Mariagnes Verosky

Adenylcyclase-phosphodiesterase system in arterial smooth muscle

Abstract Isoproterenol, epinephrine, and norepinephrine increase cyclic AMP formation in rat aorta through their stimulatory effect on adenyl cyclase. Isoproterenol, and epinephrine and norepinephrine in the presence of phentolamine, have a relaxing effect on the rat aortic strip. Propranolol prevents the rise in cyclic AMP with the three catecholamines and modifies the epinephrine-induced contraction. Inhibition of phosphodiesterase is also accompanied by relaxation of arterial smooth muscle.

The effect of catecholamines on adenyl cyclase activity in rat uterus.

Abstract Adenyl cyclase (AC) activity was assayed in uterine tissue homogenates from estrogen-pretreated rats. Epinephrine, norepinephrine and isoproterenol activate AC to the same maximum, 80–88% above control; a 20 times higher concentration of norepinephrine than of epinephrine is needed to produce the same effect. A beta adrenergic blocking agent (propranolol) antagonizes this action of catecholamines. Epinephrine in lower concentrations, unlike isoproterenol, when combined with propanolol has an inhibitory effect on AC. An alpha adrenergic blocking agent (phentolamine) does not prevent the activation of AC by catecholamines. On the contrary, the activity tends to be higher. The results show that the increase in uterine muscle AC activity is caused by the component of catecholamine action which apparently relaxes the uterus and gives some support to the possibility that another component of epinephrine action inhibits AC activity.

Effects of halothane on the cyclic 3',5'-adenosine monophosphate enzyme system in human platelets.

A study of the effects of halothane on the cyclic 3′,5′-adenosine monophosphate (cAMP) system in human platelets was undertaken since cAMP has been implicated in the regulation of the process of platelet aggregation and this anesthetic has been reported to decrease platelet aggregation and, in other tissues, to increase adenylate cyclase activity. When exposed to halothane 0.5 to 10 vol%, adenylate cyclase activity was increased in the platelet preparation in a dose-dependent manner, reaching a maximum at 5 vol% (93% increase above basal activity). Platelet aggregation was also inhibited by halothane in a dose-dependent manner, with a maximum effect at about 5 vol% halothane (a decrease of 70%). Kinetic analysis of platelet cAMP-phosphodiesterase suggested two forms of activity, neither of which was altered by halothane. The results suggest that the impairment of platelet aggregation observed with halothane may be brought about by the halothane-induced activation of platelet adenylate cyclase, which may result in a higher cAMP level, inhibiting platelet aggregation.

Acetylcholine and the cyclic AMP system in smooth muscle

Abstract The effect of acetylcholine on the cyclic AMP system and its interaction with the epinephrine effect on this system was studied in vitro in rat uterus. In the presence of acetylcholine (1–100 μMolar), epinephrine-induced cyclic AMP formation in intact tissue is decreased; this inhibitory effect of acetylcholine is more pronounced at higher concentrations of epinephrine and is reversed by atropine. In broken cell preparations, acetylcholine does not alter the activity of adenyl cyclase or phosphodiesterase, nor the stimulatory effect of epinephrine. It appears that acetylcholine has an effect on the cyclic AMP system of rat uterine smooth muscle only when the structural and functional relationships in the cell are preserved. The possible mechanisms are discussed.

The passage of THAM across the peritoneum during dialysis

The use of THAM during peritoneal dialysis for the extraction of CO2, and weak acids in dogs was compared with other dialyzing media. The rapid passage of THAM across the peritoneum is a limiting factor and to avoid reaching toxic levels, the total amount administered of a 0.075M THAM dialysate should not exceed 22 mM per kilogram per 24 hours. Dialysate pR and THAM concentration fell rapidly during the first 30 minutes and then more gradually, while dialysate CO2, content increased markedly, THAM dialysate acting as a “C02 trap.” After 3 hours 47 per cent of the THAM administered was excreted in the urine and there was a moderate diuresis of alkaline urine. After six 30 minute periods of dialysis the rate of passage of pentobarbital into the dialysate was three times greater with THAM solution than with Ringer solution and more than one and one half times greater than with NaHC03. Comparable results for the three media were obtained during the extraction of phenobarbital. The amount of sodium salicylate extracted into the three dialyzing media was similar, but the production of an alkaline urine with THAM administration enhanced salicylate excretion. Three times more salicylate was excreted in the urine during THAM administration than with Ringer solution and one and one half times more than with NaHCO3. Peritoneal dialysis with THAM should have clinical applications for the removal of exogenous or endogenous weak acids.

Halothane Interaction with Guanine Nucleotide Binding Proteins in Mouse Heart

Volatile anesthetics have been shown to decrease hormone-induced adenosine cyclic monophosphate (cAMP) formation and to increase yanosine cyclic monophosphate (cGMP) content in mouse ventricular myocardium. Hormoneinduced inhibition of adenylate cyclase, the enzyme that synthesizes cAMP, and the cGMP response to alpha adrenergic agonists are mediated by a yanine nucleotide binding protein (N) sensitive to pertussis toxin. To evaluate the involvement of N proteins in the action of halothane on cyclic nucleotides in the heart, mice were pretreated with pertussis toxin, 50 μg/kg, ip, 72 h prior to exposure to halothane, 1.2 vol%. Pretreatment with the toxin decreased the cGMP response to halothane by 65% but was without effect on the decrease in myocardial cAMP induced by the anesthetic. The results indicate that a functionally active pertussis toxin-sensitive N protein is involved in the cGMP response to halothane, but not in the cAMP response.

