742 
PHARMACOLOGY 
1000 
800 
o 
O 
> 
t 600 
> 
1- 
< 
to 
< 
>- 
X 
o 
q: 
Q 
>- 
X 
400 
to 
o 
ir 
< 
Q 
< 
O 
o 
>- 
200 
I 1 
: ^- 
FETUS 
I 1 
i 
5. p< 0.001 
"'neonate ADuLf 
(< 3dQys) 
Figure 11. — Myocardial tyrosine hydroxylase activi- 
ties at differtiit ages in the lamb and sheep. Horizon- 
tal bars: mean values. 
HiSTOCHEMICiM. OBSERVATIONS 
The monoamine fluorescence technique of 
Falck and Owman^^ was employed to evaluate 
histochemically the distribution of sympathetic 
nerves within the hearts of the different aged 
animals. These studies provided final confirma- 
tion that sympathetic innervation is incomplete 
in the fetal and early newborn heart, or that up- 
take and binding are immature. In these studies 
the myocardium is treated in such a way that 
the norepinephrine within the adrenergic 
nerves fluoresces and the fluorescence is visual- 
ized microscopically. As Figure 15 shows, in the 
adult the heart is innervated by a dense net- 
work of intensely flourescent, varicose nerve 
fibers. At all ages, there appear to be more adre- 
nergic fibers in the atria than in the ventricles, 
but more importantly, there is a reduced den- 
sity of neurons in both fetal chambers when 
compared to the adult. Similar findings were ob- 
served in the rabbit heart. 
In both the lamb and the rabbit, the fetal my- 
ocardium contained large, intensely flourescent, 
preterminal nerve trunks in the epicardium and 
the tunica adventitia surrounding coronary ar- 
teries, and coursing in the connective tissue be- 
tween cardiac muscle bundles. In these younger 
animals, intense flourescence resided only in 
terminal varicosities within the large nerve 
trunks. In contrast, the nerve trunks in the 
older sheep or rabbits did not contain terminal 
4.0 
3.0 
TYROSINE 
HYDROXYLASE 
(^moles/g/ hr.)^ ^ 
NOREPINEPHRINE 
2.0 
EPINEPHRINE 
(mg/ g ) 
• 
• 
• 
• 
t 
• 
• 
y 
• 
- 
• 
• 
- 
t 
— 
r 
• 
1- • 
• 
• 
• 
1—4—1 
• 
FETUS ADULT 
ADRENAL 
Figure 12. — Adrenal tyrosine hydroxylase activities 
and norepinephrine and epinephrine concentrations 
in the fetal lamb and adult sheep. Horizontal bars: 
mean values. 
