Renal Blood Flow, Glomerular Filtration Rate, Renal PAH Extraction Ratio, and the Role of the Renal Vasomotor Nerves in the Unanesthetized Rabbit

Diagnosis of renal disease in rabbits

There are differences in renal anatomy and physiology between rabbits and other domestic species. Neurogenic renal ischemia occurs readily. Reversible prerenal azotemia may be seen in conjunction with gut stasis. Potentially fatal acute renal failure may be due to structural kidney damage or post-renal disease. Chronic renal failure is often associated with encephalitozoonosis. Affected rabbits cannot vomit and often eat well. Weight loss, lethargy, and cachexia are common clinical signs. Polydypsia/polyuria may be present. Derangements in calcium and phosphorus metabolism are features of renal disease. Radiography is always indicated. Urolithiasis, osteosclerosis, aortic and renal calcification are easily seen on radiographs.

Bioavailability and metabolism of cidofovir following topical administration to rabbits

The bioavailability and metabolism of the antiviral nucleotide analog cidofovir (HPMPC) were examined in New Zealand white rabbits following topical administration to normal and abraded skin. Male rabbits (four per group) received 14C-cidofovir (100 microCi/kg) intravenously (1 mg/kg) as a solution or topically (2 mg/animal) as a 1% w/w gel containing hydroxyethylcellulose (HEC) with or without propylene glycol (PG). The same PG/HEC formulation was applied topically to an abraded skin site in a fourth group of animals. All radioactivity detected in plasma and skin was accounted for by cidofovir. Plasma concentrations of radioactivity declined multiexponentially following intravenous administration, with a terminal half-life of 5.4 h. For intact skin, the absolute bioavailabilities of the HEC and PG/HEC formulations were 0.2 and 2.1%, respectively. For abraded skin, the bioavailability for the PG/HEC gel was 41%. Radioactivity in kidneys was attributed to cidofovir ( > 95%) and cyclic HPMPC. Concentrations in kidney following topical administration of cidofovir to normal skin were < 4% of those following intravenous dosing. Topical application of cidofovir to intact skin led to negligible systemic exposure to the drug. The topical bioavailability and hence the flux of cidofovir through intact skin was enhanced by the presence of PG in the formulation. Abrasion of the skin removed the principal barrier to absorption and led to significant systemic exposure to cidofovir.

EFFECT OF POSTHEMORRHAGIC ANEMIA ON THE RENAL CIRCULATION OF THE UNANESTHETIZED RABBIT

In the unanesthetized rabbit made acutely anemic by bleeding with plasma replacement, there was no change in renal blood flow (RBF), a reduction in glomerular filtration rate (GFR), and a reduction in renal vascular resistance with a fall in the filtration fraction. There was evidence of renal tissue hypoxia and reduction in renal PAH extraction ratio. The extraction ratio was 97% at a hematocrit ratio of 34.5%, 91% at a hematocrit of 11.5%, and 84% with hematocrits between 6 and 10%. The effects of carboxyhemoglobinemia at normal blood viscosity were compared with the effects of anemia; a smaller reduction in renal PAH extraction ratio was found and there was no reduction in filtration fraction. The reductions in renal vascular resistance and filtration fraction in anemia were partly reversed by breathing 100% O 2 , viscosity changes again being minimized. It was concluded that renal tissue hypoxia and reduction in red cell concentration contribute in varying degrees to the changes in the renal vascular bed and the PAH extraction ratio.

The renal circulation of conscious rabbits

1. The renal circulatory instability that some believe is inherent in rabbits was studied. 2. In five, conscious rabbits, glomerular filtration rate (GFR) averaged 4.2 +/- 0.6 ml/min/kg body wt after 1 hr, but changed to an overall average of 3.5 +/- 1.5 ml/min/kg wt after 3 hr. 3. Between-measurement coefficient of variation for GFR was more than 30% for three rabbits and 10% or less for two. 4. Renal blood flow (RBF) was even more variable. 5. The renal circulatory instability may be associated with differences in sympathetic activity by mechanisms not existing in other mammals.

