[The effect increased choline levels on the synthesis and release of acetylcholine in heart atria in white rats]. / Vliv zvýsené hladiny cholinu na syntézu a uvolnování acetylcholinu v srdecních síních bílých potkanu.

The paper addresses the problem of (1) the relationship of choline in extracellular fluid and acetylcholine (ACh) synthesis in chambers of the heart of white rats, and (2) the possibility of physiological involvement of this ACh in the control of cardiac activity. Within 60 min after s.c. administration of choline in the dose of 300 mg/kg body weight the ACh content rose to 136% of the control value in isolated heart chambers and after administration of 400 mg/kg body weight to 159% of the control value. Increased ACh synthesis failed to affect the heart rate, nor did it increase the tonic effect of vagus innervation of the heart. Excessive ACh could however be released by electric transmural stimulation of isolated heart chambers as well as by potassium depolarization. The release depended on the presence of calcium ions. The obtained results demonstrate that an increase in the level of choline in extracellular fluid results in increased ACh synthesis in nerve terminals. Enhanced release of this ACh is a precondition for high choline levels to induce an increase in parasympathetic control of cardiac function.

[Noncholinergic inhibition is the cause of differences in the heart rate in well-nourished and malnourished rats]. / Necholinergní inhibice je prícinou rozdílu v srdecní frekvenci dobre zivených a podvyzivených potkanu.

The postnatal development of heart rate was compared in rats from average litters (7-10 animals) and from oversize litters (15-18 animals). Rats from oversize litters were found to have a higher heart rate between the 25th and 45th day of life compared to animals from average litters. Over the further developmental period the difference kept decreasing to disappear completely at the age of 85 days. The difference was observed also in animals which received high doses of atropine and metipranolol and is thus not attributable to difference in the tonic influence of adrenergic and cholinergic innervation. Transmural stimulation of the sinoatrial node region in isolated atria allows to demonstrate the negative chronotropic effect in young animals from average litters. This noncholinergic inhibition was not observed in animals from oversized litters and in adult animals of both groups. It was blocked by theophylline in the majority of cases. All the observed findings can be explained in the light of noncholinergic inhibition of the sinoatrial node which is tonically effective in young animals from average litters and disappears in adulthood.

Postnatal development of chronotropic responses to chemical and electrical stimulation of adrenergic nerve endings in the sinoatrial node of the heart of the albino rat.

The positive chronotropic response to stimulation of adrenergic nerve endings in the sinoatrial node was studied in isolated atria from the hearts of rats of different ages. Dimethylphenylpiperazinium (DMPP) was used for chemical stimulation and transmural stimulation of the sinoatrial node region as electrical stimulation; in both cases noradrenaline is released from the nerve endings. With both stimulation methods, postnatal development was recorded in two phases. In the first phase, positive chronotropic responses are markedly increased and attained the maximum at the age of 14 days on using DMPP and of 24 days on using electrical stimulation. In the second phase, positive chronotropic responses diminish and at the age of about 45 days, with both stimulation methods, they become reduced to adult level. The first developmental phase can be attributed to an increase in the noradrenaline content of the nerve endings and the release of a larger amount of the transmitter during stimulation, together with an increase in the noradrenaline sensitivity of the cells of the sinoatrial node. It is not clear why positive chronotropic responses decrease in the second phase, when the noradrenaline content of the myocardial tissue continues to rise and pacemaker sensitivity to noradrenaline is not reduced.

Effect of the early postnatal administration of cortisol on development of the nervous control of cardiac function in albino rats.

When infant rats were treated with cortisol, in daily s.c. doses of 20 mg X kg-1, between the ages of 2 and 15 days, the noradrenaline content of their heart and spleen, between the ages of 23 and 65 days, was lower than in the controls. The decrease in the noradrenaline content did not diminish with advancing age; on the contrary, it was the most pronounced at 65 days. Cortisol treatment did not affect the noradrenaline content of skeletal muscles. The functional significance of the decrease in the noradrenaline content was studied in nervous control of the sinoatrial node of the heart. In agreement with the drop in noradrenaline concentration, transmural stimulation of the sinoatrial node region of isolated atria led to a mild, but statistically significant reduction of the function of sympathetic nerve endings, whereas parasympathetic innervation of the node showed no signs of impairment. This peripheral functional deficiency of sympathetic innervation of the node is not seen in the intact organism, where it is masked by central nervous mechanisms. Rats given cortisol postnatally had a significantly higher heart rate at 23, 33 and 44 days, because, in the presence of normal sympathetic influence, the tone of the parasympathetic nerves was reduced. The heart rate was highest at 23 days; with advancing age the difference diminished and at 65 days it was statistically nonsignificant.

