Synaptic vesicles isolated from rat heart: l-[3H]norepinephrine uptake properties

Elevation of either axoplasmic norepinephrine or sodium level induced release of norepinephrine from cardiac sympathetic nerve terminals

Using dialysis technique, prominent accumulation of norepinephrine (NE) in the myocardial interstitial space was observed under two different conditions: (1) local administration of a monoamine oxidase inhibitor (pargyline, 1, 10 mM), (2) local administration of a Na, K-ATPase inhibitor (ouabain, 10, 100 microM). Further, pretreatment with a vesicle uptake inhibitor (reserpine, 10 microM) augmented these responses. Either condition independently caused endogenous NE release and a brisk increase in dialysate NE levels might occur as a consequence of non-exocytotic release of NE.

Endogenous catecholamine levels in chronic heart failure. Relation to the severity of hemodynamic abnormalities

Plasma free epinephrine, norepinephrine, and dopamine concentrations were determined in 48, 63, and 45 patients, respectively, with overt congestive heart failure, and compared with those in 26 patients with stable angina but without heart failure. Systemic hemodynamic values were determined to assess the severity of heart failure. Arterial epinephrine levels were not different between patients with heart failure (73 +/- 92 pg/ml) and patients without heart failure (55 +/- 73 pg/ml). In patients with congestive heart failure, norepinephrine (665 +/- 510 pg/ml, mean +/- SD) and dopamine (407 +/- 405 pg/ml) levels were significantly higher than in patients with stable angina without heart failure (norepinephrine 184 +/- 136 pg/ml, p less than 0.001, and dopamine 197 +/- 259 pg/ml, p less than 0.02). However, in patients with congestive heart failure, the plasma norepinephrine levels did not correlate with cardiac index (r = 0.21, p = NS), pulmonary capillary wedge pressure (r = 0.11, p = NS), mean arterial pressure (r = 0.11, p = NS), or systemic vascular resistance (r = 0.18, p = NS). Similarly, there was no correlation between dopamine levels and the hemodynamic abnormalities in patients with congestive heart failure. These findings suggest that although endogenous norepinephrine and dopamine levels are frequently elevated in patients with heart failure, reflecting enhanced sympathetic activity, catecholamine levels do not reflect the severity of heart failure.

Reduced uptake of noradrenaline into storage vesicles from the pregnant uterus

A noradrenaline (NA) storage vesicle fraction was isolated from the uteri of virgin as well as pregnant guinea-pigs. The uptake of 3H-NA into respective vesicle fractions was compared. Total uptake of 3H-NA in the presence of Mg2+ (2.5mM) and ATP (2.5 mM) at 30 degrees C after 20 min was 6.0 +/- 1.4 pmol . mg-1 in uterus fractions from virgin guinea-pigs as compared to 1.87 +/- 0.41 pmol . mg-1 in uterus fractions from pregnant animals. When desipramine (5mM) was added in order to block neuronal uptake the corresponding figures were 4.75 +/- 0.92 and 0.51 +/- 0.18 pmol . mg-1, respectively. Thus in the presence of desipramine (5mM) uptake was reduced by 21.4% in fractions from virgin uteri but by 72.7% in fractions from pregnant uteri. Reserpine (0.1 microM) inhibited uptake of 3H-NA by 34% in fractions from virgin uteri and by 46% in fractions from pregnant uteri. Our results indicate a decreased amount of functional storage vesicles in uteri of guinea-pigs at term pregnancy and are consistent with the proposed degeneration of adrenergic nerves during pregnancy.

Neurohumoral mechanisms involved in congestive heart failure

Congestive heart failure (CHF) promotes an array of biologic changes that are largely designed to compensate for reduced flow. These include activation of the sympathetic nervous system and the renin-angiotensin system, as well as the release of arginine vasopressin. The ultimate expression of these compensatory mechanisms is heightened vascular tone, increased sodium and water retention and antidiuresis. The peripheral circulation is normally under the fine control of circulating and neuronally released moieties, which can directly or indirectly alter vascular tone. Angiotensin II appears to be a key element in this regard because of its multiple biologic activities. Direct arteriolar vasoconstriction, facilitation of norepinephrine release and stimulation of aldosterone are some of the activities that are likely to be of major importance in the syndrome of CHF. Therefore, it is not surprising that converting enzyme inhibitors have a growing role as treatment. Other pharmacologic agents that can reduce sympathetic tone by acting on presynaptic receptors are being developed. Selective dilation of certain vascular beds may be possible with agents designed to interact with vascular dopaminergic receptors. The mechanisms whereby circulating epinephrine and norepinephrine modulate norepinephrine release and vascular tone are beginning to be understood and likely involve presynaptic, postsynaptic and nonsynaptic vascular receptors. A better appreciation of the mechanisms involved in the fine control of the peripheral circulation should allow for more selective and more imaginative pharmacologic therapy for CHF.

Central catecholaminergic lesions in the developing rat: effects of cardiac noradrenaline levels, turnover and release

1. The role of the central nervous system in regulating cardiac sympathetic tone was examined in developing rats with neonatal central catecholaminergic lesions produced by intracisternal 6-hydroxydopamine treatment. 2. Lesioned animals showed a persistent deficit in both cardiac noradrenaline levels and spontaneous turnover rate as evaluated by alpha-methyl-p-tyrosine treatment. 3. Despite these deficits, tyramine was fully capable of releasing cardiac noradrenaline and short-term centrally-mediated release also could be elicited by exposure to cold or by swimming exercise. 4. The alterations in cardiac noradrenaline content produced by the central lesions may result from long-term reductions in sympathetic tone which do not necessarily compromise short-term response capabilities of the sympathetic system.

Noradrenaline release and uptake in isolated small dense cored vesicles from rat seminal ducts

Noradrenaline (NA) release and uptake was investigated in an improved preparation of isolated small dense cored vesicles from rat seminal ducts. The vesicle preparation exhibited an Mg2+-ATP-dependent uptake of NA. Half maximal uptake after 20 min was seen at 22 muM. Exchangeability of NA between medium and vesicles was 100%. The kinetics of exchange suggested that mos NA is stored in a single pool. The t1/2 for release of NA was 43 min in the presence of Mg2+-ATP, as compared to 15 min in the absence of Mg2+-ATP. Addition of reserpine (20 muM) did not significantly alter the NA release. The kinetic properties of this preparation was compared to those of earlier reported noradrenergic vesicle preparations from different tissues.

Transport of catecholamines by native and reconstituted rat heart synaptic vesicles

Highly purified "heavy" synaptic vesicles were isolated from rat heart by differential centrifugation. Because of the high intravesicular concentrations of proteins, catecholamine, and ATP, resealed vesicle ghosts were prepared and used to study the detailed kinetics of catecholamine transport. ATP stimulated the uptake of l-norepinephrine and was saturable with a Km for l-norepinephrine at 3.3 microM and 1.8 mM for ATP. The ghosts also accumulated 5-hydroxytryptamine and l-epinephrine via an ATP-dependent mechanism. Uptake was stereospecific for the l-form. A functional catecholamine transporter could be solubilized by the detergent octyl-glucoside and incorporated into phospholipid vesicles, which, after detergent removal, generated proteoliposomes that accumulated l-norepinephrine. Reserpine- and l-propranolol-sensitive accumulation against a concentration gradient is achieved by artificially creating a pH gradient across the membrane, and lends further support to the idea that at least the initial phase of catecholamine transport is driven by the trans-membrane pH gradient created by the proton-translocating ATPase.