Pela dedicação, compreensão e acima de tudo, pelo apoio, pois eles foram, nos momentos mais difíceis, o suporte que me ajudou a continuar e a superar meus obstáculos. À minha namorada, Camila Abrahão Pelo carinho, companheirismo, dedicação e apoio nas horas boas e, principalmente, nas horas difíceis destes quase dez anos de namoro.

High doses of Vitamin A given during parenteral alimentation (PA), even if reduced by adsorption to plastic tubing, could cause toxicity if the retinyl e s t e r (RtE) overwhelms the capacity of the storage mechanism. T o check for significant serum RtE characteristic of Vitamin A toxicity, 9 infants were sampled while on peripheral PA for 1 to 31 d a y s . On the day of sample, the mean dally Vitamin A dose p e r kg body wt: 3677 I .U. (S.D.1750) or 1103 ug (S.D.525). Meangestational age: 30.2 wks (S.D.1.1), birth weight: 1222 g (S.D.264), day of a g e for sample ranged from 5 to 37 d a y s and a total of 13 samples were collected. Serum RtE levels w e r e uniformly low, i .e. 2.1 p g % o r less. Serum Retinol before PA in 5 infants was 6 . 4 p g % (S.D. 3.8) and rose to 1 2 . 7 p g % (S.D. 5.3) d u r i n g PA.Further work needs to b e done to identify the optimal Vitamin A dose, b u t it is reassuring to know that the c u r r e n t dose does not appear to b e excessive. The continuous high tone o f t h e i n t e r n a l anal sphincter rel a x e s on r e c t a l d i s t e n s i o n (rectosphincteric r e f l e x , RSR). This is an important f a c t o r i n allowing outward passage of r e c t a l cont e n t s . W e compared a n a l tone and RSR i n 70 chronically constipated (Pts) and 1 8 healthy (C) 4-12 year old children. Anal tone was measured using a s t r a i n gauge (Honeywell MP-3 esophageal pressure transducer). The rectum was distended by i n j e c t i n g a i r i n t o a 2 . 5~3 cm balloon placed i n t h e rectum. Spontaneous v a r ia t i o n s i n tone were recorded a s pressure waves i n the anal region i n almost a l l individuals. Anal r e s t i n g tone (ART) (mm Hg) was defined a s t h e low points of these waves. ART varied along the l e n g t h of the a n a l canal (LAC) and was highest a t 1-1.5 cm fr,om t h e a n a l verge. This region was used t o study the presence of RSR and t h e amplitude of RSR r e l a x a t i o n (nun Hg) t o 30 cc and 60 cc r e c t a l distension. The lowest volume of a i r t o cause RSR (2 5 mm Hg), t h e RSR threshold (RSRT), and the LAC (cm) (where tone was higher than i n t h e rectum) were a l s o determined. ART and RSR amplitude were s i g n i f i c a n t l y lower (p<0.05) i n P t s than i n C, while the RSRT and LAC were comparable. These findings (mean + S.D.) suggest t h a t p a t i e n t s with chronic constipation have a weaker and l e s s responsive i n t e r n a l anal sphincter than normal.ART RSR Amplitude W e have shown t h a t serum b i l e acid concentrations a r e elevated during e a r l y l i f e i n humans r e f l e c t i n g physiologic immaturity of the enterohepatic c i r c u l a t i o n . To f u r t h e r d e f i n e the ontogeny of b i l e acid metabolism i n mammals, we sought maturational changes i n t h e serum values of t o t a l cholyl conjugates v i a a s e n s i t i v e , spec i f i c radioimmunoassay i n f e t a l , suckling, and mature SpragueDawley r a t s . Results: F e t a l (21st day) b i l e acid l e v e l s were low (1.42 + 0....