Relative importance of sympathetic nerves and of circulating adrenaline and vasopressin in mediating hypertension after lesions of the caudal ventrolateral medulla in the rat

Electrolytic lesions of the A1 noradrenaline cells in the caudal ventrolateral medulla cause transient hypertension and bradycardia in the conscious rat, as previously described in the rabbit. The lesions produced 100-fold increases in plasma arginine vasopressin, 40-fold increases in plasma adrenaline and fourfold increases in plasma noradrenaline levels. Absence of circulating vasopressin [homozygous diabetes insipidus rats (DI)] or circulating adrenaline (adrenalectomized rats) did not affect A1 hypertension, but sympathectomy with systemic 6-hydroxydopamine (6-OHDA) significantly attenuated A1 hypertension. A factorial experiment was performed to assess the relative contributions of these three peripheral effector mechanisms in a quantitative manner, with combined deficiencies of any two or of all three of these effector systems. Results suggest A1 hypertension in the rat to be primarily mediated through increased sympatho-adrenal activity. The largest component of hypertension (66%) results from increased sympathetic vasoconstrictor nerve activity, and a smaller part (34%) reflects the action of circulating adrenaline. Increases in vasopressin levels do not contribute to A1 hypertension, although vasopressin makes a major contribution to A1 lesion bradycardia.

The mechanism of hypertension and bradycardia following lesions of the caudal ventrolateral medulla in the rabbit: the role of sympathetic nerves, circulating adrenaline, vasopressin and renin

Lesions of the ventrolateral medulla of the rabbit, coinciding with the A1 noradrenaline cell bodies (A1 lesions) produced fortyfold increases in the plasma levels of vasopressin and adrenaline, a twofold increase in plasma noradrenaline and a substantial increase in plasma renin activity. These increases accompanied the hypertension and bradycardia that follow A1 lesions. The vasoconstriction and hypertension were completely abolished by phentolamine, an alpha-adrenoceptor antagonist, when it was administered before lesions and were markedly reduced when it was given after lesions. On the other hand, administration of an antagonist to the vasoconstrictor action of vasopressin (d(CH2)5Tyr(Me)AVP) or an angiotensin converting enzyme inhibitor had little effect. Prior removal of the adrenal glands prevented any rise in plasma adrenaline levels but had no effect on the pressure response to subsequent A1 lesions. These results indicate that the vasoconstriction and hypertension were predominantly mediated by alpha-adrenoceptor stimulation, acting mainly through sympathetic vasoconstrictor nerves. The fall in heart rate following A1 lesions was approximately halved by pretreatment either with d(CH2)5Tyr(Me)AVP alone, or by blockade of the vagus and sympathetic with scopolamine and propranolol; it was completely abolished by combined pretreatment with all three agents. The experiments show that vasopressin release makes a major contribution to the bradycardia acting at least in part through mechanisms that are independent of cardiac vagal or sympathetic nerves.

Hypertension after brainstem (A1) lesions in normal rats and in rats with adrenalectomy, sympathectomy or diabetes insipidus

Lesions of the ventrolateral medulla coinciding with the A1 noradrenaline cell group, in either the rabbit or the rat, cause hypertension and bradycardia accompanied by 50-fold increases in plasma vasopressin and adrenaline and a two-to-four-fold increase in plasma noradrenaline. Following adrenalectomy in normal rats, the A1 hypertension and bradycardia were unchanged. In Brattleboro rats with diabetes insipidus, A1 hypertension was not altered but the bradycardia was reduced by 40%. In Brattleboro rats subjected to adrenalectomy, the hypertension was reduced by 50%. In normal rats, chemical sympathectomy with intravenous 6-hydroxydopamine (6OHDA) reduced the hypertension by about 50%, and when combined with adrenalectomy it abolished the hypertension altogether. In Brattleboro rats, 6OHDA reduced the hypertension after A1 lesions by about 40%. We suggest that A1 hypertension is predominantly mediated through increased activity of sympathetic vasoconstrictor nerves, and that circulating adrenaline and vasopressin only make a minor contribution to the increase in pressure.

