Effect of progressive exercise on lung fluid balance in sheep

The purpose of this study is to determine the roles of cardiac output and microvascular pressure on changes in lung fluid balance during exercise in awake sheep. We studied seven sheep during progressive treadmill exercise to exhaustion (10% grade), six sheep during prolonged constant-rate exercise for 45-60 min, and five sheep during hypoxia (fraction of inspired O2 = 0.12) and hypoxic exercise. We made continuous measurements of pulmonary arterial, left atrial, and systemic arterial pressures, lung lymph flow, and cardiac output. Exercise more than doubled cardiac output and increased pulmonary arterial pressures from 19.2 +/- 1 to 34.8 +/- 3.5 (SE) cmH2O. Lung lymph flow increased rapidly fivefold during progressive exercise and returned immediately to base-line levels when exercise was stopped. Lymph-to-plasma protein concentration ratios decreased slightly but steadily. Lymph flows correlated closely with changes in cardiac output and with calculated microvascular pressures. The drop in lymph-to-plasma protein ratio during exercise suggests that microvascular pressure rises during exercise, perhaps due to increased pulmonary venous pressure. Lymph flow and protein content were unaffected by hypoxia, and hypoxia did not alter the lymph changes seen during normoxic exercise. Lung lymph flow did not immediately return to base line after prolonged exercise, suggesting hydration of the lung interstitium.     

The effect of anti-L on ouabain binding to sheep erythrocytes.

Binding of 3H-ouabain was studied in high potassium (HK) and low potassium (LK) sheep red cells. In particular, we investigated the effect of anti-L, an antibody raised in HK sheep against L-positive LK sheep red cells, on 3H-oubain binding and its relation to K+ -pump flux inhibition in LK cells. HK cells were found to have about twice as many 3H-ouabain binding sites and a higher association rate for 3H-ouabain than homozygous LL-type LK cells. The number of 3H-ouabain molecules bound to heterozygous LM-type LK cells is lower than that on LL cells, but the rate of ouabain binding is between that of HK and LL red cells. A close correlation was observed between the rates of 3H-oubain binding and fraction K+-pump inhibition. Exposure of LM and LL cells to anti-L did not affect the number of 3H-ouabain molecules bound at saturation, but increased the rates of glycoside binding and K+ -pump inhibition proportionately, so that for LK cells in the presence of anti-L, the rates of the two processes approximate those of HK cells. These data exclude the possibility that anti-L generates entirely new pump sites in LK sheep cells, but suggest that the antibody increases the affinity of the existing -a+ -K+ pumps for the glycoside.     

Effect of potassium concentration and ouabain on the renal adaptation to potassium depletion in isolated perfused rat kidney

Renal adaptation for potassium (K) conservation has been demonstrated in isolated perfused kidneys from rats within 3 days of K depletion and appears to be independent of aldosterone and sodium excretion. This study was designed to investigate whether the renal adaptation for K conservation is independent of ambient [K] and renal tissue levels of K and whether ouabain may have effects on K excretion, which are in contrast to the effects on K excretion in normal animals. In the first study, rats K depleted for 3 days received 2500 mu equiv. KCI intraperitoneally, while other K-depleted rats and a group of control diet animals received intraperitoneal H2O alone to determine whether simple restoration of K deficits would reverse the renal adaptation for K conservation. Intraperitoneal KCI increased plasma [K] and kidney tissue K significantly within 3 h in the K-repleted group compared with the K-depleted rats. Isolated Kidneys were perfused from the three groups of rats 3 h after intraperitoneal injection. Despite K repletion in vivo, perfused kidneys from the K-repleted group still had significantly decreased K excretion (1.28 +/- 0.085 mu equiv./min) compared with controls (2.05 +/- 0.291 mu equiv./min), and K excretion was still not different from the K-depleted group (0.57 +/- 0.134 mu equiv./min). However, fractional K excretion by the kidneys from K-repleted rats was increased above K-depleted kidneys (0.48 +/- 0.051 vs. 0.18 +/- 0.034, p less than 0.01). Despite the increased renal tissue K in K-repleted kidneys at the start of perfusion (285 +/- 5.1 vs. 257 +/- 5.4 mu equiv./g), by the end of the perfusion tissue K in perfused kidneys was identical in all three groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibitory effect of ouabain on epinephrine-induced stimulation of adrenal corticosterone secretion in rats.

