After the maternal abdomen was opened under methoxyflurane anesthesia, fetal rabbits of 27.5 days gestation were given injections through the intact uterine wall of saline, pilocarpine, isoxsuprine, muscarine, phenylephrine, atropine, phenoxybenzamine, or propranolo, alone or in appropriate combinations. Fetal rabbits were delivered by hysterotomy and killed without breathing 2.5 h later. Static pressure-volume curves with air showed improved retention on deflation in fetal rabbits that had injections of pilocarpine, or isoxsuprine, but not of muscarine or phenylephrine. The effect of pilocarpine on the pressure-volume curve was blocked by atropine, phenoxybenzamine, and propranolol, and the effect of isoxsuprine was blocked by propranolol but not phenoxybenzamine. The data suggest that pilocarpine produces secretion of surfactant into lung air spaces by exciting the sympathetic nervous system, a known function of pilocarpine, rather than the parasympathetic nervous system. This may result in stimulation of the same beta-adrenergic receptors affected by isoxsuprine which is also thought to stimulate surfactant secretion.

After opening the maternal abdomen under methoxyflurane anesthesia, fetal rabbits 25.5-28.5 days gestation were given an intraperitoneal injection of pilocarpine (150 mg/kg) or saline through the intact uterine wall. They were delivered by hysterotomy and sacrificed without breathing 2.5 h later. Newborn rabbits 29.5 days gestation received an injection of pilocarpine or saline at birth and breathed 30-120 min. Other newborn rabbits 29.5 days gestation were alternately sacrificed at birth or after breathing 30 min. Static pressure-volume curves with air showed decreased recoil and improved air retention on deflation in fetal rabbits 25.5-27.5 days injected with pilocarpine. There was no change in the static pressure-volume curve of lungs filled with saline. The data suggest that pilocarpine reduced surface tension by producing secretion of surfactant into air spaces. No change in lung recoil occurred with pilocarpine at 28.5 days, or with pilocarpine or breathing at 29.5 days. This may mean that air spaces at 28.5-29.5 days contained optimal surfactant, so further secretion of surfactant stimulated by pilocarpine or breathing failed to reduce surface tension.

No abstract

(Spon. by Murdina M. Desmond).Deaartment of P e d i a t r i c s . Baylor College of Medicine. Houston.--r --. . P i l o c a r p i n e (PC) produces decreased s u r f a c e tension i n lungs o f f e t a l r a b b i t s s t 27.5 days g e s t a t i o n , which e f f e c t i s blocked w i t h propranolol (Ped. Res. 10:459. 1976). F e t a l r a b b i t s of t h e same g e s t a t i o n were i n j e c t e d with PC o r s a l i n e , k i l l e d 3 hours l a t e r and the lungs lavaged. I n PC i n j e c t e d f e t a l r a b b i t s recovered a i r s p a c e phospholipid (PL) was 38118 p e r gram dry lung weight (+ SE 3.4) compared with 23ug (+ SE 2.7) i n s a l i n e i nj e c t e d c o n t r o l s (p<0.001).Isoxsuprine ( I x ) b u t not p h e n y l e~h r i n e i n j e c t e d 3 hours b e f o r e d e l i v e r y produced decreased s u r f a c e t e n s i o n i n lungs of f e t a l r a b b i t s a t 27.5 days a s shown by s t a t i c pressure-volume curves. The lungs of I x i n j e c t e d r a b b i t s r e t a i n e d 47% t o t a l lung c a p a c i t y a t 5cm. water p r e s s u r e compared with 25% i n s a l i n e i n j e c t e d cont r o l s (p<0.001). This e f f e c t was blocked by propranolol, but not by p h e n o~~b e n z a m i n e o r a t r o p i n e . The lungs of I x i n j e c t e d f e t a l r a b b i t s contained 83% water compared with 89% i n s a l i n e c o n t r o l s (p<0.001), but an increased i n PL could not be demons t r a t e d , 25ug p e r gram dry lung weight compared with 23ug i n sal i n e c o n t r o l s . Decreased tension may r e s u l t from increased conc e n t r a t i o n of s u r f a c t a n t a t t h e s u r f a c e . However a t 26.5 days PL i n lavage from I x i n j e c t e d f e t a l r a b b i t s was 25ug p e r gram dry lung weight compared with lLug i n c o n t r o l s (p<0.001). The d a t a a r e taken a s f u r t h e r evidence t h a t t h e sympathetic nervous system c o n t r o l s t h e a c t i v i t y of pulmonary s u r f a c t a n t . . ~l t h o b~h c r y i n g -v i t a l c i p a c i t y has been recorded i n i n f a n t s recovering from RDS, l i t t l e is known about physiological e f f e c t s o f vigorous cry?ng a t t h i s s t a g e o f t h e i l l n e s s . Detailed analy-:is o f intraesophageal pressure (Pes) and abdaminal a o r t i c blood pressure (B.P.) t r a c i n g s were made on 15 p a t i e n t s recokering from RDS. Mean b i r t h weight 2.04 kg (range 1.28-3.08). mean g e s t a t i o n 34 wecks (range 29-40) and mean age s t u d i e d 63 hours (range 22-137). During c r y i n g maximum Pes ranged from -18.0 t o -30.5 cm HZ0 during i n s p i r a t i o n and from +6.2 to +34.3 during e x p i r a t i o n .Pes remained p o s i t i v e during 66% o f t h e r e s p i r a t o r y c y c l e (range 54 t o 85%) and mean Pes durina inmiration was -12.3 cm H2D. during e x p i r a t i o n mean Pes wai +11:2 cm H20. Heart r a t e roie s i g n i f i c a n t l y , mean i n c r e a s e 1 5 S e a t s p e r minute (S.E.+3), P

To evaluate the usefulness of the foam stability test (FST) on gastric aspirate for predicting respiratory distress syndrome (RDS) in premature infants, samples were collected at delivery or within 30 min from 194 infants less than or equal to 36 weeks gestation. Of 123 samples adequate for complete testing, 44 were positive at 1 : 2 dilution, 43 were positive only at dilutions less than 1 : 2 and 36 were negative at all dilutions. RDS was found in 2%, 21% and 25% of each group respectively. The FST on gastric aspirate at birth gives useful information only if positive at 1 : 2 when a very low incidence of RDS may be expected. However, a large proportion of infants with FST negative at 1 : 1 do not develop RDS, and hence the test is of limited value in screening for those with highest risk.