Effect of repeated exercise on postnatal development of the noradrenaline content of the albino rat heart, spleen and skeletal muscle.

The authors studied the effect of repeated elevation of sympathetic activity on the postnatal development of the noradrenaline content of tissues of the albino rat. Between the ages of 15 and 29 days, young rats were forced to swim in water heated to 25 degrees C, 3 X 30 min on weekdays and 1 X 30 min on Saturdays and Sundays. At 30, 45 and 65 days, the noradrenaline content of the tissues was determined spectrofluorometricaLly by the trihydroxyindole method. The noradrenaline content of the heart of trained rats was higher than in the controls in all the given age groups and the size of the absolute difference rose with advancing age. The noradrenaline content of the spleen developed similarly. Repeated exercise did not lead to an increase in the noradrenaline content of skeletal muscle. The results show that the repeated elevation of the activity of sympathetic adrenergic neurones which occurs in young rats during exercise is a long-term factor stimulating the development of sympathetic innervation of the heart and spleen. The development of the neurones innervating skeletal muscle was not stimulated, probably because the activity of these neurones is not increased by stress.

Dependence of the cytotoxic effect of guanethidine on the degree of sympathetic activity.

Young rats aged 15-29 days received a subcutaneous injection of guanethidine sulphate (5 mg/kg body weight) every day. Owing to damage to the postganglionic sympathetic neurones, on about the 60th day of life we observed a significant decrease in the noradrenaline concentration in these animals' hearts compared with the controls. If every guanethidine injection was followed immediately by intensive physical exercise, there was no drop in the heart noradrenaline concentration. Physical exercise of the same intensity performed a few hours before injecting guanethidine did not prevent the drop in the noradrenaline concentration in the heart. The results show that an exercise-induced increase in sympathetic activity, at a time when guanethidine is circulating in the blood and accumulating in the adrenergic neurones, inhibits the cytotoxic effect of guanethidine. Isolated physical exercise performed between the 15th and 29th day of life leads to an increase in the noradrenaline content of the heart of rats aged 60 days.

Adult neurovisceral lipidosis compatible with Niemann-Pick disease type C.

The authors present a case of neurovisceral storage disease with the whole of its clinical course confined to adult life (symptoms from 26 to 46 years of age) and marked by mainly neurological symptomatology with dystonia, vertical supranuclear ophthalmoplegia and progressive mental deterioration as the dominant features. From the results of postmortem structural histochemical and chemical analysis the case was diagnosed as Niemann-Pick disease type C. This case, together with sporadic observations reported by other authors, represents a significant shift in our view of the incidence of NPD type C in older age groups.

Acetylcholinesterase and butyrylcholinesterase activity in the atria of the heart of adult albino rats.

In experiments on adult albino rats the authors used the substances BW 284 C51 (1.5-bis(allyldimethylammoniumphenyl)-pentane-3-one-dibromide) as a specific inhibitor of acetylcholinesterase (AChE) and ethopropazine (10-(2-diethylaminopropyl) phenothiazine hydrochloride) as a specific inhibitor of butyrylcholinesterase (BuChE) to determine the two enzyme activities in atrial homogenates and to investigate changes after AChE or BuChE inhibition of the negative chronotropic effect of acetylcholine (ACh) on atria incubated in vitro. AChE accounted for only 12% and BuChE for 88% of the total ability of atrial homogenates to hydrolyse acetylcholine. The concentration of exogenous ACh needed to reduce the spontaneous frequency of contractions of the isolated right atrium by 30, 60, or 90/min fell by 78%, 79% and 84% respectively after BW 284 C51 inhibition of AChE and by 95%, 94% and 94% after simultaneous inhibition of AChE and BuChE. The significance of AChE in control of the negative chronotropic effect of ACh is thus evidently significantly greater than would correspond to the percentual proportion of AChE in cholinesterase activities in the atria of the rat heart. In can be assumed that AChE is functionally associated with parasympathetic innervation of the heart and that it is probably present in a high concentration in the primary pacemaker region.

Cholinesterases and postnatal development of the negative chronotropic effects of acetylcholine in albino rats.

