The effects of furosemide and bumetanide on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 61 +/- 3 days of gestation were supported in vitro for 3 h, and lung liquid secretion rates were measured by a dye dilution technique based on Blue Dextran 2000. Ten preparations that had received no treatment showed an average secretion rate of 1.12 +/- 0.28 mL.kg-1 body weight.h-1 during the first hour, and there were no significant changes over the following 2 h. In studies of 54 fetal lungs, furosemide, bumetanide, control ethanol carrier, or saline alone were placed in the supporting medium during the middle hour of the 3-h incubations (ABA design). Furosemide at 10(-3) M reduced secretion 83.4 +/- 16.8%; at 10(-4) and 10(-5) M it produced smaller reductions. Bumetanide at 10(-3) M usually produced reabsorption (129.9 +/- 23.0% reduction), at 10(-4) M it reduced secretion 30.9 +/- 11.8%, but at 10(-5) M it was ineffective. Control carrier and saline were without effect. The ability of the loop diuretics to produce reabsorption of fluid in some preparations suggests the unmasking of an active reabsorptive process. The results also suggest that lung liquid secretion in the fetal guinea pig, as in the sheep, is dependent on a Na+ and Cl- cotransport system.     

Fluid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs (54-67 days of gestation) were supported in vitro, and lung liquid secretion rates were measured by a dye-dilution technique. The average secretion rate in the first hour was 2.14 +/- 0.08 (SE) mL x kg-1 body weight.h-1 (0.21 +/- 0.01 mL/h) (n = 450); this was comparable to intact preparations. In an independent study of 30 lungs, secretion continued unchanged for 3 h, with no significant change in fluid composition. Between 54 days and term, production appeared to fall in terms of millilitres per kilogram per hour. The following agents were placed in the supporting saline during the middle hour of incubation. (i) Sodium iodoacetate: at 10(-4) M this produced a fall in secretion (fall, succeeding hours; 55.4 +/- 23.0 and 64.9 +/- 17.5%; n = 6); at 10(-3) M it stopped secretion (fall, succeeding hours; 87.2 +/- 10.3 and 100%, n = 6). (ii) Ouabain: at 10(-5) M there was no change in production (n = 6); at 10(-4) M, four preparations were unaffected, two reduced production. (iii) Epinephrine (10(-7) M) produced a significant fall in production in all cases (n = 6); in four preparations secretion reduced (average fall, 64.4 +/- 10.8%); in two preparations there was reabsorption (average rate, -1.03 mL.kg-1.h-1). This extends the effect of epinephrine to the guinea pig, and suggests that the in vitro preparation is a useful model for studies of the fetal lung.     

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.     

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)     

The effects of temperature change on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 58-65 days of gestation were supported in vitro for 3 h, and lung liquid production rates were measured by a dye dilution technique. In 36 control preparations, incubated continuously at 37 degrees C, the average production rate in the first hour was 1.46 +/- 0.23 ml/h per kg body weight; there was no significant change over the following two h. In 36 further preparations the temperature was changed during the middle hour (ABA), with the following % reductions in production rates: at -1 degrees C (relative to 37 degrees C), 68.2 +/- 17.1%; -2 degrees C, 125.5 +/- 30.1% (reabsorption); -3 degrees C, 103.8 +/- 32.8% (reabsorption); -5 degrees C, 82.7 +/- 16.6%, -8 degrees C, 94.7 +/- 1.8 %; +2 degrees C, 100.7 +/- 12.6% (all significant, P less than 0.025-0.005). Slow recoveries followed a return to starting conditions, except after the increase in temperature, 10(-6) M amiloride abolished reabsorption, but not depression, during the maximal effects of temperature reduction (at -2 degrees C, n = 6); amiloride had no effect on control preparations (n = 6). These results suggest that: (a) reductions of 2-3 degrees C, as seen in the delivery room, abolish secretion, but not reabsorption of lung fluid; larger reductions stop both processes; (b) the reabsorptions seen after a fall in temperature depend on Na(+)-transport mechanisms; (c) lung liquid production was sensitive to a rise in temperature, so that fevers might adversely affect lung development, and (d) the fall in temperature at birth may be an important factor in the early reabsorption of lung liquid.     