Chronic administration of ouabain (3 mg/Kg body weight, subcutaneously, once daily for consecutive 15 days) definitely inhibited epinephrine-induced increase of adrenal corticosterone secretion. The inhibition rate increased along with frequency of ouabain administration. Increase in adrenal corticosterone synthesis and secretion by ACTH (20-50 mU/rat) administration was partially suppressed by pretreatment with chronic ouabain administration. A slight but significant increase of adrenal corticosterone secretion caused by epinephrine administration in hypophysectomized rats was also inhibited by pretreatment with ouabain administration. Chronic administration of neither phentolamine (1 mg/rat, intraperitoneally, once daily for consecutive 15 days) nor propranolol (3 mg/Kg body weight, subcutaneously, once daily for consecutive 15 days) caused significant changes in adrenal corticosterone secretion in response to ACTH as well as to epinephrine. Chronic administration of ouabain in rats causes not only elevated secretion of ACTH from anterior pituitary but also functional change in adrenals leading to suppression of corticosterone secretion in response to ACTH or epinephrine administration.     

Stimulating role of potassium ions and ouabain on glycogen synthesis in adipose tissue.

1. Exposure of fat-pads to increasing concentrations of K+ in the presence of insulin stimulates the incorporation of labelled glucose into glycogen. In the absence of hormone, only a slight incorporation of glucose into glycogen and slight glucose oxidation were detectable. 2. Ouabain alone, up to 100 microM, had no effect on synthesis of glycogen. Ouabain reinforced the effect of insulin on the conversion of glucose into glycogen in a Na+ medium and in a equimolar Na+-K+ medium, but not in a K+ medium. In addition, ouabain modified the optimal K+/Na+ ratio for glycogen synthesis. 3. The proportion of glycogen synthase in the active form was increased in a K+ medium, and a faster rate of conversion of synthase b into a was observed under these conditions. No difference was detected in the rate of inactivation of phosphorylase in a K+ or a Na+ medium. 4. Even though these results, taken together, are consistent with the proposed role of phosphorylase a in the regulation of synthase activation, the molecular mechanism of action of K+ in adipose tissue in increasing synthesis of glycogen cannot be explained simply by a faster inactivation of phosphorylase a. It is concluded that some undetermined effector(s) or signal could itself be a primary determinant for the greater activation of synthase observed in a K+ medium.     

Effect of metoclopramide on adrenal secretion in sheep: influence of dexamethasone and sodium intake

Metoclopramide, a competitive dopamine antagonist, stimulates aldosterone in man and monkey without affecting cortisol secretion. In sheep, metoclopramide also stimulates aldosterone but ist action on adrenocortical secretion is more controversial. To clarify the action of metoclopramide in conscious sheep, the response of plasma aldosterone, cortisol, angiotensin II and potassium were studied after 0.16 and 0.64 mg/kg metoclopramide, with and without pretreatment with dexamethasone. The effect of sodium status on the response was also studied by repeating the experiments after 7 days of dietary sodium restriction. In the absence of dexamethasone, plasma aldosterone was significantly increased by metoclopramide in both sodium-replete and restricted sheep. In sodium-replete sheep, plasma cortisol was also increased by 0.64 mg/kg, and by both doses when salt-restricted. However all cortisol responses were completely suppressed by dexamethasone pretreatment. Dexamethasone also suppressed the aldosterone response to metoclopramide in sodium-replete but not in sodium-restricted sheep where significant responses of aldosterone to both doses of metoclopramide still occurred without changes in plasma angiotensin II or potassium. While a nonspecific stress effect of metoclopramide can contribute to the aldosterone response, these results show that the sheep's adrenal glomerulosa is capable of responding to metoclopramide without change in ACTH, angiotensin or potassium.