Role of angiotensin II in renal wrap hypertension

The role of angiotensin II in the development of renal wrap hypertension was studied in rabbits that underwent either bilateral renal cellophane wrap or sham operation. In half the rabbits, angiotensin II production was blocked by continuous administration of enalapril. Four weeks after renal wrapping, mean arterial pressure had risen by 48 +/- 5 mm Hg in untreated rabbits, but by only 25 +/- 4 mm Hg in enalapril-treated rabbits (p less than 0.01). Similar differences were also measured 6 weeks after wrapping. In untreated rabbits, plasma renin activity had increased fourfold 4 and 6 weeks after renal wrapping. There were no significant changes in blood pressure or plasma renin activity following sham operation. Compared with that in sham-operated rabbits, renal blood flow was reduced by 60% in the untreated rabbits 4 weeks after wrapping but by only 30% in the enalapril-treated wrapped rabbits (p less than 0.05). Renal vascular resistances were 5.5 +/- 1.7 mm Hg . ml-1 . min-1 and 1.2 +/- 0.1 mm Hg . min . ml-1 in the untreated wrapped and sham-operated rabbits respectively and 1.9 +/- 0.4 mm Hg . min . ml-1 and 0.8 +/- 1 mm Hg . min . ml-1 in the enalapril-treated wrapped and sham-operated rabbits. Renal wrapping did not alter filtration fraction in untreated rabbits, but markedly reduced it in enalapril-treated rabbits. These results suggest that angiotensin II had two major effects in rabbits after bilateral renal wrapping: it contributed substantially to the increase in blood pressure and caused renal vasoconstriction, primarily at a postglomerular site.

The cortical and medullary blood flow at different levels of renal nerve activity

The effect of (1) renal denervation and (2) stimulation of the renal nerve on the regional renal blood flow were determined by the Rb uptake method. Under control conditions the total renal blood flow was 3.64 +/- 0.09 ml X min-1 X g-1 tissue increasing significantly (p less than 0.02) to 4.39 +/- 0.28 ml X min-1 X g-1 after denervation. Upon stimulation of the peripheral portions of the sectioned renal nerves the blood flow decreased almost linearly with the frequency of stimulation reaching 0.99 +/- 0.24 ml X min-1 X g-1 at 10 Hz. Utilizing the relation between blood flow and stimulation frequency the control blood flow correspond to a spontaneous activity of 1.5 Hz. As expected the cortical blood flow responded in the same way as for the total renal blood flow. In the renal medulla denervation gave a much more pronounced response where e.g. the inner medullary flow increased from 0.88 +/- 0.09 to 1.30 +/- 0.16 ml X min-1 X g-1, i.e. a 50% increase (p less than 0.05). Stimulation with 2 Hz produced a steep fall in the blood flow, whereafter it decreased linearly with the stimulation frequency reaching 0.11 ml X min-1 X g-1 at 10 Hz stimulation. This demonstrates again that the renal medulla is sensitive to renal nerve activity primarily in the low level range. It should be remarked, however, that the 86-Rb uptake method reflects the effective blood flow, which might differ from the blood flow in absolute terms.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of graded renal nerve stimulation on renal function in the anaesthetized rabbit

The renal nerves of the rabbit were stimulated to cause less than 5, 9 or 22% reduction in renal blood flow. Glomerular filtration rate was reduced by 0, 3 and 11% respectively when the renal nerves were stimulated at these increasing rates. At low and moderate rates of renal nerve stimulation absolute and fractional sodium excretions were reduced by between 17 and 22%, but at the highest rates they were reduced by 55 and 53% respectively. At increasing rates of renal nerve stimulation plasma renin activity was increased by 40, 70 and 180%.

Organ scaling in mammals: the kidneys

Values of kidney weight in adult male and female mammals, both terrestrial and aquatic, as well as values for renal blood flow and glomerular number and diameter, were submitted to linear (log-log) regression analysis. The slope of the regression line for kidney weight in 63 species of adult terrestrial mammals was 0.85 %/- 0.01. No statistically significant difference was found between the slopes of the regression lines for male and female terrestrial mammals. The slope of regression line for kidney weight in eight species of adult aquatic mammals was 0.92 +/- 0.01. Again, no statistically significant difference was found between the slopes for males and females. However, the slope (0.92) of the regression line for aquatic mammals was significantly different from the slope (0.85) for terrestrial mammals (P much less than 0.001). The slope of the regression of renal blood flow on body weight was 0.82 +/- 0.01. This value is consistent with the hypothesis that renal blood flow represents a constant fraction of cardiac output (over about 3.4 orders of magnitude in body weight). The slopes of the regression lines for glomerular number (per kidney) and mean glomerular diameter were 0.59 +/- 0.02 and 0.11 +/- 0.01, respectively. A schematic model representing the scaling of energy-partitioning in mammals is introduced.

The glomerular filtration rate in unrestrained rabbits determined by means of an implanted telemetrical device

An implanted radio-telemetrical device, which consists of a Geiger-Müller detector, a high voltage supply and a FM transmitter, incapsulated in araldite (weight 130 g) was used to measure the body disappearance rate of 125I-iothalamate following a single i.v. bolus in unrestrained and undisturbed rabbits. The disappearance curve is practically monoexponential from 10 to 60 minutes after administration of the indicator and the disappearance rate constant (Ke) is closely correlated to the "final slope" of the plasma disappearance curve of 125I-iothalamate (kp) r=0.99). A linear correlation was also found between Ke and GFR measured simultaneously by constant infusion clearance technique, using an indicator not detected by the Geiger-Müller detector (51Cr-EDTA) (r=0.98). The ratios between the renal clearances of 125I-iothalamate, 51Cr-EDTA and inulin were determined by constant infusion clearance technique in a separate series of experiments since no data were available in the present literature. The results show that GFR can be determined by means of the telemetrical method and in a series of experiments in undisturbed rabbits GFR was found to be on average 4.7 ml . min-1 . kg-1 (expressed as inulin clearance). Using the same technique in lightly pentobarbital anesthetized rabbits GFR was on average 3.5 ml . min-1 . kg-1.

