Estimation of lung liquid production in fetal sheep with blue dye dextran and radioiodinated serum albumin.

Lung liquid production and reabsorption rates and lung volumes were measured in 99 fetal sheep (119-148 days of gestation) by indicator-dilution methods with the simultaneous use of blue dye dextran (BDD) and radioiodinated serum albumin (RISA). There were no significant differences between rates of lung liquid production or reabsorption by the two methods (n = 71 pairs; paired t-test; Wilcoxon test; ANOVA); this was equally true for rates in milliliters per hour or milliliters per kilogram body weight per hour and was independent of age. Volumes measured by both methods showed a close linear relationship (r = 0.97; for slope P < 0.0001; n = 99), whether expressed as milliliters or milliliters per kilogram body weight. Either method could give the higher volume. Values differed by only approximately 4%, independent of age or parameter (ml or ml/kg body wt; volumes regressed to original volume, or as measured in untreated control hours). However, this small difference was significant by paired t-test or Wilcoxon test when all data were combined irrespective of age; it was not significant after allowance for gestational age (two-way ANOVA). Both indicators showed the same increase in lung volume toward birth and the same fall when related to body weight (slopes significant P = 0.0003-0.0004; r = 0.93). Two-way ANOVA showed that the declines were significant (P = 0.003). The data suggest that 1) there was no significant difference in production or reabsorption rates measured by BDD or RISA, 2) differences in volumes measured by the two indicators were only significant if gestational age was ignored and were too small to have physiological importance, and 3) although BDD and RISA each may have methodological weaknesses, for purposes of measuring lung liquid volumes both are sufficiently accurate and reproducible to obtain meaningful physiological results.

The association between meconium and the production and reabsorption of lung liquid and lactate loss by in vitro lungs from fetal guinea pigs.

OBJECTIVE: We sought to use an in vitro approach to determine relationships between meconium and fetal lung liquid production and to relate meconium to possible problems in lung liquid removal at birth. STUDY DESIGN: Near-term fetal guinea pigs were divided according to the level of spontaneously occurring meconium (no meconium, light meconium, or heavy meconium). Their lungs were maintained in vitro in Krebs-Henseleit saline solution for 3 hours. Lung liquid production or reabsorption was measured by a dye-dilution method, and loss of lactate to the lung liquid and outer Krebs-Henseleit solution was monitored. Reabsorptions were investigated by activating powerful responses with dinitrophenol during the middle hour. RESULTS: During the first hour, lungs from meconium-free fetuses produced liquid at 1.25 +/- 0.12 mL/kg(-1) body weight. h(-1); rates from light or heavy meconium groups were not significantly different (n = 18). Similarly, total lactate loss was not significantly different between the meconium-free and light-meconium groups but was twice as high in heavy-meconium preparations (73.68 +/- 10.60 micromol/L. g(-1) dry lung tissue. h(-1); P <.025, analysis of variance). The meconium-free and heavy-meconium groups continued to produce fluid, with no significant change throughout the 3 hours of incubation; lactate losses fell slightly. Therefore there were no problems with fluid production with meconium present, but the high-lactate losses with heavy meconium suggested long-term intrauterine hypoxia. Dinitrophenol produced powerful reabsorptions in lungs from meconium-free fetuses (-0.85 +/- 0.35 mL. kg(-1) body weight. h(-1); P <.005, analysis of variance; P <.0005, regression analysis) but failed to do so in heavy-meconium fetuses (n = 36). Lactate losses rose 2-fold in both groups (P <.005 to P < 0.0005, analysis of variance and regression analysis), despite already elevated losses with heavy meconium (n = 12). Therefore, in heavy-meconium fetuses, dinitrophenol affected metabolic pathways but did not activate fluid reabsorption, suggesting damage to reabsorptive mechanisms. CONCLUSION: Unless major airways are blocked, meconium is not associated with reduced fetal lung liquid production, which can cause poor lung development, but there may well be poor fluid removal after birth because of compromised reabsorptive mechanisms, which are unlikely to be helped by possible hormonal intervention.

Effects of glucagon on in vitro liquid production by lungs from fetal guinea pigs.

