The escape of the renal blood flow response during sympathetic nerve stimulation

Sympatho-renal interactions

The renal nerves appear to be involved in the control of cardiovascular homeostasis and volume balance both in physiological and in pathological conditions such as experimental hypertension. Anatomical and electrophysiological evidence suggests that the kidney has a diffuse sensory innervation connected with areas in the brain and spinal cord that are known to regulate cardiovascular functions by both neural and humoral mechanisms. The demonstration of the existence of neural reno-renal reflexes controlling several renal functions indicates that a functional balance between the two kidneys exists and may play an important role in the moment-to-moment control of kidney functions.

Comparison of the effects of hepatic nerve stimulation on arterial flow, distribution of arterial and portal flows and blood content in the livers of anaesthetized cats and dogs

1. The responses to hepatic nerve stimulation were studied in cats and dogs anaesthetized with sodium pentobarbitone. In three series of experiments, hepatic arterial flow was recorded by an electromagnetic flowmeter, intrahepatic distributions of arterial and portal flows were studied by radioactive microspheres, and hepatic volume responses were measured by a plethysmographic method.2. In cats, nerve stimulation produced a frequency-dependent decrease in hepatic arterial flow which was not maintained and autoregulatory escape occurred. In dogs, the initial decrease in arterial flow was similar but escape did not occur and the vasoconstriction was well maintained.3. In both cats and dogs, stimulation of the hepatic nerves did not cause a redistribution of either arterial or portal flows within the liver. Autoregulatory escape in the liver of the cat was not associated with an intrahepatic redistribution of arterial flow and is best interpreted as relaxation of the same vessels which were initially constricted, due to increased production of a vasodilator factor.4. Stimulation of the hepatic nerves caused a marked frequency-dependent decrease in hepatic volume which was well maintained and the responses were similar in cats and dogs. The quantitative importance of the liver as a blood reservoir is compared in relation to other vascular beds and the concept of the blood volume reserve is discussed.

Output of prostaglandins from the rabbit kidney, its increase on renal nerve stimulation and its inhibition by indomethacin

1. In each of six experiments, prostaglandins were identified in the renal venous blood of the rabbit. The concentrations in renal venous blood were up to 45 times higher than in aortic blood, suggesting that most of the prostaglandins originate from the kidney.2. Prostaglandins E(2), F(2a) and a prostaglandin of the A, C or B series were estimated by biological assay after solvent partition and column or thin-layer chromatography.3. Prostaglandins E(2) and F(2a) were identified conclusively by combined gas chromatography-mass spectrometry.4. Electrical stimulation of the renal nerve increased the output of prostaglandins.5. Indomethacin (10 mg/kg) injected intravenously, reduced the output of prostaglandins into renal venous blood and prevented the increase in output on renal nerve stimulation.

Changes in regional blood flow and cardiodynamics evoked by electrical stimulation of the fastigial nucleus in the cat and their similarity to orthostatic reflexes

1. Changes in regional blood flow and cardiodynamics were measured in anaesthetized paralysed cats during electrical stimulation of the rostral fastigial nucleus.2. Fastigial stimulation results in a graded, highly reproducible and stereotyped cardiovascular response characterized by (a) increased systolic, diastolic and mean arterial pressures without changes in central venous or occluded vein pressure, (b) decreased blood flow and increased vascular resistance in the axillary, renal, femoral and mesenteric arteries, increased flow without any change in vascular resistance in the common carotid artery, and increase in total peripheral resistance, (c) a small increase in heart rate and myocardial contractile force, decrease in calculated stroke volume, and no change in the cardiac output.3. Changes in regional arterial flow were abolished by transection of sympathetic nerves or blockade of alpha-adrenergic receptors by systemic administration of phentolamine.4. Changes in heart rate and myocardial contractility were abolished by stellate ganglionectomy or blockade of beta-adrenergic receptors by propranolol.5. No changes in pupillary diameter or retraction of the nictitating membrane were seen during fastigial stimulation with stimuli producing substantial changes in blood pressure.6. The fastigial pressor response represents a highly reproducible, stereotyped, graded, and differentiated pattern of activation of sympathetic preganglionic neurones.7. The pattern of cardiovascular effects of fastigial stimulation simulates the compensatory (orthostatic) reflex response to maintenance of an upright posture.8. Fastigial stimulation appears to excite the neural network subserving orthostatic reflexes.