Two weeks of muscle immobilization impairs functional sympatholysis but increases exercise hyperemia and the vasodilatory responsiveness to infused ATP.

During exercise, contracting muscles can override sympathetic vasoconstrictor activity (functional sympatholysis). ATP and adenosine have been proposed to play a role in skeletal muscle blood flow regulation. However, little is known about the role of muscle training status on functional sympatholysis and ATP- and adenosine-induced vasodilation. Eight male subjects (22 ± 2 yr, Vo(2max): 49 ± 2 ml O(2)·min(-1)·kg(-1)) were studied before and after 5 wk of one-legged knee-extensor training (3-4 times/wk) and 2 wk of immobilization of the other leg. Leg hemodynamics were measured at rest, during exercise (24 ± 4 watts), and during arterial ATP (0.94 ± 0.03 µmol/min) and adenosine (5.61 ± 0.03 µmol/min) infusion with and without coinfusion of tyramine (11.11 µmol/min). During exercise, leg blood flow (LBF) was lower in the trained leg (2.5 ± 0.1 l/min) compared with the control leg (2.6 ± 0.2 l/min; P < 0.05), and it was higher in the immobilized leg (2.9 ± 0.2 l/min; P < 0.05). Tyramine infusion lowers LBF similarly at rest, but, when tyramine was infused during exercise, LBF was blunted in the immobilized leg (2.5 ± 0.2 l/min; P < 0.05), whereas it was unchanged in the control and trained leg. Mean arterial pressure was lower during exercise with the trained leg compared with the immobilized leg (P < 0.05), and leg vascular conductance was similar. During ATP infusion, the LBF response was higher after immobilization (3.9 ± 0.3 and 4.5 ± 0.6 l/min in the control and immobilized leg, respectively; P < 0.05), whereas it did not change after training. When tyramine was coinfused with ATP, LBF was reduced in the immobilized leg (P < 0.05) but remained similar in the control and trained leg. Training increased skeletal muscle P2Y2 receptor content (P < 0.05), whereas it did not change with immobilization. These results suggest that muscle inactivity impairs functional sympatholysis and that the magnitude of hyperemia and blood pressure response to exercise is dependent on the training status of the muscle. Immobilization also increases the vasodilatory response to infused ATP.

Ocular findings in cystic fibrosis patients receiving vitamin A supplementation.

BACKGROUND: Vitamin A deficiency with eye symptoms has been reported in patients with cystic fibrosis who received the recommended daily intake of vitamin A. METHODS: We measured serum retinol, dark adaptation, contrast sensitivity, and dry eye status in 35 adult cystic fibrosis patients to ascertain whether they had ocular signs or symptoms. RESULTS: Median serum retinol concentration was 1.95 mumol/l, range 1.08-4.01 mumol/l, with no values indicating vitamin A deficiency. Retinal light sensitivity was normal. Nineteen patients had reduced contrast sensitivity. Conjunctival imprints all showed plenty of goblet cells, but were characteristic of dry eye in 42% of patients (n = 14). Decreased tear film stability was found in 49% (n = 17), tear production was low in 31% (n = 11), and 23% (n = 8) showed an increased amount of dying epithelial cells. Nine patients (26%) had keratoconjunctivitis sicca according to the Copenhagen criteria. CONCLUSION: Our patients had no biochemical or clinical signs of vitamin A deficiency. We speculate that the high incidence of dry eye could be a primary manifestation of cystic fibrosis.