Hyperkalemia in the elderly

Hyperkalemia is a common and potentially dangerous condition in elderly patients. These subjects are more likely to have a disease or be taking medications that may induce this disorder. We describe three such cases where the increased concentration of potassium in plasma resulted from decreased renal excretion of this ion, and suggest a simple approach to the etiological diagnosis of hyperkalemia.

Hyperkalemia in the elderly

Hyperkalemia is a common and potentially dangerous condition in elderly patients. These subjects are more likely to have a disease or be taking medications that may induce this disorder. We describe three such cases where the increased concentration of potassium in plasma resulted from decreased renal excretion of this ion, and suggest a simple approach to the etiological diagnosis of hyperkalemia.

Biomimetic approach to potential benzodiazepine receptor agonists and antagonists

Several beta-carbolines, isoquinolines, imidazopyridines , and canthin -6-ones prepared in biomimetic fashion were tested for their ability to bind to the benzodiazepine receptor. Methyl isoquinoline-3-carboxylate, methyl 6,7- dimethoxyisoquinoline -3-carboxylate (3b) 1-phenyl-3- carbomethoxyimidazopyridine , (6B,) and canthin -6- one ( 13a ) bound with moderate affinities, while 2- carbomethoxycanthin -6- one ( 13b ) bound to benzodiazepine receptors with an affinity comparable to several pharmacologically active benzodiazepines. The potency of 13b suggests that the benzodiazepine receptor(s) can tolerate substitution at positions 1 and 9 of a beta-carboline without loss of activity if the substituents are trigonal and maintain a planar topography. Moreover, displacement of the carbonyl group by two atoms from the aromatic ring (C) of the beta-carboline skeleton caused a marked decrease in binding to the benzodiazepine receptor. This observation supports the hypothesis that maximum binding affinity of beta-carbolines is achieved when the carbonyl group at position 3 is attached directly to the aromatic pyridine ring.

A benzodiazepine receptor antagonist decreases sleep and reverses the hypnotic actions of flurazepam

The benzodiazepine receptor antagonist 3-hydroxymethyl-beta-carboline, which blocks several of the pharmacological actions of benzodiazepines, induces a dose-dependent increase in sleep latency in the rat. Furthermore, at a low dose that by itself does not affect sleep, 3-hydroxymethyl-beta-carboline blocks sleep induction by a large dose of flurazepam. The benzodiazepine receptor may play a role in both the physiological regulation and pharmacological induction of sleep.

Blockade of 3-carbomethoxy-beta-carboline induced seizures by diazepam and the benzodiazepine antagonists, Ro 15-1788 and CGS 8216

The benzodiazepine antagonists Ro 15-1788 and CGS 8216 blocked the clonic and tonic convulsions elicited by 3-carbomethoxy-beta-carboline (beta-CCM). The PD50 values for Ro 15-1788, CGS 8216, and diazepam were: 2.0, 0.6, and 2.0 mg/kg, respectively. Neither Ro 15-1788 nor CGS 8216 potentiated the effect of a threshold convulsant dose of beta-CCM. Moreover, these benzodiazepine antagonists neither attenuated nor potentiated the tremorigenic actions of another beta-carboline, harmaline. Diazepam, however, considerably reduced the tremorigenic actions of this drug.

Beta-carbolines: synthesis and neurochemical and pharmacological actions on brain benzodiazepine receptors

We have prepared a series of tetrahydro-beta-carbolines (TH beta C), beta-carbolines (beta-C), and other nitrogen heterocycles and evaluated them in vitro with respect to their ability to bind to benzodiazepine receptors. The fully aromatic beta-C's were more potent than their corresponding TH beta C derivatives. When substituents possessing a carbonyl (CO2Me, COCH3, CHO) were introduced at the beta-C 3-position the in vitro potency was augmented. Alcohol substituents (CH2OH, CHOHCH3) demonstrated decreased in vitro potency. The importance of the carbonyl moiety was further demonstrated when beta-carboline-3-carboxylic acid was shown to bind tighter to benzodiazepine receptors at lower pH. A lower pH increases the concentration of the acid and decreases the concentration of the anion. 3-(Hydroxymethyl)-beta-carboline (24), 3-formyl-beta-carboline (25) and 3-acetyl-beta-carboline (27) were benzodiazepine antagonists in vivo. Methyl isoquinoline-3-carboxylate (31a) also had in vitro activity. The same structure-activity relationships seen in beta-C's were also observed for isoquinolines.