BACKGROUND: Lung liquid reabsorption in newborns with respiratory distress syndrome can be deficient. Respiratory distress syndrome is often seen in infants of diabetic mothers, in whom the neonatal surge of glucagon is suppressed. AIM: To investigate the possible effects of glucagon on lung liquid reabsorption. METHODS: Lungs from near term fetal guinea pigs (62 (2) days gestation; term = 67 days) were supported in vitro for three hours; lung liquid production and reabsorption were monitored by a dye dilution method. RESULTS: Untreated control preparations produced fluid at 1.75 (0.33) ml/h per kg body weight, and did not change significantly in three hours; those immersed in 10(-12) M glucagon during the middle hour showed no significant change, but those given higher concentrations all showed significant reductions in fluid production or even reabsorption (65.6 (10.3)% fall at 10(-11) M, 70.0 (6.3)% fall at 10(-10) M, and 90.6 (11.1)% fall at 10(-9) M; based on 54 preparations). At 10(-9) M glucagon, 12 out of 30 preparations reabsorbed fluid. The linear log dose-response curve (r(2) = 0.94) gave a theoretical threshold at 4 x 10(-15) M glucagon. Responses appeared to involve the amiloride sensitive Na(+) based reabsorptive system: responses to 10(-9) M glucagon appeared to be reduced by 10(-6) M amiloride, and were abolished by 10(-5) M amiloride (based on 72 preparations). CONCLUSIONS: The results suggest that the surge of glucagon at birth may help to drain the lungs of fluid. As glucagon liberates cAMP, which also stimulates surfactant, glucagon is worth consideration for possible use in neonatal respiratory distress.

The pulmonary neuroendocrine system and drainage of the fetal lung: effects of serotonin.

The neuroendocrine system of the lungs is maximally developed and activated at birth, but has no clear function. Here, one of its products, serotonin, was tested for an ability to stop lung fluid production or activate reabsorption. Lungs from fetal guinea pigs (61 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye dilution method. Initial studies on 36 young fetuses (61 +/- 1 days of gestation) showed that untreated controls produced fluid at 1.17 +/- 0.23 ml.kg-1.h-1, with no significant change over 3 h (ANOVA; regression analysis); those given 10(-8) M serotonin during the middle hour showed no significant changes, but those given 5 x 10(-8), 10(-7), 10(-6), or 10(-5) M serotonin reduced production significantly (P < 0.01 to P < 0.0005). Responses were linear up to 10(-7) M (threshold, 10(-9) M) and then become maximal at 50% reduction. However, responses increased with age. Comparison of 40 fetuses divided into groups of 60-61 or 65-67 days of gestation showed a large and significant increase in responses in the older fetuses (P < 0.01), where half the preparations reabsorbed fluid. Serotonin receptors were involved, since 10(-6) M cyproheptadine abolished responses (based on 24 preparations). Amiloride-sensitive Na+ channels were involved, since 10(-6) M amiloride abolished responses (based on 24 preparations). These results, in combination with earlier results from somatostatin and dopamine, together with histochemical and clinical observations, strongly suggest that the neuroendocrine system of the lungs may find a function in clearing fluid from the lungs at time of birth.

The effect of dopamine on lung liquid production by in vitro lungs from fetal guinea-pigs.

