The Newborn Kidney in Health & Disease pps

Water Reabsorption : Fractional reabsorptionwater channels are less Aquaporins Glucocorticoids: 1.. increase Na+ transporters for reabsorption 2.. Collecting Duct:Final sodium modulation

Victor S Doctor, MD

SERUM URINE GFR = 110 ml/min

Na – 140 meq/liter = 150 liters in 24 hours

210 meq lost in 1% URINE

2 liter urine output (105 meq Na/liter

Less filtered Less to absorb

(Slightly used!)

for growthReason for less work

Tubule Epithelium Blood

DCT CCT

99% Absorption

Less capacity to reabsorb Na and fluids

There is less to reabsorb anyway

(due to filtration)

WHAT / WHEN : Increase in transporter

activity (absorption)

Water Reabsorption : Fractional reabsorption

water channels are less (Aquaporins)

Glucocorticoids:

1 increase Na+ transporters for reabsorption

2 increase Aquaporin activities

Studies show that –

Prenatal Glucocorticoid administration

increases Na+ transporter and aquaporin maturation and activities

Collecting Duct:

Final sodium modulation segment to

maintain homeostasis

Less Na channels are found in neonates

* Tendency to lose more Na thru the urine

Acid-Base Balance

80% HCO3 absorbed at proximal tubule

Neonates: HCO3 reabsorption is lower by 1/3 that

of adults

= low HCO3 transporter activity

= all transporter steps for reabsorption of

H

Na

There is clear evidence that

glucocorticoids stimulate development of HCO3 transport (Pregnant rabbits injected glucocorticoids prior to delivery = their

neonates have proximal tubule HCO3

transport rate comparable to that of the

adults

Amonia Genesis

GLUTAMINE NH3 NH4

NH3 catches H+ NH4

In Acidosis amonioagenesis increase 10x

in adults

* Neonates CANNOT

Normal adult protein metabolism = produce acid 1 meq / kg / day

Produce acid 2-3 meq/k/day

Aggressive Total Parenteral Nutrition (TPN) may cause acidosis.

Large amount of Arginine in TPN for

premature infants can result in metabolic acidosis (Arginine is a source of HCl)

Why is neonate not acidotic if excretion is

decreased?

Mother’s milk contains base equivalents to

maintain acid/base balance.

Premature milk contains higher proteins,

sodium, potassium to compensate for faster

growth rate and specific electrolyte needs for her premature baby

Renal K+ Handling by Healthy and

Sick Neonates

contractility

growth and cellular division

Adult = 0 K+ balance

into new cells for somatic growth

K+ like Fe+ = actively transported via

placenta even in maternal K+ deficiency

Neonatal Hyper K+ = failure of Na K pump in very premature neonates

= corrected by prenatal steroid treatment

stabilizing cell membrane

Filtered K+ - almost entirely absorbed at proxime tubule (in normal newborn)

Na K Cl – tubular absorption process is related to common transporters

Tendency to retain K due to relative

or immaturity ofDecreased K+ excretion CCD

transporter which improves with maturation

Role of Glucocorticoids (available drugs)Thyroid Hormone (not usual drug regimen)

Evidence:

1 Rats treated with dexamethasone

prenatally developed HPN as they

become adults

2 Their kidneys developed glomerulo

SCLEROSIS

Glucocorticoids may initially show beneficial effects thru neonatal interventions for

specific situations BUT may have

ADVERSE effects in later life

MAN GETS INTO TROUBLE BY RE-DIRECTING NATURES FORCES.