Control of renin release. Effects of d-propranolol and renal denervation on furosemide-induced renin release in the dog

Mecamylamine blocks the [Asp1,Val5]-ANG II-induced attenuation of salt gland activity in Pekin ducks

An intravenous injection of 2 microg of [Asp1,Val5]-ANG II attenuated fluid secretion by the nasal salt glands of Pekin ducks. Ganglionic blockade with mecamylamine stopped salt gland secretion. Flow was reestablished by intravenous methacholine bromide during ganglionic blockade. A second injection of 2 microg of [Asp1, Val5]-ANG II failed to attenuate secretion during ganglionic blockade, showing that the peptide acts via the central nervous system and postganglionic parasympathetic nerves that supply the salt glands. Sympathetic nerves are located in the walls of blood vessels within the salt glands, and adrenergic fibers with "varicosities" supply extensively the secretory tubules. [Asp1, Val5]-ANG II decreased salt gland secretion both before and after alpha1-adrenergic blockade with prazosin, showing that the lowered activity was not caused by the release of norepinephrine from nerve endings and/or duck adrenal chromaffin cells. beta-Adrenergic blockade with propranolol also failed to prevent the attenuation of secretion in response to an intravenous injection of 2 microg of [Asp1,Val5]-ANG II, which showed that epinephrine did not mediate the response to the peptide.

Pharmacokinetics and renal function in preterm infants

There is an increase in the survival rate of preterm infants due to rapid advances in medical knowledge and technology. However, the research and attention paid to the proper use of pharmacotherapy in these infants is still a relatively underdeveloped field. Effective and safe drug therapy requires a thorough understanding of human developmental biology and of the dynamic ontogeny of drug absorption, drug disposition, drug metabolism, and drug excretion. It is apparent that maturation of organ system function and changes in body composition during gestation and during the neonatal period exert a significant effect on the disposition of drugs. This review focuses on the effects of maturational and drug-induced changes in renal function on clinical pharmacokinetics in the preterm infant.

A decade of developments in diuretic drug therapy

New diuretics introduced into clinical medicine during the past decade include potent new loop diuretics such as bumetanide and piretanide, the uricosuric indanyloxyacetic acid derivative indacrinone, and a new generation of sulfamoyl diuretics such as indapamide and xipamide, which are recommended primarily for the treatment of hypertension. Pharmacokinetic studies of individual diuretics have demonstrated that the diuretic and natriuretic responses to the newer agents generally follow the plasma drug concentration-time curves and urinary drug excretion rates. Therapeutic monitoring can therefore be achieved in most patients with edema or hypertension by close clinical observation and laboratory analysis of plasma electrolyte and creatinine concentrations and urinary electrolyte excretion rates. Interest in the mechanisms involved in the renal and extrarenal vascular actions of the newer diuretics has led to a better understanding of how changes in venous compliance, peripheral vascular resistance, and renal blood flow distribution may contribute to the overall therapeutic response to these agents, especially in patients with severe congestive heart failure, renal insufficiency with low glomerular filtration rates, and hypertension with cardiorenal complications. Adverse reactions to modern diuretics, which are mainly an extension of their renal pharmacodynamic effects, have proved to be minimal, provided that the dosage is adjusted to meet but not exceed individual patient requirements. However, the long-term consequences of prolonged periods of diuretic-induced alterations in plasma potassium levels, and metabolic effects that include elevated blood lipids, are still under investigation.

Sequential changes in plasma renin activity and plasma catecholamines in mildly hypertensive patients during acute, furosemide-induced body-fluid loss

To evaluate the role of adrenergic mechanisms in the acute response of renin to furosemide, plasma renin activity (PRA) and plasma catecholamine concentrations were measured for 3 h after i.v. administration of furosemide 1 mg/kg to 8 patients with mild essential hypertension. Furosemide induced a prompt and long-lasting increase in renin, with PRA more than doubled at all times. The increase in PRA within the first 30 min paralleled the peak increases in urinary water and sodium flow rates, and significant decreases in plasma volume and central venous pressure. There was no change in plasma catecholamine concentrations. Plasma noradrenaline was increased significantly at 60 min and adrenaline at 90 min, once furosemide had induced a marked loss of body-fluid and approximately 65% decrease in central venous pressure. Both catecholamines remained elevated until the end of the study, whereas urinary water and sodium flow rates had returned to their pre-treatment values by 150 min. Mean blood pressure was essentially unchanged throughout the study, whereas heart rate increased significantly after 90 min. The findings suggest that in mildly hypertensive patients adrenergic mechanisms are not involved in the initial renin response to furosemide, but they come into play later, probably as a result of reflex sympathetic activation triggered by marked volume depletion.

