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Biomedical subjects

E Giacobini

Publications and source records attributed to E Giacobini.

At least 91 records · Page 5Linked to original sources
PubMed1987

Release of acetylcholinesterase from the caudate nucleus of the rat.

Acetylcholinesterase (AChE) can be released in the perfusate of rat caudate nucleus (CN) slices by two different modes of stimulation, with electrical stimulation at 5 Hz and with high concentrations of K+ (105 mM) using K+-propionate. We were unable to demonstrate AChE release with lower K+ concentrations (50 mM); however, at this concentration the drop in AChE activity seen in resting conditions was prevented. Practically all (95%) cholinesterase (ChE) found in the rat CN is AChE, which is represented by two major molecular forms (4S and 10S). In the perfusate, only AChE activity could be detected. A comparison of acetylcholine (ACh) and AChE release showed that maximal 3H-outflow and AChE release occurred at the same frequency (5 Hz), but the onset of AChE release was delayed. With high K+ (105 mM) depolarization, AChE release started after termination of the stimulation and continued for at least 50 min. These findings are consistent with the view that soluble form(s) of AChE can be slowly released from neurons under specific conditions of depolarization. In the caudate of the rat, the most likely sites for this release are processes of cholinergic interneurons. A hypothesis of AChE release is presented, and possible physiological and pathological implications of such a mechanism are discussed.

Acetylcholinesterase↗
PubMed1987

Pharmacokinetics and pharmacodynamics of physostigmine after intravenous administration in beagle dogs.

The time course of physostigmine (Phy), its metabolites and activity of cholinesterase (ChE) in plasma were studied after intravenous bolus administration of [3H]Phy (100 micrograms/kg) to beagle dogs. The maximal inhibition of ChE (78%) in plasma at 2 min correlated with the largest concentration of physostigmine (124 ng/ml). The concentration of physostigmine decreased by 88% to 16 ng/ml at 45 min when the activity of ChE was still 59% inhibited. Acetylcholinesterase activity in four regions of the brain (medulla, striatum, cerebellum and cortex) was not significantly different from controls at 70 +/- 5 min after administration of physostigmine. Concentrations of physostigmine and its metabolites determined by HPLC were not significantly different in different regions. In plasma, physostigmine was found, together with eseroline and two other metabolites M1 and M2. At 45 min, only 18% of total radioactivity was due to physostigmine and 52% was due to the major metabolite M1. On the contrary, in regions of the brain, metabolite M1 represented only 1.9-3.37% of total radioactivity at 70 +/- 5 min. Pharmacokinetic parameters, obtained in the dog, were compared to previously published data in rat and man. The elimination half-life (beta) was 30.7 min in the dog as compared to 15 min in rat and and 21.7 min in man. The Vd (ml/kg) was higher than total body water volume in all three species: dog (1832), rat (1352) and man (664), indicating sequestration of the drug in body compartments. Clearance (ml/min/kg) was found to be 41.2 in dog, which compares to 62 in rat and 22 in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

A comparison of the effects of two inhibitors on brain cholinesterase.

In the present paper various routes of administration (i.m., i.v. and i.c.v.) of physostigmine are compared and the effect of two drugs producing inhibition of cholinesterase, physostigmine and metrifonate, on the activity of cholinesterase in the brain of the rat and on levels of acetylcholine (ACh) and choline (Ch). After intramuscular administration of physostigmine (500 micrograms/kg), the activity of cholinesterase in brain was maximally inhibited (76%) at 5 min and recovered to 50% at 40 min. At 5 min, areas of the brain such as the striatum and medulla oblongata showed 49 and 67% inhibition, respectively. Levels of physostigmine in brain peaked at 5 min (1.28 nmol/g). With the exception of the cerebellum, there was a direct correlation between the concentration of physostigmine and inhibition of cholinesterase in a given area. With the intravenous route of administration (100 micrograms/kg), the activity of cholinesterase in brain was maximally inhibited (67%) at 3 min and recovered to 50% at 12 min. At 60 min, the activity of cholinesterase was 90% of control. Levels of physostigmine in brain peaked at 2 min (0.47 nmol/g). At 15 min, with intraventricular administration (4 micrograms), the activity of cholinesterase was 73% and 31% inhibited in the hippocampus and striatum, respectively. Other areas of brain showed intermediate values of inhibition. Levels of acetylcholine were increased 18 and 22% above control in the striatum and hippocampus, respectively and did not change in the medulla. After intramuscular administration of metrifonate (80 mg/kg), the activity of cholinesterase decreased to 26% at 30 min, recovered to 50% at 180 min and returned to 74% at 360 min. Levels of acetylcholine increased by 45% at 45 min, then returned to normal by 120 min. When metrifonate (2.5 mg) was given intraventricularly the activity of cholinesterase decreased in the left side injected at 30 min to 20% in hippocampus; 22% in the medulla; 50% in the cerebellum; 58% in the striatum and 72% in cortex. Levels of acetylcholine increased maximally at 45 min in hippocampus and cortex and peaked in the striatum at 60 min. The greatest increases were seen in the hippocampus and cortex with 60 and 55%, respectively. The results of this study reveal some major differences between the effects of the two substances in brain. Four major conclusions are apparent from this study. First, based on these results, it is concluded that metrifonate is more likely to produce a therapeutic effect in humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1987