1. The neuroendocrine system of the lungs has no clear function. However, previous studies of one of its products, somatostatin, have implicated it in lung liquid removal at birth. The present study extends this concept by investigating the effects of dopamine, a major product of this system, on lung liquid reabsorption. 2. The effects of dopamine on fetal lung liquid production and reabsorption were tested on in vitro lungs from fetal guinea-pigs of 60 +/- 2 days of gestation (term = 67 days). Dopamine was placed in the outer bathing saline during the middle hour of 3 h incubations. Fluid movements across the pulmonary epithelium were monitored by a dye dilution method, and changes in rates over 1 h intervals were tested for significance by analysis of variance and regression analysis. 3. Dopamine was able to reduce fluid production or cause reabsorption (based on 42 preparations). Control preparations and those given 10-8 M dopamine showed no significant changes; those given higher concentrations showed significant reductions in production or reabsorption (P < 0.025 to P < 0.0005), according to dose (42.6 +/- 10.8% reduction at 10-7 M; 75.4 +/- 5.9% reduction at 10-6 M; 92.1 +/- 7.0% reduction at 10-5 M and 121.4 +/- 12.8% (reabsorption) at 10-4 M dopamine). The linear log dose-response curve (r = 0.99) showed a theoretical threshold at 1.7 x 10-9 M dopamine. 4. Effects were mediated through specific dopamine receptors (based on 78 preparations). Dopamine at 10-6 M was tested together with each of three dopamine receptor antagonists at 10-5 M. The general dopamine receptor antagonist haloperidol and the more specific D2 receptor blocker domperidone both abolished responses, but the D1 receptor antagonist SCH 23390 was without effect. This suggested that D2 dopamine receptors mediated the responses, and that responses were not due to conversion of dopamine to adrenaline or noradrenaline. 5. There was no evidence that responses involved amiloride-sensitive Na+ transport (based on 54 preparations). Apical amiloride at 10-6, 10-5 or 10-4 M, and the more specific Na+ channel blocker benzamil (10-5 M), had no effect on responses to dopamine, in contrast to their effects on responses to adrenaline in sheep. 6. It is suggested that internal release of dopamine by the neuroendocrine system of the lungs may influence lung liquid reabsorption at birth. This system, which also produces somatostatin, another agent active on lung liquid production, is maximally developed and activated at birth; it is also deficient in hyaline membrane disease.

Alpha-adrenoreceptor influences on liquid movements by in vitro lungs from fetal guinea pigs.

Lungs from near-term fetal guinea pigs (60 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye-dilution method. Studies of 30 fetuses showed that untreated preparations produced fluid at 1.34 +/- 0.21 ml.h-1.kg body wt-1, but epinephrine at concentrations known at delivery (10(-8) and 10(-7) M) produced significant reductions or fluid reabsorption (analysis of variance, regression analysis); at high levels (10(-6) and 10(-5) M, epinephrine had no effect. Maximal responses from 10(-7) M epinephrine involved alpha-adrenoreceptors, since they were abolished by 10(-6) M phentolamine (alpha-antagonist) but were unaffected by 10(-6) M propranolol (beta-antagonist; n = 36). Activation was through alpha2-adrenoreceptors, since responses were abolished by 10(-4) M yohimbine (alpha-antagonist; n = 24) but were resistant to 10(-5) M prazosin (alpha 1-antagonist; n = 24). At high levels of epinephrine (10(-5) M), where responses did not normally occur, reductions in lung liquid production were large if prazosin was also present (n = 24), and increases were significant if yohimbine was included (n = 24). In guinea pigs, epinephrine appears to activate lung fluid reabsorption through alpha 2-adrenoreceptors; at high concentrations only, it can also increase production through alpha 1-adrenoreceptors. Therefore, species differences appear to exist.

Effects of norepinephrine on lung liquid production by in vitro lungs from fetal guinea pigs.

Lungs from near-term fetal guinea pigs (61 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye dilution method. Untreated control preparations produced fluid at 1.38 +/- 0.30 mL x kg(-1) body weight x h(-1), with no significant change (ANOVA; regression analysis); those given 1.24 x 10(-9) or 1.24 x 10(-8) M norepinephrine during the middle hour showed no significant change, but those given concentrations between 5.24 x 10(-8) and 1.24 x 10(-5) M all showed significant reductions or fluid reabsorption (based on 42 fetuses). The responses showed a linear relationship with the log concentration (r = 0.97). They appeared to involve alpha-adrenoreceptors, since responses to 10(-7) M norepinephrine were unaffected by 10(-6) M propranolol, but those to 10(-7) and 1.24 x 10(-6) M norepinephrine were abolished by 10(-6) and 1.78 x 10(-5) M phentolamine, respectively (based on 48 fetuses). Activation was through alpha2-adrenoreceptors, since responses to 10(-7) and 10(-5) M norepinephrine were abolished by 10(-4) M yohimbine, but not by 10(-5) M prazosin (based on 60 fetuses). The results show that norepinephrine is able to reduce lung liquid production when at plasma levels present at birth, and that it can produce reabsorption; unlike epinephrine, there was no reduction in responses at high concentrations. This work reintroduces a neglected factor, norepinephrine, into possible controls of lung liquid reabsorption, and opens up the potential for neural controls.

Effects of epinephrine on lung liquid production by in vitro lungs from fetal guinea pigs.