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.     

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)     

Changing responsiveness to growth hormone releasing factor in the perinatal sheep

Synthetic human pancreatic growth hormone releasing factor 1-44-amide was administered (8 micrograms/kg iv bolus) to chronically catheterised fetal sheep between 77 and 135 days of gestation and to infant sheep. At all ages human pancreatic growth hormone releasing factor induced a significant growth hormone response. In fetuses less than 120 days the integrated growth hormone response to human pancreatic growth hormone releasing factor (n = 5) was 250 +/- (SE) 50 ng X hr X ml-1 compared (p less than 0.001) to -22.8 +/- 8.6 ng X hr X ml-1 in saline treated controls (n = 7). In fetuses older than 120 days (n = 5), the response to human pancreatic growth hormone releasing factor was 110.8 +/- 15.6 ng X hr X ml-1 compared to -12.0 +/- 17.6 ng X hr X ml-1 in saline treated controls (n = 4 p less than 0.001). In 4 infant lambs (4-12 days) the response to human pancreatic growth hormone releasing factor (56.5 +/- 14.5 ng X hr X ml-1) was greater than in 6 control injected lambs (0.95 +/- 1.5 ng X hr X ml-1). The magnitude of the response to growth releasing factor decreased progressively with increasing postconceptual age (r = -0.80, p less than 0.001). These observations demonstrate that the fetal somatotrope can respond to exogenous growth releasing factor from at least 77 days of gestation. The progressive decrease in responsiveness may reflect the gradual development of somatostatin mediated inhibitory control or altered responsiveness of the somatotrope.     

Effect of epidermal growth factor on lung liquid secretion in fetal sheep

Fetal lung liquid secretion depends on active transport of chloride ions. Chloride secretion in the stomach is inhibited by epidermal growth factor (EGF). For this reason, the effect of EGF on lung liquid secretion was measured using the impermeant-tracer technique in chronically-prepared fetal sheep. Infusion of EGF over 4 h resulted in decreased lung liquid secretion (from 4.2 +/- 0.6 to 1.7 +/- 0.8 ml/h, P = 0.02) and significant dose related tachycardia. During the infusion, plasma epinephrine levels increased from 27 +/- 5 to 67 +/- 13 pg/ml (P = 0.05) and norepinephrine levels increased from 257 +/- 31 to 544 +/- 69 pg/ml (P = 0.01). Since it is known that beta-adrenergic agonists inhibit lung liquid secretion, subsequent studies were performed with beta-adrenergic blockade using propranolol. Infusion of EGF and propranolol resulted in a significant decrease in lung liquid secretion (from 8.9 +/- 2.1 to 3.0 +/- 1.1 ml/h, P = 0.03). Infusion of propranolol alone had no demonstrable effect on lung liquid secretion. It is concluded that acute EGF infusion increases heart rate and stimulates catecholamine secretion in fetal sheep. EGF also inhibits lung liquid secretion, an effect which appears to be independent of a possible indirect catecholamine effect.     

Alpha 2-adrenoceptor control of ion and water transport in the newt renal distal tubule.

To study the nature of adrenergic stimulation of ions and water reabsorption in the newt renal distal tubule, stationary microperfusion of the nephron and electron probe analysis were used. After application of norepinephrine (NE 10(-6) M) to the tubule surface, the fractional reabsorption of fluid increased from 15.0 +/- 3.1 to 41.30 +/- 10.4% (n = 7, p < 0.01), of Na+ from 69.30 +/- 6.6 to 79.10 +/- 7.5% (p < 0.05), Cl- from 63.30 +/- 7.6 to 72.40 +/- 7.9% (p < 0.05). Instead of secretion (control), there was reabsorption of K+. Fractional reabsorption of Ca2+ decreased from 51.00 +/- 6.0 to 43.00 +/- 7.0% (p < 0.05). The nonspecific alpha-adrenergic antagonist dibenamine 10(-6) M completely inhibited the effect of NE while, under the action of propranolol (2 x 10(-6) M) NE increased ion and water reabsorption significantly. When applied alone, or with NE, the specific alpha 2-adrenoblocker idazoxan, 2 x 10(-6) M, did not interfere with reabsorption in the distal tubule. At the same time, under the action of alpha 1-adrenoblocker prazosin 2 x 10(-6) M NE, increased the fractional reabsorption of fluid from 24.10 +/- 3.4 to 44.40 +/- 4.0% (n = 6, p < 0.001). These results serve as evidence that there exist specific alpha 2-adrenoceptors in the newt distal tubule the stimulation of which increases membrane permeability of the distal tubule to water, Na+, K+, Cl-, but not to Ca2+.     