Role of the autonomic nervous system in the acute responses to renal artery pressure reduction in conscious dogs

1. Plasma renin and arterial pressure responses to acute renal artery pressure reduction were compared in intact dogs and "autonomically-blocked" dogs subjected to adrenalectomy, chronic guanethidine treatment and acute vagal block (methscopolamine). 2. Following reduction of renal artery pressure plasma renin activity and concentration rose more in the autonomically blocked dogs than in the intact dogs. When renal artery pressure was held at 30 mmHg for 1 h, plasma renin activity rose by 19.1 ng/ml per h (range 11.6-28.7) in autonomically blocked dogs and 3.65 ng/ml per h (range 1.54-5.89) in intact dogs. When renal artery pressure was held at 60 mmHg plasma renin activity rose 3.28 ng/ml per h (range 2.4-4.7) and 1.90 ng/ml per h (range 1.30-3.56), respectively. 3. Arterial blood pressure also rose more in autonomically blocked dogs in accord with the greater rise in plasma renin activity. The relationships between the increases in arterial pressure and plasma renin were closely similar in the two groups. 4. We conclude that the release of renin and increase in arterial blood pressure in response to renal artery stenosis is normally inhibited by arterial baroreflexes.

The use of radioactive microspheres to compare the effects of hydralazine, guanethidine and SK & F 24260 on the redistribution of cardiac output in anaesthetized rabbits

1 The use of radioactive microspheres is described for the measurement of cardiac output in anaesthetized rabbits and its redistribution after the administration of drugs which lower blood pressure. 2 Hydralazine increased peripheral vascular conductance by 123%. The vascular beds in which it had most effect were those of the carcass (mainly muscle) and the kidneys. 3 SK&F 24260, (1,4 dihydro-2, 6-dimethyl-4(2-trifluoremethylpheny)-3,5,-pyridinedicarboxylic acid diethyl ester), had similar vasocilator actions. Its effect in the carcass contributed relatively more to the increase of total peripheral conductance. It also caused a remarkable degree of cerebral vasodilatation. 4 Guanethidine had a relatively small effect on total peripheral conductance and lowered blood pressure mainly by reducing stroke volume and cardiac output.

Influence of intracranial osmotic stimuli on renal nerve activity in anaesthetized cats

In baroreceptor denervated cats one internal carotid artery (ICA) or the cerebral ventricular system (CVS) was perfused with isotonic, hypertonic and hypotonic sodium chloride solutions. Renal sympathetic activity (RSA) and blood pressure (BP) were recorded. ICA perfusion with isotonic sodium chloride (150 mM NaCl) produced no changes of RSA compared to control level,. RSA was increased from plus 30% to plus 350% in 44 tests out of 45 tests following hypertonic (425 mM NaCl) ICA perfusion. RSA was decreased following hypotonic (aqua dest.) ICA perfusion from minus 30% to minus 100% in 37 tests out of 50 tests. The degree of RSA changes was found to depend upon the osmolarity of the solutions. 425mM NaCl and aqua dest. produced greater RSA changes than 290 mM NaCl and 75 mM NaCl. CVS perfusion with isotonic sodium chloride produced a slight increase of RSA compared to control levels (plus 15%). Hypertonic sodium chloride produced a RSA increase from plus 15% to plus 135% in 10 tests out of 14 tests. Hypotonic sodium chloride produced a RSA decrease from minus 15% to minus 80% in 8 tests out of 14 tests. Changes of RSA following ICA perfusions and CVS perfusions were accompanied by changes of BP in the same direction. A quantitative correlation between delta RSA and delta BP could not be found. Results suggest that renal osmoregulatory response to osmotic stimuli in the carotid artery may not just arise in response to changing ADH levels but may also be induced by changes in RSA.