Lungs from near-term fetal guinea pigs (62 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye dilution method. Studies based on 42 preparations investigated effects of epinephrine at different concentrations. Untreated preparations produced lung liquid with no significant change (ANOVA; regression analysis; rates in successive hours 1.37 +/- 0.30; 1.36 +/- 0.30, and 1.28 +/- 0.27 mL.kg-1 body weight.h-1); those given epinephrine at 10(-9), 10(-8), 5 x 10(-8), and 10(-7) M showed significant reductions in production or fluid reabsorption, and there was a linear relationship (r = 0.99) between log concentration and the percent reductions. Above these levels, responses decreased, and at 10(-5) M epinephrine there was no response. There was no evidence for activation of beta-adrenoreceptors; responses to 10(-8) M epinephrine were resistant to propranolol (based on 24 studies), and the specific beta-agonist isoproterenol was without effect (based on 18 studies). However, the alpha-antagonist phentolamine completely eliminated responses to epinephrine at physiological levels (10(-8) M epinephrine; based on 24 studies) and also at levels that gave maximal responses (10(-7) M epinephrine; based on 24 studies). It is concluded that epinephrine is able to promote lung fluid reabsorption at concentrations reported at birth, but that, in contrast with beta-activation in sheep, responses in the guinea pig are mediated through alpha-adrenoreceptors. Clearly, species differences exist.

Effects of acetylcholine on lung liquid production by in vitro lungs from fetal guinea pigs.

Lungs from near-term fetal guinea pigs (61 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye dilution method. Untreated preparations produced lung liquid with no significant changes (ANOVA; regression analysis) (rates in successive hours, initial study: 1.37 +/- 0.30, 1.36 +/- 0.30, and 1.28 +/- 0.27 mL.kg-1 body weight.h-1; n = 6). Preparations given acetylcholine at 10(-4) (n = 6), 10(-5) (n = 6), and 10(-6) M (n = 18) during the middle hour showed marked and significant fluid reabsorption (p < 0.025-0.0005); 10(-8) M acetylcholine was without effect. Reductions were linearly related to log concentration of acetylcholine (r = 0.97; theoretical threshold, 1.0 x 10(-7) M acetylcholine). Atropine, at 10(-5) M, greatly reduced responses to acetylcholine, and all reabsorptions were abolished; 10(-4) M atropine completely abolished all responses to acetylcholine; atropine alone had no effect (based on 48 studies). The alpha-adrenoreceptor antagonist phentolamine (1.78 x 10(-5) M) abolished the effects of 10(-6) M acetylcholine, but had no effect alone (based on 48 studies); the beta-adrenoreceptor antagonist propranolol (10(-5) M) had no effect on responses to 10(-6) M acetylcholine (based on 24 studies). It is suggested that acetylcholine at physiological levels can produce lung liquid reabsorption by activating muscarinic receptors and releasing catecholamines within the lungs; these catecholamines act via alpha-receptors. This raises the possibility of neural controls of lung liquid reabsorption during the early stages of delivery or neonatal life.

Effects of lung expansion on lung liquid production in vitro by lungs from fetal guinea-pigs. I. Basic studies and the effects of amiloride and propranolol.