Cerebrospinal fluid changes in experimental cardiac arrest (maximal stress).

Cardiac arrest produces a prompt and maximal increase of plasma catecholamines, with associated elevations of the hormones involved in the endocrine response to stress. To investigate the participation of the central nervous system (CNS) in the generation of the endocrine response, the catecholamines epinephrine and norepinephrine in cerebrospinal fluid (CSF) were measured before, during, and after cardiac arrest accompanied by cardiopulmonary resuscitation (CPR) in adrenalectomized (ADX) and sham-operated (SHAM) dogs. We also determined the activity of acetylcholine esterase (AChE), an intracellular enzyme released into the CSF after hypothalamic or caudate stimulation. During CPR, plasma epinephrine increased significantly in SHAM but not ADX dogs, increasing from (mean +/- SE) 480 +/- 171 to 29,800 +/- 14,200 pg/ml (P less than 0.05). Prearrest CSF norepinephrine was higher in ADX than SHAM dogs and increased in both groups with cardiac arrest, but the increase was significant only in SHAM animals; CSF epinephrine remained unchanged during or after cardiac arrest. CSF AChE activity increased during and after defibrillation; the difference with basal levels became significant when the peak postarrest values were considered (P less than 0.05). These results document biochemical changes occurring in the CNS during maximal stress represented by cardiac arrest. It is suggested that CSF norepinephrine and AChE activity elevations are markers for hypothalamic activation from the stress of cardiac arrest.

Acetylcholinesterase↗
PubMed1986

Esophageal dischalasia: serendipity during 99mTc thyroid scan.

It is rare for a large amount of pooled radioactive saliva to be observed in the neck during a thyroid scan. Such a finding would imply abnormal salivation and/or esophageal kinesis. The case of esophageal dischalasia reported here suggests that a complete study of the esophagus is advisable when a large area or amount of radioactive saliva is observed in the neck during a thyroid scan.

Adult↗
PubMed1986

Relation of brain regional physostigmine concentration to cholinesterase activity and acetylcholine and choline levels in rat.

The relationship between physostigmine (Phy) concentration, acetylcholine (ACh), choline (Ch) and cholinesterase (ChE) activity was examined in whole rat brain after the administration of [3H]Phy (650 microgram/kg i.m.). Cholinesterase inhibition was found to be inversely related to Phy levels. Maximal inhibition (80%) was seen at 5 min and by 2 hrs ChE activity had returned to control levels. Acetylcholine levels in whole brain peaked at 30 min at a concentration (80 nmol/g) 2.3 times higher than controls (33 nmol/g). Choline levels were not significantly altered. The regional distribution of Phy concentration and ChE activity was studied in six areas of the brain following i.m. administration of three different dosages of ( 3H]Phy. Physostigmine concentration and ChE activity showed a dose dependency in each area examined except in SP (medial septum). Striatum (ST) showed the greatest relative increase of ACh up to 30 min, when compared to other areas. Choline levels were not changed in any area with the exception of ST at 5 min where a decrease was seen. There was a relationship between ChE activity, Phy concentration and ACh levels in all areas examined with exception of the medulla oblongata (MO). Our results indicate that even though ChE was inhibited practically uniformly in all brain areas, the percent increase with respect to control animals and the relative increase of ACh varied widely from area to area. This finding has clinical implications in cases in which cholinomimetic therapy is used to elevate ACh levels in specific brain areas which show a cholinergic deficit.