Effects of changes in pO2, pCO2 and pH on the total vascular resistance of perfused cat kidneys

1. The effects of change in arterial P(O2), P(CO2) and pH on the total vascular resistance (RVR) of the perfused cat kidney have been separately measured and expressed as +/- percentage deviations from control values.2. Control levels in arterial blood were pH 7.38, P(-) (O2) 160 mm Hg, in equilibrium with 5% CO(2).3. Increase in P(O2) alone, in excess of 220 mm Hg, raised RVR reversibly reading 108% control levels at a P(O2) 280 mm Hg (P = < 0.001).4. High levels of P(O2) favoured the onset of ;outflow block', which was characterized by irreversible increase in RVR accompanied by rise in plasma filtration fraction (F.F.) and in the extraction ratio for p-aminohippuric acid (PAH extraction).5. Reduction in P(O2) to 80 mm Hg decreased RVR by 4% (P = < 0.001).6. RVR was not significantly affected by pH changes within the range 7.25-7.45. Lowering arterial pH to 7.15 raised RVR by 4% (P = < 0.001) reversibly. Increase in arterial pH to 7.56 raised RVR by 6% (P = < 0.001) reversibly.7. Changes in arterial P(CO2) produced large inverse reversible changes in RVR. Halving P(CO2) raised RVR by 18%; doubling P(CO2) decreased RVR by 25%.8. Changes in RVR caused by alteration of arterial pH or P(CO2) were not accompanied by changes either in F.F. or in PAH extraction.

Distribution of peripheral blood flow in primary tissue hypoxia induced by inhalation of carbon monoxide

1. The effects of primary tissue hypoxia induced by the inhalation of small concentrations of carbon monoxide in air on the distribution of blood flow in the portal, renal, muscle and skin beds have been studied in normal unanaesthetized rabbits, in animals without functioning autonomic effectors (;de-efferented' rabbits) and in animals with section of the carotid sinus and aortic nerves (;de-afferented' rabbits).2. The pattern of blood flow distribution during CO hypoxia was similar in ;de-efferented' and ;de-afferented' animals, suggesting that the effects in the latter were determined by local mechanisms. The susceptibility of the various beds to the local dilator effects of CO hypoxia was markedly different, the greatest dilator effects being observed in the portal bed, followed by skin, kidney, and muscle. The pattern is somewhat different from that observed in arterial hypoxia.3. In this type of hypoxia the arterial baroreceptors are probably the main afferent source of reflex activity. In normal animals reflex constrictor effects affect the portal and renal beds most, ;moderating' the local dilator effects of hypoxia in these beds. In muscle there is vasodilatation, probably the result of adrenaline secretion, but the response in skin is largely determined by the local effects of hypoxia. The total orthosympathetic activity evoked in this type of hypoxia appears to be less than in severe arterial hypoxia.

Local and reflex factors affecting the distribution of the peripheral blood flow during arterial hypoxia in the rabbit

1. The effects of severe arterial hypoxia on the blood flow in the portal vein, and in kidney, muscle and skin beds have been determined in normal unanaesthetized rabbits, in animals without functioning autonomic effectors, and in rabbits with section of the carotid sinus and aortic nerves.2. The resting blood flows in the above regions were not significantly different in the three groups.3. The susceptibilities of the various beds to the local dilator effects of arterial hypoxia (assessed from the responses of animals without functioning autonomic effectors) were markedly different; vasodilatation was by far the greatest in the portal bed, followed in order by the renal, skin and muscle beds.4. Section of the carotid sinus and aortic nerves completely abolished reflex activity, and the pattern of peripheral blood flow changes was similar to that of animals without functioning autonomic effectors. The findings suggest that the arterial chemoreceptors are the primary afferent source of reflex control of the peripheral circulation in arterial hypoxia.5. In normal animals with intact reflexes there was sustained vasoconstriction throughout the treatment period in the portal and renal bed. The net vasomotor effects in muscle and limb skin were small owing to the operation of a number of factors, which opposed the effects of reflexly increased sympathetic nerve activity.

Role of the autonomic nervous system in the renal vasoconstriction response to hemorrhage in the rabbit

In normal unanesthetized rabbits with intact autonomic effectors, rapid removal of 26% of the blood volume resulted in prolonged renal vasoconstriction. This response was completely absent in rabbits without functioning autonomic effectors (after guanethidine treatment + adrenalectomy + atropine), despite the greater arterial hypotension in this group. The effects of removing 26% and 32% of the blood volume were compared in the normal innervated and chronically surgically denervated kidney of the same animal. After 26% hemorrhage, the vessels of both kidneys constricted, but the response was significantly greater on the innervated side; reduction in GFR was the same in both kidneys. After 32% hemorrhage the renal constrictor response was greater than after 26% hemorrhage, the difference largely resulting from additional humoral effects, as estimated by the greater vasoconstriction observed in the hypersensitive surgically denervated kidney at this level of hemorrhage; GFR also fell more on the denervated side. The results indicate that sympatho-adrenal activity is essential in the production of renal vasoconstriction after hemorrhage, and suggest that this response is normally produced by the synergistic action of increased sympathetic nerve activity and humoral effects, including those of the adrenal catecholamines.