Lungs from near-term fetal guinea-pigs were supported in vitro for 3 h; lung liquid production was measured by a dye-dilution method using Blue Dextran 2000 (fetuses 62 +/- 2 days of gestation, 97.6 +/- 19.0 (SD) g body weight; n = 134). Untreated control preparations produced fluid at 1.30 +/- 0.22 ml/kg body weight per h, and showed no significant changes during incubation (n = 30). After 1 h of incubation, experimental lungs were expanded with Krebs-Henseleit saline in volumes estimated to be below or approximating those of the first breath (n = 30; first breath, 0.6-1.2 ml). Expansions were graded at 18 +/- 4%, 31 +/- 4%, 43 +/- 3%, 50 +/- 3% and 72 +/- 2% of lung volume (volumes used for expansion at the maximal level, 0.64 +/- 0.25 ml). All expansions of 31% or above produced reductions in fluid production significant by analysis of variance (P < 0.01-0.001); production halted at 50% expansion, and there was strong reabsorption at 72% expansion (-0.87 +/- 0.45 ml/kg body weight per h by the final hour). There was an exponential relationship between percentage expansion and percentage fall in production (r = 1.00). There was no evidence for excessive pressure, and no evidence for lung damage as judged by electron microscopy or entry of intracellular materials into the fluid (lactic dehydrogenase, protein, K+). In studies based on 36 preparations, 10(-6) M amiloride present in the lung lumen (apically) abolished the reabsorptions seen at 70 +/- 3% expansion, but not the arrest of production; it had no effect on control preparations. Studies based on 24 preparations showed that responses to 72 +/- 2% expansion were not affected by 10(-7) M propranolol placed in the outer saline. In studies of 14 fetuses of widely different body weights (68.3-124.9 g), responses to 74 +/- 2% expansion showed an exponential increase with increasing body weight (r = 0.96). Although caution is needed, the results suggest that expansion of the lungs at birth may induce fluid reabsorption by an action independent of tissues outside the lungs, probably involving both activation of a Na(+)-based reabsorptive system and arrest of production, but not requiring beta-receptor activation. The probability that the responses are maximal at birth is discussed, and it is suggested that the effect of expansion may be a specialization of the perinatal lung.

Effects of lung expansion on lung liquid production in vitro by lungs from fetal guinea-pigs. II. Evidence for generation of an inhibitory factor.

Lungs from near-term fetal guinea-pigs were supported in vitro for 3 h; lung liquid production was measured by a dye-dilution method using Blue Dextran 2000 [fetuses 63 +/- 2 days of gestation, 97.6 +/- 19.8 (SD) g body weight]. Preparations were incubated in pairs taken from the same mother. Twenty lungs incubated in pairs without treatment (controls) showed no significant changes in fluid production throughout incubation (analysis of variance; regression analysis); rates in successive hours were: first lung, 1.36 +/- 0.39, 1.09 +/- 0.34 and 1.27 +/- 0.42 ml/kg body weight per h; second lung, 1.46 +/- 0.52, 1.09 +/- 0.41 and 1.18 +/- 0.43 ml/kg body weight per h. Twenty lungs were incubated similarly in pairs, but after one hour one lung from each pair was expanded with Krebs-Henseleit saline in volumes approximating those of the first breath (68 +/- 10% of lung volume). The expanded lungs began to reabsorb fluid immediately after expansion; the untreated lungs also stopped production or reached reabsorption by the final hour. Rates in successive hours were: expanded lungs; before expansion, 1.00 +/- 0.21, after expansion, -0.23 +/- 0.17 and 0.14 +/- 0.09 ml/kg body weight per h; unexpanded lungs, 1.27 +/- 0.49, 0.02 +/- 0.01 and -0.01 +/- 0.004 ml/kg body weight per h. The decrease in production was significant for each type of lung. The effects persisted in both expanded and unexpanded lungs in the presence of 1.78 x 10(-5) M phentolamine (n = 12; 70 +/- 2% expansion). The results suggest that expansion of the lungs at birth may release an unknown inhibitory factor, provisionally termed Expansion Factor (EF), within the lungs; this agent, probably not a catecholamine, can change lung fluid production into reabsorption and may partly account for the failure of beta-antagonists to prevent fluid reabsorption at delivery.

Regulation of lung liquid secretion in immature fetal sheep: hormonal interaction.

The present studies were designed to test the hypothesis that arginine vasopressin (AVP) can interact with hydrocortisone and 3,5,3'-triiodothyronine (T3) to induce maturation of lung liquid reabsorptive processes in fetal sheep < 130 days gestation. Lung liquid production rates were measured in chronically catheterized thyroidectomized fetal sheep during eight different experimental treatments. Each experiment consisted of a 2-h control period followed by a 5-h treatment period. Net secretion or reabsorption of lung liquid was measured by using impermeant marker dilution techniques. AVP alone (50 mU/kg bolus plus 5.0 mU.kg-1.min-1 i.v. infusion) does not alter lung liquid secretion in fetal sheep 125 +/- 0.72 (SE) days gestation. In contrast, AVP (same dose as above) with T3 (30 micrograms) and hydrocortisone (6.94 mg/min) depressed lung liquid secretion and caused reabsorption of fluid. T3 alone, T3 and hydrocortisone, T3 and AVP, hydrocortisone alone, hydrocortisone and AVP, and saline did not result in net lung liquid reabsorption over a 5-h treatment period. These investigations demonstrate that AVP, T3, and hydrocortisone interact to cause lung liquid reabsorption in immature fetal lungs.

