E A Nancekievill | Search PubMed

PubMed1985

Ventilation threshold and aging.

The ventilation threshold (VeT) in 60 healthy men ages 22 to 65 years was determined on a maximal treadmill test. The VeT was identified as the highest VO2 before the ventilatory equivalent for oxygen began to increase without a corresponding increase in the ventilatory equivalent for carbon dioxide. The VO2 max was significantly lower in the 60 compared with the 20-year-old group (with age, r = -.81). The VeT was significantly lower in the oldest compared with the youngest group (with age, r = -.69); however, the VeT as a percentage of VO2 max was significantly greater in the oldest group, (with age, r = .37). The reserve capacity (VO2 max minus VeT) was significantly lower in the older men (with age, r = -.75) and was due to a greater reduction in VO2 max than in VeT. With multiple regression analysis, the variability in VeT was determined primarily by VO2 max (65.8%) and not age. Decrease in strenuous activity with age may account for the large reduction in VO2 max, whereas maintained submaximal activity may attenuate the reduction in VO2 at the ventilation threshold, thus resulting in a large loss in functional reserve above the level of the VeT.

Adult↗

PubMed1985

Possible role of cortisol in the stimulation of cortisol-binding capacity in the plasma of fetal sheep.

In sheep, the prepartum rise in fetal plasma cortisol (F) is associated with an increase in the corticosteroid-binding capacity (CBC) of the plasma. We examined whether CBC changed during preterm labor, induced by administering ACTH to the fetus, and we examined the role of F in such changes. Beginning on day 127, chronically catheterized fetal sheep were divided into six groups; 1) saline control infusions (n = 4); 2) pulsatile ACTH (P-ACTH; 66 ng/min for 15 min every 2 h; n = 5); 3) P-ACTH (as 2) plus metopirone (MET; 500 mg/24 h n = 5); 4) P-ACTH and MET (as 3) plus F (13.3 micrograms/min for 15 min every 2 h; n = 3); 5) P-ACTH and MET (as 3) plus F (133 micrograms/min for 15 min every 2 h; n = 4); 6) P-ACTH and MET (as 3) plus dexamethasone (0.56 micrograms/min for 15 min every 2 h for 50 h, then 5.6 micrograms/min for 15 min every 2 h until 100 h; n = 4). All infusions continued for 100 h. Fetal blood samples were collected at 8-h intervals for determination of plasma F concentration and CBC. Estrone and progesterone were measured in 8-h samples of maternal femoral arterial blood. P-ACTH resulted in a significant increase in CBC within 24 h; values at 72-96 h were 2- to 3-fold greater than controls. Rises in CBC were positively correlated with the changes in plasma F in the P-ACTH-treated fetuses and preceded changes in plasma progesterone or estrogens. MET treatment prevented the P-ACTH-induced increases in F and CBC. Exogenous F and dexamethasone overcame the MET-induced inhibition of P-ACTH-induced increases in CBC. We conclude that in fetal sheep 1) CBC is elevated by P-ACTH treatment; and 2) F may mediate this stimulation of its own binding protein.

Adrenocorticotropic Hormone↗