F. M. Karlsen

Dynamic Autoregulation and Renal Injury in Dahl Rats

The Dahl salt-sensitive (Dahl S) rat develops hypertension and renal injuries when challenged with a high salt diet and has been considered to be a model of chronic renal failure. Renal injuries appear very early in life compared with the spontaneously hypertensive rat (SHR). During the course of hypertension, a gradual impairment of autoregulatory control of renal blood flow might expose the glomerular circulation to periods of elevated pressure, resulting in renal injuries in Dahl S rats. Dynamic autoregulatory capacity was assessed in Dahl S and Dahl salt-resistant (Dahl R) rats, SHR, and Sprague-Dawley rats by inducing broad-band fluctuations in the arterial blood pressure and simultaneously measuring renal blood flow. Dynamic autoregulation was estimated by the transfer function using blood pressure as the input and renal blood flow as the output. Renal morphological injuries were evaluated in Dahl S rats and SHR and were scored semiquantitatively. Dynamic autoregulation was efficient and comparable in the low-frequency range (<0.015 Hz) in Dahl R rats, SHR, and Sprague-Dawley rats. The response in Dahl S rats depended strongly on the initiation time of the high salt diet. Autoregulation was preserved during a low salt diet and in rats exposed to a late-onset hypertension of short duration, only partly preserved if the late-onset hypertension was of a longer duration, and abolished in early-onset hypertension. All Dahl S rats on a high salt diet showed severe morphological changes in the kidney. In conclusion, autoregulatory capacity in the kidney of Dahl S rats is gradually impaired when rats are rendered hypertensive with a high salt diet. Renal morphological injuries develop before loss of dynamic autoregulation. Impaired autoregulation appears to be the result, not the cause, of the process that ultimately leads to renal failure in the Dahl S rat.

Paroxysmal atrial fibrillation occurs often in cryptogenic ischaemic stroke. Final results from the SURPRISE study

Atrial fibrillation (AF) increases the risk of stroke fourfold and is associated with a poor clinical outcome. Despite work‐up in compliance with guidelines, up to one‐third of patients have cryptogenic stroke (CS). The prevalence of asymptomatic paroxysmal atrial fibrillation (PAF) in CS remains unknown. The SURPRISE project aimed at determining this rate using long‐term cardiac monitoring.

Tubuloglomerular feedback in Dahl rats

We have previously demonstrated a loss of autoregulation in Dahl salt-sensitive (Dahl-S) rats rendered hypertensive on a high-salt diet. To determine whether this was due to a decreased activity of either the myogenic or the tubuloglomerular feedback (TGF) response, we tested the TGF response in both Dahl-S and salt-resistant Dahl rats on high- and low-salt diets. TGF was investigated in the closed-loop mode with a videometric technique, in which the response in late proximal flow rate to perturbations in Henle flow rate was measured. All Dahl rats showed a similar compensatory response to perturbations around the natural operating point, with a TGF response that was more efficient than in normotensive Sprague-Dawley rats. No evidence of decreased TGF responsiveness in hypertensive Dahl-S rats was found. The results suggest that the loss of autoregulation in hypertensive Dahl-S rats is due to a compromised myogenic response. We also measured the free-flow proximal intratubular pressure in Dahl rats. Perfectly regular oscillations were demonstrated in all Dahl series, including the hypertensive Dahl-S rats. This is the first demonstration of regular oscillations in an experimental rat model of hypertension.We have previously demonstrated a loss of autoregulation in Dahl salt-sensitive (Dahl-S) rats rendered hypertensive on a high-salt diet. To determine whether this was due to a decreased activity of either the myogenic or the tubuloglomerular feedback (TGF) response, we tested the TGF response in both Dahl-S and salt-resistant Dahl rats on high- and low-salt diets. TGF was investigated in the closed-loop mode with a videometric technique, in which the response in late proximal flow rate to perturbations in Henle flow rate was measured. All Dahl rats showed a similar compensatory response to perturbations around the natural operating point, with a TGF response that was more efficient than in normotensive Sprague-Dawley rats. No evidence of decreased TGF responsiveness in hypertensive Dahl-S rats was found. The results suggest that the loss of autoregulation in hypertensive Dahl-S rats is due to a compromised myogenic response. We also measured the free-flow proximal intratubular pressure in Dahl rats. Perfectly regular oscillations were demonstrated in all Dahl series, including the hypertensive Dahl-S rats. This is the first demonstration of regular oscillations in an experimental rat model of hypertension.

LA emptying fraction improves diagnosis of paroxysmal AF after cryptogenic ischemic stroke: results from the SURPRISE study.

In 25% of patients with ischemic stroke, no etiologic factor is identified: so-called cryptogenic strokes (CS) [(1)][1]. Asymptomatic paroxysmal atrial fibrillation (PAF) is often suspected to be the cause of stroke in these patients. Echocardiographic estimates of left atrial (LA) function, such