Amiloride inhibits arginine vasopressin-induced decrease in fetal lung liquid secretion.

The effects of arginine vasopressin (AVP) and amiloride were studied in 16 unanesthetized fetal sheep (129-135 days of age) with indwelling catheters. Secretion was measured by an impermeant tracer technique. Control fetuses showed no change in lung liquid secretion over a 5-h period with an average secretion rate of 3.6 +/- 0.31 ml.kg-1.h-1. Infusion of AVP (23.4 +/- 2.23 mU.kg-1.min-1) in seven fetuses (134-140 days of age) produced significant decreases (from control) in the secretion rate over a 5-h period: the secretion rate decreased by 68% in the last hour. Amiloride placed in the lung liquid during infusion of AVP, but after AVP effects had taken place, reversed the AVP-induced decrease in lung liquid secretion. AVP in conjunction with other hormones that are elevated during the stress of birth (epinephrine and cortisol) may be important in the removal of lung fluid at birth.

Fluid production by in vitro lungs from near-term fetal guinea pigs: effects of cortisol and aldosterone.

Lungs from near-term fetal guinea pigs (62 +/- 1 days of gestation) were supported in vitro for 3 h and fluid production was determined by a dye dilution method (Blue Dextran 2000). Three groups of control preparations (N = 6 for each group) showed no changes during incubation. However, cortisol or aldosterone placed in the outer saline during the middle hour caused profound reductions in fluid production. Cortisol at 10(-6) or 10(-8) mol/l reduced production 80.3 +/- 10.8% and 47.8 +/- 20.5%, respectively (p < 0.05-0.001; N = 6 for each group); at 10(-10) mol/l it failed to affect production significantly. Aldosterone was effective at lower concentrations (N = 12). At 10(-11) mol/l it reduced production 67.1 +/- 10.0% (p < 0.01-0.001); at 7 x 10(-10) mol/l it produced similar effects. In contrast, there were no significant changes after treatment with 10(-11) mol/l aldosterone together with an aldosterone antagonist (5 x 10(-8) mol/l spironolactone; N = 6). Spironolactone alone was without effect (N = 6). The highest steroid concentrations tested corresponded to plasma concentrations in the guinea pig at delivery; therefore, it is suggested that both steroids may have a role in reducing lung fluid production close to birth in this species.

Lung liquid production by in vitro lungs from fetal guinea pigs: effects of arginine vasopressin and arginine vasotocin.

Lungs from near-term fetal guinea pigs were supported in vitro for 3 h; lung liquid production rates were measured by a dye dilution technique. Seventy preparations were used to study the effects of arginine vasopressin (AVP) placed in the outer saline for the middle hour, at concentrations reported at birth [fetuses 61 +/- 2 days of gestation; 94.7 +/- 16.2 g (SD) body weight]. At 1200 microU/ml, AVP arrested fluid production (rates, successive hours, 3.03 +/- 0.60, 0.50 +/- 0.14 and 0.02 +/- 0.08 ml/kg body weight per h; falls significant, P < 0.01-0.0005). At 600, 300 and 100 microU/ml there were significant but smaller reductions. Reabsorptions were seen in 8 preparations given 600-1200 microU/ml, AVP. Preparations given 10 microU/ml AVP, AVP carrier or control saline showed no significant change. The responses (% reductions during treatment), were linearly related to the log concentration of AVP (r = 0.99); theoretical threshold, 8 microU/ml). Increasing treatment to 2h did not increase final responses. Preparations from 5 fetuses > 120 g body weight showed significantly greater responses (P < 0.025) [fetuses 64 +/- 2 days of gestation; 135.1 +/- 18.6 g (SD) body weight]. 10(-6) M amiloride abolished responses to AVP [fetuses 62 +/- 1 days of gestation; 93.4 +/- 18.5 g (SD) body weight, n = 30; rates, succeeding hours; AVP alone, 1.78 +/- 0.22, 0.48 +/- 0.09, 0.16 +/- 0.99 (P < 0.01-0.0005); AVP with amiloride, 1.15 +/- 0.07, 0.93 +/- 0.10, 0.86 +/- 0.08 (no significant fall) ml/kg body weight per h]. Thirty-six preparations treated with arginine vasotocin (AVT, 10-600 microU/ml) showed closely similar responses to those from AVP. These studies extend results to fetal guinea pigs, and show that AVP, at concentrations reported at delivery, can slow lung liquid production or cause reabsorption by a direct action on the lung. The effect increases close to term, and is due to activation of amiloride-sensitive Na+ channels.