Improved thin-layer chromatography of disaturated phosphatidylcholine in amniotic fluid

We describe an indirect test of fetal lung maturity: the quantitation of disaturated phosphatidylcholine in amniotic fluid. The lipids in samples of amniotic fluid from 172 patients were reacted with osmium tetroxide, and disaturated phosphatidylcholine was then isolated by thin-layer chromatography. Interfering substances were retained by a pre-adsorbent layer. The charred disaturated phosphatidylcholine, quantitated by densitometry, was compared to standard dipalmitoyl phosphatidylcholine. Both within-run and between-run coefficients of variation were about 10%. Blood and meconium do not interfere. Six infants developed respiratory distress when disaturated phosphatidylcholine concentrations of amniotic fluid drawn within 72 h of delivery were less than 5.5 mg/L. A concurrently determined lecithin/sphingomyelin ratio falsely predicted lung maturity in one of these. In seven other samples for which lecithin/sphingomyelin ratios suggested lung immaturity but disaturated phosphatidyl-choline predicted maturity, none of the infants developed respiratory distress. In normal pregnancies, measurement of disaturated phosphatidylcholine in amniotic fluid appears to be a better predictor of fetal lung maturity than is measurement of the lecithin/sphingomyelin ratio. Further studies are needed to determine if this analysis is a better predictor in diabetic pregnancies.

Improved thin-layer chromatography of disaturated phosphatidylcholine in amniotic fluid

We describe an indirect test of fetal lung maturity: the quantitation of disaturated phosphatidylcholine in amniotic fluid. The lipids in samples of amniotic fluid from 172 patients were reacted with osmium tetroxide, and disaturated phosphatidylcholine was then isolated by thin-layer chromatography. Interfering substances were retained by a pre-adsorbent layer. The charred disaturated phosphatidylcholine, quantitated by densitometry, was compared to standard dipalmitoyl phosphatidylcholine. Both within-run and between-run coefficients of variation were about 10%. Blood and meconium do not interfere. Six infants developed respiratory distress when disaturated phosphatidylcholine concentrations of amniotic fluid drawn within 72 h of delivery were less than 5.5 mg/L. A concurrently determined lecithin/sphingomyelin ratio falsely predicted lung maturity in one of these. In seven other samples for which lecithin/sphingomyelin ratios suggested lung immaturity but disaturated phosphatidyl-choline predicted maturity, none of the infants developed respiratory distress. In normal pregnancies, measurement of disaturated phosphatidylcholine in amniotic fluid appears to be a better predictor of fetal lung maturity than is measurement of the lecithin/sphingomyelin ratio. Further studies are needed to determine if this analysis is a better predictor in diabetic pregnancies.

Blood-perfused working isolated rat heart

We describe a method for perfusion of a working isolated rat heart with washed erythrocytes suspended in a Krebs-Henseleit bicarbonate buffer containing bovine albumin (fraction V). With washed pig red cells, as hematocrit was varied between 0 and 40%, coronary flow (CF), aortic flow (AF), external work (W), and myocardial oxygen consumption (MVO2) were measured. Hemodynamic data at a hematocrit of 30% (CF = 5.4 +/- 0.7 ml/min per g, AF = 75 +/- 8 ml/min per g) were identical with those reported for the intact animal. Coronary sinus PO2 was highest with a red cell-free perfusate suggesting that coronary flow is partially shunted. Human red cells obtained from banked blood, were tried also with success. With careful filtration, the preparation is stable for 2 h and well suited for study of the dynamics of myocardial oxygen delivery.