Role of renal kallikrein in control of renin release in conscious rats

Renal kallikrein was reported to activate human inactive renin and to release active renin from rat renal cortical slices. To evaluate the role of renal kallikrein in the control of renin release in vivo, Trasylol and soybean trypsin inhibitor (SBTI) were used to determine whether they can inhibit renin release stimulated by the administration of furosemide and a 2-wk low-sodium diet. Plasma renin activity (PRA) was increased by furosemide and also by the low-sodium diet. Urinary kallikrein excretion was increased by the sodium depletions. Trasylol did not affect basal PRA; however, it inhibited PRA and urinary kallikrein excretion, when stimulated by furosemide and by a low-sodium diet. These results suggest that furosemide and low-sodium diet act on the kidney to release renin via protease production. Because SBTI affected neither PRA nor urinary kallikrein excretion stimulated by these sodium depletions, it is suggested that renal kallikrein may play an important role in the control of renin release stimulated by furosemide and by low-sodium diet.

Renin release after furosemide and ethacrynic acid in man. Evidence for neural reflex control mechanisms

The mechanisms of renin release after furosemide (F) and ethacrynic acid (EA) in man were examined. We evaluated whether acute volume shifts within the low pressure system after F induce renin release via neural pathways. Immersion in a water-bath or beta-blockade reduced the increase of plasma renin concentration after F but not after EA. It is concluded that acute renin release after F but not after EA in man is partially due to neurally mediated reflexes originating from volume receptors in the cardiopulmonary area.

Mechanisms of hemodynamic actions of furosemide: differentiation of vascular and renal effects on blood pressure in functionally anephric hypertensive patients

To differentiate diuretic and direct cardiocirculatory properties of furosemide for elucidation of the vasodepressor mechanisms of action of the agent in the acute treatment of hypertension, the peripheral vascular effects of intravenous furosemide (3 mg/kg) on supine blood pressure (BP) and forearm hemodynamics in 11 functionally anephric hypertensive patients (creatinine clearance less than 2 ml/min) were studied. BP was recorded by sphygmomanometer and forearm hemodynamics were measured by strain gauge plethysmography. While diastolic BP decreased only 2.7 mm Hg at 30 minutes, forearm blood flow increased 55% (p less than 0.01) mediated by decreased peripheral vascular resistance of 30% (p less than 0.01) at 15 minutes which dissipated by 30 minutes. Systolic BP, indices of venous capacity, weight, hematocrit, serum electrolytes, and plasma renin activity were unchanged. No diuresis occurred. It is concluded that the early hypotensive effect of furosemide depends upon diuresis.

Effect of beta-adrenoreceptor blockade on the renin response to acute natriuresis

1. The response of plasma renin activity to frusemide 40 mg given intravenously, was examined before and after oral propranolol 160 mg daily for 7 days in normal and hypertensive subjects. 2. Although basal renin levels were often reduced, the increase following frusemide was essentially unaltered by propranolol therapy. 3. These findings indicate that enhanced renin activity associated with diuretic use may not be prevented by concurrent propranolol administration. Limitation of hypotensive action of combined beta-blocker diuretic therapy can therefore be anticipated. 4. Preservation of the renin stimulatory effect of frusemide during beta blockade confirms the value of this procedure in the investigation of mineralocorticoid and renovascular hypertension were discontinuation of treatment may be undesirable.