Reabsorption of lung liquid produced by 2,4-dinitrophenol in in vitro lungs from fetal guinea pigs.

Lungs from near-term fetal guinea pigs (62 +/- 2 days of gestation) were supported in vitro for 3 h, and lung liquid production was measured by a dye dilution technique. Twelve untreated preparations produced fluid at 1.54 +/- 0.29 mL.kg-1 body weight.h-1 during the 1st h, with no significant changes in later hours. Twelve preparations treated with 2 x 10(-4) M 2,4-dinitrophenol (DNP) showed strong reabsorptions (significant, ANOVA and regression analysis); total loss of lactate from the preparations doubled (significant, same tests). In 12 additional preparations, increasing DNP fivefold did not abolish reabsorption; results resembled those at the lower concentration. Amiloride at 10(-6) M abolished reabsorptions after 2 x 10(-4) M DNP, although fluid production still halted (n = 6; reductions significant, same tests). Amiloride alone had no effect (n = 6); untreated controls showed no change (n = 6). Similarly, 10(-4) M sodium iodoacetate virtually abolished reabsorptions after 2 x 10(-4) M DNP, although fluid production still stopped (n = 6; reductions significant, same tests). Iodoacetate alone only reduced fluid production (n = 6; significant, same tests); untreated controls showed no change (n = 6). The results suggest that reabsorptions seen after inhibition of oxidative processes depend on amiloride-sensitive Na+ channels and glycolytic metabolism.

Changes in somatostatin-like immunoreactivity in lungs from perinatal guinea pigs and the effects of somatostatin-14 on lung liquid production.

Somatostatin-like immunoreactivity was measured by radioimmunoassay with a monoclonal antibody in lungs from perinatal guinea pigs (62 +/- 2 days of gestation). Fetuses delivered by Caesarean section and dissected before breathing showed 4748 +/- 758 pg/lung (n = 25). Fetuses allowed to breathe (neonates) showed marked increases in activity: 7629 +/- 1355 pg/lung (n = 12) after breathing 30 seconds, and 10729 +/- 1064 pg/lung (n = 6) after breathing 3 minutes (2.3-fold increase, P < 0.005). Values then declined (5203 +/- 1050 pg/lung (n = 9) at 30 minutes; 1458 +/- 105 pg/lung (n = 4) at 60 minutes). Changes were similar in pg/g wet tissue. HPLC characterized the immunoreactive peptides as somatostatin-14 (SS-14) and somatostatin-28 (SS-28) in both fetuses and neonates (n = 11). SS-28 made up only 13.7 +/- 1.7% of the activity; this percentage did not change with breathing. The effects of synthetic SS-14 on lung liquid production were investigated in in vitro lungs from 42 fetal guinea pigs. All 21 preparations immersed in 10(-5)-10(-7) M SS-14 during the middle hour of 3 h incubations reduced production, often approaching zero after treatment (rates, ml/kg body weight per h, succeeding hours: 10(-5) M (n = 9), 3.09 +/- 0.68, 0.93 +/- 0.39, -0.05 +/- 0.60 (fall significant during and after treatment, P < 0.025-0.005); 10(-6) M (n = 6), 3.06 +/- 0.68, 1.29 +/- 0.58, 0.36 +/- 0.38 (P < 0.05-0.005); 10(-7) M (n = 6), 1.96 +/- 0.66, 1.11 +/- 0.34, 0.64 +/- 0.28 (P < 0.05-0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intravenous saline infusion on fetal ovine lung liquid secretion.

