The development of adrenergic innervation in some human foetal blood vessels.

The development of adrenergic innervation was examined in saphenous and brachial veins, femoral, brachial and superficial temporal arteries from human foetuses of 7-19 weeks gestation. Fluorescence histochemical and electron microscopic techniques were used on transverse sections of the vessels. No specific adrenergic fluorescence was detected within any of the vessels before 11 weeks gestation, by which time the arteries showed specific adrenergic fluorescence. However, there was no evidence of adrenergic innervation of veins even at 19 weeks gestation. Incubation of the vessels with alpha-methylnoradrenaline did not lead to earlier detection of fluorescence. Electron microscopy showed that the adrenergic nerves found in the arteries were arranged as bundles of axons partially enclosed within Schwann cell processes, often lying close to capillaries in the outer regions of the tunica adventitia.