as aromatase and desmolase. From the data one can calculate the dissociation constant (Km) of ACTH with its receptor(s) to be 0.27 pg/ml and the inhibiting constant (Kl) of aminoglutethimide to be 49.78 x 10(-10) M. The maximal response of ACTH was 52.9 ng/ml.