These studies were designed to investigate the relationship between body fluid volume expansion and secretion of lung liquid in fetal sheep. Twelve fetal animals were used for saline infusion studies after providing them with indwelling vascular catheters and an exteriorized tracheal loop. An additional 10 animals were used as controls. Lung liquid production was measured using an impermeant tracer technique (Blue Dye Dextran). Saline infusion at 1.6, 4.0, 15.6, and 19.2 ml.kg-1.h-1 did not alter significantly lung liquid secretion rates. These results demonstrate that 1) intravenous infusion of saline at relatively high rates in the ovine fetus does not affect net fetal lung liquid formation rate, and 2) the lungs of chronically catheterized, unanesthetized fetal sheep probably do not participate in regulation of excess fluid and electrolytes.

Effects of cAMP, its analogues, and forskolin on lung fluid production by in vitro lung preparations from fetal guinea pigs.

Lungs from fetal guinea pigs (62 +/- 1 days of gestation) were supported in vitro for 3 h and fluid production was determined by a dye dilution method, based on Blue Dextran 2000. Twenty untreated lungs produced fluid at 1.41 +/- 0.22 mL.kg-1 body weight.h-1, with no significant changes during later hours. Treatments with analogues of cAMP, cAMP, or forskolin during the middle hour reduced production significantly. Dibutyryl cAMP at 10(-3) M produced reabsorption (117.8 +/- 13.6% reduction, p less than 0.001, n = 10); at 10(-4) M it reduced production (77.3 +/- 11.0% fall, p less than 0.001, n = 10). 8-Bromo-cAMP appeared more effective; at 10(-4) M it caused slight reabsorption (109.0 +/- 8.9% reduction, p less than 0.001, n = 6) and at lower concentrations it decreased production (at 10(-6) M, 67.6 +/- 9.6% fall, p less than 0.001, n = 6; at 10(-7) M, 40.0 +/- 14.3% fall, p less than 0.001, n = 6). At high doses, cAMP itself produced similar effects (at 5 x 10(-3) M, 141.6 +/- 22.8% reduction, p less than 0.001, n = 6); at 10(-4) it was ineffective (n = 3). Forskolin at 10(-6) M induced the strongest reabsorptions seen (159.1 +/- 10.9% reduction, p less than 0.001, n = 6); at lower concentrations it reduced production (at 10(-8) M, 73.8 +/- 5.5% fall, p less than 0.001, n = 6; at 10(-9) M, 29.2 +/- 9.2% fall, p less than 0.05, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)

Lung liquid production by in vitro lungs from fetal guinea pigs: studies with metabolic inhibitors.

Lungs from fetal guinea pigs (62 +/- 2 days of gestation) were supported in vitro for 3 h, and lung liquid production was measured by dye dilution. Eighteen untreated preparations produced fluid at 1.76 +/- 0.30 mL.kg-1 body weight.h-1 during the first hour, with no significant changes in later hours. When inhibitors of respiratory processes were placed in the outer saline during the middle hour, production changed significantly, as follows: (a) sodium iodoacetate at 10(-3) M stopped production (87.2 +/- 10.3 and 100% reductions, successive hours; n = 6), at 10(-4) M it reduced production (60.0 +/- 10.3 and 63.4 +/- 9.3% reduction, successive hours; n = 12); (b) sodium fluoride, 10(-3) M, almost stopped production (93.2 +/- 12.1 and 89.5 +/- 9.3% reductions, successive hours; n = 6); (c) sodium cyanide at high concentration (10(-3) M) reduced production slowly (35.5 +/- 12.3 and 73.1 +/- 22.4%; successive hours; n = 6); (d) sodium azide, 10(-3) M, also reduced production (67.6 +/- 14.2 and 59.7 +/- 14.0%, successive hours; n = 6); total lactate lost rose 1.8 +/- 0.5 fold; (e) dinitrophenol produced strong reabsorptions; at 10(-3) M, production fell 115.4 +/- 15.9 and 113.1 +/- 47.3%, successive hours (n = 4), and at 2 x 10(-4) M it fell 143.8 +/- 33.8 and 153.4 +/- 26.7%, successive hours (n = 6); total lactate lost rose 2- to 3-fold. Control preparations showed no significant changes. The results suggest that lung liquid production requires glycolysis and aerobic metabolism. However, reabsorption appears to continue on glycolysis alone, a particularly useful situation for neonates suffering respiratory distress.