Effect of propranolol on the renin response to frusemide in man

The response of plasma renin activity (PRA) to frusemide, 40 mg given intravenously, was examined before and after oral propranolol 160 mg daily for seven days in normal and hypertensive subjects. Although basal PRA was reduced in many cases, the increase following frusemide was essentially unaltered by propranolol therapy. Evidence is presented that adequate beta adrenoceptor blockade was attained in these studies. Increasing the dose of propranolol to 240 mg daily for seven days in two subjects did not alter renin responsiveness to frusemide. Stimulation of renin release by oral frusemide, examined in one subject, was also unaltered by propranolol therapy. These findings indicate that enhancement of renin activity associated with diuretic use may not be prevented by concurrent propranolol administration. Limitation of the hypotensive action of combined beta blocker-diuretic therapy can therefore be expected. The fact that the renin stimulating effect of frusemide is preserved during beta blockade indicates that this procedure can be used in the investigation of hypertension even in those patients in whom discontinuation of beta blocking treatment may be undesirable.

Glomerular filtration during furosemide diuresis in the dog

Simultaneous clearance and micropuncture experiments were performed in pentobarbital-anesthetized dogs to determine the effect of furosemide (F; 5 mg/kg) on some of the determinants of GFR during replacement of urine losses. Glomerular capillary pressure (PG) was estimated from stop flow pressure (SFP) plus systemic colloid osmotic pressure (pi alpha). Because renal vasodilation during F administration occurs more often when blood pressure is elevated, two groups of dogs were studied. At endogenous renal perfusion pressure (RPP) of 130 mm Hg, one group responded to F with a 28% increase in renal blood flow (RBF). PG rose (a rise of 18 mm Hg) in proportion to the rise in proximal tubule pressure (PT) (a rise of 20 mm Hg). Thus, the difference in pressures (PG - PT) was unchanged, as was GFR. The second group had RPP lowered by renal artery constriction to a point near the lower limit of autoregulation (104 mm Hg). These dogs responded to F with no increase in RBF; PG was lower and remained constant during F, PT, however, increased (a rise of 10 mm Hg). The difference in pressures (delta P) decreased by 30%, and GFR decreased by 40%. Single nephron glomerular filtration rate (SNGFR) also decreased, and estimated Kf, the ultrafiltration coefficient, actually rose slightly. The major reason for the fall in GFR and SNGFR was due to a decrease in delta P rather than a decrease in Kf. The decrease in delta P can be attributed to failure of the renal vasculature to dilate because PG and RBF remained constant. It is likely that these events will be observed less often at hypertensive BP than at normal BP where renal vascular resistence is already close to a minimum value.

Role of the renin-angiotensin system in the blood pressure rebound to sodium nitroprusside in the conscious rat

Intravenous infusions of sodium nitroprusside (SNP) at doses of 20, 40 or 80 micrograms/kg min-1 for 30 min produced dose-related decrements in blood pressure in conscious rats fitted with indwelling aortic and vena caval catheters. Immediately upon termination of SNP infusions, blood pressure rebounded to levels which were significantly above pre-SNP control values. The following evidence indicates that the rebound increase in blood pressure was due to increased activity of the renin-angiotensin system: (1) plasma renin activity was increased approximately four-fold by SNP, (2) rebound did not occur in nephrectomized rats, (3) rebound was markedly attenuated in animals treated with an angiotensin converting enzyme inhibitor, SQ14225, (D-3-mercapto-2-methylpropanoyl-L-proline) and (4) beta-adrenergic receptor blockade with propranolol reduced the rebound response. In addition, the magnitude of the rebound following SNP infusions was directly related to the dose of SNP infused. These results are consistent with the hypothesis that renin accumulates during SNP infusion more rapidly than it is metabolized. Consequently, the accumulated renin elicits a hypertensive response when SNP treatment is withdrawn.

The relationship of urinary prostaglandins and plasma renin to sodium balance and diuresis in normal man

The significance of changes in sodium balance and urinary sodium excretion for renal PG excretion was studied in normal man. In protocol B a strongly negative sodium balance was produced in 5 healthy young subjects by a low sodium diet given for 7 days (lo mmol Na/day) with 80 mg furosemide p.o. added on the last two days. 24 hour urinary PGE2 excretion remained constant, while plasma renin increased. In protocol A the effect of i.v. furosemide (1 mg/kg bwt) on urinary PGE2 and PGF2 alpha excretion rates was examined in 5 healthy young subjects. Rapid but short-lasting increases in PG excretion rates ran in parallel with the changes in urine flow rate. The study suggests that PGE2 is not of importance for the sodium homeostasis in normal man. Renal prostaglandins may play a modifying role for the renal response to loop diuretics but are hardly instrumental for the diuretic effect.