Estrogen effects on lymph flow as a function of outflow pressure in ewes

The purpose of the present study was to assess whether acute estrogen administration decreased the lymphatic vessel's "pumping" ability. An additional goal was to assess whether estrogen affected the capillary filtration (used here as the total transfer of fluid and protein across the capillaries evidenced by the thoracic duct lymph flow rate). We reasoned that if estrogen administration decreases the lymph pumping ability against outflow pressure, then this phenomenon could help to explain the interstitial fluid retention seen during chronic estrogen. In six nonpregnant ewes we studied the thoracic lymph flow rate measured at different outflow pressures, before and after the acute administration of 50 mg of Premarin (conjugated estrogenic hormones). We also continuously determined arterial and venous pressures and heart rate. The arterial pressure declined from a mean of 99 +/- 0.33 (SE) mmHg to 95.4 +/- 0.2 mmHg (P less than 0.05) after the administration of estrogen. Heart rate increased from 88.5 +/- 0.8 to 111.3 +/- 1.2 beats/min (P less than 0.01). Venous pressure, plasma and lymph protein concentrations, and hematocrit did not change significantly (P greater than 0.1). Lymph flow rate declined progressively when measured against positive outflow pressure, whereas it remained stable when measured against negative pressure. Lymph flow rate during negative outflow pressure was higher after the administration of estrogen 0.044 +/- 0.002 vs. 0.032 +/- 0.002 ml.min-1.kg-1 for the control period (P less than 0.05). The calculated outflow pressure at which lymph flow rate became zero was similar for the period before or after the estrogen administration (P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)