Hormonal regulation of prolactin release by human prolactinoma cells cultured in serum-free conditions

Thyrotropin-releasing hormone (TRH) stimulates the prolactin (PRL) release from normal lactotrophs or tumoral cell line GH3. This effect is not observed in many patients with PRL-secreting tumors. We examined in vitro the PRL response to TRH on cultured human PRL-secreting tumor cells (n = 10) maintained on an extracellular matrix in a minimum medium (DME + insulin, transferrin, selenium). Addition of 10(-8) M TRH to 4 X 10(4) cells produced either no stimulation of PRL release (n = 6) or a mild PRL rise of 32 +/- (SE) 11% (n = 4) when measured 1, 2 and 24 h after TRH addition. When tumor cells were preincubated for 24 h with 5 X 10(-11) M bromocriptine, a 47 +/- 4% inhibition of PRL release was obtained. When TRH (10(-8) M) was added, 24 h after bromocriptine, it produced a 85 +/- 25% increase of PRL release (n = 8). This stimulation of PRL release was evident when measured 1 h after TRH addition and persisted for 48 h. The half maximal stimulatory effect of TRH was 2 X 10(-10) M and the maximal effect was achieved at 10(-9) M TRH. When tumor cells were pretreated with various concentrations of triiodothyronine (T3), the PRL release was inhibited by 50% with 5 X 10(-11) M T3 and by 80% with 10(-9) M T3. Successive addition of TRH (10(-8) M) was unable to stimulate PRL release at any concentration of T3. The addition of 10(-8) M estradiol for up to 16 days either stimulated or had no effect upon the PRL basal release according to the cases. In all cases tested (n = 4), preincubation of the tumor cells with estradiol (10(-8) M) modified the inhibition of PRL release induced by bromocriptine with a half-inhibitory concentration displaced from 3 X 10(-11) M (control) to 3 X 10(-10) M (estradiol). These data demonstrate that the absence of TRH effect observed in some human prolactinomas is not linked to the absence of TRH receptor in such tumor cells. TRH responsiveness is always restored in the presence of dopamine (DA) at appropriate concentration. This TRH/DA interaction seems specific while not observed under T3 inhibition of PRL. Furthermore, estrogens, while presenting a variable stimulatory effect upon basal PRL, antagonize the dopaminergic inhibition of PRL release.     

Contribution of Starling and lymphatic flows to pleural liquid exchanges in anesthetized rabbits

We studied the time course of volume and protein reabsorption of a 2-ml hydrothorax using whole (WP) or diluted (DP) homologous plasma injected into the right pleural cavity in anesthetized spontaneously breathing supine rabbits. Animals were killed at 5 (WP, n = 4; DP, n = 3), 36 (WP, n = 3; DP, n = 4), 55 (WP, n = 4), 90 (WP, n = 8; DP, n = 4), and 150 (WP, n = 4; DP, n = 5) min after the injection. The volume and protein content of the pleural liquid in control conditions (n = 12) amounted to 0.35 +/- 0.015 (SE) ml/kg and 1.8 +/- 0.27 g/100 ml, respectively, which are not significantly different at 90 min (n = 7). Pleural liquid volume decreased at a similar rate during WP or DP reabsorption according to the equation V = 0.84 +/- 0.05 X e-0.02t, with net reabsorptive flow expressed as dV/dt. The globulin quantity (Q) of the pleural liquid for WP and DP, respectively, decreased according to the equations Qwp = 1 + 1.5 X e-0.04t and Qdp = 0.7 + 0.6 X e-0.03t. Assuming a major lymphatic globulin clearance and no filtration into the cavity, we obtained lymph flow using the equation VL = dQ/dt X l/C where dQ/dt is calculated from the equations for Qwp and Qdp and C represents globulin concentration. The Starling flow (Vs) was then calculated by the equation Vs = dV/dt-VL. With increasing time, lymph flow was found to decrease progressively and was not significantly different from net flow with DP, which implied a Starling flow value of zero. During WP reabsorption, lymph flow initially exceeded the net flow, with the difference disappearing at approximately 60 min; accordingly, Starling filtration flow decreased progressively, becoming zero at the same time.     