Acetylcholine↗
PubMed1986

The effects of physostigmine on acetylcholinesterase activity of CSF plasma and brain. A comparison of intravenous and intraventricular administration in beagle dogs.

The effects of various doses of physostigmine (Phy) on the activity of acetylcholinesterase (AChE) in plasma, cerebrospinal fluid (CSF) and brain were studied in beagle dogs. Two routes of administration were compared: intravenous (i.v.) and intracerebroventricular (i.c.v.). With intracerebroventricular administration, over 90% inhibition of the activity of AChE in CSF was reached within 5 min of injection at all doses (10-120 micrograms). Even at the smallest dose (10 micrograms), 50% inhibition of activity of the enzyme in CSF was still present at 90 min. The activity of AChE in plasma was only minimally inhibited by intraventricular administration of physostigmine. A different response was obtained following intravenous administration of physostigmine (250-1000 micrograms). The activity of AChE in plasma was inhibited but the activity of AChE in CSF was increased (36-80% at 180 min). This increase was dose-dependent and was blocked by pretreatment with atropine (1.5 mg i.v.) which suggests the involvement of a muscarinic receptor mechanism. The time course of the accumulation and regional distribution of [3H]physostigmine in brain also varied with the route of administration. At 5 min, with intravenous administration, physostigmine (1000 micrograms) reached greater concentrations and caused greater inhibition of AChE in the cortex. With intraventricular administration, physostigmine (80 micrograms) reached greater concentrations in two regions adjacent to the ventricular surface: the striatum and hippocampus. These regions also showed greater inhibition of the activity of AChE. Moderate to severe symptoms of cholinergic hyperactivity were seen only with the largest intraventricular dose (120 micrograms). This study suggests that intraventricular administration of physostigmine, a reversible inhibitor of cholinesterase (ChE), may offer distinct advantages over intravenous administration. Inhibition of acetylcholinesterase in CSF was more pronounced and persisted longer when physostigmine was administered directly into the CSF than when given intravenously. The implications of this study for a cholinergic therapy of Alzheimer's disease are discussed.

Acetylcholinesterase↗
PubMed1986

Experimental maternal hyperpipecolatemia decreases DNA in the mouse brain.

Pipecolic acid represents the major metabolite of lysine in the CNS. This study aimed to mimic the known pathological condition of hyperpipecolatemia in human neonates by maintaining high and steady concentrations in the mouse brain both pre- and postnatally. Although histological observations did not reveal any abnormal findings in the brain, liver and kidney, the offsprings of mothers which were injected during pregnancy with 250 mg/kg PA presented a significant decrease in both cortical and whole brain DNA content. Protein, RNA and CNPase activity were not altered. The changes in DNA content are of particular interest since they demonstrate that a high and steady level of pipecolic acid, which is comparable to the level seen in human hyperpipecolatemic brain, can induce a neurotoxic effect in the fetal mouse brain. Mice injected with the same dose from day 1 to day 29 after birth did not show any change in DNA content in the cortex. These results suggest that the critical period from pipecolic acid neurotoxic effect is prenatal, probably due to a selective vulnerability of developing neurons to high levels of pipecolic acid. The decrease in DNA concentration induced by maternal hyperpipecolatemia suggests a neurotoxic effect of pipecolic acid on cell proliferation during fetal development which could be related to the neuronal damage observed in the brain of hyperpipecolatemic neonates.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1985

Identification and characterization of pipecolic acid binding sites in mouse brain.

Pipecolic acid (PA, piperidine-2-carboxylic acid) is the major product of lysine metabolism in the mammalian brain (Giacobini et al., 1980). In this study we have characterized the binding of [3H]PA to P2 fraction membranes and its distribution in the mouse brain. The binding was found to be saturable (70 nM), temperature and Na+ and Cl- dependent. A high affinity binding site with an apparent KD of 33.2 nM and a Bmax of 0.2 pmol/mg protein was demonstrated. The regional distribution of [3H]PA specific binding in mouse brain showed the highest concentration in cerebral cortex, thalamus and olfactory bulb. Unlabeled PA (10(-3)-10(-11) M) displaced specific binding of [3H]PA in a concentration dependent manner. Out of several substances tested, only proline showed a similar pattern of displacement. Pre-incubation of the membrane preparation with GABA (10(-3)-10(-11) M) resulted in either an increase or decrease of [3H]PA binding depending on the concentrations of GABA and PA. These results suggest a modulatory action of GABA on PA binding sites. The postnatal development of [3H]PA specific binding was studied in the whole brain of the mouse. [3H]Pipecolic acid binding increased progressively (8-fold) from one day after birth to 16 days. Following this developmental peak, the binding decreased gradually to 30 days at which age, adult values were attained.