Halothane Effect on cGMP and Control of Motor Activity in Mouse Cerebellum

The effect of halothane on cerebellar control of motor activity and on cerebellar cyclic 3′,5′-guanosine monophosphate (cGMP) content was studied in mice. Isoniazide and picrotoxin were used to increase motor activity and induce seizures associated with an increase in cerebellar cGMP content. Halothane markedly decreased the cerebellar cGMP content (by 60 per cent at 0.61 per cent, the concentration at which 50 per cent of mice lost righting reflex) and prevented the isoniazide-induced increase in cGMP content. Halothane, 0.61 per cent, significantly reduced both isoniazide- and picrotoxin-induced motor activity; the ED50 convulsive dose of isoniazide (137.7 ± 7.04) and of picrotoxin (1.9 ± 0.2 mg·kg−1, sc) was about three times higher (402.2 ± 17.9 and 5.8 ± 0.6 mg·kg−1, sc, respectively) in mice exposed to halothane. In contrast, halothane did not alter the ED50 convulsive dose of strychnine, which has a different site and mechanism of action, blockade of glycine receptors, a mechanism not involving the cerebellar system. These results indicate that halothane has a significant effect on the cerebellar control of motor activity and that cGMP plays an important role in the alteration of cerebellar function by halothane.

ACID‐BASE CHANGES IN THE CEREBROSPINAL FLUID FOLLOWING RAPID CHANGES IN THE BICARBONATE/CARBONIC ACID RATIO IN THE BLOOD

Equilibration of dissolved C02 between blood and cerebrospinal fluid (CSF) is a rapid process. However as shown by Robin el d . , l H+ and HC0,ions equilibrate slowly between the two compartments. This paper deals with the acid-base relationship between blood and CSF in dogs, following rapidly induced changes in the arterial bicarbonate/carbonic acid ratio. I t was felt that such a study could throw some light on the acid-base relationships of different body fluid compartments when different bases are added to the blood with or without a concomitant acid load.

Halothane Effect on Beta-adrenergic Receptors in Canine Myocardium

Halothane depresses the inotropic state of the heart, possibly by decreasing the rate of formation of cyclic 3′, 5′-adenosine monophosphate (cAMP) through depression of the activity of adenylate cyclase, the cAMP-generating enzyme. As catecholamines regulate the inotropic state and adenylate cyclase activity by binding to myocardial beta-adrenergic receptors, the effect of halothane on binding to these receptors was studied to determine whether this was a site of halothane effect. Beta-adrenergic binding was measured at binding equilibrium in vitro in a canine myocardial membrane preparation in the absence and presence of halothane, 3 to 5 vol%, using as the radioligand 3H-dihydroalprenolol (3H-DHA), a beta-adrenergic antagonist with high affinity and radioactivity. In addition, the effect of halothane on the binding of /-isoproterenol, a beta-adrenergic agonist, was measured by displacement of 3H-DHA. The results indicate that halothane has no effect on either the affinity of canine myocardial beta-adrenergic receptors for 3H-DHA or /-isoproterenol, nor does it alter the number of available receptors at binding equilibrium.

Action of Halothane on Myocardial Adenylate Cyclase of Rat and Cat

Summary The effect of halothane on myocardial adenylate cyclase was studied since cAMP is thought to participate in the regulation of myocardial contractility and since halothane has been shown to alter the activity of the cAMP-generating enzyme in other organs. Halothane significantly decreased the stimulatory effect of catecholamines on myocardial adenylate cyclase without altering the basal or the sodium fluoride-induced adenylate cyclase activity. In the presence of halothane (2%, vol/vol) the effect of 5 μM norepinephrine on adenylate cyclase in rat myocardium, 74.0 ± 3.0, was reduced to 53.0 ± 3.0 pmol/mg protein/5 min (P < 0.001) (control adenylate cyclase activity, 140.0 ± 1.0 pmol/mg protein/5 min). The activation of adenylate cyclase by isoproterenol was also significantly decreased by halothane in rat and cat myocardium. The maximum stimulatory effect of isoproterenol (2.5 μM) on adenylate cyclase in rat myocardium, 71.0 ± 8.0, was decreased to 26.0 ± 6.0 pmol/mg protein/5 min (P < 0.001) in the presence of halothane (2%, vol/vol). Furthermore, halothane diminished the effects of 5-guanylyl imidodiphosphate, which is thought to act at a site linking the regulatory and catalytic units of adenylate cyclase. The results suggest possible sites of halothane action on myocardial adenylate cyclase and raise the possibility that this inhibitory action of halothane and the decreased positive inotropic action of catecholamines in the presence of halothane may be related.