Ion transport regulation of lung liquid secretion in foetal lambs.

To test the hypothesis that liquid formation in the foetal lung reflects the balance between Cl- secretion and Na+ absorption by the respiratory tract epithelium, we studied the independent and combined effects of selective ion transport inhibitors on basal production of lung liquid in foetal lambs. We prepared 19 foetal lambs (gestation 125 +/- 4, term = 147 days) with chronic indwelling catheters for subsequent measurement of luminal liquid production over time (JV). Using an impermeant tracer technique, we measured JV before and after tracheal instillation of 2 different inhibitors of ion transport: bumetanide, a Na(+)-K(+)-2Cl- co-transport inhibitor, and amiloride, a Na+ transport inhibitor. In 7 foetuses we sequentially added bumetanide (10(-4) M) and 2 different concentrations of amiloride (10(-6) M, 10(-4) M) to the liquid within the lung lumen. After we gave bumetanide, JV decreased from 12 +/- 4 ml/h to 0 +/- 5 ml/h and subsequently increased during the 2 periods of amiloride exposure (10(-6) M: 6 +/- 5 ml/h; 10(-4) M: 7 +/- 7 ml/h). In 5 control studies we gave bumetanide, followed by only amiloride vehicle. JV for all time periods in the control studies was similar to the experimental group, demonstrating no effect of amiloride. In 5 foetuses we administered the 2 concentrations of amiloride before bumetanide. There was no change in JV with either concentration of amiloride (baseline: 13 +/- 2 ml/h; 10(-6) M amiloride: 15 +/- 5 ml/h; 10(-4) M amiloride: 13 +/- 6 ml/h).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cation transport in lung epithelial cells derived from fetal, newborn, and adult rabbits

Recent studies done with fetal and adult sheep and with monolayers of cultured rat alveolar type II cells suggest that active transport of Na+ across the lung epithelium may contribute to liquid absorption from air spaces, an essential component of the normal switch from placental to pulmonary gas exchange at birth. The goals of this work were 1) to study the ontogeny of cation transport in lung epithelial cells derived from fetal, newborn, and adult rabbits and 2) to determine the influence of premature birth, air breathing, labor, and postnatal lung maturation on K+ uptake in these cells. We harvested granular pneumonocytes by tracheal instillation of proteolytic enzymes followed by centrifugation of the dispersed cells over a discontinuous density gradient of metrizamide. This procedure yielded 65-90% granular pneumonocytes, of which more than 80% excluded vital dye. Using freshly isolated cells, we measured uptake of 86Rb+, which mimics transmembrane movement of K+, in the presence or absence of 10(-4) M ouabain and in the presence or absence of 5 X 10(-4) M furosemide or bumetanide. In adult rabbit studies, 86Rb+ uptake was twice as fast in lung epithelial cells (98 +/- 7 nmol X 10(6) cells-1 X h-1) as it was in alveolar macrophages (51 +/- 6 nmol X 10(6) cells-1 X h-1). Ouabain inhibited 55-60% of the uptake by pneumonocytes, and "loop" diuretics inhibited an additional 15-20%. The rate of 86Rb+ uptake in fetal cells was less than 10% (6 +/- 1 nmol X 10(6) cells-1 X h-1) of the rate in adult cells; ouabain inhibited 80-85% of 86Rb+ uptake in fetal cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

