Handling 22NaCl by the blood-brain barrier and kidney: its relevance to salt-induced hypertension in dahl rats.

We previously reported that inappropriate renal vasoconstriction in Dahl salt-sensitive (DS) rats fed high NaCl diets may cause sodium retention. The present study examined the distribution and elimination of 22Na in DS and Dahl salt-resistant (DR) rats, and we determined whether an abnormality in renal function might also cause sodium retention in DS rats. Following an intravenous bolus of 4 microCi 22NaCl in prehypertensive DS and DR rats with similar blood pressures on low (0.23%) or high (8% for 4 days) NaCl diets, urinary clearance of 22Na in 1 hour was about 4 times less in DS than DR rats, and renal retention of 22Na was up to 8 times greater in DS than DR rats (P<0.01), suggesting that a renal functional defect may contribute to salt retention in DS rats; however, its uptake in tail artery, heart, lungs, liver, and spleen was similar in DS and DR rats. Uptake in brain was up to 5 times greater in DS than DR rats (P<0.01). Cerebrospinal fluid 22Na radioactivity (in counts per minute) revealed that the blood-brain barrier is 5 to 8 times more permeable to sodium in DS than DR rats (P<0.01). Cerebrospinal fluid volume and brain water content increased significantly (P<0.01) in DS but not DR rats on an 8% NaCl diet. Intracerebroventricular bolus injection of 0.06 mL of 4.5 mol/L NaCl acutely and transiently induced the same degree of hypertension in DR and DS rats, whereas similar volume injections of isotonic saline, 4.5 mol/L Na-acetate, or 4.5 mol/L NaBr did not produce hypertension in either strain. We conclude that functional abnormalities in DS rat kidneys may cause retention of NaCl and that an increased blood-brain barrier permeability to NaCl may enhance its access to sites in the brain that are then activated and induce hypertension.

Cerebral hemisphere function and laterality of migraine.

We report preliminary findings of a study exploring the hypothesis that migraine is the experience of a protective cerebrovascular mechanism arising in response to unilateral cerebral information overload. The necessary population to be studied, namely those with exclusive one-sided migraine, proved to be rare. The measures of cerebral hemisphere function were the verbal and non-verbal scales of Wechsler's Adult Intelligence Scale. Preliminary results suggest that it is worthwhile continuing to explore the notion using additional and more sophisticated measures.

Tracheal tube cuffs and tracheal dilatation.

Although tracheal tube cuffs are well known to injure the trachea, attempts to design safer cuff systems have been only partially successful. In 14 dogs, we compared three models of high residual volume, low pressure cuffs, which are considered to be among the safest. Two were air-filled cuffs -- a maintained pressure cuff and a balloon reservoir cuff -- and the third was foam-filled. Tracheal dilatation was considerably more severe with mechanical ventilation than with spontaneous breathing, but the foam cuff produced significantly less dilatation (P less than .005) than the air-filled cuffs.