Aging↗
PubMed1985

Transport of pipecolic acid in adult and developing mouse brain.

In an effort to develop an animal model of hyperpipecolatemia, the uptake of pipecolic acid (PA) in the brain and changes of PA levels in serum following administration of D,L-PA were studied in the mouse using a new sensitive HPLC-EC method. Following i.p. injections (250 mg/kg) to adult male mice, the brain concentration peaks at 5-10 min (40 nmol/g). The level remains relatively stable up to 5 hrs and then declines slowly to 24 hrs. In serum, the level of PA increases rapidly to reach the maximum value at 10 min and then decreases rapidly in the first hour and continues to decline more slowly to 24 hrs. The net uptake of PA following administration of various amounts of D,L-PA is saturable at low doses (3.9-15.6 mg/kg), and it increases linearly at higher doses in a dose-dependent manner up to the maximum dose (500 mg/kg) used in the present study. Kinetic analysis suggests the presence of two kinds of transport systems. These findings are in good agreement with the previous results using D,L-[3H]PA in the mouse (7) and L-[14C]PA in the rat (13). There were no significant differences between uptake of D-pipecolic acid and L-pipecolic acid (250 mg/kg, i.p., 10 min), suggesting the absence of stereospecificity for PA uptake in the mouse brain. Developmental changes in net brain uptake of PA following injections of D,L-PA (250 mg/kg, s.c., 10 min) showed an age-dependent decrease which continues until adult levels are reached at four weeks after birth. The results suggest that the blood brain barrier (BBB) for PA is completed during the first month of life. Following administration of D,L-PA (250 mg/kg, s.c.) to pregnant mice during the period 19-21 days of gestation, PA level increases in fetal brain to a maximum value at 2 hrs (420 nmol/g). This level is unchanged during 24 hrs. The maximum level of PA in fetal serum is reached at 30 min to 1 hr. The level gradually decreases after 1 hr over 24 hrs. These results indicate that PA taken up by the placenta and into the brain is transported from the fetal circulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Acute effects of cholinesterase inhibitors on uptake of choline in the rat iris.

The choline uptake system has been characterized in the albino rat iris. The isolated iris of the rat accumulates choline (Ch) by a high affinity (Km = 3.23 microM) and a low affinity (Km = 68.4 microM) process. The uptake of 1 microM Ch at 37 degrees C was inhibited in a dose-dependent manner by hemicholinium (IC50 is 70 microM) and by ouabain (IC50 is 1 mM). The high affinity uptake was temperature and sodium-dependent. At 0 degrees C uptake of Ch was reduced by over 85% and it was not sensitive to hemicholinium. This suggests that choline is taken up by a high affinity active transport into the cholinergic terminals of the iris. The uptake of 1 microM Ch at 37 degrees C was inhibited by 1 mM scopolamine and was reduced in a dose-dependent manner by the irreversible anticholinesterase diisopropylfluorophosphate (DFP). Physostigmine, an anti-cholinesterase lacking agonistic action, decreased the uptake of Ch to 73% of control at 1 mM. The rat iris is a much more homogeneous and readily accessible tissue than the CNS, therefore, it offers several advantages in pharmacological studies of drug action on a selective population of cholinergic terminals.

Absorption↗
PubMed1985

Pipecolic acid levels and transport in developing mouse brain.