The negative chronotropic effects of acetylcholine were studied in the isolated atria of the hearts of albino rats aged 2, 15, 29 and 47 days and adult. In untreated preparations, i.e. with full cholinesterase activity, the strongest effects were observed in newborn animals; with advancing age the reaction grew weaker. If cholinesterase activity was inhibited with physostigmine, the differences between the various age groups were obliterated. It is thus evident that the actual acetylcholine sensitivity of the sinoatrial node tissue does alter during postnatal life, but that growing cholinesterase activity reduces the amount of acetylcholine diffusing from the medium into the acetylcholine receptor zone. The change which takes place in cholinesterase activity in the myocardial tissue during postnatal life is so great that is must be taken into account when considering the development of cholinergic control of cardiac function.

Specific characteristics of sympathetic fibres innervating the heart of young rats.

The noradrenaline content of the heart of albino rats was determined spectrofluorometrically by the trihydroxyindole method after adsorption to aluminium oxide. The concentration (mg/kg tissue) changed during postnatal life as follows: at 10 and 18 days--0.13, 24 days--0.18, 35 days--0.21, 45 days--0.34, over 3 months--0.68. We determined whether the low transmitter concentration in the heart tissue of the young was reflected in the function of the sympathetic fibres innervating and sinoatrial node. We stimulated the region of the sinoatrial node electrically in isolated atria and compared the positive chronotropic reaction of preparations from 15-day-old young and adult rats to various forms of stimulation (bursts of 1-5 s, frequencies of 10-100 Hz, voltage 10-25 V, duration of individual pulses 0.02-0.08 ms). The reactions of young and adult rats were all identical except for two: 1. with the shortest pulses (0.02 ms), the sympathetic innervation of the young hardly reacted at all, while adult animals had a marked positive chronotropic reaction; 2. with 5-s bursts, young rats reacted significantly more strongly than adult animals. The first of these differences could be related to lower excitability of infant rat nerve fibres, while insufficient reuptake of noradrenaline in the heart of infant rats could have accounted for the second.

Postnatal development of postganglionic parasympathetic neurones in the heart of the albino rat.

Electrical stimulation of the sinoatrial node region of isolated atria in medium containing physostigmine (0.1 micrograms/ml) produces a negative chronotropic effect whose intensity and duration depend mainly on the amount of acetylcholine released from postganglionic parasympathetic fibres endings. This technique was used to study functional maturation of the given neurones during postnatal development of albino rats. Preparations from animals of different ages were stimulated with 2-second bursts of rectangular pulses (frequency 50 Hz, pulse duration 0.02 ms, voltage 22.5--27.5 V) and frequency changes of the preparation were registered by recording extracellular action potentials. At 10 days the negative chronotropic effect is very weak and at 15 days it is only slightly stronger, but at 18 days it is almost the same as in adult animals. At 24 and 34 days the reaction is somewhat stronger than in adulthood. It can be concluded from these observations that functional maturation of the postganglionic parasympathetic neurones innervating the sinoatrial node in albino rats occurs between the 10th and 20th day of postnatal life.

Postnatal changes in the amount of acetylcholine in the atrial tissue of the albino rat heart.

Changes in the acetylcholine (ACh) content and concentration in the atrial tissue of albino rats between the third day of postnatal life and adulthood were studied. The ACh content (ng in whole atria) rose during the whole of the period in question, from 5.6 ng at 3--4 days to 307.5 ng in adult rats. The ACh concentration (micrograms/g fresh tissue) rose up to the 53rd day after birth, when it attained adult values. The fastest increase in both the ACh content and concentration was observed between the 10th and the 17th postnatal day, when it amounted to over 46% of the total concentration increase between the third day of life and adulthood.

Ion transport in the heart atrial tissue of young and adult guinea-pigs and albino rats.

Rubidium shifts between the extracellular fluid and cells were studied in the isolated atria of guinea-pig and albino rat hearts. In the young of both species, rubidium transport from the incubation medium to the cells was much slower than in preparations from adult animals. That implies that the efficiency of membrane mechanisms for the transport of Na+ and K+ ions in the atrial tissue increases during postnatal life. This conclusion is further confirmed by the finding that the intracellular potassium concentration in the atrial tissue of the young of both species is lower, and the intracellular sodium concentration higher, than in adult animals. Conversely, the serum potassium concentration in the young is higher, and the serum sodium concentration lower, than in adult individuals.

Functional autonomic innervation of mammalian cardiac pacemaker during the perinatal period.

Sinoatrial node pacemaker tissues from perinatal and adult rabbits, guinea pigs and rats were examined in vitro. Changes in spontaneous pacemaker rate produced by stimulation of intranodal vagal and sympathetic nerve endings, were taken as a measure of functional postganglionic innervation of the pacemaker. Results show marked species differences in the development of functional innervation of the cardiac pacemaker in the perinatal period.