VIP and hormone secretion from thyroidal follicular and C-cells

The effect of vasoactive intestinal peptide (VIP) on the cAMP system of the thyroid and on the secretion of T4 and T3 from the follicular cells and calcitonin and somatostatin from the C-cells was studied in perfused dog thyroid lobes. Activation of the cAMP system was evaluated by measurements of the amount of cAMP released into the perfusion medium. T4, T3, calcitonin and somatostatin were measured by radioimmunoassays. 3 X 10(-6) M VIP induced increases in cAMP release and T4 and T3 secretion from the thyroid while there were no significant alterations in calcitonin and somatostatin release (n = 4). In experiments employing both of the two isolated thyroid lobes 100 microU/ml TSH gave considerably higher increases in T4 and T3 secretion than 10(-6) M VIP (n = 4). The effect of 10(-9) M VIP on T4 and T3 secretion was similar to that of 10(-6) M VIP (n = 4). 10(-10) M VIP induced a small but statistically significant increase in T4 and T3 secretion in two experiments while no effect was observed in two dogs. This high sensitivity of the follicular cells to VIP and the demonstration by others of VIP containing nerves in the thyroid suggest that VIP-ergic nerves may be involved in the regulation of thyroid hormone secretion.     

Acute N-methyl-D,L-aspartate administration stimulates the luteinizing hormone releasing hormone pulse generator in the ovine fetus

To assess whether fetal luteinizing hormone releasing hormone (LH-RH) neurosecretory neurons have the capacity to respond to an exogenous stimulus, a synthetic excitatory amino acid analogue, N-methyl-D-L-aspartate (NMDA; 15 mg/kg), was given rapidly intravenously to 8 chronically catheterized fetuses (130-142 days of gestation; term 147 +/- 3 days). All 8 fetuses exhibited a rise in plasma ovine luteinizing hormone (oLH) and ovine follicle-stimulating hormone (oFSH) within 5 min. The mean maximal increments of oLH (2.25 +/- 0.36 ng/ml) and oFSH (1.21 +/- 0.32 ng/ml) were significantly greater than in 6 normal saline-injected controls (oLH p < 0.0002; oFSH p < 0.03). The secretion of ovine prolactin (oPRL) and ovine growth hormone (oGH) was unaffected. LH-RH (5 microg) evoked a greater oLH response (p < 0.0009) and a greater oFSH response (p < 0.03) than NMDA (n = 6). Desensitization of the fetal gonadotrope by a potent LH-RH agonist, D-Trp6Pro9NEt-LH-RH (10 microg/day i.v. x 4 days), abolished the fetal oLH and the oFSH response to NMDA (n = 5). Moreover, D, L-2-amino-5-phosphonovalerate, a specific competitive antagonist for the NMDA receptor, completely inhibited the fetal oLH and oFSH response to NMDA, whereas D-L-2-amino-5-phosphonovalerate alone did not affect the plasma oLH or oFSH levels, the gonadotropin response to LH-RH, or the release of oGH or oPRL (n = 3). In primary ovine fetal pituitary cell cultures, NMDA (10(-10) to 10(-6) M) had no effect on oLH, oFSH, oGH, or oPRL secretion, whereas LH-RH stimulated oLH (10(-8) M; p < 0.0004) and oFSH (10(-8) M; p < 0. 0001) release, evidence that NMDA did not have a direct pituitary effect. The results suggest that NMDA induces oLH and oFSH secretion by stimulation of the fetal LH-RH pulse generator and is mediated by central NMDA receptors. Fetal LH and FSH secretion and the response to LH-RH decrease in late gestation in the ovine and human fetus. The relative importance of sex steroid dependent and sex steroid independent central nervous system inhibition in this developmental change is unclear. It appears that central neural inhibition in addition to sex steroid negative feedback contributes to the decrease in fetal gonadotropin concentrations in late gestation. NMDA did not affect fetal oGH or oPRL secretion.     

Stimulation of HCO3- secretion by the prostaglandin E2 analog enprostil: studies in human stomach and rat duodenum