The regional distribution of pipecolic acid (PA) in newborn mouse brain, measured by a new sensitive high performance liquid chromatography with electrochemical detection (HPLC-EC) method, shows a two-fold difference among various areas. Diencephalon, olfactory bulb and anterior telencephalon show the highest PA levels, while the lowest PA levels are seen in mesencephalon and rhombencephalon. The pattern of regional distribution of PA is identical to the regional accumulation in brain of the newborn seen by us following i.p. injections of D,L-[3H]PA9. The highest levels of PA are seen in both brain and serum during the perinatal period of development. Pipecolic acid levels decrease in brain and serum at one day of age and reach adult values within two weeks postnatal. The brain/serum PA ratio (2.9-3.5) during the perinatal period declines gradually after birth to adult values (0.7-0.8) at 30 days. The liver and kidney follow the same pattern with higher levels of PA seen during the perinatal period; however, these levels decreased rapidly to adult levels within one week postnatal. Following injections (250 mg/kg, i.p. and s.c. in the adult and newborn, respectively), D,L-PA accumulates for up to 24 h in the newborn mouse brain. In adult, the cerebral concentration of PA increases rapidly and reaches its peak level in 5-10 min. It remains relatively constant up to 5 h and then declines slowly to 24 h. Pipecolic acid levels in serum show essentially the same pattern of accumulation between adult and newborn mice with some quantitative differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1984

Quantitative determination and regional distribution of pipecolic acid in rodent brain.

A rapid and sensitive method for the quantitative determination of pipecolic acid (PA), one of the three cyclic secondary imino acids present in mammalian brain is described. The quantification and identification of PA are accomplished in rat and mouse brain using high performance liquid chromatography with electrochemical detection (LCEC) and nipecotic acid (NPA) as an internal standard. The cyclic imino acids are derivatized with 2,4-dinitrofluorobenzene (DNFB) to dinitrophenyl derivatives. The remaining time for LCEC analysis is less than 30 min and the limit of sensitivity is in the lower picomole range. The levels of PA found in rat and mouse brain are comparable to those reported using gas chromatography/mass spectrometry. The regional distribution of PA shows higher concentrations of PA in hypothalamus, pons-medulla oblongata and cerebellum. The present results demonstrate that LCEC is sensitive enough to determine endogenous levels of PA in mg amounts of rodent brain tissue. Due to its simplicity and rapidity, the technique represents an alternative to existing methods. This method can also be used for determination of PA in CSF, blood or urine of hyperpipecolic patients.

Animals↗
PubMed1984

Effects of DFP on iridic metabolism and release of acetylcholine and on pupillary function in the rat.

The time course of the effects of the topical administration of 1 microgram of diisopropylfluorophosphate (DFP) onto the cornea of the rat on the function of the iris and the biochemistry of acetylcholine (ACh) was followed for 6 hr after the acute inhibition of acetylcholinesterase (AChE) in the iris. Pupil diameter was normal at 1 min but from 5 min to 6 hr after DFP, the size of the pupil was less than 50% of control. As measured by infra-red video pupillography, complete miosis occurred within 3.5 to 4.0 min after the application of DFP. From this time on, up to 6 hr, a pupillary light reflex could not be elicited. Acetylcholinesterase activity in the iris was reduced to 36% of control 1 min after the application of DFP, decreased to 8% at 5 min and still remained far below control values at 6 hr. Levels of acetylcholine in the iris were increased by 34% 1 min after the application of DFP and by 54% at 5 min. This increase remained stable for 120 min and then started to return to control values but was still 28% above control at 6 hr. Levels of choline (Ch) in the iris were decreased by 22% 5 min after the application of DFP but quickly returned to normal and were the same as controls at all other times tested. Evidence consistent with the presence of muscarinic presynaptic autoreceptors on cholinergic nerve terminals in the iris of the rat was provided by experiments involving electrically stimulated release of labelled ACh from isolated rat irises.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1984

Amitriptyline and imipramine inhibit the release of acetylcholine from parasympathetic nerve terminals in the rat iris.

The electrically stimulated release of [3H]acetylcholine from the parasympathetic nerve terminals of the rat iris in vitro is increased in a dose-dependent manner by scopolamine but is decreased by the tricyclic antidepressants amitriptyline and imipramine. The increased release in the presence of scopolamine seems to be due to the blockade of a presynaptic muscarinic autoreceptor that, in the drug-free state, inhibits the release of acetylcholine. However, at drug concentrations that should have comparable antimuscarinic potency, the antidepressants inhibit the release of acetylcholine. This suggests that the anticholinergic side effects of the antidepressants may be due to the reduced release of acetylcholine from parasympathetic nerve terminals as well as a possible direct postsynaptic muscarinic receptor blocking action. Whatever the mechanism of this action, the antidepressants do not have the same effect as scopolamine at the presynaptic muscarinic autoreceptor in the rat iris.

Acetylcholine↗