Mijares, Antonio Hernández

Jensen, Michael D., Tu T. Nguyen, A. Hernández Mijares, C. Michael Johnson, and Michael J. Murray. Effects of gender on resting leg blood flow: implications for measurement of regional substrate oxidation. J. Appl. Physiol. 84(1): 141–145, 1998.—These studies were designed to examine whether the respiratory quotient (RQ) of leg tissue (primarily skeletal muscle) would increase to a greater degree in women than in men during meal ingestion. We found that mean leg and systemic RQ values were similar in men under both basal and fed conditions, whereas the agreement was poor in women. In women, leg RQ values tended to be greater than the systemic RQ, whereas splanchnic RQ values tended to be lower than the systemic RQ. The possibility that measurement imprecision accounted for the different findings in women could not be excluded because the arteriovenous blood O2 differences were almost twice as great in men as in women (53.7 ± 5.4 vs. 28.6 ± 2.9 ml of O2/l, respectively; P < 0.01), as were venoarterial blood CO2 differences. The smaller arteriovenous differences in women appeared to limit our ability to accurately measure their leg RQ values. O2 uptake relative to leg fat-free mass (FFM) was not different between men and women, whereas leg blood flow relative to leg FFM was greater in women than in men (55 ± 3 vs. 39 ± 2 ml ⋅ kg FFM−1 ⋅ min−1, respectively; P < 0.001). These findings were confirmed by examining data from other studies conducted in our laboratory to create a larger data set. We conclude that resting leg blood flow in women is greater (relative to FFM) than in men, making it more difficult to accurately measure leg RQ in women.

These studies were conducted to determine whether there are gender-specific regional differences in meal triglyceride fatty acid uptake. Systemic and regional oleate ([3H]oleate) kinetics were measured in nine nonobese men and eight nonobese women before and at the end of a 6-h meal, administered as small frequent feedings to achieve steady-state chylomicronemia. Chylomicron uptake in the splanchnic bed accounted for 71 +/- 15% of meal triglyceride disappearance in men and 20 +/- 7% in women (P < 0.01), whereas leg chylomicron uptake could only account for 12 +/- 2 and 8 +/- 4% (P not significant in men vs. women) of meal triglyceride disappearance. Meal ingestion suppressed (P < 0.05) systemic and regional free fatty acid release in both men and women. Splanchnic nonchylomicron triglyceride release and leg nonchylomicron triglyceride uptake were not significantly different in men and women. In summary, the largest quantitative difference between men and women in fatty acid kinetics during meal ingestion is a substantially greater splanchnic uptake of meal triglyceride fatty acids in men. This could represent greater meal fatty acid storage in visceral adipose tissue.

Insulin has important effects to increase skeletal muscle (leg) blood flow under euglycemic hyperinsulinemic clamp conditions and after oral glucose tolerance testing. The present studies examined the effects of mixed meal consumption on the components of leg glucose uptake (LGU) in lean, healthy adults. Seventeen men and women underwent measures of leg plasma flow and arteriovenous (AV) glucose difference before and for 6 h after a mixed meal providing one-third of daily energy expenditure. Another eight men and women underwent the same studies before and during the consumption of the same-size meal administered in small frequent feedings over 6 h. After the bolus meal, peak leg AV glucose gradient increased ∼ fivefold (P &lt; 0.001), whereas the peak increase in leg plasma flow was 20% (NS). No significant contribution of increased leg blood flow to the increase in postprandial LGU was apparent. Over the last 100 min of the frequent-feedings meal, the leg AV difference increased ∼ fourfold (P &lt; 0.001 vs. basal), whereas leg blood flow increased only by 16% (NS vs. basal). We conclude that after a mixed meal, leg (primarily skeletal muscle) blood flow does not increase enough for blood flow to be a major contributor to glucose uptake. These findings raise questions regarding the relative importance of insulin's hemodynamic effects in modulating glucose tolerance under more usual conditions.