This study investigated the action of enprostil, a synthetic analog of PGE2, on gastric HCO3- secretion in humans and on duodenal HCO3- secretion in the anesthetized rat. A previously validated 2-component model was used to calculate gastric HCO3- and H+ secretion in 10 human subjects. Compared to placebo, a single 70 micrograms oral dose of enprostil increased basal gastric HCO3- secretion from 1810 +/- 340 to 3190 +/- 890 mumol/hr (P less than 0.05). In addition, enprostil reduced basal gastric H+ secretion from 5240 +/- 1140 to 1680 +/- 530 mumol/hr (P less than 0.02). Enprostil also increased HCO3- secretion and reduced H+ secretion during intravenous pentagastrin infusion. In the rat, duodenal HCO3- secretion was measured by direct titration in situ using perfused segments of duodenum just distal to the Brunner gland area and devoid of pancreatic and biliary secretions. Addition of enprostil (10 micrograms/ml) to the duodenal bathing solution increased duodenal HCO3- secretion from 6.3 +/- 1.3 to 15.1 +/- 2.0 mumol/cm X hr (P less than 0.01, n = 6). The stimulatory action of enprostil on duodenal HCO3- secretion at 10 micrograms/ml was comparable in magnitude and duration to that of 10 micrograms/ml natural PGE2. In summary, the PGE2 analog enprostil stimulated gastroduodenal HCO3- secretion, effects which may be beneficial in protection of the gastroduodenal mucosa against luminal acid.     

Saliva secretion and ionic composition of saliva in the cockroach Periplaneta americana after serotonin and dopamine stimulation,and effects of ouabain and bumetamide

Isolated salivary glands of Periplaneta americana were used to measure secretion rates and, by quantitative capillary electrophoresis, Na(+), K(+), and Cl(-) concentrations in saliva collected during dopamine (1 micro M) and serotonin (1 micro M) stimulation in the absence and presence of ouabain (100 micro M) or bumetanide (10 micro M). Dopamine stimulated secretion of a NaCl-rich hyposmotic saliva containing (mM): Na(+) 95 +/- 2; K(+) 38 +/- 1; Cl(-) 145 +/- 3. Saliva collected during serotonin stimulation had a similar composition. Bumetanide decreased secretion rates induced by dopamine and serotonin; secreted saliva had lower Na(+), K(+) and Cl(-) concentrations and osmolarity. Ouabain caused increased secretion rates on a serotonin background. Saliva secreted during dopamine but not serotonin stimulation in the presence of ouabain had lower K(+) and higher Na(+) and Cl(-) concentrations, and was isosmotic. We concluded: The Na(+)-K(+)-2Cl(-) cotransporter is of cardinal importance for electrolyte and fluid secretion. The Na(+)/K(+)-ATPase contributes to apical Na(+) outward transport and Na(+) and K(+) cycling across the basolateral membrane in acinar P-cells. The salivary ducts modify the primary saliva by Na(+) reabsorption and K(+) secretion, whereby Na(+) reabsorption is energized by the basolateral Na(+)/K(+)-ATPase which imports also some of the K(+) needed for apical K(+) extrusion.     

Lung liquid secretion, flow and volume in response to moderate asphyxia in fetal sheep

The effects of moderate fetal asphyxia, induced by constriction of the maternal common internal iliac artery, on lung liquid secretion, tracheal fluid efflux and lung liquid volume have been investigated in unanaesthetized fetal sheep (111-142 days) in utero. During periods of fetal asphyxia the percent oxygen saturation, PO2, pH, and PCO2 of fetal carotid arterial blood changed from 57.2 +/- 1.3% (mean +/- SEM), 22.9 +/- 0.6 mmHg, 7.35 +/- 0.01 and 45.6 +/- 1.0 mmHg to 26.3 +/- 0.5% (P less than 0.001), 14.7 +/- 0.2 mmHg (P less than 0.001), 7.28 +/- 0.02, (P less than 0.001) and 47.8 +/- 0.4 mmHg (P less than 0.02), respectively. Fetal asphyxia, over 6 h, decreased the efflux of tracheal fluid from 7.07 +/- 0.47 ml/h to 3.97 +/- 0.36 ml/h (P less than 0.01) and, over 4 h, decreased the rate of lung liquid secretion from 9.42 +/- 1.76 ml/h to 4.91 +/- 1.54 ml/h (P less than 0.005), whereas it had no significant effect on lung liquid volume. The incidence of fetal breathing movements decreased from 52.9 +/- 2.5% to 22.6 +/- 3.5% during 6-h periods of fetal asphyxia. Thus, although fetal asphyxia decreased the net production of lung liquid, lung liquid volume was maintained probably, because the net efflux of fluid from the lungs via the trachea decreased to a similar extent.